Local power of the LR, Wald, score and gradient tests in dispersion models

We derive asymptotic expansions up to order $n^{-1/2}$ for the nonnull distribution functions of the likelihood ratio, Wald, score and gradient test statistics in the class of dispersion models, under a sequence of Pitman alternatives. The asymptotic distributions of these statistics are obtained for testing a subset of regression parameters and for testing the precision parameter. Based on these nonnull asymptotic expansions it is shown that there is no uniform superiority of one test with respect to the others for testing a subset of regression parameters. Furthermore, in order to compare the finite-sample performance of these tests in this class of models, Monte Carlo simulations are presented. An empirical application to a real data set is considered for illustrative purposes.Comment: Submitted for publicatio

Unstable g-modes in Proto-Neutron Stars

In this article we study the possibility that, due to non-linear couplings, unstable g-modes associated to convective motions excite stable oscillating g-modes. This problem is of particular interest, since gravitational waves emitted by a newly born proto-neutron star pulsating in its stable g-modes would be in the bandwidth of VIRGO and LIGO. Our results indicate that nonlinear saturation of unstable modes occurs at relatively low amplitudes, and therefore, even if there exists a coupling between stable and unstable modes, it does not seem to be sufficiently effective to explain, alone, the excitation of the oscillating g-modes found in hydrodynamical simulations.Comment: 10 pages, 3 figures, to appear on Class. Quant. Gra

Features controlling the early stages of creep deformation of Waspaloy

A model has been presented for describing primary and second stage creep. General equations were derived for the amount and time of primary creep. It was shown how the model can be used to extrapolate creep data. Applicability of the model was demonstrated for Waspaloy with gamma prime particle sizes from 75 - 1000 A creep tested in the temperature range 1000 - 1400 F (538 - 760 C). Equations were developed showing the dependence of creep parameters on dislocation mechanism, gamma prime volume fraction and size

Verrucae pedis in children with juvenile idiopathic arthritis and other paediatric rheumatic diseases: a cross-sectional study

Background Verrucae pedis (verrucae / VPs) are a common viral infection of the skin seen in children. There are limited studies of the prevalence, duration and impact of verrucae pedis in children who are immunosuppressed. The studies available suggest that, in these children, the warts are more widespread and are more long-standing. The primary aim of this study was to determine the prevalence of verrucae pedis in children attending rheumatology clinics who may have some degree of immunosuppression due to their prescribed medication and compare this to the reported prevalence in the healthy population. Method Children attending out-patient rheumatology appointments were recruited. The young people were aged between four and 17 years old. A visual inspection of both feet was used to identify potential verrucae. Diagnosis of a verruca pedis was confirmed on observation of the typical clinical features. The location, duration of presence, previous treatments, presence of verrucae in other family members and psychological impact was recorded. Results A total of 71 children were included. Of the group, 55 children had no verrucae present, 16 children had one or more verrucae. The prevalence of verrucae was 22.5%. Medication impacting on the immune system was prescribed in 80% of the group. There appeared to be no greater chance of having verrucae if taking immunosuppressive medication than compared to having no medication (OR = 1.1, 95%CI 0.26 to 4.48, p = 0.46). Children with verrucae tended to be between 9 and 12 years old. In total, 37.5% of the young people with verrucae had lesions reportedly present for 24 months or more. Two-thirds of the participants were not concerned about verrucae being present and most participants with a verruca were not aware of what a verruca was, but despite this the majority of participants (81%) had sought treatment for the verrucae. Conclusion Children with Juvenile Idiopathic Arthritis and other rheumatic conditions have no greater prevalence of verrucae compared to the general population. The verrucae present were of a similar clinical type and did not seem to be more widespread or have atypical features, which has been reported in other immunocompromised populations. The percentage of lesions remaining beyond 24 months was found to be slightly greater than has been reported in other healthy populations. The children in this study seemed to be less emotionally concerned about their verrucae, despite this most families had sought treatment for the verrucae