A Study on the Parallelization of Terrain-Covering Ant Robots Simulations

Agent-based simulation is used as a tool for supporting (time-critical) decision making in differentiated contexts. Hence, techniques for speeding up the execution of agent-based models, such as Parallel Discrete Event Simulation (PDES), are of great relevance/benefit. On the other hand, parallelism entails that the final output provided by the simulator should closely match the one provided by a traditional sequential run. This is not obvious given that, for performance and efficiency reasons, parallel simulation engines do not allow the evaluation of global predicates on the simulation model evolution with arbitrary time-granularity along the simulation time-Axis. In this article we present a study on the effects of parallelization of agent-based simulations, focusing on complementary aspects such as performance and reliability of the provided simulation output. We target Terrain Covering Ant Robots (TCAR) simulations, which are useful in rescue scenarios to determine how many agents (i.e., robots) should be used to completely explore a certain terrain for possible victims within a given time. © 2014 Springer-Verlag Berlin Heidelberg

The Impact of the Carrollton GreenBelt on Residential Housing Prices: A Spatial Approach

The Carrollton GreenBelt is a linear park encircling the City of Carrollton Georgia. The GreenBelt differs from other linear parks in that it is an entirely new construction and was not built upon existing rail lines, as was the Atlanta Beltline and the nearby Silver Comet Trail. Using GIS, data from the Carroll County Tax Assessor\u27s office and spatial econometric techniques, we estimate local fair-market housing values within the hedonic framework to measure the relationship between home prices and access to the GreenBelt. We find the expected positive effects from the number of bedrooms, bathrooms and square footage, but access to the GreenBelt is associated with lower housing sale prices during the period; however, these lower prices may also be the result of conscious location decisions of the GreenBelt developers in an attempt to lower land acquisition costs in the development phase. Despite our efforts to control for distance to the center of the city, the negative association between the GreenBelt and housing values may be impacted by the endogeneity between GreenBelt location and residential housing prices

A systematic review of conceptualizations and operationalizations of youth polyvictimization

Violence against youth is a global issue impacting millions each year. Increasingly, research has focused on studying those impacted by multiple forms of violence, or polyvictims. Evidence strongly suggests that polyvictimized youth tend to have worse physical and mental health outcomes than those who have experienced single forms of violence. Moreover, minoritized youth (i.e., racial and/or sexual minority youth, youth with disabilities) are more likely to experience polyvictimization, making this a social justice and equity concern. To date, there is no universal consensus on what exactly constitutes polyvictimization. This systematic review aims to examine the ways in which polyvictimization is being studied to inform both research and practice. As such, relevant databases were searched to amass the extant literature related to youth polyvictimization internationally. Empirical studies published since 2006 that focused on youth (under age 18) polyvictimization were included. After the review process, 264 studies met eligibility criteria, however 55 studies employed person-centered/finite mixture analyses and were removed for a separate review, resulting in 209 featured in the current systematic review. Results demonstrate that researchers are defining and operationalizing polyvictimization in different ways: (a) using individual victimization event counts; (b) employing domain-based counts; and (c) taking a “highest-victimized” percentage of their sample. The most used measurement tool was the Juvenile Victimization Questionnaire, though other validated tools and researcher-constructed questions were frequently utilized. Research on polyvictimization is burgeoning worldwide; however, this research is being conducted in disparate ways, making it difficult to compare findings and further advance the field.</p

A Search for Very Low-mass Stars and Brown Dwarfs in the Young sigma Orionis Cluster

We present a CCD-based photometric survey covering 870 sq. arcmin in a young stellar cluster around the young multiple star sigma Orionis. Our survey limiting R, I, and Z magnitudes are 23.2, 21.8, and 21.0, respectively. From our colour-magnitude diagrams, we have selected 49 faint objects, which smoothly extrapolate the photometric sequence defined by more massive known members. Adopting the currently accepted age interval of 2-10 Myr for the Orion 1b association and considering recent evolutionary models, our objects may span a mass range from 0.1 down to 0.02 Msun, well within the substellar regime. Follow-up low-resolution optical spectroscopy (635-920 nm) for eight of our candidates (I=16-19.5) shows that they have spectral types M6-M8.5 which are consistent with the expectations for true members. Compared with their Pleiades counterparts of similar types, Halpha emission is generally stronger, while NaI and KI absorption lines appear weaker, as expected for lower surface gravities and younger ages. Additionally, TiO bands and in particular VO bands appear clearly enhanced in our candidate with the latest spectral type, SOri 45 (M8.5, I=19.5), compared to objects of similar types in older clusters and the field. We have estimated the mass of this candidate at only 0.020-0.040 Msun, hence it is one of the least massive brown dwarfs yet discovered. We also discuss in this paper the potential role of deuterium as a tracer of both substellar nature and age in very young clusters.Comment: Accepted for publication in ApJ Main Journal. 32 pages of text and tables + 9 pages of figures. Figures 3a and 3b (gif format) provided separatel