Comparaison du monitorage cérébral dans la chirurgie carotidienne sous anesthésie générale (Near Infrared-Spectroscopy versus Amplitude Integrated électro-encéphalogramme. Étude prospective uni centrique sur 41 patients)

En cas de sténose carotidienne menaçante, il est recommandé une intervention chirurgicale. Cette intervention peut être source d'ischémie cérébrale lors du clampage carotidien. Il est donc nécessaire de monitorer la fonction cérébrale chez le patient sous anesthésie générale, pour intervenir en cas de souffrance. L'objectif de cette étude était d'évaluer la Near Infra Red Spectroscopy pour le dépistage d'une souffrance cérébrale aigüe au clampage carotidien, comparativement à un aEEG, ainsi qu'à la mesure des pressions moyennes résiduelles carotidiennes. Matériel et méthodes : Nous avons inclus tout patient nécessitant une chirurgie carotidienne sous anesthésie générale sur une durée de 9 mois, Chaque patient était monitoré à l'aide d'un aEEG et d'un INVOSO. Le chirurgien décidait de la mise en place d'un shunt uniquement selon la pression carotidienne moyenne résiduelle, sans connaître les résultats INVOS® et aEEG. Nous avons ensuite comparé la survenue d'une baisse de plus de 20% par rapport à la ligne de base de rS02 avec la survenue ou non d'anomalie aEEG. Nous avons également recueilli la mesure des pressions carotidiennes résiduelles, les événements per opératoires, et la morbi-mortalité post opératoire, Résultats : 41 patients ont été inclus. Comparativement à l'aEEG, l'INVOS® a une sensibilité de 50%, une spécificité de 72,4%. Le taux de faux positifs est élevé (57%). Cependant, il n'existe pas de corrélation statistique significative entre ces deux moyens de dépistage. Comparativement à la mesure des pressions carotidiennes résiduelles moyennes, avec un seuil de 50 mmHg, il y a une concordance significative avec l'INVOS®, avec une sensibilité de 48% mais un spécificité de 87,5%. Trois patients ont reçu de la terlipressine entraînant une anomalie significative du signal INVOS® sans anomalie aEEG, rendant impossible son interprétation. Conclusion : L'INVOSO ne peut être recommandé comme monitorage cérébral unique dans la chirurgie carotidienne sous anesthésie générale. Cependant, il pourrait être utilisé en complément de la mesure des pressions carotidiennes résiduelles. Il existe probablement des facteurs confondants dans l'interprétation de la rS02, et la participation de la vascularisation carotidienne externe ne peut être exclue.ROUEN-BU Médecine-Pharmacie (765402102) / SudocSudocFranceF

Memories of the world of the mountains

This paper describes a particular book called Souvenirs du monde des montagnes, which draws its iconography from the history of a Swiss mountain family from 1910 to 1930. By simply dipping into the first few pages, the reader will be lost between real and virtual universes, wonder about the evolution of the images' meanings, and question an object's true content. This setup, developed using state-of-the-art computer vision technology, offers unprecedented freedom: we can make technological references disappear to place the user in fruitful turmoil between visible and hidden meanings. The shadow of a bird flies over the pages, foxes' lanterns light up the text, paper mountains emerge. Once the last page has been turned, the reader will never look at books in the same way again

The evolution of a network of cosmic string loops

We set up and analyse a model for the non-equilibrium evolution of a network of cosmic strings initially containing only loops and no infinite strings. Due to this particular initial condition, our analytical approach differs significantly from existing ones. We describe the average properties of the network in terms of the distribution function n(l,t) dl, the average number of loops per unit volume with physical length between l and l + dl at time t. The dynamical processes which change the length of loops are then estimated and an equation, which we call the `rate equation', is derived for (dn/dt). In a non-expanding universe, the loops should reach the equilibrium distribution predicted by string statistical mechanics. Analysis of the rate equation gives results consistent with this. We then study the rate equation in an expanding universe and suggest that three different final states are possible for the evolving loop network, each of which may well be realised for some initial conditions. If the initial energy density in loops in the radiation era is low, then the loops rapidly disappear. For large initial energy densities, we expect that either infinite strings are formed or that the loops tend towards a scaling solution in the radiation era and then rapidly disappear in the matter era. Such a scenario may be relevant given recent work highlighting the problems with structure formation from the standard cosmic string scenario.Comment: LaTeX, 27 pages, 10 figures included as .eps file

