An Empirical Study of Cohesion and Coupling: Balancing Optimisation and Disruption

Search based software engineering has been extensively applied to the problem of finding improved modular structures that maximise cohesion and minimise coupling. However, there has, hitherto, been no longitudinal study of developers’ implementations, over a series of sequential releases. Moreover, results validating whether developers respect the fitness functions are scarce, and the potentially disruptive effect of search-based remodularisation is usually overlooked. We present an empirical study of 233 sequential releases of 10 different systems; the largest empirical study reported in the literature so far, and the first longitudinal study. Our results provide evidence that developers do, indeed, respect the fitness functions used to optimise cohesion/coupling (they are statistically significantly better than arbitrary choices with p << 0.01), yet they also leave considerable room for further improvement (cohesion/coupling can be improved by 25% on average). However, we also report that optimising the structure is highly disruptive (on average more than 57% of the structure must change), while our results reveal that developers tend to avoid such disruption. Therefore, we introduce and evaluate a multi-objective evolutionary approach that minimises disruption while maximising cohesion/coupling improvement. This allows developers to balance reticence to disrupt existing modular structure, against their competing need to improve cohesion and coupling. The multi-objective approach is able to find modular structures that improve the cohesion of developers’ implementations by 22.52%, while causing an acceptably low level of disruption (within that already tolerated by developers)

Driver scheduling problem modelling

The Drivers Scheduling Problem (DSP) consists of selecting a set of duties for vehicle drivers, for example buses, trains, plane or boat drivers or pilots, for the transportation of passengers or goods. This is a complex problem because it involves several constraints related to labour and company rules and can also present different evaluation criteria and objectives. Being able to develop an adequate model for this problem that can represent the real problem as close as possible is an important research area.The main objective of this research work is to present new mathematical models to the DSP problem that represent all the complexity of the drivers scheduling problem, and also demonstrate that the solutions of these models can be easily implemented in real situations. This issue has been recognized by several authors and as important problem in Public Transportation. The most well-known and general formulation for the DSP is a Set Partition/Set Covering Model (SPP/SCP). However, to a large extend these models simplify some of the specific business aspects and issues of real problems. This makes it difficult to use these models as automatic planning systems because the schedules obtained must be modified manually to be implemented in real situations. Based on extensive passenger transportation experience in bus companies in Portugal, we propose new alternative models to formulate the DSP problem. These models are also based on Set Partitioning/Covering Models; however, they take into account the bus operator issues and the perspective opinions and environment of the user.We follow the steps of the Operations Research Methodology which consist of: Identify the Problem; Understand the System; Formulate a Mathematical Model; Verify the Model; Select the Best Alternative; Present the Results of the Analysis and Implement and Evaluate. All the processes are done with close participation and involvement of the final users from different transportation companies. The planner‘s opinion and main criticisms are used to improve the proposed model in a continuous enrichment process. The final objective is to have a model that can be incorporated into an information system to be used as an automatic tool to produce driver schedules. Therefore, the criteria for evaluating the models is the capacity to generate real and useful schedules that can be implemented without many manual adjustments or modifications. We have considered the following as measures of the quality of the model: simplicity, solution quality and applicability. We tested the alternative models with a set of real data obtained from several different transportation companies and analyzed the optimal schedules obtained with respect to the applicability of the solution to the real situation. To do this, the schedules were analyzed by the planners to determine their quality and applicability. The main result of this work is the proposition of new mathematical models for the DSP that better represent the realities of the passenger transportation operators and lead to better schedules that can be implemented directly in real situations.Drivers Scheduling Problem, Duties, Modelling

El aula virtual: estrategia didáctica en la enseñanza del Derecho Penal General

Caracterizar un Aula Virtual como estrategia didáctica adecuada para la enseñanza del Derecho Penal General, es el resultado de la inevitable inserción de las TIC en la Educación de nuestro tiempo. Más aún cuando dicha materia es una de las que más soportan resistencia entre los estudiantes de Derecho, en razón de sus contenidos mal comprendidos, lo cual genera desmotivación y apatía por ella, viciando así los procesos de enseñanza y aprendizaje que allí yacen. Es por ello que un Aula Virtual pensada para dinamizar y vigorizar lo anterior, debe configurarse a partir de todo aquello que hace a los discentes Seres Humanos (emociones, sentimientos), los cuales de desenvuelven diariamente en ámbitos donde reina la interacción. Y son justamente estas características las que han de tomarse como principios rectores para el diseño de un entorno virtual dinámico y atractivo, que como estrategia didáctica que explote todos los recursos y posibilidades que le son propios y en su papel de extensión de las cátedras de Penal General, se propone sensibilizar a los jurisconsultos en dicha asignatura, despertando creciente motivación e interés por sus contenidos, lo cual vigoriza el desarrollo de las competencias básicas que ha de ostentar virtuosamente todo Abogado, especialmente en un área de enorme impacto social como lo es Derecho Penal General

