New Strong-Field QED Effects at ELI: Nonperturbative Vacuum Pair Production

Since the work of Sauter, and Heisenberg, Euler and K\"ockel, it has been understood that vacuum polarization effects in quantum electrodynamics (QED) predict remarkable new phenomena such as light-light scattering and pair production from vacuum. However, these fundamental effects are difficult to probe experimentally because they are very weak, and they are difficult to analyze theoretically because they are highly nonlinear and/or nonperturbative. The Extreme Light Infrastructure (ELI) project offers the possibility of a new window into this largely unexplored world. I review these ideas, along with some new results, explaining why quantum field theorists are so interested in this rapidly developing field of laser science. I concentrate on the theoretical tools that have been developed to analyze nonperturbative vacuum pair production.Comment: 20 pages, 9 figures; Key Lecture at the ELI Workshop and School on "Fundamental Physics with Ultra-High Fields", 29 Sept - 2 Oct. 2008, Frauenworth Monastery, Germany; v2: refs updated, English translations of reviews of Nikishov and Ritu

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

A model for fluids in metamorphosed ultramafic rocks. IV. Metasomatic veins in metaharzburgites of Cima di Gagnone, Valle Verzasca, Switzerland

The high grade metamorphic part of the Penninic zone of the Central Alps is characterized by 1 to 100 meters large ultramafic lenses of originally harzburgitic composition. A usually concentric zonation of these lenses indicates a syntectonic hydrothermal alteration related to the regional metamorphism. Five different zones can be distinguished : 1) original rock (mainly olivine-enstatite-chlorite-Cr-Fe-spinel), 2) hydrated zone (olivine-talc-chlorite-Cr-Fe-spinel ± amphibole), 3) hydrated and carbonatized zone (talc-magnesite-chlorite-amphibole-Fe-spinel), 4) zone strongly enriched in Ca, Al and Si (amphibole-chlorite-Fe-spinel ± magnesite, pentlandite), 5) complex marginal zonation (mono-and bimineralic zones of biotite, amphibole and plagioclase). The spectacular zone boundaries allow reconstruction of fluid-rock reactions in detail. Using temperature and pressure estimations of 580-650 °C and 5 kbar, the fluid composition in the various zones can be estimated : CO₂, O₂ and S₂ increase towards the margins of the lenses, X[CO₂] showing values between 0 and 0.9. Aqueous species concentrations like SiO₂, Ca, A1 and Mg also increase towards the margins. The pH is predicted to vary between 5 and 7. Direction and extent of mass fluxes are estimated on the basis of field observations and various assumptions concerning mass and volume of the zones. Whereas Mg and Fe appear to be internally redistributed, large amounts of Si, Al and Ca are predicted to move in from felsic and mafic country rocks, leading to a volume increase of up to 30 %. The only slightly affected country rocks and stable isotope data exclude a local origin of these elements and suggest a more distant source of the fluid phase. The dominant mass transport mechanism for aqueous species is assumed to be infiltration in a fluid pressure gradient. Locally at zone boundaries, composition — distance plots for Fe indicate a combination of diffusion and infiltration.Le domaine le plus fortement métamorphique de la zone pennique des Alpes centrales est caractérisé par la présence de lentilles ultramafiques métriques à hectométriques d'origine harzburgitique. On observe dans celles-ci une zonation souvent concentrique indiquant une altération hydrothermale liée au métamorphisme régional. Du centre au bord, cinq zones ont été distinguées : 1) roche originale (olivine-enstatite-chlorite-Fe-Cr-Spinelle), 2) zone hydratée (olivine-talc-chlorite-Cr-Fe-spinelle), 3) zone hydratée et carbonatée (talc-magnésite-chlorite-amphibole-Fe-spinelle), 4) zone fortement enrichie en Ca, Al et Si (amphibole-chlorite-Fe-spinelle ± magnésite-pentlandite), 5) zone marginale complexe (diverses zones mono-et biminérales à biotite, amphibole ou plagioclase). Les limites de chaque zone sont très spectaculaires et significatives ; elles permettent de reconstruire les réactions d'interaction entre le fluide et la toche. Sur la base de conditions de température et de pression de 580-650 °C et 5 kbar, la composition du fluide dans les diverses zones peut être déduite et nous constatons que CO₂, O₂ et S₂ augmentent vers l'extérieur des lentilles, X[CO₂] variant entre 0 et 0,9. Les concentrations des espèces aqueuses telle que SiO₂, Ca, Al et Mg augmentent également vers l'extérieur. Le pH varierait entre 5 et 7. A partir de critères de terrain et d'hypothèses sur les modifications de volume et de masse de chaque zone, le sens et la quantité de transferts de masse sont déterminés. Alors que Mg et Fe resteraient constants, de grandes quantités de Si, Al et Ca d'origine externe pénétreraient dans les lentilles ultramafiques en provoquant jusqu'à 30 % d'augmentation de volume. Le fait que les roches encaissantes (gneiss, amphibolite, marbre) ne soient guère altérées indique une origine plus lointaine de la phase fluide, ce qui est confirmé par des analyses d'isotopes stables. Le mécanisme dominant de transport des espèces aqueuses serait celui d'infiltration dans la direction du gradient de pression de la phase fluide. Localement, à la limite des zones, le changement de la composition avec la distance de certains minéraux indique une combinaison de diffusion et infiltration.Pfeifer Hans-Rudolf. A model for fluids in metamorphosed ultramafic rocks III. Mass transfer under amphibolite facies conditions in olivine˗enstatite rocks of the Central Alps, Switzerland. In: Bulletin de Minéralogie, volume 104, 6, 1981. 26e congrès géologique international – Paris – Juillet 1980. Section Minéralogie. Section Pétrographie : symposium « Interactions fluides, minéraux, roches »