Clarisse Didelon

Socio-spatial frameworks of spatial representations

Keywords: Europe, mental representation, social variation

This EuroBroadMap working paper provides a coherent and synthetic vision of the analysis conducted in nearly all the work packages of the Euro-BroadMap project from the social variation in the representation of Europe perspective. It also tries to benet an interdisciplinary approach by having recourse to both sociology and disciplinary elds and borrowing inputs from geopolitical science. The theoretical framework used is based on what can be called a paradox: the wish to analyse the mental representations of the world (or a piece of the world: Europe). In order to overcome this paradox, we will analyse deeply how representations are formed at the individual, community or dierent collective level (nation, world) and the time scales associated to each level.

Introduction

The central question of the EuroBroadMap project 1 was about the representation of Europe in the World. Throughout the project, the researchers from both European and non-European countries tried to adopt a non-Eurocentric perspective. One of the main solution chosen consisted of analysing how Europe is perceived without dening it to the people investigated: doing this, we did not imposed our own representation of what Europe is. The cross country synthesis report 2 , the WP3 nal report on migrants and borders 3 ) and the WP6 cross country report 4 that are mainly used here provided a descriptive partial analysis of the results obtain thoughtout the project's work packages.

The rst one provides analysis on a thematic perspective and the second one on a country perspective. Many materials have been gathered in the analysis of the dierent parts of the questionnaire and, like a famous cartoon character, we can state that, `In these little bric-a-brac, a secret's waiting to be cracked'5 . This report is the occasion to adopt a synthesis perspective and to go deeper into the analysis by cross-referencing the results and trying to explain them in the framework of a theoretical perspective in the representation eld. This report provides a coherent and synthetic vision of the analysis conducted in nearly all the work packages of the Euro-BroadMap project6 from the social variation in the representation of Europe perspective. It also tries to benet an interdisciplinary approach by having recourse to both sociology and disciplinary elds and borrowing inputs from geopolitical science.

In the rst part of our presentation we will present the theoretical background and perspective we propose to use in order to analyse the results of the WP2 (mental maps of students) survey. This theoretical framework is based on what can be called a paradox: the wish to analyse the mental representations of the world (or a piece of the world: Europe). In order to overcome this paradox, we will analyse deeply how representations are formed at the individual, community or dierent collective level (nation, world) and the time scales associated to each level. In the following parts, we propose to test how much the socio-spatial perspective is operational in the analysis of mental maps of Europe at each of the relevant level of the `social' framework of representation identied: world level, national level and individual level. In this report, our approach is mainly dened by the scientic background of representations and more precisely spatial representations and mental maps.

Representations are usually dened as a set of knowledge and beliefs encoded in memory that can be mentally extracted and manipulated (Dortier, 2002).

Representations of objects and concepts are used to `read' and `understand' the world around us, but they are also mobilised to make plans and take decisions. The objects on which we have representations are at the same time cognitive schemes and social representations varying in space and time. The representations, shared by a community (group of persons, but also national community), are one of the bases of the collective consciousness that transcend the inner social divisions that contribute to group consistency. These representations are durable and shared by many generations.

In this general framework, we will focus on the representation of spatial objects (the world, Europe) and then mobilise some concepts from the geography of representations that was born in the 1960s, from the encounter between spatial psychology and geography. The analyses of representations are based on the theory of `man's shells' [START_REF] Moles | Psychologie de l'espace[END_REF], a series of circles organised around individuals that dene the level of knowledge of dierent places: closer spaces are the best known. Among geographers analysing representations, the precursor was [START_REF] Lynch | The image of the city[END_REF] who focused on the intra-urban scale before further works explored smaller scales. [START_REF] Gould | Mental maps[END_REF] established mental maps at the national level. In the 1970s and 1980s, [START_REF] Saarinen | Centering of mental maps of the world[END_REF][START_REF] Saarinen | Centering of mental maps of the world[END_REF] focused on mental maps at the world level and made many surveys at this scale. His analyses concentrated principally on the centring of mental maps. The research that followed aimed to demonstrate a great diversity of points of view about the world, but also stress the dierences of the knowledge of the world space (Saarinen andMacCabe, 1995, Pinheiro, 1998).

To analyse mental representations on the world scale: A paradox?

