194 research outputs found
LE RISQUE PROFESSIONEL DES RADIATIONS IONISANTES ET LA SECURITE SOCIALE. EUR 168.f = THE PROFESSIONAL RISK OF IONIZING RADIATION AND SOCIAL SECURITY. EUR 168.f
Implications of the Optical Observations of Neutron Stars
We show that observations of pulsars with pulsed optical emission indicate
that the peak flux scales according to the magnetic field strength at the light
cylinder. The derived relationships indicate that the emission mechanism is
common across all of the observed pulsars with periods ranging from 33ms to 385
ms and ages of 1000-300,000 years. It is noted that similar trends exist for
ray pulsars. Furthermore the model proposed by Pacini (1971) and
developed by Pacini and Salvati (1983,1987) still has validity and gives an
adequate explanation of the optical phenomena.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Electron heat transport in ASDEX Upgrade: experiment and modelling
The electron heat transport is investigated in ASDEX Upgrade using electron cyclotron heating (ECH) combining steady-state and power modulation schemes. Experiments in which the electron heat flux has been varied in the confinement region while the edge was kept constant were performed. They demonstrate that Te and Te/Te can be varied by a factor of 3 and 2, respectively. They allow a detailed determination of the transport characteristics by comparing steady-state and modulation data with modelling. The analyses clearly show the existence of a threshold ( Te/Te)crit above which transport increases. Both steady-state and modulation experiments agree with such a transport model. The experiments have been carried out at low density in the L-mode to ensure low electron–ion coupling and good conditions for studying electron heat transport. The experiments were carried out at two different values of plasma current and show that transport increases at low current, as well-known from global scaling laws for confinement time. In the pure off-axis cases the region inside the ECH deposition is just at the ( Te/Te)crit threshold, which allows it to be measured directly from the profile of Te/Te deduced from the experimental Te profile. Using this technique, it appears that the turbulence threshold agrees with that expected from the trapped electron mode driven turbulence. It has the correct absolute value and seems to have the correct radial dependence that is determined by the trapped electron fraction and by the density gradient. It almost does not vary with other plasma parameters. In contrast, the threshold calculated for electron temperature gradient modes is higher than the experimental values of Te/Te and this turbulence is therefore not expected to be excited under these experimental conditions
An Optical Survey for mm-Sized Interstellar Meteoroids
We report high resolution multi-station observations of meteors by the
Canadian Automated Meteor Observatory (CAMO) recorded from June 2009 to August
2010. Our survey has a limiting detection magnitude of +5 mag in R-band,
equivalent to a limiting meteoroid mass of ~2*E-7 kg. The high metric
trajectory accuracy (of the order of 30 m perpendicular to the solution and 200
m along-track) allows us to determine velocities with average uncertainty of <
1.5% in speed and ~0.4 degr in radiant direction. A total of 1739 meteors had
measured orbits. The data has been searched for meteors in hyperbolic orbits,
which are potentially of interstellar origin. We found 22 potential hyperbolic
meteors among our sample, with only two of them having a speed at least three
sigma above the hyperbolic limit. For our one year survey we find no clear
evidence of interstellar meteoroids at mm-sizes in a weighted time-area product
of ~1*E4 km^2*h. Backward integrations performed for these 22 potentially
hyperbolic meteors to check for close encounters with planets show no
considerable changes in their orbits. Detailed examination leads us to conclude
that our few identified events are most likely the result of measurement error.
We find an upper limit of f_ISP < 2*E-4/(km^2*h) for the flux of interstellar
meteoroids at Earth with a limiting mass of m > 2*E-7 kg.Comment: 15 pages, 2 figures, accepted by Ap
Subaru optical observations of the two middle-aged pulsars PSR B0656+14 and Geminga
We carried out a deep subarcsecond BRI imaging of the two middle-aged pulsars
to establish their properties in the optical range. Both pulsars are detected
at >10 sigma level. Geminga is for the first time reliably detected in the I
band with a magnitude of 25.10+/-0.14. We also reanalyze archival ESO/NTT and
HST broadband data and find that some published fluxes for Geminga were
estimated inaccurately. The resulting dereddened broadband spectra of both
pulsars are remarkably similar to each other and show significant flux
increases towards the far-UV and near-IR, and a wide flux excess in V-I bands.
