Optimizing Emergency Transportation through Multicommodity Quickest Paths

In transportation networks with limited capacities and travel times on the arcs, a class of problems attracting a growing scientific interest is represented by the optimal routing and scheduling of given amounts of flow to be transshipped from the origin points to the specific destinations in minimum time. Such problems are of particular concern to emergency transportation where evacuation plans seek to minimize the time evacuees need to clear the affected area and reach the safe zones. Flows over time approaches are among the most suitable mathematical tools to provide a modelling representation of these problems from a macroscopic point of view. Among them, the Quickest Path Problem (QPP), requires an origin-destination flow to be routed on a single path while taking into account inflow limits on the arcs and minimizing the makespan, namely, the time instant when the last unit of flow reaches its destination. In the context of emergency transport, the QPP represents a relevant modelling tool, since its solutions are based on unsplittable dynamic flows that can support the development of evacuation plans which are very easy to be correctly implemented, assigning one single evacuation path to a whole population. This way it is possible to prevent interferences, turbulence, and congestions that may affect the transportation process, worsening the overall clearing time. Nevertheless, the current state-of-the-art presents a lack of studies on multicommodity generalizations of the QPP, where network flows refer to various populations, possibly with different origins and destinations. In this paper we provide a contribution to fill this gap, by considering the Multicommodity Quickest Path Problem (MCQPP), where multiple commodities, each with its own origin, destination and demand, must be routed on a capacitated network with travel times on the arcs, while minimizing the overall makespan and allowing the flow associated to each commodity to be routed on a single path. For this optimization problem, we provide the first mathematical formulation in the scientific literature, based on mixed integer programming and encompassing specific features aimed at empowering the suitability of the arising solutions in real emergency transportation plans. A computational experience performed on a set of benchmark instances is then presented to provide a proof-of-concept for our original model and to evaluate the quality and suitability of the provided solutions together with the required computational effort. Most of the instances are solved at the optimum by a commercial MIP solver, fed with a lower bound deriving from the optimal makespan of a splittable-flow relaxation of the MCQPP

Fattori protettivi per lo stress lavorativo degli insegnanti: programmi psicoeducativi basati sull’autoefficacia e sulla speranza per rafforzare le risorse personali

Teaching at school is subject to stress and tension, which in some cases can lead to pathological conditions and can also lead to the abandonment of the same profession. In literature, the work of the teacher is often associated with stress, so much so that it is often indicated as one of the jobs most exposed to this phenomenon. As a matter of fact, there are many different sources of stress. For example, teaching unmotivated students, dealing with educational changes, and unsatisfactory working conditions. Persistence over time can lead to a strong personal exhaustion and also to the perception of a decline in one's working abilities accompanied by high levels of fatigue and negative attitudes towards one's work. Starting from some personal resources such as self-efficacy and hope, this study analyses the correlation between these resources and stress in a sample of 95 primary and lower secondary school teachers and then proposes a possible psychoeducational intervention.Fare formazione a livello scolastico può essere fonte di stress e tensione che in alcuni casi può sfociare in situazioni patologiche e portare all’abbandono della professione stessa. In letteratura il lavoro dell’insegnante è spesso accumunato allo stress tanto che viene indicato come uno dei lavori maggiormente esposti a tale fenomeno. Le fonti di stress sono molteplici. Ad esempio insegnare a studenti non motivati, far fronte al cambiamento educativo e condizioni di lavoro insoddisfacenti. Il perdurare nel tempo di queste situazioni può portare a un forte esaurimento personale e anche la percezione di un declino delle proprie capacità lavorative, accompagnati da alti livelli di stanchezza e atteggiamenti negativi nei confronti del proprio lavoro. Il presente studio, partendo da alcune risorse personali come l’autoefficacia e la speranza, analizza, su in campione di 95 insegnanti di una scuola primaria e secondaria di 1° grado, la correlazione tra queste risorse rispetto allo stress, al fine di proporre un possibile intervento di tipo psicoeducativo di supporto

