On artificial transits feasibility and SETI

It is known that the shape of a planet (oblateness, rings, etc.) slightly modifies the shape of the transit light curve. The forthcoming space missions (Corot, Kepler), able to detect the transit of Earth-like planets, could a fortiori also detect the transit of artificial planet-size objects if their shape is significantly different from a natural (planetary) object. Multiple artificial objects would also produce transit light curves easily recognizable from natural transits. Artificial transits, especially of multiple objects, could be used for the transmission of clear attention-getting signals, with a sky coverage (efficiency) comparable to that of the laser pulse method. Although out of reach of current human technologies, the building of an Earth-size 1-micron thick mask would require energy and bulk material amounts already managed on Earth today. The migration of the mask toward an inner orbit and its protection against asteroids or meteoroids are also briefly discussed.Comment: A 2-page paper to appear in 'Scientific Highlights 2005', proceedings of the 'Semaine de l'Astrophysique Francaise - Journees de la Societe Francaise d'Astronomie et d'Astrophysique', 27th June - 1st July 2005, Strasbourg, eds. F. Casoli et al., EDP Science

Transit Lightcurve Signatures of Artificial Objects

The forthcoming space missions, able to detect Earth-like planets by the transit method, will a fortiori also be able to detect the transit of artificial planet-size objects. Multiple artificial objects would produce lightcurves easily distinguishable from natural transits. If only one artificial object transits, detecting its artificial nature becomes more difficult. We discuss the case of three different objects (triangle, 2-screen, louver-like 6-screen) and show that they have a transit lightcurve distinguishable from the transit of natural planets, either spherical or oblate, although an ambiguity with the transit of a ringed planet exists in some cases. We show that transits, especially in the case of multiple artificial objects, could be used for the emission of attention-getting signals, with a sky coverage comparable to the laser pulse method. The large number of expected planets (several hundreds) to be discovered by the transit method by next space missions will allow to test these ideas.Comment: Accepted for publication in ApJ. Manuscript: 17 pages, 8 figure

Associations between poor oral health and reinjuries in male elite soccer players : a cross-sectional self-report study

Background: Although it is well known that oral pathogens can enter the systemic circulation and cause disease, it is largely unknown if poor oral health increases the risk of sports injuries. The purpose of this study is to investigate the association between poor oral health and reinjuries in male elite soccer players, adjusted for psychosocial problems and player characteristics. Methods: 184 Players in premier league soccer clubs and 31 elite, junior soccer players in the Netherlands, Belgium and England, were enrolled in a retrospective cross-sectional study. The Sports Injury Risk Indicator, a self assessed questionnaire, was used to obtain information on reinjuries, age and player position, oral health and psychosocial problems. The number of different types of oral health problems was used as an indicator of poor oral health. (SumDental, range 0-2: 0 = no oral health problems, 1 = one type of oral health problem and 2 = two or more types of oral health problems). Multivariable logistic regression was used to investigate whether SumDental was associated with reinjuries, after adjustment for psychosocial problems and player characteristics. Results: 37% of the players reported no oral health problems, 43% reported one type of oral health problem and 20% reported two or more types of oral health problems. After full adjustment for age, player position and psychosocial problems (i.e. injury anxiety, psychophysical stress, unhealthy eating habits and dissatisfaction with trainer/team), poor oral health (SumDental) was positively associated with all kind of reinjuries whether analyzed as a continuous variable or as a categorical variable. The fully adjusted odds ratios for SumDental analyzed as a continuous variable were: in relation to repeated exercise-associated muscle cramps: 1.82(95% confidence interval (CI): 1.07, 3.12), in relation to muscle or tendon reinjury 1.57 (95% CI: 1.01, 2.45) and in relation to multiple types of reinjury 1.88 (95% CI: 1.19, 2.97). Conclusion: The results from this study justify a thorough examination of the effects of oral health problems on the injury risk of playing elite soccer

The Earth as an extrasolar planet: The vegetation spectral signature today and during the last Quaternary climatic extrema

The so-called Vegetation Red-Edge (VRE), a sharp increase in the reflectance around $700 nm$, is a characteristic of vegetation spectra, and can therefore be used as a biomarker if it can be detected in an unresolved extrasolar Earth-like planet integrated reflectance spectrum. Here we investigate the potential for detection of vegetation spectra during the last Quaternary climatic extrema, the Last Glacial Maximum (LGM) and the Holocene optimum, for which past climatic simulations have been made. By testing the VRE detectability during these extrema when Earth's climate and biomes maps were different from today, we are able to test the vegetation detectability on a terrestrial planet different from our modern Earth. Data from the Biome3.5 model have been associated to visible GOME spectra for each biome and cloud cover to derive Earth's integrated spectra for given Earth phases and observer positions. The VRE is then measured. Results show that the vegetation remains detectable during the last climatic extrema. Compared to current Earth, the Holocene optimum with a greener Sahara slightly increases the mean VRE on one hand, while on the other hand, the large ice cap over the northern Hemisphere during the LGM decreases vegetation detectability. We finally discuss the detectability of the VRE in the context of recently proposed space missions.Comment: 31-page manuscript, 12 figures, accepted for publication in Int. J. of Astrobiolog

