Valentin Frédéric
email: frederic.valentin@telecom-paristech.fr

Keywords: Interdisciplinarity, Indiscipline, Mood-Board, Design, Design Education, Discretization

This paper analyses the use of mood boards in design education not only as a means of conception and communication but also as a method that brings interdiciplinarity into play. It presents a longitudinal study of two use cases in two different educational contexts: a design school and an engineering school. After analyzing mood boards, their production and presentation, the authors suggest that mood boards actually help practitioners to draw pertinent questions and responses because they organize three conceptual activities: discretization, coherence, and relevance. The discretization of fields, objects, facts, deconstructs the disciplines as such, but also organizes the interplay of disciplines. This interplay could be dismissed as undisciplined. But we suggest that the format-i.e. the formal meaning of the media-shapes the process and organizes a rationally and efficiently constructed space of conception. After Rancière, we suggest that the concept of "indiscipline" covers not only the deconstruction and the stepping out of disciplines, necessary to the process of conception, but also that it reflects the rigorous framing of this process through formal and practical meaning making.

level to demand a specific space for a multidisciplinary practice and at the epistemological level to establish the rationale of a discipline while it borrows and modifies concepts and methods from other disciplines as well as develops its own. More importantly in our perspective, it structures the way design education is defined and prescribed in France. After studying multiple texts formalizing design education in France (Arrêté du 17 juillet 1984; Arrêté du 30 juillet 2012; Arrêté du 5 avril 2012; Extraits du Bulletin officiel spécial du 29 avril 2010), we noted that one of the recurrent characteristics associated with the designer's practice is her "capacity to interact and work with other disciplines", her capacity to interact with various actors of different disciplines while understanding and integrating them into her own practice (as an example, a transversal capacity expected from HND students in graphical, product and environment design is to "communicate at all levels in a pluridisciplinary manner"(Arrêté du 22 août 2006 and Arrêté du 8 avril 2009).

Without repeating the entire debate on interdisciplinarity [START_REF] Dubreuil | Défauts de savoirs[END_REF][START_REF] Findeli | Rethinking design education for the 21st century: Theoretical, methodological, and ethical discussion[END_REF], Bremner & Rodger, 2013), we wish to identify the relations between design educational tools and scientific disciplines. We find that tools are often considered either in their creative or managerial capacity but here we want to question their role as interdisciplinary research tools. Following the principle of "design oriented research" as defined by Daniel Fallman (2008), we would argue that mood boards are not only design tools but also a means of production of knowledge and concepts that deconstructs disciplines as such, but also formally and pragmatically frame the research findings. Saying so does not mean a consideration of design and its tools as "disciplined"-that is following a set of well defined steps-nor "undisciplined"-in the sense that it would not follow any rigorous rationale-but rather that the pragmatic and semiotic traits of these documents and their circulation organize not only the deconstruction of disciplines but also the re-organization of data to produce a new object, an X.

In the first section of this article, we present a review on design education and the interplay of disciplines. We then draw on the literature on mood boards to point out the way they elicit "emotions" and their creative and managerial qualities. We also take into consideration the criticisms that they raise. After presenting our research setting, we move on to analyze a series of mood boards created in two contexts of education to better understand how they structure the design practice in terms of formal properties and cognitive operations. In the next section, we identify their epistemological properties. Then, we discuss how these properties operate a synthesis and the expansion of the design project. We ask the following questions: How are they related to the rationale of a scientific process? How do they organize a design space? We finally conclude on the "in-discipline" of design.

Design Education and the Interplay of Disciplines

In our review of design education literature, we identified three major topics of inquiry: the acquisition of a theoretical and visual culture (Brookes,1992;[START_REF] Dutton | The Hidden Curriculum and the Design Studio: Toward a Critical Pedagogy[END_REF][START_REF] Gall | Navigating a way through plurality and social responsibility[END_REF][START_REF] Chin | Critiquing commonly available multicultural art education resources[END_REF][START_REF] Hadjiyanni | Beginning with concept: Deconstructing the complexity of "culture" through art in design education[END_REF], the development of methodological and analytical techniques (Schon & Wiggins,1992;[START_REF] Goldschmidt | Variances in the impact of visual stimuli on design problem solving performance[END_REF][START_REF] Adams | Educating effective engineering designers: the role of reflective practice[END_REF][START_REF] Ozkan | Cognitive strategies of analogical reasoning in design: Differences between expert and novice designers[END_REF][START_REF] Daalhuizen | A personal matter? An investigation of students' design process experiences when using a heuristic or a systematic method[END_REF] and the fostering of students creative skills (Cross, Christiaans, and Dorst, 1994;[START_REF] Folkmann | Enabling creativity. Imagination in design processes[END_REF][START_REF] Van Dooren | Making explicit in design education: generic elements in the design process[END_REF][START_REF] Lu | The relationship between student design cognition types and creative design outcomes[END_REF]. While all these acquisitions are legitimate to become designers, what is also at stake is the interplay of these different competences in a design project [START_REF] Hatchuel | Teaching innovative design reasoning: How conceptknowledge theory can help overcome fixation effects[END_REF]. In particular: how do creative skills intersect with theoretical knowledge? [START_REF] Findeli | Research Through Design and Transdisciplinarity: A Tentative Contribution to the Methodology of Design Research[END_REF] explores the interplay between design practice and scientific practice. While he criticizes an approach of design education that focuses only on practice, he also points out the limits of design considered as an applied science. In the latter case, he emphasizes first the impossibility of listing the infinite number of sciences that could be applied by design. Second, he contends that design cannot be an applied science. Just as engineering sciences are not applied sciences for fundamental sciences but constitute a specific field with their own complexity of knowledge [START_REF] Schmid | Une nouvelle logique de l'interdisciplinarité[END_REF], design sciences constitute a field of concepts, methods, and theories that are autonomous from "fundamental" sciences. Yet design also builds a relation to other sciences. This relation is to be understood through the practice of design. Following Findeli's analysis of design education (2001), we want to understand the practice of design through the artefacts that are produced during design classes and projects and to see how these practices can be understood from an epistemological point of view. We are interested in the implied theories of design supporting these artefacts and their production. In this article, we focus on the data that is collected from contextual research, and how they are organized and presented. Among these artefacts, mood boards are tools that support designers' search of materials, and synthetic approach.

