On the decay of correlations in Sinai billiards with infinite horizon

We compute the decay of the autocorrelation function of the observable $|v_x|$ in the Sinai billiard and of the observable $v_x$ in the associated Lorentz gas with an approximation due to Baladi, Eckmann and Ruelle. We consider the standard configuration where the disks is centered inside a unit square. The asymptotic decay is found to be $C(t) \sim c(R)/t$. An explicit expression is given for the prefactor $c(R)$ as a function of the radius of the scatterer. For the small scatterer case we also present expressions for the preasymptotic regime. Our findings are supported by numerical computations.Comment: 6 pages LaTeX, 5 postscript figure

The strong interaction limit of continuous-time weakly self-avoiding walk

The strong interaction limit of the discrete-time weakly self-avoiding walk (or Domb--Joyce model) is trivially seen to be the usual strictly self-avoiding walk. For the continuous-time weakly self-avoiding walk, the situation is more delicate, and is clarified in this paper. The strong interaction limit in the continuous-time setting depends on how the fugacity is scaled, and in one extreme leads to the strictly self-avoiding walk, in another to simple random walk. These two extremes are interpolated by a new model of a self-repelling walk that we call the "quick step" model. We study the limit both for walks taking a fixed number of steps, and for the two-point function

Periodic orbit sum rules for billiards: Accelerating cycle expansions

We show that the periodic orbit sums for 2-dimensional billiards satisfy an infinity of exact sum rules. We test such sum rules and demonstrate that they can be used to accelerate the convergence of cycle expansions for averages such as Lyapunov exponents.Comment: 19 pages, 5 postscript figures, submitted to Journal of Physics

Plio-Pleistocene changes in water mass exchange and erosional inputs in the Fram Strait

We determined the isotopic composition of neodymium (Nd) and lead (Pb) of past seawater to reconstruct water mass exchange and erosional input between the Arctic Ocean and the Norwegian-Greenland Seas over the past 5 Ma. For this purpose, sediments of ODP site 911 (leg 151) located at 900 m water depth on the Yermak Plateau in the Fram Strait were used. The paleo-seawater variability of Nd and Pb isotopes was extracted from the sea water-derived metal oxide coatings on the sediment particles following the leaching method of Gutjahr et al. (2007). All radiogenic isotope data were acquired by Multi-Collector (MC) ICP-MS. The site 911 stratigraphy of Knies et al. (2009) was applied. Surface sediment Sr and Nd isotope data, as well as downcore Sr isotope data obtained on the same leaches are close to seawater and confirm the seawater origin of the Nd and Pb isotope signatures. The deep water Nd isotope time series extracted from site 911 was in general more radiogenic ("Nd = -7.5 to -10) than present day deep water ("Nd = -9.8 to -11.8) in the area of the Fram Strait (Andersson et al., 2008) and does not show a systematic trend with time. In contrast, the radiogenic isotope composition of Pb evolved from 206Pb/204Pb ratios around 18.7 to more radiogenic values around 19.2 between 2 Ma and today. The data indicate that mixing of water masses from the Arctic Ocean and the Norwegian-Greenland Seas has controlled the Nd isotope signatures of deep waters on the Yermak Plateau over the past 5 Ma. Prior to 1.7 Ma the Nd isotope signatures on the Yermak Plateau were less radiogenic than waters from the same depth in the central Arctic Ocean (Haley et al., 2008) pointing to a greater influence from the Norwegian-Greenland Seas. After 1.7 Ma the central Arctic and Yermak Plateau data have varied around similar values indicating water mass mixing overall similar to today. In contrast, the Pb isotope composition of deep waters in the Fram Strait appears to have been dominated by weathering inputs from glacially weathering old continental landmasses, such as Greenland or parts of Svalbard since 2 Ma. A similar control over the Pb isotope evolution of seawater since the onset of Northern Hemisphere Glaciation was recorded by ferromanganese crusts that grew from North Atlantic DeepWater in the western North Atlantic. References: Gutjahr, M., Frank, M., Stirling, C.H., Klemm, V., van de Flierdt, T. and Halliday, A.N. (2007): Reliable extraction of a deepwater trace metal isotope signal from Fe-Mn oxyhydroxide coatings of marine sediments.- Chemical Geology 242, 351-370 Haley B. A., M. Frank, R.F. Spielhagen and A. Eisenhauer (2008): Influence of brine formation on Arctic Ocean circulation over the past 15 million years. Nature Geoscience 1, 68–72 Andersson, P.S., Porcelli, D., Frank, M., Björk, G., Dahlqvist, R. and Gustafsson, Ö. (2008): Neodymium isotopes in seawater from the Barents Sea and Fram Strait Arctic- Atlantic gateways.- Geochim. Cosmochim. Acta 72, 2854-2867 Knies, J., J. Matthiessen, C. Vogt, J.S. Laberg, B.O. Hjelstuen, M.Smelror, E. Larsen, K. Andreassen, T. Eidvin and T.O. Vorren (2009): The Plio-Pleistocene glaciation of the Barents Sea–Svalbard region: a new model based on revised chronostratigraphy - Quaternary Science Reviews 28, 9-10, 812-82

Effect of Etanercept on anti-carbamylated protein antibodies in patients with rheumatoid arthritis

