Anabela Gonçalves

Response of the warm absorber cloud to a variable nuclear flux in active galactic nuclei

Recent modeling of the warm absorber in active galactic nuclei has proved the usefulness of constant total (gas plus radi ation) pressure models, which are highly stratified in temperature and density. We ex plore the consistency of those models when the typical variation of the flux from the central source is taken into account. We perform a variability study of the warm absorber response, based on timescales and our photoionization code TITAN. We show that the ionization and recombination timescales are much shorter than the dynamical timescale. Clouds very close to the central black hole will maintain their equilibrium sinc e the characteristic variability timescales of the nuclear source are longer than cloud timescales. For more distant clouds, the density structure has no time to vary, in response to the variations of the temperature or ionization structure, and such clouds will show the departure from the constant pressure equilibrium. We explore the impact of this departure on the observed properties of the transmitted spectrum and soft X-ray variability: (i) non uniform velocities, of the order of sound speed, appear due to pressure gradients, up to typical values of 100 km s −1 . These velocities lead to the broadening of lines. This broa dening is usually observed and very diffi cult to explain otherwise. (ii) Energy-dependent fraction al variability amplitude in soft X-ray range has a broader hump around∼ 1− 2 keV, and (iv) the plot of the equivalent hydrogen column density vs. ionization parameter is steeper than for equilibriu m clouds. The results have the character of a preliminary study and should be supplemented in the future with full time-dependent radiation transfer and dynamical computations.

Aspects of the acquisition of object control and ECM-Type verbs in European Portuguese

ABSTRACT We investigate the acquisition of sentential complementation under causative, perception, and object control verbs in European Portuguese, a language rich in complement types, including the typologically marked inflected infinitives. We tested 58 children between 3 and 5 years of age and 24 adults on a sentence completion task. The results support two main hypotheses concerning children’s initial biases in representing complement structure. The first pertains to argument structure—a verb selects only one internal (propositional) argument (Single Argument Selection Hypothesis), the other to syntactic structure—propositional complements are complete functional complements (Complete Functional Complement Hypothesis). These initial biases lead children to avoid raising-to-object and object control structures, in favor of finite complements and inflected infinitive complements, the latter appearing in both target and nontarget contexts.

Sequence of tenses in complementation structures: Lexical restrictions and effects on language acquisition

In this paper we discuss the combinations of tenses in main and complement clauses of European Portuguese, focusing on the issue that restrictions on the tenses allowed in complement clauses are observed with some predicates but not with others. We show that these lexical restrictions are independent of the mood occurring in the complement clause, though an integrated analysis of mood and tense may be achieved. The proposal is made that the observed lexical restrictions on embedded tenses have a semantic basis and follow from the fact that Portuguese is an SOT-language, that is, a language where embedded tenses have semantic import. A preliminary investigation is conducted on the sequences of tenses produced at early stages of language acquisition.