Mood boards in the literature

Mood boards are regularly cited as design tools [START_REF] Takano | Proposal of A Multispace Design Method Corresponding to Diverse Usage[END_REF][START_REF] Michura | Seeing the forest and its trees. A hybrid visual research tool for exploring look an feel interface design[END_REF]. First, mood boards elicit emotions and therefore tend to structure the user's experience (Eckeert & Stacey, 2000;[START_REF] Mcdonagh | Exploring the degree to which individual students share a common perception of specific mood boards: observations relating to teaching, learning and team-based design[END_REF]. Baxter contends that "the mood of a product is the sentiment feeling or emotion which the product engenders when first seen. […] A good mood board captures these feelings in images but without referring to specific product features which might limit the range of styling options considered" (Baxter, 1995 p. 222). Mood boards also collect styling features that have been successful in the past. This second characteristic of mood boards helps gather aesthetic cues for future designs (Tan & Melles, 2010). Mood boards therefore serve a double purpose in the design practice. First, they serve as a "reservoir" of qualities, aesthetic properties, for the design work (See also [START_REF] Gonçalves | What inspires designers? Preferences on inspirational approaches during idea generation[END_REF]. Second, they serve a communication purpose. They play a managerial role [START_REF] Mcdonagh | Mood boards as a design catalyst and resource: Researching an underresearched area[END_REF] as they convey styling objectives to members of the design team and customers. But, as pointed out by [START_REF] Garner | Problem interpretation and resolution via visual stimuli: the use of "mood boards" in design education[END_REF], mood boards also raise mixed feelings for practitioners, students and professors alike. First, there is no guarantee that the communicational purpose is fully conveyed as participants can have a very different interpretation of what the images mean. The inspirational function of mood boards is not obvious either. First, mood boards can be too abstract. They do not help to make design choices and are therefore difficult to relate to tangible positioning and to actually embed in a real project. Second, mood boards may induce fixation in the design process [START_REF] Cheng | A new strategy to reduce design fixation: Presenting partial photographs to designers[END_REF][START_REF] Crilly | Fixation and creativity in concept development: The attitudes and practices of expert designers[END_REF][START_REF] Purcell | Design and other types of fixation[END_REF]. The choice of images does not represent a starting point but rather serves to legitimate design choices already made. In between fixation and defixation, mood boards have therefore a delicate balance to strike. The consequence is that mood boards, like other reflective and messy synthesis processes, "are considered a 'waste of time,' as they aren't positioned as actionable or immediately predictive" [START_REF] Kolko | Abductive thinking and sensemaking: The drivers of design synthesis[END_REF]. As we observed in both use cases, mood boards can be qualified by students as a simple stage to reach the desired goal, and may be easily discarded (when asked, our students revealed that they did not keep their mood boards). Mood boards are not seen as "proper work" that should be archived, because they seem too specific in time and space to be considered as relevant for further design enquiries. These criticisms show that the art of doing good "mood boards" is not formally defined and that the method could finally be detrimental to the design process. Our first hypothesis is that by understanding the semio-pragmatic elements of mood boards, we should be able to better design them and show their functions and limits. Mood boards are specific documents that organize representations in a special way and that are meaningful within particular situations of design and design education. By analyzing both the documents and their reception, we want to understand their role in the design process and the type of knowledge they produce. Our second hypothesis is that mood boards, as part of a rationale of design, are related to fields of knowledge and disciplines. We want to better address this connection between practice and scientific disciplines.

Research Setting

To address the question of the semiotic and pragmatic properties of mood boards in the context of education, and how this particular practice is related to scientific disciplines, we selected two use cases of design education that involved mood boards in the design process.

The cases reported in this paper were selected for three main reasons. First, the observations could take place at the very beginning of the education projects, which was a condition for the success of our longitudinal approach, as we could follow the various steps from brief to brief refinement through moodboards, to the development of a project. From the first discussions on the overall purpose and format of the class in June 2014, to the more specific meetings preparing the class from September 2014 to march 2015, implying a continuous discussion with the professor in charges (through regular inquiries about the class and interviews) and participation in the definition of the different exercises, the authors could follow the different stages that framed the workshop of Use Case 1. For Use Case 2, the authors also participated in meetings that prepared, then evaluated the class that took place from March to June 2014. Second, the groups that participated in the project under study accepted that the authors could carry out an in-depth empirical study, which was another necessary condition to sustain our comprehensive approach to design practices at work. Third, the studied cases can be compared as they took place in different organizations-one design school and one engineering school-which makes it possible to see commonalities and differences.

Use Case 1 presents an observation done from January to February 2015 in a class of 16 master degree students enrolled in the "global design" program of a private design school in Paris. The design brief was presented as a reflection on "Design and Misbehaving" or "how to misbehave in design". The students had to propose uncanny design practices. In this context, the students were organized in four groups of four and presented four mood boards.

Use Case 2 took place in an engineering school in Paris from March to June 2014. The program is called "Design and Innovation" and brings together competences in design, management and economics. Students have to develop a detailed scenario of use, interaction specifications, and aesthetics recommendations. In this use case, the students had to develop scenarios and interfaces after the following brief : "what would be an intelligent car that cares for me?" The brief was given by a car company that wished to tap into the technical culture of students. Each of the 20 students had to present a mood board.

We will compare these two use cases to extract the distinctive principles of the use of mood boards.

Description of mood boards

In both use cases, mood boards had at least two explicit goals: creating a minimal culture for students who had never had a chance to work on these subjects and creating a resource for design cues.

Context and Pragmatic aspects

The students used digital tools to make their mood boards (Power point, Adobe Illustrator, etc.). There were no other media. The presentations were made of various numbers of slides with collected images on each. Some were annotated. Mood boards were shared amongst students, whether during a formal public presentation or informally. In the design school (Case 1), the term "mood board" was not explained. The professors relied on the tacit understanding that it was part of the students' culture of design practice, a common tool. In the second use case, examples were shown to help the engineering students to produce their own.

In both use cases, the students were evaluated on their capacity to be coherent but also "expansive" (Use Case 1's evaluation chart uses the criteria "richness of the universe"), that is, to develop an original approach to the project. The other explicit goal was that the students had to build a "minimum culture" on the subject. In Use Case 2, the professor also added that the process was part of the acquisition of a visual culture quite foreign to engineering students. She posited that they had to go "from ideas to concretization". While it was assumed that design students were comfortable with the use of visual references and their manipulation, it was assumed that engineering students were not.

Both curriculums have strong relations with the professional and industrial world. The mood board exercise also aimed at developing their professional skills. But at the same time, the purpose of the programs is also to disorient the students whether by the use of uncommon tools or methods, and/or by encouraging a deeply personal approach to an undefined problem.

Analysis of mood boards

In Use Case 1, mood boards presented visual elements from different origins: other design projects, art photographs or actual products. For instance, one of the mood boards presented a photomontage of a design project (the portrait of a man with a vegetal beard) on the same level as artistic photographs (see Figure 1). A number of images came from critical design [START_REF] Dunne | Hertzian Tales: Electronic Products, Aesthetic Experience, and Critical Design[END_REF][START_REF] Mollon | Critical design[END_REF] which emphasizes uncanny associations reinforcing the overall feeling of design as a source of tensions and questions. Pictures in the mood boards were also decontextualized and did not present obvious hierarchies between elements of various nature and origins.

But the documents also demonstrated a form of coherence. In the mood board already mentioned, coherence was achieved around the theme of vegetal hybridization. The two visuals on the left, while they lost the reference to the vegetal, kept the idea of a graft, here producing energy. Through this mood board, the students efficiently communicated an ecological discourse based on an aesthetical research around the hybridization of plants and human body. The visual of "TomTato", if it is not directly depicting the adjunction of vegetal to the body, denotes (as it is described in the caption) hybridization. Because this reference is a real commercialized product, it is possible that the students saw it as a proof of concept, as a way to make their fictional project more plausible.

When presenting their mood boards, students focused more on the visuals of the projects rather than an actual description or analysis of the quoted projects. When present, the captions referring to the artists and projects were hardly visible. Students admitted later that they used these elements with two distinct purposes. The first was to "reassure" the professor by showing references related to the exercise, demonstrating the assimilation of the brief. But the focus on the visual aspect of references was a deliberate extraction from the project to display a personal interest engaging a novel interpretation and perspective that could lead to an original production. Also, during the presentation, student commented less on the mood boards, and far more about their future projects. According to their professor, it is because the mood board is supposed to speak by itself, to express emerging aspects of the project that revolve around a set of ideas only revealed through the project. The mood board finds its resolution in the future project and is otherwise very vague.

In Use Case 2, students were primarily discovering an industrial field without previous knowledge. Their mood boards therefore reflected their exploration of the field. They did not come up with "ordinary" cars but with innovative -concept or prototype -cars that were getting them nearer to the design brief. Their mood boards showed different research fields related to cars. As we can see in Figure 2, they picked up innovation in terms of safety, new driving panels, new forms of energy. They also looked into cars that fly or swim. In terms of materials, they were interested in changing pigments, in pliable material, in eco-friendly cars. They also looked into infrastructure: connected cars in smart cities, evolving like a swarm. In terms of aesthetics, they chose very unusual vehicles that helped them reframe the vision of what a car is. Mostly their mood boards showed technological surveys of car innovations (see Figure 3). Nevertheless the students also looked for "things" that would be inspiring first in terms of physical sensations: for instance wet crabs, fish, water backgrounds that conveyed smooth, sliding, to the point of slimy sensations; second in terms of imaginary references: cartoons that showed a partnership between the person and her vehicle, whether "fusional" or friendly (Figure 4). The images also built an ambiguity between the hyper adapted, hyper connected, hyper controlled, and the chummy, comfortable, fun vehicle. One student who was thinking of going into marketing, actually came up with the most extreme choice of images as he picked up cars related to nature in all kind of ways: with tree growing out of the boot, garden cars, compost, etc.