Rheumatoid Arthritis (RA) is a systemic, chronic inflammatory disease characterized by inflammation of synovial joints and production of autoantibodies such as Rheumatoid Factor and antibodies directed against modified proteins - i.e. anti-citrullinated peptides antibody (ACPA). Carbamylation, as a post translational modification, has been recently associated to RA since anti-carbamylated protein antibodies (anti-CarP) have been detected in the sera of RA patients. The effect of treatment on anti-CarP level has been never addressed before. Through this study we aimed to investigate the short term effect of anti-TNF treatment with Etanercept on anti-CarP. We enrolled consecutive RA patients before starting treatment with Etanercept. Clinical data and serum samples were gathered from each patient at baseline and after 3 months of treatment. Disease activity was assessed at baseline and after 3 months by using the C-reactive protein - Disease Activity Score (DAS) 28. Sixty-three age and sex matched healthy donors served as controls. Anti-Car-P antibodies were investigated by immune-enzymatic assay. We enrolled 17 RA patients (F:M 15:2, mean age 44.1 ± 10.7 years, mean disease duration 7.9 ± 5.8 years). Six patients (35.3%) were positive for anti-CarP antibodies at baseline while three months after only 4 patients (23.5%) remained positive. Mean serum level of anti-CarP antibodies at baseline and after 3 months were: 253.0 ± 139.8AU/ml and 271.0 ± 132.4AU/ml respectively. Considering the persistently anti-CarP positive patients, the mean antibody titre increases from 386.2 ± 49.3AU/ml at baseline to 421.8 ± 144.0AU/ml at follow up. The effect of anti-TNF treatment on autoantibody status is still controversial; in particular, data on ACPA variation during treatment are discordant. In our cohort of long standing RA patients, a short term course of Etanercept did not affect the anti-CarP status. In conclusion, this pilot study demonstrated a slight reduction in the percentage of anti-CarP positive patients but an overall increase of antibody titres unrelated to the clinical response to TNF blockade was observed

Modeling the Nd isotopic composition in the North Atlantic basin using an eddy-permitting model

International audienceBoundary Exchange (BE – exchange of elementsbetween continental margins and the open ocean) hasbeen emphasized as a key process in the oceanic cycle ofneodymium (Nd) (Lacan and Jeandel, 2005a). Here, we usea regional eddy-permitting resolution Ocean General CirculationModel (1/4) of the North Atlantic basin to simulatethe distribution of the Nd isotopic composition, consideringBE as the only source. Results show good agreementwith the data, confirming previous results obtained using thesame parameterization of the source in a coarse resolutionglobal model (Arsouze et al., 2007), and therefore the majorcontrol played by the BE processes in the Nd cycle onthe regional scale. We quantified the exchange rate of theBE, and found that the time needed for the continental marginsto significantly imprint the chemical composition of thesurrounding seawater (further referred as characteristic exchangetime) is of the order of 0.2 years. However, thetimescale of the BE may be subject to large variations as avery short exchange time (a few days) is needed to reproducethe highly negative values of surface waters in the LabradorSea, whereas a longer one (up to 0.5 years) is required tosimulate the radiogenic influence of basaltic margins and distinguishthe negative isotopic signatures of North AtlanticDeep Water from the more radiogenic southern origin watermasses. This likely represents geographical variations inerosion fluxes and the subsequent particle load onto the continentalmargins. Although the parameterization of the BEis the same in both configurations of the model, the characteristicexchange time in the eddy-permitting configuration issignificantly lower than the previous evaluations using a lowresolution configuration (6 months to 10 years), but howeverin agreement with the available seawater Nd isotope data.This results highlights the importance of the model dynamicsin simulating the BE proces

An Internal Language for Categories Enriched over Generalised Metric Spaces

Programs with a continuous state space or that interact with physical processes often require notions of equivalence going beyond the standard binary setting in which equivalence either holds or does not hold. In this paper we explore the idea of equivalence taking values in a quantale ?, which covers the cases of (in)equations and (ultra)metric equations among others. Our main result is the introduction of a ?-equational deductive system for linear ?-calculus together with a proof that it is sound and complete (in fact, an internal language) for a class of enriched autonomous categories. In the case of inequations, we get an internal language for autonomous categories enriched over partial orders. In the case of (ultra)metric equations, we get an internal language for autonomous categories enriched over (ultra)metric spaces. We use our results to obtain examples of inequational and metric equational systems for higher-order programs that contain real-time and probabilistic behaviour

Dilemma - An Instant Lexicographer

Dilemma is intended to enhance quality and increase productivity of expert human translators by presenting to the writer relevant lexical information mechanically extracted from comparable existing translations, thus replacing - or compensating for the absence of - a lexicographer and stand-by terminologist rather than the translator. Using statistics and crude surface analysis and a minimum of prior information, Dilemma identifies instances and suggests their counterparts in parallel source and target texts, on all levels down to individual words. Dilemma forms part of a tool kit for translation where focus is on text structure and over-all consistency in large text volumes rather than on framing sentences, on interaction between many actors in a large project rather than on retrieval of machine-stored data and on decision making rather than on application of given rules. In particular, the system has been tuned to the needs of the ongoing translation of European Community legislation into the languages of candidate member countries. The system has been demonstrated to and used by professional translators with promising results.Comment: 3 pages, LaTeX, in proceedings of COLING 9