Scaling in Numerical Simulations of Domain Walls

We study the evolution of domain wall networks appearing after phase transitions in the early Universe. They exhibit interesting dynamical scaling behaviour which is not yet well understood, and are also simple models for the more phenomenologically acceptable string networks. We have run numerical simulations in two- and three-dimensional lattices of sizes up to 4096^3. The theoretically predicted scaling solution for the wall area density A ~ 1/t is supported by the simulation results, while no evidence of a logarithmic correction reported in previous studies could be found. The energy loss mechanism appears to be direct radiation, rather than the formation and collapse of closed loops or spheres. We discuss the implications for the evolution of string networks.Comment: 7pp RevTeX, 9 eps files (including six 220kB ones

Cosmic string loops and large-scale structure

We investigate the contribution made by small loops from a cosmic string network as seeds for large-scale structure formation. We show that cosmic string loops are highly correlated with the long-string network on large scales and therefore contribute significantly to the power spectrum of density perturbations if the average loop lifetime is comparable to or above one Hubble time. This effect further improves the large-scale bias problem previously identified in earlier studies of cosmic string models.Comment: 5 pages, 5 figure

Scale-dependent bias induced by local non-Gaussianity: A comparison to N-body simulations

We investigate the effect of primordial non-Gaussianity of the local f_NL type on the auto- and cross-power spectrum of dark matter haloes using simulations of the LCDM cosmology. We perform a series of large N-body simulations of both positive and negative f_NL, spanning the range between 10 and 100. Theoretical models predict a scale-dependent bias correction \Delta b(k,f_NL) that depends on the linear halo bias b(M). We measure the power spectra for a range of halo mass and redshifts covering the relevant range of existing galaxy and quasar populations. We show that auto and cross-correlation analyses of bias are consistent with each other. We find that for low wavenumbers with k<0.03 h/Mpc the theory and the simulations agree well with each other for biased haloes with b(M)>1.5. We show that a scale-independent bias correction improves the comparison between theory and simulations on smaller scales, where the scale-dependent effect rapidly becomes negligible. The current limits on f_NL from Slosar et al. (2008) come mostly from very large scales k<0.01 h/Mpc and, therefore, remain valid. For the halo samples with b(M)<1.5-2 we find that the scale- dependent bias from non-Gaussianity actually exceeds the theoretical predictions. Our results are consistent with the bias correction scaling linearly with f_NL.Comment: 13 pages, 10 figures. (v2): substantial changes. added a physically motivated scale-independent bias correction which improves significantly the agreement with the simulations (v3): matches published versio

Signatures of Topological Defects

We argue that due to various restrictions cosmic strings and monopole-string networks are not likely to produce the observed flux of ultra-high energy cosmic rays (UHECR). Among the topological defects studied so far, the most promising UHECR sources are necklaces and monopolonia. Other viable sources which are similar to topological defects are relic superheavy particles. All these sources have an excess of pions (and thus photons) over nucleons at production. We demonstrate that in the case of necklaces the diffuse proton flux can be larger than photon flux, due to absorption of the latter on radiobackground, while monopolonia and relic particles are concentrated in the Galactic halo, and the photon flux dominates. Another signature of the latter sources is anisotropy imposed by asymmetric position of the sun in the Galactic halo. In all cases considered so far, including necklaces, photons must be present in ultra-high energy radiation observed from topological defects, and experimental discrimination between photon-induced and proton-induced extensive air showers can give a clue to the origin of ultra-high energy cosmic rays.Comment: version accepted for publication in Phys. Rev. D. No changes in the conclusions and in figure