Interestingly enough, the main difference between novice and expert practices of moodboards lies in their formal organization: design students used more rigorous ways of organizing materials and have a stronger inclination to pick up materials based on aesthetic properties.

Epistemological properties of mood boards

We suggest that the semiotic and pragmatic characteristics of mood boards can be analyzed as four cognitive and aesthetics operations: decontextualization, discretization, coherence, and relevance.

Decontextualization

The analysis of mood boards presents several striking features for the design process. First, most of these images were not situated-the original websites were not mentioned. Rather than functioning as part of complex situations of use or part of a historical tradition, they were presented as decontextualized items. There were no examples taken out of the "history" of design. All the examples were contemporary. The design projects were therefore less thought in terms of family of objects, tradition, or inscription in social uses, but more like radical innovations that needed to capture the latest aesthetic and technical traits.

Discretization

Students and professors consider what can be obtained from these images, not the images as such. Only certain aspects of the represented objects will be kept for the future design. Mood boards constitute a reservoir of traits that can be extracted from the representations. The aspects that are discretized can be formal: a shape, a color, a structure, a technology. But designers do not necessarily retain the tangible features of the objects. The discretization can be symbolical: representations of emotions or sensations, for example a fish that stands for a weightless nautical environment, or political and social, for example a graft of grass that questions our relation to nature. Either as symbols for something else, or as parts for a design production, the students discretize the representation of the objects. They display a design competence that sees a cue for something else through a particular object or representation, or situation. This competence is based on a discretization of the elements so that they can be moved, translated, or recomposed in a new object.

Coherence

The mood boards are not only a tool to discretize objects and representations. They strive towards a certain form of coherence. While gathered images can be considered as very heterogeneous at first sight, they are displayed on the same document. This collection is claimed to be meaningful for the design project. In other words, what is claimed behind the diversity is a convergence and a coherence of at least two kinds.

In the first type of coherence, images are presented as correlated in some way because they function as index of what can be done. For instance, in use case 2, students pointed out technical features that they would use in the design project. They therefore posited the articulation of different materials and/or technologies to build the design project. Coherence here is indexical because it focuses on the articulation of causes and effects.

Second, coherence can also be conveyed by a claim of similarity. Images function as iconic elements of an atmosphere, an aesthetic space. For instance, in case 1, colors and materials were evocative of the same palette. Coherence is therefore built in the mood boards either because the technical elements behind the images will be articulated, or because the aesthetic qualities of the design project are already staged.

The first type of coherence is generally associated with feasibility. Certain students stress more than others the need to make sure that the whole projected system will work (for instance in Use Case 2, a group of students supported a pragmatic approach of infrastructures versus services to counterbalance and support the more original propositions).

The second type of coherence is seen more in terms of originality. Another way to interpret the coherence of the document mood board is therefore to see that it tries to maintain a balance between feasibility and originality, something that is also at stake in brainstorming methods [START_REF] Kazakci | Brainstorming versus creative design reasoning: a the-ory-driven experimental investigation of novelty, feasi-bility and value of ideas[END_REF].

Relevance

In our analysis, relevance is the last expected property of mood boards. Students claim that the elements that they choose and display contribute to define the value of the design project. Mood boards are not media for their own sake. They support the design of future projects. "The mood board has to help showing 'where we are going'." "One of the objectives of the mood board is to spot a visual universe, materials, a cosmology of objects and productions in which to find 'something' of their project." Here the discourse that goes with mood boards has several functions. Not only does it describes for the audience what items should be seen "behind" the apparent heterogeneity and how to discretize the images for future design projects, it also anticipates the values of the design project. Students talk about future scenarios of use and the ethics of their projects. Every discretized item is a cue for a design that foregrounds the values that it wants to support.

Relevance in this context, means the social role and ethics of the designer "for a better world." For designers, there is a "real world" that needs to be changed. Relevance is a claim and property of projects that can produce better situations [START_REF] Harfield | On the roots of undiscipline[END_REF]. Second, relevance defines how the project will be integrated in society. When cars were concerned, the students were optimistic that they could get rid of the car as we know it, so that it could become a real, highly connected, partner in mobility. The design project has to display its relevance in terms of contemporary values. For instance, none of the students recommended cars that would use more energy. And all the students envisioned a highly connected and social car. There is a rationale of norms that connects the projects to society [START_REF] Habermas | The Theory of Communicative Action: Reason and the Rationalization of Society[END_REF][START_REF] Harfield | On the roots of undiscipline[END_REF].

Discussion: synthetic and expansive values of mood boards

The rational of mood boards is to create new knowledge based on observation of gathered images and items. But contrary to a traditional corpus in human sciences that helps to understand already existing objects [START_REF] Rastier | Arts et sciences du texte[END_REF], corpuses in design find their resolution in objects to be. In design projects, the rational of the corpus is present, in the sense that items are collected so as to address their commonality. But the commonality is not a given, it will only happen with the new design project. One strong sign that mood boards are not analytical tools is that the images are decontextualized. This decontextualization has at least one effect. It helps consider the object represented not as an example sustaining a theory demonstrated somewhere else but as a reservoir of traits that can be cut from the objects and recomposed or translated somewhere else. This first decontextualization helps define the represented object not as a whole within a specific situation but an ensemble of traits to be considered for its future potential in different situations.

In that sense mood boards are not primarily analytical but synthetic and expansive. First, we consider how mood boards are synthetic. Kolko in her article on design synthesis points out a number of "messy" properties of the design process: "Synthesis methods have been continually referenced as critical in sensemaking, organization, and in drawing the important connections between apparently unrelated elements. These are the keys for relating research to design-synthesis methods are the ways in which ethnographic insights lead to new, innovative, appropriate, or compelling ideas" (Kolko, 2010, p.17). Synthesis is an abductive sensemaking process. Through efforts of data manipulation, organization, pruning, and filtering, designers produce information and knowledge for a future project. The coherence that is achieved by mood boards, relies on strong synthetic activities that extract common points and organize them around a theme or a quality: for example, the "buddy car", the "sleek car", the "witch car" in Case 2. Students have to demonstrate the commonalities of the represented artefacts or situations from a certain angle. One of the professors describes the mood board as an "exercise to bring homogeneity out of heterogeneity". She emphasizes the need to "generate homogeneity".

At the same time, the collection of items organizes a tension. The representations are really incompatible at first sight. The work of interpretation is highly regarded if the capacity to organize tensions is generative of a variety of unpredictable combinations. For the professors, this is a key element to judge of the originality of the students' work. In other words, the corpus does not close on a type, a genre, but has to be expansive of a new object that will solve the "apparent" contradictions: as stated in an interview by the professor supervising Case 1, "for the professor, ideally, soliciting heterogeneous sources allows students to generate more fertile ideas out of analogies, metaphors, etc." Mood boards are therefore documents that structure expansion through a number of semiotic properties that we analyzed in the previous sections of this article.

Conclusion: Sciences of conception and in-discipline

Findeli (2001) following Moholy Nagy (1947) suggests that it is more important to focus on the design project and its formal operations -such as those that we describe in the practice of mood boards -rather than focusing on inter-disciplinarity per se. The attention is therefore drawn to relations within documents whose goal is precisely to be conceptive through formal meaning making as well as the pragmatics of these documents. Following Joyce S. R. Yee and Craig Bremner and on the basis of the analysis of the properties of these mood boards, we propose that a mood board "consists of combining methods from the social sciences, humanities, and hard sciences to derive a suitable model of inquiry." (Yee, Bremner, 2011, p.1). The following section discusses how these practices are related to disciplines and / or scientific methods.

