Secular orbital dynamics of the innermost exoplanet of the υ -Andromedæ system

We introduce a quasi-periodic restricted Hamiltonian to describe the secular motion of a small-mass planet in a multi-planetary system. In particular, we refer to the motion of υ -And b which is the innermost planet among those discovered in the extrasolar system orbiting around the υ -Andromedæ A star. We preassign the orbits of the Super-Jupiter exoplanets υ -And c and υ -And d in a stable configuration. The Fourier decompositions of their secular motions are reconstructed by using the well-known technique of the (so-called) frequency analysis and are injected in the equations describing the orbital dynamics of υ -And b under the gravitational effects exerted by those two external exoplanets (that are expected to be major ones in such an extrasolar system). Therefore, we end up with a Hamiltonian model having 2 + 3 / 2 degrees of freedom; its validity is confirmed by the comparison with several numerical integrations of the complete four-body problem. Furthermore, the model is enriched by taking into account also the effects due to the relativistic corrections on the secular motion of the innermost exoplanet. We focus on the problem of the stability of υ -And b as a function of the parameters that mostly impact on its orbit, that are the initial values of its inclination and the longitude of its node (as they are measured with respect to the plane of the sky). In particular, we study the evolution of its eccentricity, which is crucial to exclude orbital configurations with high probability of (quasi)collision with the central star in the long-time evolution of the system. Moreover, we also introduce a normal form approach, that is based on the complete average of our restricted model with respect to the angles describing the secular motions of the major exoplanets. Therefore, our Hamiltonian model is further reduced to a system with 2 degrees of freedom, which is integrable because it admits a constant of motion that is related to the total angular momentum. This allows us to very quickly preselect the domains of stability for υ -And b , with respect to the set of the initial orbital configurations that are compatible with the observations

Improved convergence estimates for the Schröder-Siegel problem

We reconsider the Schröder–Siegel problem of conjugating an analytic map in ℂ in the neighborhood of a fixed point to its linear part, extending it to the case of dimension n>1 . Assuming a condition which is equivalent to Bruno’s one on the eigenvalues λ1,…,λn of the linear part, we show that the convergence radius ρ of the conjugating transformation satisfies lnρ(λ)≥−CΓ(λ)+C′ with Γ(λ) characterizing the eigenvalues λ , a constant C′ not depending on λ and C=1 . This improves the previous results for n>1 , where the known proofs give C=2 . We also recall that C=1 is known to be the optimal value for n=1

Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS

We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. We find at the base of the jet high electron density, $n_e \sim$ 10$^5$, and very low ionisation, $x_e \sim 0.02-0.05$, which combine to give a total density up to $n_H \sim$ 3 10$^6$. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of $x_e$ from 0.05 to a plateau at 0.7 downstream at 2$''$ from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, $\dot{M}_j$, in the blue-shifted lobe in different velocity channels, that contribute to a total of $\dot{M}_j \sim$ 8 $\pm$ 4 10$^{-9}$ M$_\odot$ yr$^{-1}$. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of $\dot{L}_j \sim$ 2.9 $\pm$ 1.5 10$^{-6}$ M$_\odot$ yr$^{-1}$ AU km s$^{-1}$. The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution.Comment: 16 pages, 18 figure

Sulla stabilit\ue0 del problema planetario dei tre corpi

Si discute se il celebre teorema di Kolmogorov sulla persistenza di moti quasi periodici si applichi al sistema solare, prendendo a modello il problema dei tre corpi nel caso in cui le masse ed i parametri orbitali siano quelli di Sole, Giove e Saturno. Facendo ricorso a metodi di manipolazione algebrica al calcolatore si mostra per la prima volta che almeno in questo caso il teorema si puo' applicare, e dunque che le orbite dei due pianeti maggiori, almeno nell'approssimazione del problema dei tre corpi, giacciono in prossimita' di tori invarianti di Kolmogorov. Si discutono poi brevemente le possibili estensioni di questo lavoro accennando alla possibilita' di affrontare il problema classico della stabilita' del sistema solare alla luce della teoria della stabilita' esponenziale alla Nekhoroshev

Secular dynamics of a planar model of the Sun-Jupiter-Saturn-Uranus system; effective stability into the light of Kolmogorov and Nekhoroshev theories

We investigate the long-time stability of the Sun-Jupiter-Saturn-Uranus system by considering a planar secular model, that can be regarded as a major refinement of the approach first introduced by Lagrange. Indeed, concerning the planetary orbital revolutions, we improve the classical circular approximation by replacing it with a solution that is invariant up to order two in the masses; therefore, we investigate the stability of the secular system for rather small values of the eccentricities. First, we explicitly construct a Kolmogorov normal form, so as to find an invariant KAM torus which approximates very well the secular orbits. Finally, we adapt the approach that is at basis of the analytic part of the Nekhoroshev's theorem, so as to show that there is a neighborhood of that torus for which the estimated stability time is larger than the lifetime of the Solar System. The size of such a neighborhood, compared with the uncertainties of the astronomical observations, is about ten times smaller.Comment: 31 pages, 2 figures. arXiv admin note: text overlap with arXiv:1010.260