This suggests a multicomponent structure of the optical emission. The
nonthermal power law component of the pulsar magnetospheric origin dominates in
the most part of the optical range. For PSR B0656+14 it is compatible with a
low energy extension of the power law tail seen in hard X-rays. For Geminga the
respective extension overshoots by a factor of 100 the nonthermal optical flux,
which has a less steep spectral slope than in X-rays. This implies a spectral
break at a photon energy of about 1 keV. The flux increases towards the far-UV
are compatible with contributions of the Rayleigh-Jeans parts of the blackbody
components from whole surfaces of the neutron stars dominating in soft X-rays.
The V-I excess, which is most significant for PSR B0656+14, suggests a third
spectral component of still unidentified origin. Faint, a few arcseconds in
size nebulae extended perpendicular to the proper motion directions of the
pulsars, are seen around both objects in our deepest I band images. They can be
optical counterparts of the bow-shock head of Geminga and of the tentative
pulsar wind nebula of PSR B0656+14 observed in X-rays.Comment: 15 pages, 8 figures, A&A, accepted. For higher resolution images see
http://www.ioffe.ru/astro/NSG/obs/map
Patentes como instrumento de aumento da dependência tecnológica e econômica: estudo da indústria farmacêutica
Overview of ASDEX Upgrade results
Recent results from the ASDEX Upgrade experimental campaigns 2001 and 2002 are presented. An improved understanding of energy and particle transport emerges in terms of a 'critical gradient' model for the temperature gradients. Coupling this to particle diffusion explains most of the observed behaviour of the density profiles, in particular, the finding that strong central heating reduces the tendency for density profile peaking. Internal transport barriers (ITBs) with electron and ion temperatures in excess of 20 keV (but not simultaneously) have been achieved. By shaping the plasma, a regime with small type II edge localized modes (ELMs) has been established. Here, the maximum power deposited on the target plates was greatly reduced at constant average power. Also, an increase of the ELM frequency by injection of shallow pellets was demonstrated. ELM free operation is possible in the quiescent H-mode regime previously found in DIII-D which has also been established on ASDEX Upgrade. Regarding stability, a regime with benign neoclassical tearing modes (NTMs) was found. During electron cyclotron current drive (ECCD) stabilization of NTMs, βN could be increased well above the usual onset level without a reappearance of the NTM. Electron cyclotron resonance heating and ECCD have also been used to control the sawtooth repetition frequency at a moderate fraction of the total heating power. The inner wall of the ASDEX Upgrade vessel has increasingly been covered with tungsten without causing detrimental effects on the plasma performance. Regarding scenario integration, a scenario with a large fraction of noninductively driven current (≥50%), but without ITB has been established. It combines improved confinement (τE/τITER98 ≈ 1.2) and stability (βN ≤ 3.5) at high Greenwald fraction (ne/nGW ≈ 0.85) in steady state and with type II ELMy edge and would offer the possibility for long pulses with high fusion power at reduced current in ITER
Ionospheric gas dynamics of satellites and diagnostic probes
The gas dynamics of interactions of a tenuous ionosphere with moving satellites and probes that have bearings on the diagnostics of the ionosphere are discussed. Emphasis is on the cases where the body is moving at mesothermal speeds, namely intermediate between the thermal speeds of ions and electrons of the ambient ionosphere. Methods of collision-free plasma kinetics with self-consistent field are used. The development of the topics for discussion starts with stationary Langmuir probe which entails the basic mechanism of body-plasma interaction that becomes further intricated as the body moves at a higher and higher speed. Applications of the theory of plasma interaction to meteors which move in the ionosphere are also presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43801/1/11214_2004_Article_BF00212707.pd
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