At first sight, practices like mood boards seem un-disciplinary as suggested by Bremner and Rodger (2013). They might be described as un-disciplined because:

• Those documents need the author's and the audience's capacity of interpretation. These means of interpretation, the ways to make sense of the elements, are not specified in the exercise, hence an accusation of subjectivity; • They seem to pick indiscriminately between elements of different natures;

• Mood boards channel ways of doing work without disciplinary restrictions. They maintain a goal (an issue that needs to be solved between the elements) but remain vague on the ways to achieve it.

As we have seen in the previous sections of this article, this perception is in fact disproved by the analysis of the semio-pragmatic characteristics of mood boards. In our conclusion, we want to suggest that rather than un-disciplinary, they are part of an "in-discipline" as Rancière defines it [START_REF] Dubreuil | Défauts de savoirs[END_REF].

Following Rancière [START_REF] Dubreuil | Défauts de savoirs[END_REF], we suggest that a mood board is part of the indiscipline of design. Rancière, who is a philosopher of art and design, qualifies a certain number of forms that deliberately reframe what can be seen and what can be thought. As he studies contemporary art forms, he concludes that conception is based on formal constraints that help reframe the set of solutions. These "dispositifs", or arrangements, deliberately create a plane of conception independent of any set discipline. This autonomous plane of conception makes it possible to select items from disciplines-either their facts, methods, or theories-to compose new relations. In this respect, design entertains a special relation to other disciplines by its capacity to organize a rigorous method of interplay with the disciplines [START_REF] Schmid | Une nouvelle logique de l'interdisciplinarité[END_REF]) which, we suggest, could help define design as an indiscipline: that is a discipline that plays with disciplines in a rigorous formal way.

But the question is how do these autonomous conceptive spaces produce rigorous results. The tools of conceptive sciences (including engineering sciences) cannot be the same as sciences of nature that observe the real. Conceptive sciences build new artifacts and therefore need to address the question of a rigorous conception. What needs to be guaranteed from an epistemological point of view is the conceptive validity of the processes and tools.

In this respect, mood boards can be considered as a design rationale that organizes an indiscipline with formal meaning making. By creating a purposefully oriented set of heterogeneous objects within a document, mood boards create a cluster of possible relations.

In other words, the formal qualities of the documents frame the different operations that we suggest are the rationale of design: decontextualization, discretization, coherence, and relevance.

To summarize our findings:

• Moodboards have four epistemological properties: Decontextualization, Discretization, Coherence, Relevance;

• In Design Education, moodboards present synthetic and expansive values as they organize tensions while generating homogeneity, which helps to reframe what can be seen and what can be thought; • They suggest that design is an "in-discipline," as it picks elements of different natures to constitute a formal assemblage that plays with disciplines in a rigorous formal way.

He seeks understand the properties of an "open work of design" by analyzing current and previous work in art, design, etc.

Brulé Émeline

Émeline Brulé is a PHD Student in Design and Media Studies at Telecom ParisTech. Her research focuses on wearable technologies dedicated to health. She studies "smart" objects to develop a comprehensive framework of this family of objects. Using critical design, she explores the way we define our bodies via this new kind of prosthetics.

Figure 1 :

 1 Figure 1: Mood board from Case 1: Visual elements come from different origins, design projects, art photographs or actual products. Here a photomontage (the portrait of a man with a vegetal beard) is on the same level as artistic photographs and products.

Figure 2 :

 2 Figure 2: Mood board from Case 2 displaying various innovations innovation in terms of safety, new driving panels, infrastructure or new forms of energy.

Figure 3 :

 3 Figure 3: Mood board from Case 2 displaying unusual cars, such as an eco-friendly car, one made of lego, one crowd-funded and the last displaying an external airbag.

Figure 4 :

 4 Figure 4: Mood board from Case 2 displaying inspirations in terms of physical sensations such as wet crabs, fish, that conveyed smooth, sliding, to the point of slimy sensations and imaginary references: cartoons showing a partnership between the person and her vehicle, whether "fusional" or friendly. It induces an ambiguity between the hyper adapted / connected / controlled car and the chummy, comfortable, fun vehicle.

Author Biographies

Gentès Annie

Annie Gentes is associate professor in Information and Communication Sciences at Telecom ParisTech and Head of the Codesign Lab. Her research focuses on "extreme design"design in research and design in society -and the invention of ICT. She works with artists, designers and engineering scientists to understand their specific conceptive activities that turn a technology into meaningful artifacts.

Valentin Frédéric

Frédéric Valentin is a PHD Student in Design and Media Studies at Telecom ParisTech. His research takes interest in "openness" in design practices through an historical perspective.


Sofiane Ghenna

Frederic Giraud

Christophe Giraud-Audine

Michel Amberg

Betty Lemaire-Semail

Preliminary design of a multi-touch ultrasonic tactile stimulator

Keywords: Multi-touch, Haptics, Tactile stimulation, Multi-modal approach, Ultrasonic waves

This paper presents a method to control ultrasonic waves on a beam, allowing to obtain a Multi-touch ultrasonic tactile stimulation in two points, to give the sensation to two fingers, from two piezoelectric transducers. The multi-modal approach and the vector control method are used to regulate the vibration amplitude, in order to modulate the friction coefficient with the fingers. An analytical modelling is presented, with experimental validation. Finally a psychophysical experiment shows that a multi-touch ultrasonic tactile stimulation is possible.

I. INTRODUCTION

Nowadays, the sense of touch plays an important role for the recognition, discovery and use of objects around us. This attracted the interest of researchers to implement a simulative approach similar to vision or hearing, and to recreate the touch sensation. Some modern devices are able to reproduce the illusion of the textured surfaces under the finger [START_REF] Biet | Squeeze film effect for the design of an ultrasonic tactile plate[END_REF], [START_REF] Giraud | Design of a transparent tactile stimulator[END_REF]. Some techniques are based on friction control between a surface and the finger. They involve ultrasonic vibrations [START_REF] Meyer | Fingertip friction modulation due to electrostatic attraction[END_REF] [4], [START_REF] Watanabe | A method for controlling tactile sensation of surface roughness using ultrasonic vibration[END_REF], or electro-vibration [START_REF] Vezzoli | Electrovibration Modeling Analysis[END_REF], [START_REF] Strong | An Electrotactile Display[END_REF]. For the first, a squeeze film effect is used to modulate the friction coefficient, by creating an air film between the user's finger and the surface. For the second electrostatic forces are employed to attract the finger toward the physical surface. The provided stimulation is uniform under the fingertip, so they are categorized as global stimulation. To give the illusion of textured surfaces, these devices modulate the stimulation amplitude, according to the position of the finger. The main issue of these techniques is that the sensation are identical all over the touched area. Hence, it is not possible to control the sensation on more than one finger, in spite of the temporal modulation [START_REF] Biet | Discrimination of Virtual Square Gratings by Dynamic Touch on Friction Based Tactile Displays[END_REF]. There exist however devices with localised tactile stimulation. For example, [START_REF] Hudin | Localized tactile stimulation by time-reversal of flexural waves: Case study with a thin sheet of glass[END_REF] focuses the vibrations in one or more points of a plate, using time-reversal of flexural waves. It should be noted that this method requires a learning step, and Christophe.Giraud-Audine@ircica.univ-lille1.fr a large number of piezoelectric actuators. For the electrovibration, the authors in [START_REF] Nakamura | Position and Force-direction Detection for Multi-finger Electrostatic Haptic System Using a Vision-based Touch Panel[END_REF] proposed an approach based on detecting position, direction and force for multi-finger electrostatic haptic system, through a stimulator pad. By employing multiple stimulator pads and applying different voltages to different stimulators, it provides independent stimulus to several fingers. However, the system requires a multiple stimulator pads attached to the user's fingers for generating force feedback, and is limited to the speed of the stimulation pads. Others techniques such as matrix interface [START_REF] Prescher | A Tactile Windowing System for Blind Users[END_REF], [START_REF] Schiewe | What You Feel is What You Get: Mapping GUIs on Planar Tactile Displays[END_REF] are based on the generation of a 3 D surface, allowing the use of one or more fingers, which may vary in both space and time. So the resolution is related to the number of used actuators.

