Star formation efficiency in galaxy interactions and mergers: a statistical study

We investigate the enhancement of star formation efficiency in galaxy interactions and mergers, by numerical simulations of several hundred galaxy collisions. All morphological types along the Hubble sequence are considered in the initial conditions of the two colliding galaxies, with varying bulge-to-disk ratios and gas mass fractions. Different types of orbits are simulated, direct and retrograde, according to the initial relative energy and impact parameter, and the resulting star formation history is compared to that occuring in the two galaxies when they are isolated. Our principal results are: (1) retrograde encounters have a larger star formation efficiency (SFE) than direct encounters; (2) the amount of gas available in the galaxy is not the main parameter governing the SFE in the burst phase; (3) there is an anticorrelation between the amplitude of the star forming burst and the tidal forces exerted per unit of time, which is due to the large amount of gas dragged outside the galaxy by tidal tails in strong interactions; (4) globally, the Kennicutt-Schmidt law is retrieved statistically for isolated galaxies, interacting pairs and mergers; (5) the enhanced star formation is essentially occurring in nuclear starbursts, triggered by inward gas flows driven by non-axisymmetries in the galaxy disks. Direct encounters develop more pronounced asymmetries than retrograde ones. Based on these statistical results, we derive general laws for the enhancement of star formation in galaxy interactions and mergers, as a function of the main parameters of the encounter.Comment: 22 pages, 37 figures, 4 tables. Accepted on Astronomy & Astrophysic

L'étude des phénomènes de marée gravimétrique

Cet article présente une description des phénomènes de marée terrestre et des méthodes de mesure. Les résultats des profils mondiaux de marée gravimétrique sont corrigés des effets indirects liés aux marées océaniques. Une corrélation entre marées gravimétriques, flux de chaleur et tectonique globale est proposé

Calibration biases in measurements of weak lensing

As recently shown by Viola et al., the common (KSB) method for measuring weak gravitational shear creates a non-linear relation between the measured and the true shear of objects. We investigate here what effect such a non-linear calibration relation may have on cosmological parameter estimates from weak lensing if a simpler, linear calibration relation is assumed. We show that the non-linear relation introduces a bias in the shear-correlation amplitude and thus a bias in the cosmological parameters Omega_matter and sigma_8. Its direction and magnitude depends on whether the point-spread function is narrow or wide compared to the galaxy images from which the shear is measured. Substantial over- or underestimates of the cosmological parameters are equally possible, depending also on the variant of the KSB method. Our results show that for trustable cosmological-parameter estimates from measurements of weak lensing, one must verify that the method employed is free from ellipticity-dependent biases or monitor that the calibration relation inferred from simulations is applicable to the survey at hand.Comment: 5 pages, 3 figures, submitted to A&

Old stellar counter-rotating components in early-type galaxies from elliptical-spiral mergers

We investigate, by means of numerical simulations, the possibility of forming counter-rotating old stellar components by major mergers between an elliptical and a spiral galaxy. We show that counter-rotation can appear both in dissipative and dissipationless retrograde mergers, and it is mostly associated to the presence of a disk component, which preserves part of its initial spin. In turn, the external regions of the two interacting galaxies acquire part of the orbital angular momentum, due to the action of tidal forces exerted on each galaxy by the companion.Comment: 6 pages, 15 figures. Accepted on Astronomy & Astrophysic

Quantification of valvular regurgitation by cardiac blood pool scintigraphy: correlation with catheterization

The diagnosis of valvular regurgitation (R) is usually based on clinical signs. Quantification conventionally requires catheterization (C). We have quantified R with cardiac blood pool scintigraphy (CBPS) and compared the results with those obtained by C. Regurgitant fraction (RF) determined by C was calculated with the technique of Dodge. Forward output was measured by thermodilution or cardiogreen dilution. The RF at CBPS was obtained by the stroke index ratio (SIR) minus 1.2 divided by SIR, where SIR is the ratio of the stroke counts of left venticle over those of the right ventricle. Stroke counts are calculated directly from the time-activity curves. Each time-activity curve was obtained by drawing one region of interest around each diastolic image. The correction factor (1.2) was calculated from a large normal population. 22 patients had aortic R, 7 mitral R, 12 both, 8 patients had no evidence of regurgitation. RF of the patients with R varied from 27 to 71% (x = 42%) at C and from 26 to 74% (Y = 41%) at CBPS. Linear regression shows a good correlation coefficient (r = 0.82). The regression equation is y = 0.93x + 1.8. No correlation was found between RF (CBPS or C) and the severity of R assessed visually from angiography. In conclusion: CBPS, a non-invasive method, allows easy and repeatable determination of RF and correlates well with data obtained at catheterizatio

Early risk factors for hyperactivity-impulsivity and inattention trajectories from age 17 months to 8 years.

