Advances in Aging Compact Model for Hot Carrier Degradation in SiGe HBTs under Dynamic Operating conditions for reliability-aware circuit design

International audienc

Anisotropic Magnetoresistance in Ga1−x_{1-x}Mnx_xAs

We have measured the magnetoresistance in a series of Ga$_{1-x}$Mn$_x$As samples with 0.033$\le x \le$ 0.053 for three mutually orthogonal orientations of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in these materials is negative (i.e. the sample resistance is higher when its magnetization is perpendicular to the measuring current than when the two are parallel) and has a magnitude on the order of 5% at temperatures near 10K and below. This stands in contrast to the results for most conventional magnetic materials where the SRA is considerably smaller in magnitude for those few cases in which a negative sign is observed. The magnitude of the SRA drops from its maximum at low temperatures to zero at T$_C$ in a manner that is consistent with mean field theory. These results should provide a significant test for emerging theories of transport in this new class of materials.Comment: 4 pages with 4 figures. Submitted to Physical Review

A computational study of magnesium point defects and diffusion in forsterite

We have studied the formation and migration of point defects within the magnesium sub-lattice inforsterite using a combination of empirical and quantum mechanical modelling methodologies. Empiricalmodels based on a parameterised force field coupled to a high throughput grid computing infrastructureallow rapid evaluation of a very large number of possible defect configurations. An embedded clusterapproach reveals more accurate estimates of defect energetics for the most important defect configurations. Considering all defects in their minimum energy, equilibrium positions, we find that the lowest energy intrinsic defect is the magnesium Frenkel type, where a magnesium atom moves from the M1 site to form a split interstitial defect. This defect has 2 four-co-ordinated magnesium atoms located outside opposite triangular faces of an otherwise vacant M1 octahedron. The split interstitial defect is more stable than regular interstitials where magnesium is located in either of the two structurally vacant octahedral sites in the hexagonally close packed oxygen lattice. M1 vacancies are also found to form when iron(II) oxidises to iron(III). The energy of the defects away fromthe equilibrium positions allows the energy barrier to diffusion to be calculated.Wehave considered the migration of both magnesium vacancies and interstitials and find that vacancies are more mobile. When the contribution from the formation energy of the defects is included we arrive at activation energies for vacancy diffusion that are in agreement with experiment

Anisotropic Magnetoresistance Effects in Fe, Co, Ni, Fe_4N, and Half-Metallic Ferromagnet: A Systematic Analysis

We theoretically analyze the anisotropic magnetoresistance (AMR) effects of bcc Fe (+), fcc Co (+), fcc Ni (+), Fe$_4$N (-), and a half-metallic ferromagnet (-). The sign in each ( ) represents the sign of the AMR ratio observed experimentally. We here use the two-current model for a system consisting of a spin-polarized conduction state and localized d states with spin--orbit interaction. From the model, we first derive a general expression of the AMR ratio. The expression consists of a resistivity of the conduction state of the $\sigma$ spin ($\sigma=\uparrow$ or $\downarrow$), $\rho_{s \sigma}$, and resistivities due to s--d scattering processes from the conduction state to the localized d states. On the basis of this expression, we next find a relation between the sign of the AMR ratio and the s--d scattering process. In addition, we obtain expressions of the AMR ratios appropriate to the respective materials. Using the expressions, we evaluate their AMR ratios, where the expressions take into account the values of $\rho_{s \downarrow}/\rho_{s \uparrow}$ of the respective materials. The evaluated AMR ratios correspond well to the experimental results.Comment: 17 pages, 12 figures, to be published in J. Phys. Soc. Jpn, minor mistakes corrected, final versio

L'Union Européenne des Paiements

[eng] The circumstances leading up to the establishment of the E.P are summarised and the essential features of its mechanism are examined one by one multilateral compensations automatic grants of credits and gold settlements allowing the regulation of temporary fluctuations in the balanec of payments of the Western European countries and tlieir associated mone tary areas The analysis brings out the advantages of this multilateral system which has enabled the European countries despite the otw level of their currency reserves to develop their visible and invisible trade with each other on non-discriminatory basis At the present moment the member countries of O.E.E.G are examining the ways in Iwhich the E.P system might be improved on the occasion of its prolongation for further financial year at the same time return to convertibility of certain European currencies is envisaged The present analysis clarifies the origins of the operating difficulties of the Union and of the criticisms Which are levelled at it

Convergence et disparités régionales du poids de l'enseignement supérieur en France : 1964-2000

National audienceUn des thèmes dominants traité dans la littérature macro-économique depuis une dizaine d'années est celui de la convergence des économies régionales ou nationales. L'objet de l'article est d'appliquer cette démarche de recherche à l'évolution du poids de l'enseignement supérieur français dans le total des effectifs scolarisés sur la période 1964-2000. Comment l'enseignement supérieur est-il réparti sur le territoire ? Comment cette répartition a-t-elle évolué ? Observe-t-on un processus de convergence entre les régions françaises