Currently there are no solutions able to provide a multitouch tactile stimulation based on the squeeze film effect. The main objective of this paper is to present a control method, allowing to have a differentiated tactile stimulation, using a squeeze film effect to obtain different sensations for the use of two fingers simultaneously. In the second section we propose the principle of the applied method. The excitation conditions are presented in the third section. Finally the result of this study is illustrated with an experimental validation in the fourth part.

II. PRINCIPLE

A. Limitations of current devices

In squeeze film effect one flexion vibration mode at a resonance frequency above 20 kHz is used [START_REF] Giraud | Design of a transparent tactile stimulator[END_REF]. This standing wave is a function of the location x and time t, with vibration amplitude named W . Then the vibration at any point of the beam is given by:

w(x,t) = W sin(ωt)φ (x) (1)
where φ (x) denote the spatial mode shape function, and ω is the angular frequency. The vibration amplitude at position x i of this standing wave is determined by a single and dependant variable W . Hence, there is no possibility to control areas with different vibrations amplitude, in order to get predefined friction coefficients μ under different fingers. And by using one vibration mode, the vibration amplitude being zero at the nodal lines as described in [START_REF] Marchuk | Friction measurements on a Large Area TPaD[END_REF]. However, it is known that a mechanical structure responds to the excitations with infinite modes. This property will be used to obtain the required vibration shape of multi-touch interaction. In the following, we are interested in the simplest case of a beam.

B. Forced vibration in finite beam

Considering a thin beam, with rectangular cross section denoted by A, length by L. ρ, E are respectively density and modulus of elasticity, I is the moment inertia of the cross section. The transverse vibration of a uniform elastic homogeneous isotropic Euler-Bernoulli beam [START_REF] Graff | Wave Motion in Elastic Solids[END_REF] can be written in Cartesian coordinates as

EI δ 4 w x 4 + ρA δ 2 w δt 2 + r a δ w δt = p(x,t) (2)
with: w = w(x,t) the deflection of the beam at point x and time t, δ is the partial-derivative, and p(x,t) denotes the load per unit length of the beam at point x and time t, while r a represents the coefficient of external damping of the beam. It is possible to determine the deformation mode shapes, and the frequency spectrum of the beam, by using the analytical model of Euler-Bernoulli eq.2 developed in [START_REF] Abu-Hilal | Forced vibration of Euler-Bernoulli beams by means of dynamic Green functions[END_REF]. For a free-free boundary conditions, the first four mode shapes are represented in shows that the solution of wave propagation in a finite beam has solutions for special frequency values. In this paper, harmonic vibrations are only considered enabling the use of the complex notation so that: w, with w is the real part of w, and w = W e jωt , where W = We jα , α and W are respectively the argument and the magnitude of W . If we take into account the contribution of every vibration mode excited in the beam, then the variation can be written as:

w(x,t) = ∞ ∑ n=1 W n φ n (x)e jωt ( 3
)
Where w includes real and imaginary part of the vibration, at location x, and time t, ω is the angular frequency of the flexural wave, and j = √ -1. φ n (x) is the deformation mode shapes of the n th mode, and is fixed for the beam. W n represents the modal amplitude of the n th mode. We suppose that we can control each mode independently. Hence, the deformation w(x,t) depends theoretically on an infinite degrees of freedom which are W n . This property is used in the case of multi-touch interaction.

C. Multi-touch ultrasonic tactile stimulation

For a multi-touch ultrasonic tactile stimulation the vibrations, w(x i ,t) must be imposed independently to obtain a different friction coefficients μ i predefined at several positions x i , where i is an integer.

In this paper, we limit the study to two flexion modes to generate the deformation of a beam, allowing the use of two fingers. From eq.3, considering two vibration modes denoted A and B, we have:

W (x) = W A φ A (x) +W B φ B (x) (4)
From the combination of two flexion modes, it is possible to obtain a function W (x) which depends on the modal amplitude W A and W B . To obtain this, we need a specific excitation conditions of flexural waves, a multi-modal approach thus is required to realize this.

D. Multi-modal approach

The multi-modal approach consists in exciting two successive flexion modes of the beam, around the middle of their resonant frequency as depicted in Fig. 2. It has been shown Fig. 2. Excitation between two successive flexion modes in [START_REF] Watanabe | A method for controlling tactile sensation of surface roughness using ultrasonic vibration[END_REF], that the frequency of vibration has no influence on the perceived sensation, above a threshold value of 20 kHz. The dimensions of the beam are adjusted in order to have the modes A and B above 20 kHz.

Several studies were focused on the generation of ultrasonic waves on a beam, including the transportation of objects by travelling wave [START_REF] Giraud | Vector control method applied to a traveling wave in a finite beam[END_REF], [START_REF] Loh | An object transport system using flexural ultrasonic progressive waves generated by two-mode excitation[END_REF]. This methodology has been used for the generation of two vibration modes with the same amplitude shifted by π 2 . Here we use this principle in another way to generate a differentiated tactile stimulation as shown in Fig. 3. By the combination of two Fig. 3. Generating principle of two successive flexion modes successive bending modes, ( the red and blue curve represent vibration mode A, and mode B respectively), it is possible to obtain two different vibrations amplitude in two points of the beam, as shown under the two fingers, because each vibration mode has a specific modal amplitude. These vibration amplitudes W (x a ), W (x b ) depend on both of the deformation mode shapes, and their modal amplitude, which makes two independent variables. Figure 4 shows a beam operated by two piezoelectric actuators located at distance x A , x B from each end of the beam. The blue curve represents the contribution of the two vibration modes in a transverse direction at a given moment, expressed by eq.4, at each position of the beam. If we consider two points of the beam x a and x b , the harmonic vibration at these positions is given by:

W (x a ) = W A φ A (x a ) +W B φ B (x a ) (5)
W (x b ) = W A φ A (x b ) +W B φ B (x b ) (6)
Introducing the matrix notation, eq.5 and eq.6 become:

W xa W xb = φ A (x a ) φ B (x a ) φ A (x b ) φ B (x b ) W A W B ( 7
)
the two vibration amplitude can be controlled directly by the modal amplitude. Then the control of these modal amplitudes is necessary. Inversely, under the assumption of a non-singular matrix φ x a ,x b , the vibration amplitude of mode A and B are given by:

W A W B = φ -1 x a ,x b W x a W x b ( 8
)
Similarly for the vibration amplitude at the position of the actuator w x A , and w x B :

W x A W x B = φ A (x A ) φ B (x A ) φ A (x B ) φ B (x B ) W A W B = φ x A ,x B W A W B ( 9
)
The vibrations of transducers impose the dynamic of the modal amplitudes. Substituting eq.8 in eq.9 gives:

W x A W x B = φ x A ,x B .φ -1 x a ,x b W x a W x b ( 10
)
eq.10 allows us to calculate the required vibration amplitude of the transducers as a function of the predefined vibration amplitude under each finger. Hence, to generate a differentiated tactile stimulation, it is necessary to know the position of each finger x a and x b , the positions of the actuators x A and x B , the deformed shape matrix at the position of the actuators φ x A ,x B , which is a constant matrix, and the deformed shape matrix φ x a ,x b , which depends on the position of the two fingers. By imposing a desired vibration amplitude W x a and W x b under two fingers, we determine the reference vibration amplitude W x A and W x B , to be imposed on each actuator as described in Fig. 5. By this way, it is possible to obtain two

III. EXCITATION CONDITIONS OF FLEXURAL WAVE AND TRANSDUCERS

A. Wavelength

The wavelength depends on the excitation frequency, and the different physical characteristics of the beam material. However, to differentiate the sensations, it is necessary to have a gap between nodes and anti-nodes. Hence the half wavelength should be larger than width of finger, which is approximately equal 17 mm.

