Gravitational Instantons and Euclidean Supersymmetry

Supersymmetric instanton solutions in four dimensional Euclidean ungauged Einstein-Maxwell theory are analysed and classified according to the fraction of supersymmetry they preserve, using spinorial geometry techniques.Comment: 10 pages, late

On Non-extremal Instantons and Black Holes

We consider a general analysis and a specific ansatz for the study of non-supersymmetric solutions in arbitrary dimensions and various metric signatures. In all cases, we find that the conditions on the solutions can be written in terms of quadratic forms involving the gauge coupling of the theory and constants of integration associated with the scalar fields. Depending on the signature of the metric, our analysis should provide a general framework for finding non-extremal black holes, instantons, branes and S-branes.Comment: 19 page

Null Half-Supersymmetric Solutions in Five-Dimensional Supergravity

We classify half-supersymmetric solutions of gauged N=2, D=5 supergravity coupled to an arbitrary number of abelian vector multiplets for which all of the Killing spinors generate null Killing vectors. We show that there are four classes of solutions, and in each class we find the metric, scalars and gauge field strengths. When the scalar manifold is symmetric, the solutions correspond to a class of local near horizon geometries recently found by Kunduri and Lucietti.Comment: 46 pages, typos corrected and reference added. Section 7.1 has been added: it is shown that the solutions found here correspond to a class of solutions found in arXiv:0708.3695. Uses JHEP3.cl

Parent Interventionists in Phonodialogic Emergent Reading with Preschool Children

The purpose of this study was to examine an activity-based intervention, dialogic reading with embedded explicit phonological awareness strategies, applied as a preventive approach by parents in their home settings located within a culturally and ethnically diverse urban region. This study investigated the effects of training parents to employ a phonodialogic activity-based emergent reading intervention protocol to increase the phonological awareness skills of their 4- and 5-year old children. Helping young children learn phonological awareness skills are vitally important to the development of early reading (Anthony & Lonigan, 2004; Ziolkowski & Goldstein, 2008). This investigation provided an empirical examination of a critical area which has received little experimentation. Though there is ample empirical evidence on the contribution of phonological awareness to children\u27s reading skills, there is virtually no research on the contribution of phonological awareness instruction on the early reading development of young children when it is embedded within the context of a dialogic reading activity with parents as interventionists. Accordingly, the theoretical underpinnings of this study, specifically phonological awareness, activity-based intervention, and dialogic reading are discussed in the literature review section. This dissertation describes methodology and the results of testing the hypothesis that parental phonodialogic reading strategies will have an observable positive treatment effect on preschool children\u27s phonological awareness skills when baseline, intervention, and maintenance conditions are compared

Variability of the soft X-ray excess in IRAS 13224-3809

We study the soft excess variability of the narrow line Seyfert 1 galaxy IRAS 13224-3809. We considered all five archival XMM-Newton observations, and we applied the 'flux-flux plot' (FFP) method. We found that the flux-flux plots were highly affected by the choice of the light curves' time bin size, most probably because of the fast and large amplitude variations, and the intrinsic non-linear flux--flux relations in this source. Therefore, we recommend that the smallest bin-size should be used in such cases. Hence, We constructed FFPs in 11 energy bands below 1.7 keV, and we considered the 1.7-3 keV band, as being representative of the primary emission. The FFPs are reasonably well fitted by a 'power-law plus a constant' model. We detected significant positive constants in three out of five observations. The best-fit slopes are flatter than unity at energies below $\sim 0.9$ keV, where the soft excess is strongest. This suggests the presence of intrinsic spectral variability. A power-law-like primary component, which is variable in flux and spectral slope (as $\Gamma\propto N_{\rm PL}^{0.1}$) and a soft-excess component, which varies with the primary continuum (as $F_{\rm excess}\propto F_{\rm primary}^{0.46}$), can broadly explain the FFPs. In fact, this can create positive `constants', even when a stable spectral component does not exist. Nevertheless, the possibility of a stable, soft--band constant component cannot be ruled out, but its contribution to the observed 0.2-1 keV band flux should be less than $\sim 15$ %. The model constants in the FFPs were consistent with zero in one observation, and negative at energies below 1 keV in another. It is hard to explain these results in the context of any spectral variability scenario, but they may signify the presence of a variable, warm absorber in the source.Comment: Accepted for publication in A&A, 10 pages, 7 figure