A common feature in Answer Set Programming is the use of a second negation, stronger than default negation and sometimes called explicit, strong or classical negation. This explicit negation is normally used in front of atoms, rather than allowing its use as a regular operator. In this paper we consider the arbitrary combination of explicit negation with nested expressions, as those defined by Lifschitz, Tang and Turner. We extend the concept of reduct for this new syntax and then prove that it can be captured by an extension of Equilibrium Logic with this second negation. We study some properties of this variant and compare to the already known combination of Equilibrium Logic with Nelson’s strong negation.

This study analyses the extent to which cheating occurs in a real selection setting. A two-stage, unproctored and proctored, test administration was considered. Test score inconsistencies were concluded by applying a verification test (Guo and Drasgow Z-test). An initial simulation study showed that the Z-test has adequate Type I error and power rates in the specific selection settings explored. A second study applied the Z-test statistic verification procedure to a sample of 954 employment candidates. Additional external evidence based on item time response to the verification items was gathered. The results revealed a good performance of the Z-test statistic and a relatively low, but non-negligible, number of suspected cheaters that showed higher distorted ability estimates. The study with real data provided additional information on the presence of suspected cheating in unproctored applications and the viability of using item response times as an additional evidence of cheating. In the verification test, suspected cheaters spent 5.78 seconds per item more than expected considering the item difficulty and their assumed ability in the unproctored stage. We found that the percentage of suspected cheaters in the empirical study could be estimated at 13.84%. In summary, the study provides evidence of the usefulness of the Z-test in the detection of cheating in a specific setting, in which a computerized adaptive test for assessing English grammar knowledge was used for personnel selection.

The Pristine survey uses narrow-band photometry on the region of the Ca II H & K absorption lines to find extremely metal-poor stars. With a spectroscopic follow-up sample of 205 stars in the magnitude range 14 < V < 18, we compute the success rates for finding extremely metal-poor stars and modify the selection criteria used to select stars for follow-up. This reduces the sample to 149 stars, and from these we report success rates of 22% for recovering stars with [Fe/H] < −3.0 and 70% for [Fe/H] < −2.5. When compared to previous works that search for extremely metal-poor stars, the success rates of Pristine show an improvement in efficiency by a factor of ~4 − 5.

In this paper we provide an alternative semantics for Equilibrium Logic and its monotonic basis, the logic of Here-and-There (also known as Gödel's G 3 logic) that relies on the idea of denotation of a formula, that is, a function that collects the set of models of that formula. Using the three-valued logic G 3 as a starting point and an ordering relation (for which equilibrium/stable models are minimal elements) we provide several elementary operations for sets of interpretations. By analysing structural properties of the denotation of formulas, we show some expressiveness results for G 3 such as, for instance, that conjunction is not expressible in terms of the other connectives. Moreover, the denotational semantics allows us to capture the set of equilibrium models of a formula with a simple and compact set expression. We also use this semantics to provide several formal definitions for entailment relations that are usual in the literature, and further introduce a new one called strong entailment. We say that α strongly entails β when the equilibrium models of α ∧ γ are also equilibrium models of β ∧ γ for any context γ. We also provide a characterisation of strong entailment in terms of the denotational semantics, and give an example of a sufficient condition that can be applied in some cases.

In densely-populated cities or indoor environments, limited visibility to satellites and severe multipath effects significantly affect the accuracy and reliability of satellite-based positioning systems. To meet the needs of “seamless navigation” in these challenging environments an advanced terrestrial positioning system is under development. This system is based upon Ultra-Wideband (UWB) technology, which is a promising candidate for this application due to good time domain resolution and immunity to multipath. This paper presents a detailed analysis of two key aspects of the UWB signal design that will allow it to be used as the basis of such a high performance positioning system: the modulation scheme and the multiple access technique. These two aspects are evaluated in terms of spectral efficiency and synchronisation performance over multipath channels. Thus this paper identifies optimal modulation and multiple access techniques for a long range, high performance terrestrial positioning system using UWB.