The approach of the global space though representations raises some theoretical questions. Today, are the notion of `man's shell' and the proxemics law still relevant to analyse representations? Indeed, the contemporary accessibility of information through the media and even more through the Internet seems to disturb this scheme. As McLuhan (1967) stressed in the 1960s, these new tools of communication lead to profound transformations in human practices. This new accessibility to information and knowledge disrupts the approach to spatial cognition based on proxemics. First, no more space can stay unknown and on a planet covered by `information highways' nothing that happens in one part of the world can stay, at least potentially, unknown [START_REF] Bauman | Le présent liquide : peurs sociales et obsession sécuritaire[END_REF]. If the knowledge of close spaces relies mainly on practice, the knowledge of far spaces is today easier because of the dierent sources on numeric information. Then, the hierarchy of the pieces of spatial or social information is relatively blurred and global news is mixed with local news [START_REF] Bailly | Voyage en géographie[END_REF]. The traditional organisation of scale in the space knowledge is thereby disturbed. Finally, the emergence of Web 2.0 during recent years has to be taken into account. Each Internet user is now a full information producer who transmits its world representation and feeds the ow of information `consumed' by other Internet users. The information produced by Internet users contributes to building a world image at shown by Crandall et al. (2009). Obviously, knowledge of the world is imperfect and, as we'll see that later, it is ruled by a factor of distance and of `weight' of objects known. But we have to dene both the type of distance and the type of weight (population, wealth, political inuence, real or supposed nuisance capacity).

Beyond the analysis of world representation, one question is how to catch, analyse and represent those subjective visions of the world and their variations among individuals and groups of people? The issue is to go beyond the clear-cut and simple visions provided by classications and try to map the representations of global spaces in all their shades but also to analyse the socio-spatial factors that explain variations in these representations.

Proposal of the theoretical perspective 1.2.1 Knowledge appreciation and dynamic

In the context of this project, the term `representation' is understood as the collective or personal image (of our object `Europe') developed by an individual at the crossroads of her/his knowledge of Europe and how much s/he appreciates it or not. Both knowledge and appreciation should not be considered as binary solutions but as two gradients at the crossroads of which all solutions are possible (Figure 1) at one moment (stars). A social repre-Figure 1: Variation in knowledge and appreciation sentation is a dynamic structure that is always evolving. The maintaining and evolution of the representation is because of the inuence of society and belonging groups [START_REF] Bonardi | Les représentations sociales[END_REF]. As a consequence, both knowledge and appreciation, that can be specic to each individual, can theoretically vary over time (arrows) in many directions, and not necessarily toward a better knowledge or a better appreciation. Moreover, the object we analyse seems rather fuzzy. It can be considered to be uncertain or incomplete as the level of knowledge on Europe can vary very much from one individual to another. It can also be considered to be imprecise as each individual can develop his or her own denition of Europe, through his or her own experience and history. However, being imprecise does not mean that it is impossible to catch or explain it or to nd common signicances. Thus, throughout the project we tried to catch the representation of Europe, describe it and explain it.

We propose using Figure 1 as the main tool to analyse and compare the representation of Europe in the world. Indeed, whatever the method used (qualitative or quantitative) or the sample observed (collective or individual), this concept of knowledge and appreciation seems relevant and ecient in order to analyse the social variation in the representation of Europe.

`Social scale perspective' and timescales

In this report, we also propose a specic interpretation of social variation. Indeed, `social variation' should be understood as the variation in the representation of Europe according to social class, as it is quite true that social class explains a great part to individual representations [START_REF] Bonardi | Les représentations sociales[END_REF]. Moreover, as stated by Mérenne [START_REF] Schoumaker | Analyser les territoires, savoirs et outils[END_REF], `All human behavior is based on representations, i.e. on images of reality. The latter can never be known directly and it is always partially caught. The representation of reality varies then according to the perceived object and the individual that perceives it i.e. its own values (ideas and principles that are often shared by the group one belongs to)'7 .

