Hydrodynamic capabilities of an SPH code incorporating an artificial conductivity term with a gravity-based signal velocity

This paper investigates the hydrodynamic performances of an SPH code incorporating an artificial heat conductivity term in which the adopted signal velocity is applicable when gravity is present. In accordance with previous findings it is shown that the performances of SPH to describe the development of Kelvin-Helmholtz instabilities depend strongly on the consistency of the initial condition set-up and on the leading error in the momentum equation due to incomplete kernel sampling. An error and stability analysis shows that the quartic B-spline kernel (M_5) possesses very good stability properties and we propose its use with a large neighbor number, between ~50 (2D) to ~ 100 (3D), to improve convergence in simulation results without being affected by the so-called clumping instability. SPH simulations of the blob test show that in the regime of strong supersonic flows an appropriate limiting condition, which depends on the Prandtl number, must be imposed on the artificial conductivity SPH coefficients in order to avoid an unphysical amount of heat diffusion. Results from hydrodynamic simulations that include self-gravity show profiles of hydrodynamic variables that are in much better agreement with those produced using mesh-based codes. In particular, the final levels of core entropies in cosmological simulations of galaxy clusters are consistent with those found using AMR codes. Finally, results of the Rayleigh-Taylor instability test demonstrate that in the regime of very subsonic flows the code has still several difficulties in the treatment of hydrodynamic instabilities. These problems being intrinsically due to the way in which in standard SPH gradients are calculated and not to the implementation of the artificial conductivity term.Comment: 26 pages, 15 figures, accepted for publication in A&

Propri\ue9t\ue9s psichom\ue9triques de l\u2019\ue9chelle Alarme D\ue9tresse B\ue9b\ue9 (ADBB) appliqu\ue9e \ue0 81 enfants italiens

The aim of this study is to validate the Alarm Distress Baby Scale (ADBB), designed to assess relational withdrawal in infants aged 2-24 months, on a sample of 81 Italian children. The study has been carried out in the General Paediatric Outpatient Clinic of the University General Hospital Agostino Gemelli in Rome. Both paediatricians and psychologists used the ADBB scale during ordinary paediatric check-ups. First and second axes of the Zero-To-Three scale were used as Gold Standards. The cut-off of 5 and over (4/5) yielded the best validity (0.82) and specificity (0.85), as was previously found in the French validation. Axis II DC O-3 R disorders in the mother-infant interaction always lead to a positive ADBB score. ADBB scores over the threshold were associated with maternal postpartum depression. Positive correlations between infant birth type, breast-feeding, current psychiatric pathology in the mother, and total ADBB scores were found. These data confirm that both children born by caesarian, feeling less pain, and breastfed children, who had more intense physical contacts with the maternal body, and children having good relationship with the caregiver, tend to socialize better. The present study further confirms the psychometrical qualities and the clinical value of the ADBB scale and emphasizes the importance of being able to assess maternal postpartum depression when the infant shows signs of relational withdrawal