Kapsula

Selections from the 14th Annual York University Art History Graduate Student Symposiu

Dynamic flow problems with bounded number of paths: models, algorithms and applications

In this thesis we investigate the concept of path limitations, expressed as the maximum number of paths that can be activated by each distinct commodity, hence secured by the so-called k-splittable flows, within the dynamic framework of Network Flow theory. In particular, we formally introduce the first flows over time problem explicitly encompassing path number restrictions, namely the Quickest Multicommodity k-Splittable Flow Problem (QMCkSFP). The problem asks for routing and scheduling each commodity demand through at most k different paths while minimizing the makespan of the overall process, i.e. the time required to accomplish the transshipment operations. We model the QMCkSFP in a dynamic digraph with time-independent structural features, considering flow traveling over a discretized time horizon, and motivated by practical applications, we force the transshipment operations to be performed only through elementary/loopless paths and without flow storage at intermediate nodes. In this setting, we provide a path-flow Mixed-Integer Linear Programming formulation for the problem that requires as an input the complete set of available paths for each distinct commodity. In detail, fractional variables are employed to track release of flows at each point in time for each commodity and path; a first set of binary variables allows for the identification and linear minimization of the makespan by recording arrival times at destination of each routed commodity demand, while a second set of binaries imposes k-splittable path limitations to each commodity. The formulation presents a number of columns which grows exponentially with the instance size, due to the presence of variables associated with the number of paths for each commodity multiplied by the number of instants in the discretized time horizon. The computational complexity of the introduced problem is formally investigated, proving its belongs to the class of strongly NP-hard problems by a reduction from the static Minimum Cost k-Splittable Flow Problem. When it comes to solution approaches, the first algorithm designed for the ad-hoc resolution of the QMCkSFP is an improvement matheuristic hybridizing a Very Large-scale Neighborhood Search (VLNS) with a mathematical programming strategy in its exploration routine. The method employs a state-of-the-art ranking procedure to generate a sufficiently large list of good and promising candidate paths to be used throughout its implementation. In particular, the initial solution is constructed by selecting for each commodity the k top-ranked paths from the generated list w.r.t. their transmission time, i.e. the time required to transship the entire commodity demand. The QMCkSFP path-flow formulation is restricted to these initial paths and solved to optimality via a MIP solver. Then, at each improvement iteration of the matheuristic, a different neighborhood is constructed by heuristically identifying for each commodity a collection of candidate paths from the list and it is explored to optimality by solving the related restricted path-flow formulation. The improvement search proceeds through a Variable Neighborhood Descent scheme by increasing the cardinality of the path collections to be identified till a time limit is reached. A thorough computational experience is conducted on the proposed model and matheuristic approach, starting by the resolution to optimality of a set of very reduced-size instances, making use of the path-based formulation fed with a complete enumeration of all the available paths. A tuning process is then carried out on the matheuristic's parameters for the identification of the optimal setting to be adopted in the evaluation of its performance. An exhaustive proof-of-concept for the correctness and effectiveness of the matheuristic resolution strategy is then conducted: to this aim, a comparison is performed on a set of small to medium-sized instances against the Quickest Multicommodity Flow Problem, i.e. the free-flow relaxation of the problem with no upper bounds on the number of usable paths. Finally, we test performances of our matheuristic against those of a Randomized Rounding-based algorithm on two different benchmark test sets, the first one collecting networks of large size w.r.t. number of nodes and arcs, and the second networks with an extremely high number of commodities. Our second algorithmic contribution is represented by an exact strategy for solving the QMCkSFP at the optimum. The developed technique falls within the Branch and Price paradigm and is based on original relaxation, pricing and branching procedures. In particular, the so-called Restricted Relaxed Master Problem (RRMP) is obtained by linearizing time-arrival binary variables and by substituting those related to k-splittable path restrictions from the path-based formulation of the problem. The same ranking algorithm employed in the matheuristic initialization phase is here adopted for the construction of the path-related columns to be considered at the root node of the Branch and Bound decisional tree. In particular, the best k paths w.r.t. the transmission time are generated for each commodity and all related fractional variables are included as initial columns. The Column Generation procedure is then applied to identify, through the resolution of the so-called pricing problem, new entering variables defined as pair (path,departure time), or to certify the optimality of the nodes' RRMPs. This is done on a slightly modified time-expansion of the original dynamic digraph where the time dimension is decoupled from the network structure to give rise to a novel equivalent static digraph. Two original branching rules are designed for restoring feasibility. A first one, performed whenever k-splittable flow constraints are violated, forces the usage of some paths and simultaneously forbids the activation of others over the discretized time horizon. Working on path-based variables, the generated branching cuts are included in RRMPs of the child nodes. A second rule implements a refined version of the standard 0-1 branching on fractional variables by selecting the candidate time-arrival variable at the highest time instant. In order to account for k-splittable-related branching cuts, the pricing problem is modeled as a Shortest Path Problem with Forbidden Paths where additional node-set resources are introduced to secure the generation of loopless paths. A tailored labelling algorithm based on dynamic programming is designed and employed to solve the pricing problem to optimality. All variables modeling the utilization of the optimal identified path at each point in time are included as new columns. The computational experience conducted on the designed Branch and Price algorithm begins by studying its correctness and computational performances when applied on a collection of small to medium-sized instances. As the final experiment, we employ the Branch and Price approach as a tool to assess the quality of the solutions obtained by the developed VLNS-based matheuristic. To this aim, we consider the same testbed of small to medium-sized instances used in the matheuristic experiments with our Branch and Price, feeding it with the matheuristic results as initial incumbent solutions, then measuring and comparing the residual optimality GAP achieved after the execution of the exact algorithm. The overall toolbox developed in this research lays the foundations for a number of refined and additional novel contributions within the dynamic k-splittable flow setting, whose preliminary guidelines are discussed in the closing chapter of this thesis

