Abstract
Physical properties of materials are seldom studied in the context of packing problems. In this work we study the behavior of semifluids: materials with particular characteristics that share properties both with solids and with fluids. We describe the importance of some specific semifluids in an industrial context, and propose methods for tackling the problem of packing them, taking into account several practical requirements and physical constraints. The problem dealt with here can be reduced to a variant of two-dimensional knapsack problem with guillotine cuts, where items are splittable in one of the dimensions and the number of cuts is not limited. Although the focus of this paper is on the computation of practical solutions, it also uncovers interesting mathematical properties of this problem, which differentiate it from other packing problems. A thorough computational experiment is used to assess the quality of the approaches proposed, which is analyzed and compared to relevant methods from the literature.

Abstract
The resource-constrained project scheduling problem (RCPSP) is one of the most studied problems in the project scheduling literature, and aims at constructing a project schedule with a minimum makespan that satisfies both the precedence relations of the network and the limited availability of the renewable resources. The problem has attracted attention due to its NP hardness status, and different algorithms have been proposed that solve a wide variety of RCPSP instances to optimality or near-optimality. In this paper, we analyse the hardness of this problem from an experimental point-of-view by testing different algorithms on a huge set of existing instances and detect which ones are difficult to solve. To that purpose, we propose a three-phased approach that makes use of five elementary blocks, well-performing algorithms and a huge amount of computational power to transform easy RCPSP instances into very hard ones. The purpose of this study is to create insight and understanding into what makes an RCPSP instance hard, and propose a new dataset that consists of a small set of instances that are impossible to solve with the algorithms currently existing in the literature. These instances should be as small as possible in terms of number of activities and resources, and should be as diverse as possible in terms of network structure and resource strictness. Such a dataset should enable researchers to focus their attention on the development of radically new algorithms to solve the RCPSP rather than gradually improving current algorithms that can solve the existing RCPSP instances only slightly better.

Abstract

Abstract
Digital Marketing is a decisive advantage for the business strategy of the hotel sector. Besides being a powerful tool for implementing tourism marketing actions and policies also enables the monitoring and measurement of results; helping to keep them at a level of effectiveness and success or to improve them. Digital Marketing can also be a strong ally in combating unforeseen economic crises in the hotel sector, as is the case of the current situation that we are experiencing caused by COVID-19. In this article, the Digital Marketing strategy implemented by HSL from the point of view of the digital consumer will be analyzed, through an exploratory analysis of its website, online booking platforms, social networks and how these digital tools have helped HSL throughout the pandemic. COVID-19.

Abstract
Based on an exploratory research, this study highlights the role of pure rural entrepreneurship towards rural development of an inland and mountainous area of Portugal-Montemuro. Thanks to the Institute of Cultural Affairs and the energy of the rural communities, some people of the rural area have been stimulated thirty years ago to develop endogenous, entrepreneurial and innovative initiatives in the countryside. The benefits of all these rural entrepreneurial and endogenous initiatives are visible nowadays. Some villages of the rural area have more people, socio-economic dynamics were revitalized, and some job opportunities were created. Therefore, in a context of depopulation and crisis of peripheral and interior areas, our study demonstrates that rural entrepreneurship and innovation based on endogenous resources are key for the welfare of the rural society.

Abstract
Achieving a new generation of enhanced sensors requires the development of structures that result from the fusion of different concepts and effects. In this paper, we combine a special strain sensing structure with an optical sensitivity magnification, through harmonics of the Vernier effect. The recently demonstrated harmonics of the Vernier effect result from increasing the optical path length (OPL) of one of two interferometers by multiple times the OPL of the other interferometer. The effect generates higher magnification factors, proportional to the order of the harmonics. The sensing structure is demonstrated for strain and temperature discrimination, allowing compensation for temperature fluctuations. We explore the complex case of the optical Vernier effect in series, where both interferometers are used as sensing interferometers (no reference interferometer is used). Our results also suggest that the magnification enhancement provided by harmonics of the Vernier effect for a configuration in series is the same as for a configuration in parallel: the magnification factor increases proportionally to the order of the harmonics.