B. Frequency and vibration modes

The analytical model of Euler-Bernoulli eq.2 was simulated to determine the frequency spectrum of the beam given in Fig. 6, the deformed mode shapes presented in Fig 7 . A beam made of aluminium was chosen, because of the excellent acoustical characteristics of this material; its parameters are given in Tab.I. The dimensions of the beam has been chosen in such a way that the half wavelength is 20 mm, and the resonance of the beam is around 28 kHz, to obtain the optimal operating conditions of the transducers, and a high vibration amplitude. Then, the contribution of two vibration modes to produce a squeeze-film effect was taken into account.

C. Position of transducers

The two piezoelectric actuators are positioned near the anti-nodes of each mode, in order to optimizing the electromechanical couplings. The modal analysis of Fig. 7 can be used to determine the position of the transducers on the anti-nodes, or the formula described in [START_REF] Kuribayashi | Excitation conditions of flexural traveling waves for a reversible ultrasonic linear motor[END_REF] can be used.

x A = x B = n λ 2 + 7 8 ( 11
)
where x A , x B are the position of the transducers from both ends of the beam, n is an integer, λ is the wavelength. The two transducers are placed at x A = x b = 60 mm, at the ends of the beam, with wavelength of 41.5 mm.

D. Deformation mode shapes matrix φ x a ,x b

Accordingly to eq.8, the condition is to obtain a non singular deformation mode shapes matrix φ x a ,x b , Fig8 shows the determinant of φ x a ,x b as a function of x a and x b . In this figure the area in green shows that, a dual touch interaction cannot be calculate especially for extremely close distances lower to 1 mm, and at the end of the beam. For the first it is possible to choose another adjacent point, because the finger width is approximatively 8 mm. For the second may be due to the boundary conditions, and for the anti-diagonal zones when the distance between the two fingers are very small, what is physically impossible.

E. Influence of finger pressure

The transducer is modeled in rotating frame, and the decoupling according to two-axis allows us to obtain a double independent closed loop control. It is possible to control the transducer vibration amplitude and its relative phase, in steady state even in transient by acting on the amplitude of the supply voltage. This allows the transducers to control the vibration amplitude on the surface beam W x A and W x B in a closed loop. When the finger applied a normal force, this force is rejected as perturbation. That is to say if the vibration amplitude of transducers are imposed in open loop, then when applying a force, this vibration amplitude decrease.

IV. EXPERIMENT VALIDATION

An aluminium beam is actuated by two Langevin transducers, which were associated with horns. The whole system is fixed on a solid support, which allows to move the beam for measuring the vibration velocity at every point of the beam, using an interferometer (OFV-525/-5000-S) as shown in Fig. 9. A graphical user interface is used to control the vibrations amplitude of the two actuators independently, through a DSP (TI 2812) and two amplifiers (HSA 4051).

A. Identification of vibration modes

A cartography was performed to measure the vibration amplitude of each point in the beam, for the mode shape A and B as shown in Fig. 10. Fig. 10 is used to determine the deformation mode shapes φ x A ,x B and φ x a ,x b , we obtain: Two points were arbitrarily selected x a = 120 mm, x b = 250 mm, so that the vibration amplitude at these two points do not represent nodes nor anti-nodes of mode A and B. The matrix of the deformation mode shapes at these positions are given by:

φ A (x a ) φ B (x a ) φ A (x b ) φ B (x b ) = 0.9436 0.6809 0.9715 -0.7388 (13)
Now if it is desired to obtain a vibration amplitude under the first finger 0.8 µm peak to peak and 0 µm under the second finger independently, corresponding to the smooth and the rough area respectively. In this case we determine the vibration amplitude to impose on each actuator using eq.10, then:

W x A W x B = -0.4093 0.0045 µm (14)
In Fig11 it is shown the vibrations amplitude at two different points for x a and x b as desired under the first finger W x a , and the second finger W x b , with a supply voltage of 160 V peak to peak for each transducer. The system is symmetrical between the transducers.

B. Psychophysical validation

In order to evaluate the ability of the interface to provide a multi friction modulation over the surface, a psychophysical experience has been performed using two-alternatives forcedchoice method described in [START_REF] Jones | Application of Psychophysical Techniques to Haptic Research[END_REF]. It has been asked to 6 participants (5 males, 1 female; age range: 22 -32 years) to evaluate simultaneously two different areas of the tactile interface with the index of the right and left hand. Before the exploration it was set in the middle of the right explored areas one anti-node with 1.4 µm peak to peak vibration amplitude, and one node in the left area, or inversely. It was asked to the participants to indicate "which of the two areas were the smoothest", corresponding to a smallest friction coefficient. As indicated by the applied method, the participant was forced to choose one side after the free exploration, (even if the participants could not differentiate those two sensations), which were allowed in a surrounding area, 1 cm large, for 8 seconds. The experience was repeated for 10 times with a randomization of the trials. The participants were able to identify as smoother the area with high vibration amplitude with an average success rate of 78.3% with a standard variation of 7.5. The hypothesis test against the random answer was refused with a p < 0.1 leading to accept the conclusion that a multi-touch stimulation was performed. The possibility to obtain simultaneous different sensations on different sections of the beam has been proved. The performed stimulation was static, but nevertheless the difference in friction was perceivable by the users with significance. The distance between the nodes is 2 cm, which is comparable with the finger contact area for a light touch exploration [START_REF] Adams | Finger pad friction and its role in grip and touch[END_REF]. An half wavelength above 20 mm can be implemented to obtain a larger uniform explorable area at the cost of thicker beam. In future works a larger half wavelength will be employed to obtain a bigger difference in absolute friction due to the better uniformity of the vibrations under the fingertip. Moreover, a tracking system for the fingers [START_REF] Biet | Discrimination of Virtual Square Gratings by Dynamic Touch on Friction Based Tactile Displays[END_REF] will be implemented to introduce a position based multi-touch stimulation to render different textures on different fingers. This tactile stimulator was produced in a thin beam, using its 16 th and 17 th vibration modes, but this method can be employed only with harmonic vibrations.

A. Limitations of the proposed approach

The proposed concept can be extended to 5 fingers for example, ie 5 positions by taking into account 5 vibration modes, then 5 actuators are required to generate 5 vibration amplitudes, accordingly to eq.7. Theoretically only flexion modes are excited. However, in practical, there is one problem to get these successive flexion modes. The banding modes, unfortunately, cannot be excited independently without affecting the other modes. Therefore, the modal analysis of plates will show that other types of vibration modes are existed and these conditions can highly influence the results. Thus the use of the beam is appropriate for this approach (2 fingers). The effect of actuator location can be resumed in eq.9 for example if these location presents nodes then no vibration modes are excited, because the deformation modes shape at these positions is equal to zero. The relation between the frequency of the modes and the operating frequency of the transducers is important; the optimum is to obtain two vibration modes equally distant from the resonance of the actuators.

VI. CONCLUSION

In this paper it is presented a new method to control the vibration amplitude on a finite beam in a closed loop control. And to produce a multi-touch tactile stimulation in two points of the beam independently, even in presence of perturbations, from the exploitation of two vibration modes. That is to say two vibration modes for two fingers, several fingers for several vibration modes, allowing to obtain a multi-finger tactile feedback, using a multi-modal approach.

  de Puissance, 59000 Villeneuve d'Ascq, France e-mail:

FigFig. 1 .

 1 Fig. 1. First 4 mode shapes for a free-free beam

Fig. 4 .

 4 Fig. 4. Generating principle of a differentiated tactile stimulation

Fig. 5 .

 5 Fig. 5. Control strategy for a Multi-touch ultrasonic tactile stimulation

Fig. 6 .Fig. 7 .

 67 Fig. 6. Normalized deflection amplitude at a given position of the beam

Fig. 8 .