Il contributo dell’attività fisica su cognizione e apprendimento

The motor approach can be a way that integrates itself or that presents itself as an alternative for the maintenance of cognitive abilities. More scientific research documents how motor activity has psycho-physical benefits on the individual. In Italy and in Europe, teaching physical activity in schools of all levels seems to have given it less importance than other school subjects. In this study there are some aspects of improvement in the cognitive field in relation to the consumption of oxygen linked to light motor activity with the aim of laying the foundations for a subsequent analysis on a broader spectrum, both with respect to the cognitive abilities examined and with respect to the specificity of motor activity. This is a pilot study carried out on a sample of University students to Università Niccolò Cusano di Roma, using the "Lexical research and production test", verifying the results with or without an aerobic activity performed on the treadmill.L’approccio motorio può essere una strada che si integra o che si pone come alternativa per il mantenimento delle capacità cognitive. Sempre più ricerche scientifiche documentano come l’attività motoria abbia dei benefici psico-fisici sull’individuo. Di contro, in Italia ed in Europa, l’insegnamento dell’attività motoria nelle scuole di ogni ordine e grado sembra le abbia attribuito un’importanza minore rispetto alle altre materie.In questo studio si presentano alcuni aspetti migliorativi in campo cognitivo in relazione al consumo di ossigeno legato ad un’attività motoria lieve, con il fine di porre le basi per una successiva analisi a più ampio spettro, sia rispetto alle capacità cognitive prese in esame che rispetto alla specificità dell’attività motoria. Si tratta di uno studio pilota effettuato su un campione di studenti Universitari dell’Università Niccolò Cusano di Roma utilizzando il “Test di ricerca e produzione lessicale” verificandone i risultati con o senza un’attività aerobica effettuata sul tapis roulant