However, one of the problems in the EuroBroadMap project is that we have no precise data on the social classes of the students surveyed. Some questions provide an idea of the material and symbolic capital of students (see the WP2 cross-country synthesis report). However, the students do not necessarily position themselves in the same way in all the sampled countries as the national socio-economic context can inuence their perceptions. Moreover, analysing only social class variations would deny the inuence of the other factors that contribute to building their representations of the world. One of these factors is the role of the national context, i.e. how the world is taught at school and what is the position of a specic country vis-à-vis other countries regarding global issues? Indeed, dierent factors contribute to shaping the world representation at dierent scales (individual, inter-individual, intra-group, intergroup, intra-national, international etc.) and the interactions between them [START_REF] Doise | L'étude des relations sociales, textes de base en sciences sociales, Neuchâtel, Delachaux et Niestlé. Dortier[END_REF].

To try to take into account the multiplicity of `social' factors that contribute to explaining the variation in the representation of Europe in the world both in terms of knowledge and appreciation we developed a strong hypothesis: the variation in the representation of Europe can be explained by the dierent `socio-spatial positions' of the individuals investigated. These `socio-spatial positions' are not reduced to one's socio-economic status but understood here as the multiple interactions between the four levels of social reality: the world level, the country (collective) level, the family (or social group) level and the individual level (Figure 2). For each level, the timescales of phenomena that inuence the representation are quite dierent but these should be considered both toward the past (heritage) and future (perspectives).

The world level timescale is many centuries. From the heritage perspective, it can be understood, for example, by the western domination of the world for centuries as well as how the western world `shapes' world history. How the world-level perspective inuences representation could be, for example, concerned with global warming. The country level timescale could between one and three centuries. From the heritage perspective, it concerns the `country story' built by school textbooks in which major migrations, economical exchanges, wars, colonisation and rivalries between countries can have a strong role in representations. From the perspective side, it could be national fears about a possible decline (such as in France, for example) or on the contrary some optimistic vision of the country's future (such as in Brazil or India nowadays).

The family (or social) level timescale is two to three generations backwards and forwards (grandparents and grandchildren). The socio-economic situation of the family and family events such as migrations can inuence representation both as a heritage and as a projection.

The individual level timescale is the life scale. Some categorical characteristics of the individual can inuence the representation (for example, gender) but of course also the heritages and the memories (school trajectory, space practice in travels, cultural practice. . . ) and the perspective (choice of study, wish to migrate or to travel, and capacity for adaptation), as well as all the experiences.

It is important to stress that all these levels are linked and thus they determine each other. In this report, we will try to analyse the variation in the representation of Europe according to this `socio-spatial positions' grid, and check how much it is relevant.

2

A world-level vision of Europe, shaped by Europe

Representations at the world level

The existence of a common pattern of world representations (and most, of Europe) on a global scale is maybe one of the most dicult to justify. It seems dicult to justify that all the people in the world share some common representation because of the extreme dispersion of humanity on the Earth's surface and the variety of languages, religions and cultures that contribute to such representations. However, at stake here is the representation of a spatial object, the world that encloses the entire humanity. Some discussions exist about the existence of a `society world' that could be for us a useful framework to analyse the representations of the world. However, we can also hypothesise that the long historical interactions between Earth's people has led to the emergence of some common pattern in world representation. This hypothesis is even more credible when we consider that dominating powers have long imposed their own visions of the world on the countries they colonised. Nowadays, the existence of global media and instant and constant world information availability through the Internet can also lead us to consider that some common representations of the world exist and that it is worth analysing them. Indeed, in the mental maps analysis in WP2 some striking analysis was carried out that demonstrates how much the vision of the world and, to a certain extent, of Europe are consensual and present a common pattern in the dierent countries surveyed. The analysis conducted in this part tries to make a rst synthesis of the perception of the world and the perception of Europe at the global level.

Europe in the world representation: one of the world's continents

The questionnaire in WP2 had two in parts, which allows us to analyse dierent perspectives about the image of Europe. Questions B and C were focused on the world level and this allows us to assess the existence of Europe in world representations. Part D of the questionnaire was explicitly focused on `Europe' in order to explore the spatial and semantic consistence of this concept for the students surveyed.

In question C, students were asked to divide the world in a maximum of 15 world regions. Although 7.79% of them chose to use the maximum number that was possible, the majority (38.54%) made between ve and seven regions that t with the classical vision of the world in continents (Figure 3). Students were totally free to choose the kind of division they wanted to draw; the names they gave to the regions conrmed that the main vision of the world corresponds to the continental vision (Figure 4). The word `Europe' alone is used 3633 times.

