HTN planning: Overview, comparison, and beyond

Hierarchies are one of the most common structures used to understand and conceptualise the world. Within the field of Artificial Intelligence (AI) planning, which deals with the automation of world-relevant problems, Hierarchical Task Network (HTN) planning is the branch that represents and handles hierarchies. In particular, the requirement for rich domain knowledge to characterise the world enables HTN planning to be very useful, and also to perform well. However, the history of almost 40 years obfuscates the current understanding of HTN planning in terms of accomplishments, planning models, similarities and differences among hierarchical planners, and its current and objective image. On top of these issues, the ability of hierarchical planning to truly cope with the requirements of real-world applications has been often questioned. As a remedy, we propose a framework-based approach where we first provide a basis for defining different formal models of hierarchical planning, and define two models that comprise a large portion of HTN planners. Second, we provide a set of concepts that helps in interpreting HTN planners from the aspect of their search space. Then, we analyse and compare the planners based on a variety of properties organised in five segments, namely domain authoring, expressiveness, competence, computation and applicability. Furthermore, we select Web service composition as a real-world and current application, and classify and compare the approaches that employ HTN planning to solve the problem of service composition. Finally, we conclude with our findings and present directions for future work. In summary, we provide a novel and comprehensive viewpoint on a core AI planning technique.<br/

Duality Between Spatial and Angular Shift in Optical Reflection

We report a unified representation of the spatial and angular Goos-Hanchen and Imbert-Fedorov shifts that occur when a light beam reflects from a plane interface. We thus reveal the dual nature of spatial and angular shifts in optical beam reflection. In the Goos-Hanchen case we show theoretically and experimentally that this unification naturally arises in the context of reflection from a lossy surface (e.g., a metal).Comment: 4 pages, 3 figure

Conceptual design of the enhanced coolant purification systems for the European HCLL and HCPB test blanket modules

The Coolant Purification Systems (CPSs) is one of the most relevant ancillary systems of European Helium Cooled Lead Lithium (HCLL) and Helium Cooled Pebble Bed (HCPB) Test Blanket Modules (TBMs) which are currently in the preliminary design phase in view of their installation and operation in ITER. The CPS implements mainly two functions: the extraction and concentration of the tritium permeated from the TBM modules into the primary cooling circuit and the chemistry control of helium primary coolant. During the HCLL and HCPB-TBSs (Test Blanket Systems) Conceptual Design Review (CDR) in 2015 it was recognized the need of reducing the tritium permeation into the Port Cell #16 of ITER. To achieve this and, then, to lower the tritium partial pressure in the Helium Cooling Systems in normal operation, the helium flow-rate treated by each CPS has been increased of almost one order of magnitude. In 2017, to satisfy the CDR outcomes and the new design requirements requested by Fusion for Energy (F4E, the European Domestic Agency for ITER), ENEA performed a preliminary design of the “enhanced” CPSs. This paper presents the current design of the “enhanced” CPSs, focusing on design requirements, assumptions, selection of technologies and preliminary components sizing

Grassroots Roma Women Organizing for Social Change: A Study of the Impact of 'RomaWomen Student Gatherings'

Abstract: Scientific literature has focused on the constraints that Roma women have faced to overcome the racism and inequalities that they and the Roma people as a whole have su ered. However, less attention has been paid to how Roma women organize to challenge this reality. Drawing on a qualitative case study about the Roma Association of Women Drom Kotar Mestipen (Barcelona) and specifically on the analysis of one of its activities, the 'Roma women student gatherings' (known as 'Trobades' in Catalan), this article contributes evidence to show how Roma women are fighting to improve their own living conditions and those of their people by organizing at the grassroots level. The communicative analysis reveals the impacts that these gatherings have on the individual and societal levels. First, the gatherings have impacts on the individual level, as many of the women who participate in them are exposed to and embrace new educational projects, thus acquiring more skills to be better prepared to later access the labor market. Second, their impact is also evidenced on the societal level, as the gatherings enhance Roma women's associational life, resulting in new mobilizations and often making women who were once in the shadows become community leaders

Building vicarious bridges through colour workshops for pupils with visual impairment

he inclusion of pupils with visual impairment, within Italian mainstream schools, is an area of interest for the field of special education that is involved in identifying the most effective teaching strategies to promote the teaching-learning process. The perceptive difficulties that the pupils with visual impairment encounter in the first step of development can be a significant obstacle to learning and to the development of representative thinking. For this reason, it is fundamental that the teaching style adopted is oriented to promote learning through strategies that exploit the natural vicarious activity of the brain. With this aim, the present paper describes the potential of a hands-on activity with high inclusive value, which is based on a theoretical framework, that brings together contributions from different scientific domains and which, from an interdisciplinary perspective, explores the concept of "vicariance" as proposed by the physiologist of perception Alain Bertho

A transition from river networks to scale-free networks

A spatial network is constructed on a two dimensional space where the nodes are geometrical points located at randomly distributed positions which are labeled sequentially in increasing order of one of their co-ordinates. Starting with $N$ such points the network is grown by including them one by one according to the serial number into the growing network. The $t$-th point is attached to the $i$-th node of the network using the probability: $\pi_i(t) \sim k_i(t)\ell_{ti}^{\alpha}$ where $k_i(t)$ is the degree of the $i$-th node and $\ell_{ti}$ is the Euclidean distance between the points $t$ and $i$. Here $\alpha$ is a continuously tunable parameter and while for $\alpha=0$ one gets the simple Barab\'asi-Albert network, the case for $\alpha \to -\infty$ corresponds to the spatially continuous version of the well known Scheidegger's river network problem. The modulating parameter $\alpha$ is tuned to study the transition between the two different critical behaviors at a specific value $\alpha_c$ which we numerically estimate to be -2.Comment: 5 pages, 5 figur

Grassroots Roma women organizing for social change : a study of the impact of 'Roma women student gatherings'

This investigation complies with the Universal Declaration of Human Rights adopted by the United Nations Educational, Scientific and Cultural Organization (UNESCO), the Charter of Fundamental Rights of the EU, and resolution P7_TA 0312 of 9 September 2010, of the European Parliament on the Situation of the Roma People and Free Movement in the European Union [44,45]. To protect the participants' identities and personal data, pseudonyms have been used. Consent forms with detailed information about the study and an explanation that they have the right to withdraw from it at any time were provided to all the persons participating in the research.Scientific literature has focused on the constraints that Roma women have faced to overcome the racism and inequalities that they and the Roma people as a whole have suffered. However, less attention has been paid to how Roma women organize to challenge this reality. Drawing on a qualitative case study about the Roma Association of Women Drom Kotar Mestipen (Barcelona) and specifically on the analysis of one of its activities, the 'Roma women student gatherings' (known as 'Trobades' in Catalan), this article contributes evidence to show how Roma women are fighting to improve their own living conditions and those of their people by organizing at the grassroots level. The communicative analysis reveals the impacts that these gatherings have on the individual and societal levels. First, the gatherings have impacts on the individual level, as many of the women who participate in them are exposed to and embrace new educational projects, thus acquiring more skills to be better prepared to later access the labor market. Second, their impact is also evidenced on the societal level, as the gatherings enhance Roma women's associational life, resulting in new mobilizations and often making women who were once in the shadows become community leaders