A Semi-Analytic Algorithm for Constructing Lower Dimensional Elliptic Tori in Planetary Systems

We adapt the Kolmogorov's normalization algorithm (which is the key element of the original proof scheme of the KAM theorem) to the construction of a suitable normal form related to an invariant elliptic torus. As a byproduct, our procedure can also provide some analytic expansions of the motions on elliptic tori. By extensively using algebraic manipulations on a computer, we explicitly apply our method to a planar four-body model not too different with respect to the real Sun--Jupiter--Saturn--Uranus system. The frequency analysis method allows us to check that our location of the initial conditions on an invariant elliptic torus is really accurate.Comment: 31 pages, 4 figure

Predicting erythropoietin resistance in hemodialysis patients with type 2 diabetes

<p>Background: Resistance to ESAs (erythropoietin stimulating agents) is highly prevalent in hemodialysis patients with diabetes and associated with an increased mortality. The aim of this study was to identify predictors for ESA resistance and to develop a prediction model for the risk stratification in these patients.</p> <p>Methods: A post-hoc analysis was conducted of the 4D study, including 1015 patients with type 2 diabetes undergoing hemodialysis. Determinants of ESA resistance were identified by univariate logistic regression analyses. Subsequently, multivariate models were performed with stepwise inclusion of significant predictors from clinical parameters, routine laboratory and specific biomarkers.</p> <p>Results: In the model restricted to clinical parameters, male sex, shorter dialysis vintage, lower BMI, history of CHF, use of ACE-inhibitors and a higher heart rate were identified as independent predictors of ESA resistance. In regard to routine laboratory markers, lower albumin, lower iron saturation, higher creatinine and higher potassium levels were independently associated with ESA resistance. With respect to specific biomarkers, higher ADMA and CRP levels as well as lower Osteocalcin levels were predictors of ESA resistance.</p> <p>Conclusions: Easily obtainable clinical parameters and routine laboratory parameters can predict ESA resistance in diabetic hemodialysis patients with good discrimination. Specific biomarkers did not meaningfully further improve the risk prediction of ESA resistance. Routinely assessed data can be used in clinical practice to stratify patients according to the risk of ESA resistance, which may help to assign appropriate treatment strategies.</p&gt

polluted online information surfing italian websites dealing with the topic of waste and health

In the field of health communication, a particularly critical issue is communication to the public of environmental risks, especially on topics for which there is still a high degree of scientific uncertainty regarding risk estimates. One such topic is undoubtedly the impact of waste on people's health. The aim of this study was to evaluate the presence and characteristics of Italian websites dealing with the topic of waste and health. The keywords 'waste' and 'health' were entered in 2010 in the three most commonly used search engines, and the first five pages were analysed. The selected websites were coded according to the content analysis method. For websites of interest we evaluated the 'page rank'. Out of the 150 occurrences analysed, the number of websites found to deal with this subject was only 19, four of which were of an institutional nature. The majority of websites gave a message of increased health risk associated with the three kinds of waste disposal tackled. As regards visibility, only one of the four institutional websites maintained its position on the first page of the three search engines. We found that institutional health websites have low visibility, despite extensive media coverage of waste and health issues in Italy as a result of the Naples case, which was debated globally. This indicates that public health institutions' web strategies are basically unable to meet people's health information requirements, which could strengthen rival health information providers

Definition of indicators of appropriateness in the management of neovascular age-related macular degeneration: An expert opinion

Wet age-related macular degeneration is a chronic condition culminating, in most cases, in blindness. The introduction of anti-angiogenic agents in 2006 has represented a major breakthrough in the treatment of the disease, but timely and effective treatment with regular follow-up and monitoring is mandatory to stabilize and preserve visual acuity. In clinical practice, however, appropriate therapy provision is frequently challenged by economic and organizational issues that result in suboptimal visual outcomes and increased incidence of legal blindness. International Guidelines have defined a diagnostic and therapeutic pathway to ensure the best practice in wet age-related macular degeneration management, but reference parameters to evaluate and compare the performance of Retina Centers are lacking. To address the appropriateness of wet age-related macular degeneration management in Italy, a multidisciplinary panel of ten experts gathered in three meetings. They defined three sets of indicators and relative benchmark values that each Center should comply with to ensure patients optimal care already from the first access: (a) clinical intervention indicators, to determine the possible Center\u2019s deviation from the diagnostic and therapeutic pathway; (b) outcome indicator, to evaluate the socioeconomic impact of the healthcare systems\u2019 performance; (c) management indicators, to test the size of the gap between the Center\u2019s supply and demand. Once the indicators have been analyzed, healthcare systems can plan actions to improve appropriateness and monitor their effects. However, to put this in practice, a concerted effort by all parts involved in healthcare provision is required, together with adequate systems to analyze clinical and administrative documentation