In the world visions of students, Europe has then a rather classical place as a continent. This result is coherent with the classical analysis of social representations but applied at the world level. As stated by [START_REF] Moscovisi | La psychanalyse, son image, son public[END_REF], representations are built on a central core (a knowledge scheme or central system of perception). Here, we can understand the continents as the `central core of the perception' of the world. Moreover, as explained by [START_REF] Piaget | La représentation du monde chez l'enfant[END_REF], these representations are based on a small number of characters that are quite stable over time because they are deeply rooted by perception schemes acquired early in childhood. This theory can be transposed to the world space, which is considered to be an object of representation. The vision of the world is, therefore, based on a `continental grid' taught in school since generations have used this to see and know the world. This vision of the world in continents `refers to the idea of a world ordered by the existence of physical and regional realities that scientic work would tend to identify, describe and explain (WP4, working papers on textbooks) and then it is often used as a `politically correct' division of the world. However, this representation of the world is not so `politically correct' when one knows that this vision is inherited from the geopolitical visions of Europeans about themselves and their place in the world. The continental vision of the world was built during the Middle Ages and transmitted as one of the constant schemes of European identity [START_REF] Grataloup | Géohistoire de la mondialisation[END_REF](Grataloup, , 2010)).

Question B also provides an interesting glimpse of how `Europe' is perceived at the world level. Despite the relatively small size of the Euro-BroadMap sample (18 countries) and its lack of representativeness of the world level (WP2 cross-country synthesis report, part 2), the question about the attractiveness of countries and cities shows an interesting representation of Europe. The cartogram representation (Figure 5) proposed in the WP2 cross-country synthesis report shows that Northern and Western Europe appear as very attractive to the sample, even with some minor variations. Eastern Europe is less quoted and mostly in a negative way. At the sample level, then a clear opposition can be observed between the western `free world' and the former communist part of the world, embodied by the Iron Curtain that is still quite visible on mental maps, both in terms of location and appreciation. If the vision of the world and the position of Europe in it can vary according to regions, countries and personal parameters, the cartograms tend to show the same trend of a double vision of Europe on a west/east basis.

Consensual but fuzzy representation of Europe

The last part of the WP2 questionnaire directly asked two questions on `Europe'. However, the word `Europe' was not dened in order to check its spatial and semantic denitions, from students' points of view. What is rst striking in the analysis is how much its image is, to a certain extent, consensual. This aspect can be rst analysed on the `Europe interpretative maps' produced by the students surveyed in WP2, but also in the lexical elds used by both the migrants (WP3) and the students (WP4). It can be analysed as a classical perception scheme of the world both from a spatial and from a semantic perspective. On the maps of Europe, there is great consensus on the `heart' of Europe but also on some of the limits drawn by the students. The heart of Europe is concentrated on what can be considered now to be the six founder's states of the current EU plus Switzerland, plus a large part of the Iberian Peninsula (Portugal and Spain). This is coherent with the vision of western countries that dominated the world to a certain extent from the 17th century to the beginning of the 20th century in a colonial way. It is the place of origin of the Renaissance, humanism, political liberalism and socialism. This space is also to a certain extent the place of birth of the Industrial Revolution that spread all over the world. Finally, this spatial denition corresponds to a certain extent to the vision of the European part of the `free world' facing the communist bloc for a large part of the 20th century. This spatial denition of Europe thus seems to correspond to a long-term construction of the image of Europe, probably transmitted by schoolbooks (see Work Package Politics and Ideology) and by the media and general knowledge on Europe and its relations to the world.

Again, what it is striking is the relation between the denition of Europe by Europeans and the denition of Europe outside Europe. For example, the limits of Europe are very much consensual on the southern part of the map: the Mediterranean Sea, and particularly the Gibraltar Straight, is perceived as a limit from Brazil to China and from Sweden to Cameroon. Mainly all students from the 18 countries of our sample draw the southern There is little doubt that this denition of Europe is largely inherited from attempts to dene European identity since the Middle Ages and reactivated by colonisation during the 19th century. To a large extent, European identity has been built on a common background of Christianity in a process of grouping people sharing this faith and separating them from people sharing another faith (Islam), forgetting in the process Muslims from the northern Mediterranean shore. This process can be described using the terms of `mêmeté' [START_REF] Ricoeur | Soi-même comme un autre[END_REF] on one hand and `ipséité' on the other. This crystallisation of European identity around religion is to a large extent inherited from the Middle Ages and the battles to stop the Arab conquest in southern France (eighth century), the crusades of the European kings conducted in order to restore Christian control on the Holy Land (Middle East and particularly Jerusalem) and to conquest again (Reconquista) the Iberian Peninsula (15th century). Even if the geopolitical position of the Ottoman Empire (the `sick man of Europe') in modern and recent times often perturbed this denition, this largely shared spatial denition of Europe is thus inherited from a long-term heritage of the denition of Europe. Moreover, the fact that it is a perceived geographical border strengthens this delimitation in the memories.

