Angular Momentum Evolution of Stars in the Orion Nebula Cluster

(Abridged) We present theoretical models of stellar angular momentum evolution from the Orion Nebula Cluster (ONC) to the Pleiades and the Hyades. We demonstrate that observations of the Pleiades and Hyades place tight constraints on the angular momentum loss rate from stellar winds. The observed periods, masses and ages of ONC stars in the range 0.2--0.5 M$_\odot$, and the loss properties inferred from the Pleiades and Hyades stars, are then used to test the initial conditions for stellar evolution models. We use these models to estimate the distribution of rotational velocities for the ONC stars at the age of the Pleiades (120 Myr). The modeled ONC and observed Pleiades distributions of rotation rates are not consistent if only stellar winds are included. In order to reconcile the observed loss of angu lar momentum between these two clusters, an extrinsic loss mechanism such as protostar-accretion disk interaction is required. Our model, which evolves the ONC stars with a mass dependent saturation threshold normalized such that $\omega_{crit} = 5.4 \omega_\odot$ at 0.5 \m, and which includes a distribution of disk lifetimes that is uniform over the range 0--6 Myr, is consistent with the Pleiades. This model for disk-locking lifetimes is also consistent with inferred disk lifetimes from the percentage of stars with infrared excesses observed in young clusters. Different models, using a variety of initial period distributions and different maximum disk lifetimes, are also compared to the Pleiades. For disk-locking models that use a uniform distribution of disk lifetimes over the range 0 to $\tau_{max}$, the acceptable range of the maximum lifetime is $3.5 < \tau_{max} < 8.5$ Myr.Comment: 21 pages, 7 figures, submitted to Ap

Roughness of sandstone fracture surfaces: Profilometry and shadow length investigations

The geometrical properties of fractured sandstone surfaces were studied by measuring the length distribution of the shadows appearing under grazing illumination. Three distinct domains of variation were found: at short length scales a cut-off of self-affinity is observed due to the inter-granular rupture of sandstones, at long length scales, the number of shadows falls off very rapidly because of the non-zero illumination angle and of the finite roughness amplitude. Finally, in the intermediate domain, the shadow length distribution displays a power law decrease with an exponent related to the roughness exponent measured by mechanical profilometry. Moreover, this method is found to be more sensitive to deviations from self-affinity than usual methods

Emotion regulation after traumatic brain injury: distinct patterns of sympathetic activity during anger expression and recognition

Abstract OBJECTIVE: To assess psychological and psychophysiological correlates of emotion recognition and anger experience in participants with traumatic brain injury (TBI). PARTICIPANTS: Twenty participants with TBI presenting with anger problems and 22 healthy controls. PROCEDURES: Participants were administered tasks assessing emotion recognition (The French Evaluation Task) and anger expression (Anger regulation task). The latter, designed to elicit and modulate anger feelings through verbal recall of a self-experienced event, involved 4 recall conditions that followed a resting period: neutral, uninstructed anger recall, anger rumination, and anger reappraisal. MEASURES: Skin conductance levels during recall and a self-report anger questionnaire between each condition. RESULTS: In the TBI and control groups, self-reported anger was similarly modulated across emotion regulation conditions. However, only in the TBI group did skin conductance levels significantly increase between neutral and uninstructed anger recall conditions. CONCLUSIONS: Impaired emotion regulation in TBI participants could be related to increased levels of autonomic system activity during emotional experience. However, anger feelings in these participants can also be modulated with the use of emotion regulation strategies, including adaptive strategies such as reappraisal. Thus, promoting awareness and management of physiological activation and encouraging cognitive restructuring can be recommended as a component of interventions targeting emotion regulation in TBI patients

An observation of nocturnal activity in a Central-Italian Asp (Vipera aspis francisciredi)

n/

European ornithomimosaurs (Dinosauria, Theropoda) : an undetected record

Early Cretaceous ornithomimosaurian theropod dinosaurs have been reported from various localities in Asia, whereas they remain poorly represented and extremely rare in North America, Africa and Europe. So far, the only known European ornithomimosaur is Pelecanimimus from the Barremian of Spain. The recent discovery in southwestern France of a lignitic bone bed in Angeac, which has yielded several hundred ornithomimosaur bones, sheds new light on the ornithomimosaurian fossil record. Based on this new material, we re-evaluate here the systematic position of various isolated theropod bones from the Wealden of England, including historical taxa of uncertain affinities. Based on a unique combination of derived characters, Thecocoelurus and Valdoraptor are linked to the Angeac taxon but are considered to be nomina dubia. Valdoraptor from the Valanginian of West Sussex appears to be the oldest known ornithomimosaur together with the contemporaneous Nqwebasaurus from South Africa. Ornithomimosaurs were a common component of the Early Cretaceous European dinosaur fauna. Their presence in Spain, France and England further strengthens the palaeobiogeographic affinities of the European fossil biota with that of Asia during this period