A Program-Level Approach to Revising Logic Programs under the Answer Set Semantics

An approach to the revision of logic programs under the answer set semantics is presented. For programs P and Q, the goal is to determine the answer sets that correspond to the revision of P by Q, denoted P * Q. A fundamental principle of classical (AGM) revision, and the one that guides the approach here, is the success postulate. In AGM revision, this stipulates that A is in K * A. By analogy with the success postulate, for programs P and Q, this means that the answer sets of Q will in some sense be contained in those of P * Q. The essential idea is that for P * Q, a three-valued answer set for Q, consisting of positive and negative literals, is first determined. The positive literals constitute a regular answer set, while the negated literals make up a minimal set of naf literals required to produce the answer set from Q. These literals are propagated to the program P, along with those rules of Q that are not decided by these literals. The approach differs from work in update logic programs in two main respects. First, we ensure that the revising logic program has higher priority, and so we satisfy the success postulate; second, for the preference implicit in a revision P * Q, the program Q as a whole takes precedence over P, unlike update logic programs, since answer sets of Q are propagated to P. We show that a core group of the AGM postulates are satisfied, as are the postulates that have been proposed for update logic programs

Logic Programs with Compiled Preferences

We describe an approach for compiling preferences into logic programs under the answer set semantics. An ordered logic program is an extended logic program in which rules are named by unique terms, and in which preferences among rules are given by a set of dedicated atoms. An ordered logic program is transformed into a second, regular, extended logic program wherein the preferences are respected, in that the answer sets obtained in the transformed theory correspond with the preferred answer sets of the original theory. Our approach allows both the specification of static orderings (as found in most previous work), in which preferences are external to a logic program, as well as orderings on sets of rules. In large part then, we are interested in describing a general methodology for uniformly incorporating preference information in a logic program. Since the result of our translation is an extended logic program, we can make use of existing implementations, such as dlv and smodels. To this end, we have developed a compiler, available on the web, as a front-end for these programming systems

Role Discrepancy, Maternal Hardiness and Depression in Mothers of Toddlers: A Qualitative Exploration

Maternal depression is a serious mental health and public health issue with the majority of research focused on depression occurring within the first postnatal year. Studies exploring maternal depression beyond the postpartum period have been conducted however the focus is typically the negative effects of maternal depression on child development. Thematic analysis was used to understand the subjective experience of mothering a toddler from the perspective of both depressed (n = 5) and non-depressed (n = 16) women with children between 12 to 24 months of age, using Mercer\u27s role transition theory, Becoming a mother, Higgin\u27s Self-discrepancy Theory and a material discursive perspective as an integrated theoretical framework. The findings reflected that becoming a mother of a toddler is transformative as suggested by Mercer with identifiable phases of role transition and adaptation evolving in step with toddler development. Participants in the depressed sub-group were more apt to experience incongruences between the ideological expectations and reality of mothering which resulted in a certain degree of emotional distress. Thematic representations of control, commitment and challenge, the three components of the personality trait, hardiness also emerged from the maternal narratives. Mothers in the non-depressed subgroup described use of coping methods in response to stress that were more reflective of high hardiness in contrast to mothers in the depressed subgroup. A better understanding of how maternal role transition unfolds beyond the first year postpartum, and how maternal hardiness influences coping skills can guide the clinician in the development of psychotherapeutic treatment strategies aimed at minimizing the negative impact of depression on the maternal-toddler dyad and promotion of more effective parenting behaviors for mothers with depression

Observational Properties of SNe Ia Progenitors Close to the Explosion

We determine the expected signal in various observational bands of Supernovae Ia progenitors just before the explosion by assuming the rotating Double Degenerate scenario. Our results are valid also for all the evolutionary scenarios invoking rotation as the driving mechanism of the accretion process as well as the evolution up to the explosion. We find that the observational properties depend mainly on the mass of the exploding object, even if the angular momentum evolution after the end of the mass accretion phase and before the onset of C-burning plays a non-negligible role. Just before the explosion the magnitude M_V ranges between 9 and 11 mag, while the colour (F225W-F555W) is about -1.64 mag. The photometric properties remain constant for a few decades before the explosion. During the last few months the luminosity decreases very rapidly. The corresponding decline in the optical bands varies from few hundredths up to one magnitude, the exact value depending on both the WD total mass and the braking efficiency at the end of the mass transfer. This feature is related to the exponentially increasing energy production which drives the formation of a convective core rapidly extending over a large part of the exploding object. Also a drop in the angular velocity occurs. We find that observations in the soft X band (0.5 -2 keV) may be used to check if the SNe Ia progenitors evolution up to explosion is driven by rotation and, hence, to discriminate among different progenitor scenarios.Comment: 8 pages, 6 figures, 2 tables. Accepted for the publication on MNRA