CONTEXT: Attention-deficit/hyperactivity disorder is an etiologically heterogeneous neurodevelopmental condition with long-term negative outcomes. However, the early developmental course of hyperactivity-impulsivity and inattention symptoms and their association with previous environmental risk factors are still poorly understood OBJECTIVES: To describe the developmental trajectories of hyperactivity-impulsivity and inattention symptoms and to identify their prenatal, perinatal, and postnatal risk factors. DESIGN: Birth cohort from the general population. SETTING: Quebec Longitudinal Study of Child Development. PARTICIPANTS: The sample consisted of 2057 individuals, followed up from age 5 months to 8 years. MAIN OUTCOME MEASURES: Prenatal, perinatal, and postnatal risk factors assessed at age 5 months were considered predictors of group membership in high hyperactivity-impulsivity and inattention trajectories from age 17 months to 8 years. RESULTS: The frequency of hyperactivity-impulsivity symptoms tended to slightly decrease with age, whereas the frequency of inattention symptoms substantially increased up to age 6 years. However, trajectories of hyperactivity-impulsivity and inattention symptoms were significantly associated with each other. Risk factors for high trajectories of both types of symptoms were premature birth (adjusted odds ratio [aOR], 1.93; 95% CI, 1.07-3.50), low birth weight (2.11; 1.12-3.98), prenatal tobacco exposure (1.41; 1.03-1.93), nonintact family (1.85; 1.26-2.70), young maternal age at birth of the target child (1.78; 1.17-2.69), paternal history of antisocial behavior (1.78; 1.28-2.47), and maternal depression (1.35; 1.18-1.54). CONCLUSIONS: A large range of early risk factors, including prenatal, perinatal social, and parental psychopathology variables, act independently to heighten the likelihood of having persistently high levels of hyperactivity-impulsivity and inattention symptoms from infancy to middle childhood. Early interventions should be experimented with to provide effective tools for attention-deficit/hyperactivity disorder prevention

Eradication of scrapie with selective breeding: are we nearly there?

<p>Abstract</p> <p>Background</p> <p>Following EU decision 2003/100/EC Member States have recently implemented sheep breeding programmes to reduce the prevalence of sheep with TSE susceptible prion genotypes. The present paper investigates the progress of the breeding programme in the Netherlands. The PrP genotype frequencies were monitored through time using two sets of random samples: one set covers the years 2005 to 2008 and is taken from national surveillance programme; the other is taken from 168 random sheep farms in 2007. The data reveal that although the level of compliance to the breeding programme has been high, the frequency of susceptible genotypes varies substantially between farms. The 168 sheep farms are a subset of 689 farms participating in a postal survey inquiring about management and breeding strategies. This survey aimed to identify how much these strategies varied between farms, in order to inform assessment of the expected future progress towards eradication of classical scrapie.</p> <p>Results</p> <p>On the one hand, we found that compliance to the national breeding program has been high, and the frequency of resistant genotypes is expected to increase further in the next few years. On the other hand, we observed a large variation in prevalence of the scrapie resistant PrP genotype ARR between farms, implicating a large variation of genetic resistance between farms. Substantial between-flock differences in management and breeding strategies were found in the postal survey, suggesting considerable variation in risk of scrapie transmission between farms.</p> <p>Conclusions</p> <p>Our results show that although there has been a good progress in the breeding for scrapie resistance and the average farm-level scrapie susceptibility in the Netherlands has been significantly reduced, still a considerable proportion of farms contain high frequencies of susceptible genotypes in their sheep population. Since 2007 the breeding for genetic resistance is voluntarily again, and participation to selective breeding can decrease as a result of this. This, together with the patterns of direct and indirect contact between sheep farms, might present a challenge of the aim of scrapie eradication. Communication to sheep owners of the effect of the breeding programme thus far, and of the prospects for classical scrapie eradication in The Netherlands might be essential for obtaining useful levels of participation to the voluntary continuation of the breeding programme.</p