Frames of reference in spaces with affine connections and metrics

A generalized definition of a frame of reference in spaces with affine connections and metrics is proposed based on the set of the following differential-geometric objects: (a) a non-null (non-isotropic) vector field, (b) the orthogonal to the vector field sub space, (c) an affine connection and the related to it covariant differential operator determining a transport along the given non-null vector filed. On the grounds of this definition other definitions related to the notions of accelerated, inertial, proper accelerated and proper inertial frames of reference are introduced and applied to some mathematical models for the space-time. The auto-parallel equation is obtained as an Euler-Lagrange's equation. Einstein's theory of gravitation appears as a theory for determination of a special frame of reference (with the gravitational force as inertial force) by means of the metrics and the characteristics of a material distribution. PACS numbers: 0490, 0450, 1210G, 0240VComment: 17 pages, LaTeX 2

Helium interaction with vacancy-type defects created in silicon carbide single crystal

Generation of He bubbles or cavities in silicon carbide is an important issue for the use of this material in nuclear and electronic applications. To understand the mechanisms prior to the growth of these structures, an atomic-scale study has been conducted. 6H-SiC single crystals have been implanted with 50 keV-He ions at 2×1014 and 1015 cm-2 and successively annealed at various temperatures from 150 to 1400°C. After each annealing, the defect distributions in the samples have been probed by positron annihilation spectroscopy. Four main evolution stages have been evidenced for the two investigated implantation fluences: at (1) 400°C for both fluences, (2) at 850°C for the low fluence and 950°C for the high one, (3) at 950°C for the low fluence and 1050°C for the high one and (4) at 1300°C for both fluences. The perfect correlation between the positron annihilation spectroscopy and the thermodesorption measurements has highlighted the He involvement in the first two stages corresponding respectively to its trapping by irradiation-induced divacancies and the detrapping from various vacancy-type defects generated by agglomeration processes

Determination of the disorder profile in an ion-implanted silicon carbide single crystal by Raman spectroscopy

International audienc

Multi machine scaling of fuel retention in 4 carbon dominated tokamaks

In order to benchmark predictions for the in vessel tritium inventory in ITER, a survey of fuel retention measured in 4 carbon dominated tokamaks (TEXTOR, ASDEX Upgrade in the 2002-2003 carbon configuration, Tore Supra and JET) was performed, showing retention rates from similar to 1 g D/h in TEXTOR (L mode, limiter machine) up to similar to 6-12 g D/h in AUG (H mode, divertor machine). A simple scaling used for ITER predictions is applied for comparison with experimental values: (1) estimate of wall fluxes, (2) estimate of the gross carbon erosion, (3) estimate of the net erosion/redeposition assuming a redeposition fraction and (4) estimate of the retention rate using D/C ratio scalings. The validity of each step is discussed, showing that this approach yields the right order of magnitude, but tends to underestimate the experimental values unless a high wall flux, a low local redeposition fraction and/or a high D/C ratio are used. (C) 2011 Elsevier B.V. All rights reserved.Multi machine scaling of fuel retention in 4 carbon dominated tokamak