INFORMATISATION DES DONNEES DENTAIRES POUR L'IDENTIFICATION DES VICTIMES EN ALGERIE : DEFIS ET ETAT ACTUEL

Si la base des méthodes d’identification reste la même depuis des décennies, les techniques actuelles n’ont plus grand-chose en commun avec celles des débuts. Les progrès de l’identification sont fortement corrélés à l’essor de l’informatique et aux innovations technologiques qui en découlent. L’informatique n’a pas seulement permis d’améliorer les méthodes d’identification générales (analyse ADN, empreintes digitales), elle a également eu un impact considérable sur les méthodes d’identification odontologiques.Les techniques d’identification actuelles vont, des plus classiques comme la simple comparaison d’odontogrammes ante et post-mortem, aux plus sophistiquées basées sur le traitement informatisé. L’utilisation de logiciels d’identification permet une confrontation automatisée d’une masse de données, utile surtout lors de grandes catastrophes. Ces logiciels améliorent la phase comparative en termes de temps, de performance et de fiabilité des résultats

Calculation of the singlet-triplet gap of the antiferromagnetic Heisenberg Model on the ladder

The ground state energy and the singlet-triplet energy gap of the antiferromagnetic Heisenberg model on a ladder is investigated using a mean field theory and the density matrix renormalization group. Spin wave theory shows that the corrections to the local magnetization are infinite. This indicates that no long range order occurs in this system. A flux-phase state is used to calculate the energy gap as a function of the transverse coupling, $J_\perp$, in the ladder. It is found that the gap is linear in $J_\perp$ for $J_\perp\gg 1$ and goes to zero for $J_\perp\to 0$. The mean field theory agrees well with the numerical results.Comment: 11pages,6 figures (upon request) Revtex 3.0, Report#CRPS-94-0

The Association of Cerebral Palsy with Other Disability in Children with Perinatal Arterial Ischemic Stroke

The association of cerebral palsy with other disabilities in children with perinatal stroke has not been well-studied. We examined this association in 111 children with perinatal stroke: 67 with neonatal presentation, and 44 with delayed presentation. Seventy-six children (68%) had cerebral palsy, which was hemiplegic in 66 and tri- or quadriplegic in 10. Fifty-five (72%) children with cerebral palsy had at least one other disability: 45 (59%) had a cognitive/speech impairment (moderate-severe in 20), and 36 (47%) had epilepsy (moderate-severe in 11). In children with neonatal presentation, cerebral palsy was associated with epilepsy (P = 0.0076) and cognitive impairment (P = 0.0001). These associations could not be tested in children with delayed presentation because almost all children in this group had cerebral palsy. In another analysis with multivariate logistic regression for children with cerebral palsy, children who had both neonatal presentation and history of cesarean-section delivery were more likely to have epilepsy (P = 0.001). Children with cerebral palsy after perinatal stroke who had neonatal presentation were more likely to have severe cognitive impairment (odds ratio, 7.78; 95% confidence interval, 1.80-47.32) or severe epilepsy (odds ratio, 6.64; 95% confidence interval, 1.21-69.21) than children with delayed presentation. Children with cerebral palsy after perinatal stroke are likely to have an additional disability; those with neonatal presentation are more likely to have a severe disability

A Renormalization Group Method for Quasi One-dimensional Quantum Hamiltonians

A density-matrix renormalization group (DMRG) method for highly anisotropic two-dimensional systems is presented. The method consists in applying the usual DMRG in two steps. In the first step, a pure one dimensional calculation along the longitudinal direction is made in order to generate a low energy Hamiltonian. In the second step, the anisotropic 2D lattice is obtained by coupling in the transverse direction the 1D Hamiltonians. The method is applied to the anisotropic quantum spin half Heisenberg model on a square lattice.Comment: 4 pages, 4 figure

Semiclassical description of spin ladders

The Heisenberg spin ladder is studied in the semiclassical limit, via a mapping to the nonlinear $\sigma$ model. Different treatments are needed if the inter-chain coupling $K$ is small, intermediate or large. For intermediate coupling a single nonlinear $\sigma$ model is used for the ladder. Its predicts a spin gap for all nonzero values of $K$ if the sum $s+\tilde s$ of the spins of the two chains is an integer, and no gap otherwise. For small $K$, a better treatment proceeds by coupling two nonlinear sigma models, one for each chain. For integer $s=\tilde s$, the saddle-point approximation predicts a sharp drop in the gap as $K$ increases from zero. A Monte-Carlo simulation of a spin 1 ladder is presented which supports the analytical results.Comment: 8 pages, RevTeX 3.0, 4 PostScript figure

Density Matrix Renormalization Group Study of the Spin 1/2 Heisenberg Ladder with Antiferromagnetic Legs and Ferromagnetic Rungs

The ground state and low lying excitation of the spin 1/2 Heisenberg ladder with antiferromagnetic leg ($J$) and ferromagnetic rung ($-\lambda J, \lambda >0$) interaction is studied by means of the density matrix renormalization group method. It is found that the state remains in the Haldane phase even for small $\lambda \sim 0.02$ suggesting the continuous transition to the gapless phase at $\lambda = 0$. The critical behavior for small $\lambda$ is studied by the finite size scaling analysis. The result is consistent with the recent field theoretical prediction.Comment: 11 pages, revtex, figures upon reques

Fermionic description of spin-gap states of antiferromagnetic Heisenberg ladders in a magnetic field

Employing the Jordan-Wigner transformation on a unique path and then making a mean-field treatment of the fermionic Hamiltonian, we semiquantitatively describe the spin-gap states of Heisenberg ladders in a field. The appearance of magnetization plateaux is clarified as a function of the number of legs.Comment: 2 pages, 3 figures embedded, J. Phys. Soc. Jpn. Vol. 71, No. 6, 1607 (2002

Haldane gap in the quasi one-dimensional nonlinear σ\sigma-model

This work studies the appearance of a Haldane gap in quasi one-dimensional antiferromagnets in the long wavelength limit, via the nonlinear $\sigma$-model. The mapping from the three-dimensional, integer spin Heisenberg model to the nonlinear $\sigma$-model is explained, taking into account two antiferromagnetic couplings: one along the chain axis ($J$) and one along the perpendicular planes ($J_\bot$) of a cubic lattice. An implicit equation for the Haldane gap is derived, as a function of temperature and coupling ratio $J_\bot/J$. Solutions to these equations show the existence of a critical coupling ratio beyond which a gap exists only above a transition temperature $T_N$. The cut-off dependence of these results is discussed.Comment: 14 pages (RevTeX 3.0), 3 PostScript figures appended (printing instructions included

Spin polarons in triangular antiferromagnets

The motion of a single hole in a 2D triangular antiferromagnet is investigated using the t-J model. The one-hole states are described by strings of spin deviations around the hole. Using projection technique the one-hole spectral function is calculated. For large J/t we find low-lying quasiparticle-like bands which are well separated from an incoherent background by a gap of order J. However, for small J/t this gap vanishes and the spectrum becomes broad over an energy range of several t. The results are compared with SCBA calculations and numerical data.Comment: 4 pages, 6 figs, to be publish in PR