Abstract
The need for maintenance is based on the wear of components of machinery. If this need can be defined reliably beforehand so that no unpredicted failures take place then the maintenance actions can be carried out economically with minimum disturbance to production. There are two basic challenges in solving the above. First understanding the development of wear and failures, and second managing the measurement and diagnosis of such parameters that can reveal the development of wear. In principle the development of wear and failures can be predicted through monitoring time, load or wear as such. Monitoring time is not very efficient, as there are only limited numbers of components that suffer from aging which as such is result of chemical wear i.e. changes in the material. In most cases the loading of components influences their wear. In principle the loading can be stable or varying in nature. Of these two cases the varying load case is much more challenging than the stable one. The monitoring of wear can be done either directly e.g. optical methods or indirectly e.g. vibration. Monitoring actual wear is naturally the most reliable approach, but it often means that additional investments are needed. The paper discusses the above issues and what are the requirements that follow from these for optimising maintenance based of the use of Cyber Physical Systems.

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To summarise this editorial, we attempted to briefly chart out some developments in related areas of governance and sustainability. As this field is a 'never ending story', novel questions and problems stem requiring equally novel solutions. At the end, the guest editors hope, and would like, that this special issue will beuseful, meeting the expectations of the authors and wider readership and serving for enhancing the individual and collective learning, theoretical insight and practical applications, and to incentive further scientific development and creation of new papers.

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Many of the 17 million Europeans who suffer from food allergies could benefit from a more direct information system in the identification of the 14 allergens regulated by the Parliament and Council Regulation (EU) no 1169/2011 in packages of food products. This study aimed at creating pictograms representing these 14 allergens along visual and tactile lines, through relief printing. Based on Inclusive Design approach, the project meant to overcome restrictions such as sight impairment or illiteracy. Making use of User Centered Design (UCD) methodology, and with the support of the SAED (Disabled Students Support Services of the University of Porto) and GAENEE-UP (Support Office for Students with Special Educational Needs of the University of Porto), it employed field observation processes, in which potential users recorded their tactile perception of basic elements of visual communication. The result is the creation of a universal code, which is meant to satisfy the expectations and needs of potential users, namely people with impaired sight.

Abstract
In the last few years, sustainability has become one of the priority lines for many companies and organizations, especially public administrations. This trend has been even more evident in some regions where the preservation of natural resources is of utmost importance, not only from an environmental perspective, but also from an economic one. In this context, technology has become one of the key factors to achieve sustainability goals. An example of these technologies are Unmanned Aerial Vehicles (UAVs) which are being used more and more with sustainability purposes. However, although some efforts have been made to propose software approaches to model sustainability, some examples that model the impact of technology on sustainability are still needed. This paper presents an instance of a sustainability metamodel for the UAVs domain. This model allows to specify the impact of UAV-based processes on sustainability, and also to identify potential limitations that may hinder its applicability. Finally, the paper provides some suggestions to complete the metamodel based on the instantiation process.