Convergence in the semantic eld used to describe `Europe'

Some strong common semantic elds of this denition of Europe can be observed both in students' vocabulary used to describe Europe (WP2) and in the discourse on Europe of migrants (WP3). The analysis of this common pattern is made in the previous part of this report and will not be repeated here. In a few words, we would like to underline some facts. The `developmentalist' and `imperialist' themes used in dening Europe can be also underlined as reminiscences of the historical position of Europe in the world. Some references to `freedom' in the vocabulary used can also be analysed both as a reference to the current situation of the European people and as a reference to the philosophical and political past of some European countries (British habeas corpus ; Enlightenment Age, French Revolution etc.). However, the `institutional' vision of Europe is dual and the emergence of Europe as an institution is a recent fact. Moreover, students express it differently according to the places in which they live: students from Belgium and France clearly refer to the EU institution (Schengen area, Euro, etc.), whereas non-European students and migrants refer mainly to the migratory policy of the EU. This leads us to explore one other component to the vision of Europe, the national one that is generally build over a medium-term time span.

3

The role of the local/national context

The national level in representations

In this part, we aim to show how the national level can explain the vision of the world in general and of Europe in the world in particular. What was very striking in WP2 was that when analysis was carried out at the survey level (43 dierent cities disseminated in our 18 countries), most places were grouped together. This was the case for the drawing of Europe (Figure 7) but also for the belonging analysis (idem). These two gures illustrate how much the national context inuences the vision of the world, but also the personal feeling of belonging to a space. In this part, we propose then analysing the role of the national context in terms of the formation of the collective representations of Europe and to try to provide some explanation.

Role of historical links between nations in the Europe representation

One of the most evident factors to explain the convergence of the national visions of Europe is the spatial position of the country regarding what we have identied previously as the rich, industrialised, free, western countries and, to a certain extent their positions and relations regarding the EU. For example, what it is striking in the French and Belgian students' representations of the region of the world they belong to on the world map (question C2) is that the region drawn ts nearly perfectly with the EU. More recent and peripheral member states such as Portugal and Sweden are more likely to draw the Iberian and Scandinavian regions of the world. It seems clear that France and Belgium's long historical involvement in the EU and the communication on this now familiar subject in the media and at school lead to those visions. It can also be observed in the vocabulary used by Belgian and French students to describe Europe (question D2) that this is far more `institutional' and economic than it is for students from other countries. The historical relation of countries vis-à-vis Europe also has an inuence on the representation of Europe in the country and this representation is collective. One more time, this can be illustrated by the vocabulary used by students to describe Europe, but also in the discourse of the migrants interviewed in WP3. The most striking example is that of the African countries analysed in both work packages. The historical colonial link between European and African countries leads to the formulation of a specic discourse in describing Europe. The African students in Mali (WP3) and in Senegal or Cameroon (WP2) express a feeling that African people have been exploited in the past (and to certain extent nowadays too) and that European countries have a `war debt': some family members of the students interviewed in WP3 died in a French battle eld during WW1 or WW2. This kind of discourse can also be found in some African media and political discourse as well as from the diplomatic perspective as pointed out the national political vision of Cameroon (Box 1).