Large Eddy simulation of supersonic combustion using a probability density function method

The scramjet propulsion system is regarded to be a key technology to deliver the next generation of hypersonic planes. It consists of a ramjet engine in which the combustion occurs at supersonic speed. Experiments have been used to investigate the scramjet engine, however, the high costs of gathering data is a limiting factor in its development. In this context, the numerical simulation is an affordable alternative to shed a light into supersonic combustion. The simulation of high-speed compressible and reactive flows, however, is not straightforward, including shock/boundary layer interactions and combustion. Nonetheless, most combustion models have been designed for subsonic flames and their portability to high-speed flows is non-trivial. This work investigates the use of the Probability Density Function (PDF) method for supersonic combustion within the Large Eddy Simulation (LES) framework. Two methods are considered: one is an extension of a joint scalar PDF model (SPDF) for high speed flows and the other is a new joint velocity-scalar PDF formulation (VSPDF). The LES-PDF equations are solved using the Eulerian stochastic fields method, which is implemented into the in-house compressible code CompReal. Their performance are evaluated through a reactive shock-tube, mixing layers and a homogeneous isotropic turbulence cube simulation. Two supersonic burner configurations are simulated to validate the code against experimental data. The results show that sub-grid contributions are important at coarse meshes and the stochastic fields approach can reproduce experimental results. The University of Virginia scramjet configuration A is also simulated using the joint scalar PDF model. Results of topwall pressure, temperature and molar fractions are compared with experimental data. Overall, the results suggest that the joint scalar PDF is the most robust and reliable formulation and the sub-grid closures for the joint velocity-scalar PDF require further investigation.Open Acces

Gambling and Tourism in South America: an analysis of resort casinos evolution and legislation comparison in the continent

Abstract Gambling and tourism industries have been developed by South American governments as a way of generating jobs and revenues. Of all kinds of gambling activities, casinos are the most commonly associated with the hospitality industry. Hotel and resort casinos can be found in every SA country (Argentina, Bolivia, Chile, Colombia, Ecuador, French Guyana, Guyana, Paraguay, Peru, Suriname, Uruguay and Venezuela) except for Brazil, a two hundred million consumers market that prohibited casinos back in 1946. The purpose of this paper is to better understand the resort casinos evolution in these territories and also to compare legislation aiming to predict what might happen to the Brazilian gaming sector in the future as the issue has been strongly debated. The methodology by using internet data and scientific bibliography is presented in a chronological manner, highlighting the correlation between tourism statistics evolution and the number of resort casinos development in the studied countries for the past 20 years. The findings varied significantly by country, legislation and type of casinos enterprises. And considering that Brazil leads tourism statistics in SA, it can be concluded that hotel-casinos in this continent are more related to destination competitiveness, entertainment and an integrated resort image, rather than international travel arrivals and income. So what The originality of this presentation is to identify turning points that have helped to shape the development of South America gambling and tourism industry, so encourages researchers and legislators to compare and to consider future scenarios concerning to the role of these economic activities in each country

The architecture of predator-prey and the relationship between complexity and stability

Theoretical studies predict that the stability of an ecosystem is negatively correlated with its complexity, measured by the number of interacting species. On the other hand, empirical evidence indicates that food webs are highly interconnected. In this manuscript we present results on the stability two-level predator-prey food webs. We analyzed exhaustively all possible topologies of connections among species. Our findings show that those food webs fall into two classes with clearly distinct stability properties. In one of them stability is negatively correlated with complexity, and in the other group stability is positively correlated. For a positive relationship our results reveals highly structured food webs. The positive or negative relationship is related only to the topological structure of the food web. It is independent of the number of connections, strengths of predator-prey interactions or number of species. We review empirical evidence that corroborates our results