 8 Fig. 8. Determinant of the matrix of the modal shape φ xa,xb

Fig. 9 .

 9 Fig. 9. The experimental setup

Fig. 11 .

 11 Fig. 11. Measured Vibration amplitude at position x 1 = 120 mm and x 2 = 250 mm

Fig. 12 .

 12 Fig. 12. Results of psychophysical testing

C. GIRAUD-AUDINE is with Ecole Nationale Suprieure d'Arts et Mtiers Paris-Tech, Boulevard Louis XIV, 59000 Lille, France

ACKNOWLEDGMENT

This work has been carried out within the framework of the project StimTac of IRCICA (institut dde recherche sur les composants logiciels et matériel pour la communication avancé), and the Project Mint of Inria.


Fayrouz Soualah
email: fayrouz.soualah-alila@checksem.fr

Alila Le2i

Christophe Nicolle
email: christophe.nicolle@checksem.fr

Florence Mendes
email: florence.mendes@checksem.fr

CONTEXT-AWARE ADAPTIVE SYSTEM FOR M-LEARNING PERSONALIZATION

Keywords: Context-awareness, recommendation, semantic web, m-learning, metaheuristics. JEL classification: Education and research institutions, Industry studies: services

Context-aware mobile learning is becoming important because of the dynamic and continually changing learning settings in learner's mobile environment, giving rise to many different learning contexts that are difficult to apprehend. To provide personalization of learning content, we aim to develop a recommender system based on semantic modeling of learning contents and learning context. This modeling is complemented by a behavioral part made up of rules and metaheuristics used to optimize the combination of pieces of learning contents according to learner's context. All these elements form a new approach to mobile learning.

Introduction

As mobile technologies have become pervasive, many researchers [START_REF] Liu | Wireless and mobile technologies to enhance teaching and learning[END_REF] [START_REF] Naismith | Literature review in mobile technologies and learning[END_REF] have questioned whether they can enhance learning experiences. So the learning domain started to make use of these new technologies to deliver and support a new approach of electronic learning (elearning), called mobile learning. It could be argued that mobile learning, also called mlearning, is an approach to e-learning that simply utilizes mobile devices, yet it can also be viewed as a quite different learning experience [START_REF] Wang | Context awareness and adaptation in mobile learning[END_REF]. So far, the learning environment was either defined by an educational setting (work, trainer, etc.), or imposed by the educational content (the learner must then arrange this environment to receive training). The objective of m-learning is a society with access to knowledge and learning for everyone, everywhere and at any time [START_REF] Lytras | The knowledge society: A manifesto for knowledge and learning[END_REF]. However, the dynamic and continual changing learner's settings in a mobile environment and the diversity of learner's characteristics as well as mobile devices and networks, give rise to many different learning contexts and therefore requires personalization for different cases. The educational activities and the provided infrastructure have to be automatically configured according to the learner needs, interests and objectives. Multiple sources of information would be used to adapt learning contents to every situation and condition. To achieve this objective, it is necessary to improve current e-learning systems with new technologies for representing, modeling, indexing and adapting learning contents in a mobile context. This paper presents a general architecture for context-aware adaptive system for mobile learning that aims to offer a new approach for designing and recommending learning contents as part of industrial training. Hence, we propose a m-learning system made up of two levels: a semantic level and a behavioral level (figure 1).

Figure1. Context-aware adaptive m-learning system architecture

The semantic level aims to express semantic input data characteristics, namely learning contents and mobile context (what, how, when, where, via which device, etc.). It is described in section 2. Then section 3 focuses on the behavioral level, which corresponds to the adaptation engine designed to overcome the problem of information overload. The behavioral level contains best learner practices, transformed in a set of logical rules and algorithms of combinatorial optimization. The last section concludes this paper.

Semantic learner's mobile contextual model

The adaptation engine of the system acquires input data and produces the adaptation results. Part of the input data into the adaptation engine is closely related to the context description and learning content modeling. Context is defined as "any information that can be used to characterize the situation of an entity participating in the interaction between a user and a system" [START_REF] Dey | Providing architectural support for building context-aware applications[END_REF]. Different types of information about a user can simultaneously be relevant to a given adaptation decision [START_REF] Tamminen | Understanding mobile contexts[END_REF]. In the case of m-learning, location, time, identity and the mobile technology used to learn are the primary context types for characterizing the situation of a particular learner in a mobile LMS (Learning Management System) [START_REF] Bouneffouf | Recommandation mobile, sensible au contexte de contenus évolutifs: Contextuel-e-Greedy[END_REF]. In [START_REF] Bouzeghoub | A situation-based delivery of learning resources in pervasive learning[END_REF], an ontology-based context model considered time, place, environment, and learner profile and device capacity. Personalization in mobile LMSs refers to the process of enabling the system to fit its behavior to the pedagogical needs (learning goals, knowledge, interests, etc.), the personal characteristics (learning styles and different prior knowledge, etc.) and the particular circumstances (current location, movements in the environment, environment properties, etc.) of the learner [START_REF] Wolpers | Identifying personalized context-aware knowledge structure for individual user in ubiquitous learning environment[END_REF]. Furthermore, context can be information about devices (smartphone, tablet, connectivity, etc.) and time (time of day, day of week, holidays, etc.) since this may change the way learner interact with any device they may be using. We model mobile context according to five dimensions: learner profile dimension, temporal dimension, spatial dimension, device dimension and learning content dimension (see [START_REF] Soualah Alila | A context-based adaptation in mobile learning[END_REF] for a detailed description). In e-learning, resources are designed and developed by different organizations and trainers, usually constituting semantically autonomous and heterogeneous data sources. Therefore, interoperability between these resources is complex. To build an approach of quality, international standards are developing in educational technologies. One standard largely used is the IEEE-LTSC LOM (Learning Object Metadata) standard. Learning contents are described by metadata about Learning Objects (LOs) repository. A LO is defined by the IEEE as "any entity, digital or non-digital, which can be used, re-used, referenced during technology supported learning". Learning object attributes such as LO identifier, described concept, estimated learning time, LO relationship to other LOs, multimedia nature of embedded content, semantic density of the content, are described traditionally in the LOM schema [START_REF] Soualah Alila | Une approche Web sémantique et combinatoire pour un système de recommandation sensible au contexte appliqué à l'apprentissage mobile[END_REF].

Context-aware applications need acceptable context modeling and reasoning techniques. Modeling context knowledge is an important task to support the delivery of the right contents at each moment, to adapt and to personalize contents, and to anticipate the results. There are several methods for modeling context: key-value models [START_REF] Schilit | Disseminating active map information to mobile hosts[END_REF], markup schema models like XML [START_REF] Strang | A context modeling survey[END_REF], UML graphical models [START_REF] Sheng | ContextUML: a UML-based modeling language for model-driven development of context-aware web services[END_REF], ontology-based context model [START_REF] Chen | An ontology for context-aware pervasive computing environments[END_REF]. Ontologies are a very promising instrument for modeling contextual information due to their high and formal expressiveness and the possibilities for applying ontology reasoning techniques. The use of ontologies enables also a standard-based LO metadata modeling. With a semantic modeling based on ontologies, experts could express semantic characteristics of LOs by using a common and interoperable model. This transfer of knowledge from experts to the computer enables our system to perform more intelligent reasoning, combined with expert's rules and combinatorial metaheuristics, according to changing constraints. Our ontology is defined using the OWL (Web Ontology Language) standard, so enabling interoperability at the semantic level if required, and is called contextual m-learning ontology. Once the ontological model is achieved, we integrated data using Talend Data Integration tools. Then, we used the OWLIM Sesame middleware as a triple store, to store the corresponding ontology. OWLIM includes inference engine and a semantic query engine.

The mobile context-aware ontology is stored in the triple store and is connected to the learning repository.