THE INFLUENCE OF COACHES’ LEADERSHIP STYLE ON SELF-ESTEEM AND SPORT MOTIVATION IN ADOLESCENT ATHLETES

The study investigates the relationship between coaches’ leadership styles and the level of self-esteem and sport motivation in adolescent athletes in a sample of adolescent athletes (n=85 considering different sports) and their coaches (n=10). Previous literature about the youth population suggests that contextual factors can have an important influence on the effects of the sport, e.g. the relations with adults and peers (Brustad, Babkes & Smith, 2001) or the sports program one takes part to (Whitehead & Corbin, 1997). In this research, the coaches’ leadership style was taken into consideration because it has an important influence on athletes’ self-perceptions (Coatsworth & Conroy, 2009). Scientific studies demonstrate that a more supportive, nurturing and encouraging leadership behaviour produce greater changes in youth’s self-esteem (Coatsworth & Conroy, 2006; Smith & Smoll, 1996). Additional evidence showed how the coach’s behaviour influence athletes’ motivation (Amorose & Anderson-Butcher, 2007; Gagné, Ryan & Bargmann, 2003). The results of the data analysis show a strong positive correlation between athletes' self-esteem and coach’s Training & Instruction behaviour and a negative relationship between self-esteem and lack of motivation in athletes. Besides, from a larger sample of coaches (n = 49) the relationship between the coach’s leadership behaviour and his own level of self-esteem was investigated (Rosenberg SES, Prezza et al., 1997). The results highlighted higher levels of Training & Instruction, Autocratic, Social Support and Positive Feedback behaviours in coaches with an average level of self-esteem compared to those with low levels

The influence of physical activity in resilience and coping strategies in adulthood

The purpose of the study is to investigate the relationship between the physical activity, linked to energy expenditure, and the development of resilience and adaptive coping strategies. Therefore, one more aim is to confirm the positive correlation between self-esteem and resilience. It is well known that sports and physical activity can play an important role in human health. It is not yet well defined if it is the energy and oxygen expenditure that bring benefits or the complexity of the movement, or a mix of both, in particular for resilience and coping strategies. Our sample is composed by 280 cases, all adults. The data has been collected using the Rosenberg Self-Esteem Scale, the Adult Resilience Measure, the Brief COPE Questionnaire and the IPAQ for physical activity. According to the results, there’s no correlation between physical activity / energy expenditure and resilience level and adaptive coping strategies. In this sense, new research are needed, involving different and more complex motor acts and different levels of energy expenditure

L’influenza di interventi di rinforzo dell’autostima sul grado di resilienza in atleti adolescenti

L’autostima è considerata un fattore di grande importanza per la resilienza dei giovani (Currie et al., 2004). Insieme alla famiglia, al gruppo dei pari e all’ambiente fa parte dell’architettura necessaria per la strutturazione di un livello positivo di resilienza. L’alta autostima nell’adolescenza è correlata positivamente alla tendenza a compiere uno sforzo persistente per superare le difficoltà (Coleman e Hendry, 1990), così come gli adolescenti resilienti hanno una maggiore autostima e hanno comportamenti meno rischiosi rispetto ai loro compagni meno resilienti (Buckner, Mez- zacappa, & Beardslee, 2003). D’altra parte, Trzesniewski e altri (2006), hanno dimostrato una buona correlazione tra l’autostima e l’attività fisica. Inoltre, la revisione sistematica di Ekeland (2005) ha evidenziato che l’attività fisica ha effetti positivi a breve termine sull’autostima degli adolescenti. Il nostro studio indaga la relazione tra un programma di allenamento delle abilità mentali focalizzato sulla definizione degli obiettivi, il dialogo interno e la visualizzazio- ne e il livello di autostima di un gruppo di atleti nuotatori adolescenti. Un ulteriore obiettivo dello studio è quello di indagare la correlazione tra il livello di autostima e il livello di resilienza. L’autostima è stata misurata attraverso il Multidimensional Self Esteem Test di Bracken (1992), mentre per valutare il grado di resilienza è stato utilizzato il Child & Youth Resilience Measure-Revised (CYRM-R) (Jefferies et al., 2018). I dati mostrati in questo studio sono relativi al primo step di verifica, effettuato a metà percorso, dopo 8 sessioni di Training Mentale