The detectability of extrasolar planet surroundings - I. Reflected-light photometry of unresolved rings

It is expected that the next generation of high-contrast imaging instruments will deliver the first unresolved image of an extrasolar planet. The emitted thermal infrared light from the planet should show no phase effect assuming the planet is in thermal equilibrium. But the reflected visible light will vary versus the phase angle. Here, we study the photometric variation of the reflected light versus the orbital phase of a ringed extrasolar planet. We show that a ring around an extrasolar planet, both obviously unresolved, can be detected by its specific photometric signature. A simple quantitative model is discussed, taking into account the basic optical and geometrical properties of the ringed planet.Comment: Keywords: Stars: planetary systems -- Planets: rings -- Extrasolar planet characterization. 10 pages, 16 figures. Published version is A&A 420, 1153-1162 (2004), available online at http://www.edpsciences.org/articles/aa/abs/2004/24/aa0720/aa0720.htm

Are oral health and fixed orthodontic appliances associated with sports injuries and postural stability in elite junior male soccer players?

Background: Dental caries and periodontitis are associated with elevated levels of pro-inflammatory cytokines which may trigger muscle fatigue during exercise, a strong risk factor for sports injuries. Fixed orthodontic appliances (FOA) may cause poor oral health and may disturb proprioceptive inputs of the stomatognathic system. This study aims to explore associations of poor oral health and of use of a FOA with injury frequency and postural stability. Methods: One hundred eighty seven Belgian elite junior male soccer players, aged 12-17years, completed a self-report questionnaire asking about injuries in the past year, oral health problems, use of a FOA, demographics and sports data, and stood in unipedal stance with eyes closed on a force plate to assess postural stability. Results: Ordinal logistic regression with number of injuries in the past year as ordinal dependent variable and dental caries and/or gum problems, age and player position as covariates, showed that participants who reported dental caries and/or gum problems and never had had a FOA reported significant more injuries in the past year compared to the reference group of participants who reported no oral health problems and never had had a FOA (adjusted OR=2.45; 95% CI, 1.19-5.05; p=0.015). A 2 (temporomandibular joint problems) x2 (FOA) x2 (age) ANOVA with postural stabilities as dependent variables, showed a significant FOA x age interaction for the non-dominant (standing) leg. Post-hoc t-tests showed a significant better postural stability for the non-dominant leg (and a trend for the dominant leg) for the older compared with the younger participants in the non-FOA group (p=.002, ES=0.61), while no age differences were found in the FOA-group. Conclusions: These results indicate that poor oral health may be an injury risk factor and that a FOA may hinder the development of body postural stability

No smooth beginning for spacetime

We identify a fundamental obstruction to any theory of the beginning of the universe, formulated as a semiclassical path integral. Hartle and Hawking's no boundary proposal and Vilenkin's tunneling proposal are examples of such theories. Each may be formulated as the quantum amplitude for obtaining a final 3-geometry by integrating over 4-geometries. We introduce a new mathematical tool - Picard-Lefschetz theory - for defining the semiclassical path integral for gravity. The Lorentzian path integral for quantum cosmology with a positive cosmological constant is meaningful in this approach, but the Euclidean version is not. Framed in this way, the resulting framework and predictions are unique. Unfortunately, the outcome is that primordial tensor (gravitational wave) fluctuations are unsuppressed. We prove a general theorem to this effect, in a wide class of theories.Comment: 2 figures, 1 included in latex file Abstract and introduction rewritten; typos corrected; result extended; responds to arXiv:1705.05340 by Diaz Dorronsoro et al; refers to longer companion pape

Bayesian specification analysis and estimation of simultaneous equation models using Monte Carlo methods

Bayesian procedures for specification analysis or diagnostic checking of modeling assumptions for structural equations of econometric models are developed and applied using Monte Carlo numerical methods. Checks on the validity of identifying restrictions, exogeneity assumptions and other specifying assumptions are performed using posterior distributions for discrepancy vectors and functions representing departures from specifying assumptions. Several mappings or functions of reduced form coefficients are defined and their posterior distributions are computed. A restricted reduced form approach is used to compute posterior distributions for structural parameters. These procedures are applied in analyses of two econometric models