The system uses a set of ontological expert rules to achieve personalized context-aware learning by integrating knowledge embedded in the ontology. The output of the reasoning process is the extraction of metadata that will allow discovery and adaptation of LOs. That's the role of the behavioral model described in the next section.

Adaptive model

Adaptive systems have become very popular since 1990s to allow users to access to personalized information [START_REF] Brusilovsky | Methods and techniques of adaptive hypermedia[END_REF]. In m-learning, training courses have witnessed high dropout rates as learners become increasingly dissatisfied with courses that do not engage them [START_REF] Frankola | Why online learners dropout[END_REF]. Such high dropout rates and lack of learner satisfaction are due to the "one size fits all" approach that most current learning course developments follow [START_REF] Faulkner | One size does not fit all! Gender in/exclusion in a rural community-based ICT initiative[END_REF], delivering the same static learning experience to all learners. In addition, the nonlinearity of learners' progress in their training procedure needs them to build their knowledge by creating connections between different ideas, which can cause a problem of being lost in hyperspace. Adaptive educational solutions have been used as possible approaches to address this dissatisfaction by attempting to personalize the learning experience. When connected to our system, a learner profiling is achieved by automatic collection of data based on use interactions and its device capabilities. The profile is also refined by information provided by system administrators as well as by the user itself. Mobile devices send spatio-temporal information and the learner can specify some constraints of the environment. From this profile and learner context, logical rules run through the global mlearning ontology to identify and extract relevant LOs. Certifying training is subject to various expert rules. They define how to select and combine the different items setting up the training. Each item of training is defined by a subject, a context of use (mode, duration), a type (lectures, exercises, practical work) and precedence constraints that define the possible positioning of the item relative to others. For example, some training's part modules are independent, while some modules need other modules as a precondition. Similarly, for each new concept to learn, it will be more suitable to have taken over an item of type "course" before selecting an item of type "exercise". Using the Semantic Web Rules Language (SWRL), rules are written, so that a reasoned tool can infer LOs that will be offered to a given learner. We distinguish two categories of rules: precedence rules and contextual rules. Precedence rules are used to define the possible positioning of a LO relative to others (see for example rules 1 and 2).

Learning_Object(LO1)^Learning_Object(LO2) ->has_next(LO1,LO2)

Rule 1: LO1 must be learned before the LO2 Learning_Object(LO6)^Type("quiz")^has_lo_type(LO6,"quiz") ->has_next(LO6,?x)^Type("conclusion")^has_lo_type(?x,"conclusion")

Rule 2: When a LO is a quiz it should be followed by a concluding LO Contextual rules describe how the system should act according to a particular context (see rules 3 and 4).

Learner(?x)^has_location(?x,?y)^has_location_properties(?y,"dynamic_u ser")^Learning_Object(?z)^has_format(?z,?f)^swrlb:contains(?f,"audio" )-> has_access(?x,?z)^p(?z,10)

Rule 3: Access to audio LOs for dynamic learner (running, walking, etc.)

Learner(?x)^has_device(?x,?y)^has_device_connectivity(?y,"wifi")^Lear ning_Object(?z)^has_lo_type(?z,"videocast") -> has_access(?x,?z)^p(?z,10)

Rule 4: Access to LOs on streaming when the learner is connected (wifi, 3G, etc.)

To each LO is associated a weight LOw. It reflects the importance of the knowledge presented in the course unit according to a context. For example, in the rule 3, LOw is equal to 10. The more important the learning object is, the larger the value of LOw is. We propose to weight the LOs with values belonging to the interval [0,10]. If a 𝐿𝑂 𝑖 is of high importance then 𝐿𝑂𝑤 𝑖 = 10, if a 𝐿𝑂 𝑖 is of medium importance then 𝐿𝑂𝑤 𝑖 = 5, if a 𝐿𝑂 𝑖 is of low importance then 𝐿𝑂𝑤 𝑖 = 1, and finally if a 𝐿𝑂 𝑖 is of insignificant importance then 𝐿𝑂𝑤 𝑖 = 0. Each 𝐿𝑂 𝑖 is also described by a duration 𝑑 𝑖 and affected to a particular device 𝑑𝑒𝑣𝑖𝑐𝑒 𝑖 : 𝐿𝑂 𝑖 =< 𝐿𝑂𝑤 𝑖 , 𝑑 𝑖 , 𝑑𝑒𝑣𝑖𝑐𝑒 𝑖 >, 𝑖 ∈ [1, |𝐿𝑂|] The logic behind rules reasoning is that the learner should be able to choose whether he would like to have access only to those LOs according to his context following predefined rules. These rules are defined by experts in the learning domain. As these experts do not necessarily know how to write SWRL rules, we developed a rule generator to easily manipulate m-learning ontology concepts and generate automatically SWRL rules.

The adaptive m-learning system offers an optimized panel of LOs matching to the current context of the learner. This optimization should reduce the duration of the training and maximize learner satisfaction. If the context changes during the learning, the system can immediately switch a LO by another, adapting the learning through constraints evolution.

If each LO was accessible on every learning device, it would be easy to choose at any time the best support for training according to the learner's context. Actual cases that we studied showed us, on the contrary, a great heterogeneity of LOs available on devices. Training has different structure and different duration, depending on the device used. This forbids changing learning devices while training without risking redundancy of some LOs. From this, a combinatorial optimization problem can be identified. It corresponds to a multimodal shortest path problem, which is a variant of the well-known shortest path problem [START_REF] Gräbener | Time dependent multiobjective best path for multimodal urban routing[END_REF]. This problem cannot be resolved by an exact method, because of the exponential growth in complexity depending on the size of the problem. We use a heuristic method to achieve a solution in a reasonable time. By using a greedy algorithm, we construct a first solution by starting from a given LO, then, at each step the algorithm moves along the edges of the precedence graph. At each step, we check the LO's list, accessible in a particular context and on a particular device, and we choose among the edges, that do not lead to LOs that it has already visited. The LO selected in the next step should, either, maximize learner satisfaction, or minimize learning time, or both. Algorithm stops when a LO of the particular device Target has been reached. The next step is to ameliorate the first solution obtained by the greedy algorithm. For this purpose, we are currently implementing some standard metaheuristics, such as simulated annealing and randomized variable neighborhood search.

Conclusions

In this paper, we presented an adaptive m-learning system that takes into account constraints associated to mobile context, making use of learning practices already deployed in e-learning and adopting them in m-learning. Our approach is built around an ontology defining learning contents and supporting context-awareness. The use of this ontology facilitates context acquisition and enables a standard-based LO metadata annotation. The adaptive system afterwards uses a set of ontological rules and metaheuristics to achieve personalized contextaware LOs by exploiting knowledge embedded in the ontology.

  Then we define the following function to evaluate the global relevance of the solution: 𝑅 = 𝑋. 𝑚𝑖𝑛𝑖𝑚𝑖𝑠𝑒 ∑ 𝑑 𝑖 𝑥 𝑖 |𝐿𝑂| 𝑖=1 + 𝑌. 𝑚𝑎𝑥𝑖𝑚𝑖𝑠𝑒 ∑ 𝐿𝑂𝑤 𝑖 𝑥 𝑖 |𝐿𝑂| 𝑖=1 𝑤ℎ𝑒𝑟𝑒 𝑋, 𝑌 ∈ 0,1 𝑎𝑛𝑑 𝑥 𝑖 = 1 𝑖𝑓 𝑙𝑜 𝑖 𝑖𝑠 𝑠𝑒𝑙𝑒𝑐𝑡𝑒𝑑 𝑖𝑛 𝑡ℎ𝑒 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑒𝑙𝑠𝑒 𝑥 𝑖 = 0 Equation 1. Relevance function

Acknowledgment

This work is partially supported by CrossKnowledge, the European leader in remote development of leadership and managerial skills using new technologies. This work is also backed by the CheckSem team, whose principal field of research is ontology-based interoperability. The preparation of this work also required the help of Florian Orpelière and Valériane Eymenier (computer engineers in the CheckSem team).