To this extent, the situation of India is quite dierent. India has also been a European colony and the exploitation of resources was at least equal to that in African countries. In addition, South Asian soldiers were present in European battleelds during the World Wars. However, the discourses of Indian students and migrants are quite dierent. Students have globally a kind of idealistic and romantic vision of Europe, whereas migrants (WP3) perceive Europe as a land of opportunity when they formulate their migration Table 1: National Politic Vision of Cameroon `In some aspects, and for Cameroonian diplomats, the power politics perceivably played by the EU, be it normative, soft or civilian, are considered as nothing else but the continuation on a dierent level and in dierent forms of domination relations that prevailed in former bilateral relations (especially with Germany, France and the UK). The imbalance in a number of areas (the level of economic development and nancial resources being some of the most prominent ones) and the self-interested strategies of the European in their relations with ACP countries motivate the rather defensive attitude of the Cameroonian authorities when negotiating on trade and development programmes.' Source: National political vision (WP4) projects. This can be explained by some dierences in colonisation (many more Indian civil servants have been trained and employed compared with African colonies). But the national position of India as a nation in the world is also dierent. India is a demographic power and a growing economic power and it has the wish to be recognised as a world power in the future. This has a great inuence on the representation of India in the world. As shown in WP4, in India: `the teaching of geography remains strongly marked by the national perspective'. Moreover, Indian people perceive that their country has a very ancient and long history. They do not feel that their historicity has been built by European colonisation, which appears to them a now closed chapter. If some African countries have the same ambitions of being emerging powers, unlike in India, there is a feeling that it will be dicult to be successful and that Europe has some responsibility in that situation. Thus, depending on the historical nature and strength of countries with Europe, but also of their positions vis-à-vis Europe in the national perspective (embedment, reimbursement of debt, rivalry, neutral position etc.), this has an inuence on the national representation of Europe, transmitted by the political discourses, by the media and, of course, by schools. Here, the role of school curricula in the formation of the vision of Europe is well illustrated by the very specic spatial vision of the African students of our sample in the spatial vision of Europe (Figure 7). Cameroonian and Senegalese students are almost the only ones to draw a large Europe including the entire Russia Federation. As shown in the Cameroonian country report, this corresponds to a classical school denition of Europe `from Brest to Vladivostok'.

Because of the disparities

Another point that seems consistent in the building to the national vision of Europe is the existence of socio-economic disparities that inuence the vocabulary used to describe Europe or the image of Europe of migrants. Indeed, in `developing' and less rich countries, the terms rich, developed and industrialised are often used to describe Europe. But what is the most striking example is the image of Europe of the Somali women analysed in WP3. For them, Europe is seen as a place of security and freedom above all, because that is what they miss most in their county. This example will not be developed further because the previous part of this report analyses in detail the crossings between the vocabulary of students and the representation of migrants. However, this illustrates one more time very well the role of `otherness' (`ipséité') in the building of representations.

National representation: reects national visions of the world

In addition to the knowledge grid inherited mainly from childhood, the representations of the world are also rooted in social norms inuenced by the national level. These representations are quite stable but can vary over time, because the timescale of the heritage is shorter (maybe around 200 years) and because the perspectives could have a great inuence. The perspectives are very much linked to the political context at the national level. These representations at the national level have an operational role in the construction of identity, in the position of the group in the world and in the way the group perceives the world. These representations are produced and transmitted by institutional groups (the media, political groups or, as shown in WP3, NGOs). As a consequence, it seems highly possible that the country level could explain some convergence in the pattern of the representations of people from the same countries.

We can thus try to analyse the positions of the countries surveyed in regard to their knowledge and appreciation of Europe, using the knowledge/appreciation dynamic graph set up in part one of this report (Figure 9). In our sample, the role of the spatial distance to EU / Western Europe (historical dominant core) is quite clear. This conrms one of the main hypotheses of the entire project (see answer to the tender) and the choice of the countries to be surveyed: we chose countries in regard to their positions vis-à-vis the area of inuence of Europe established using various criteria in the ESPON 3.4.1. `Europe in the world' project [START_REF] Didelon | Europe in the World, Final Report[END_REF]. What we may have underestimated in this previous project is the role of historical links between non-European with European countries, even though some historical variables were used. The gure is an attempt to analyse the positions of the countries surveyed in WP2 in order to assess the `knowledge and appreciation' of Europe. Countries have been grouped into four main categories:

• The Western European core category gathers western European countries that had a role in the historical emergence of Europe as a world power thanks to colonisation and industrialisation.

• The `former rival empire / other cores' category group Turkey and Russia, which are former powerful rival empires of European countries, and China, which has long been technologically and socially advanced. Those empires have been, to a large extent, independent of European colonisation most of the time, and they have been themselves colonisers, or, at least places having a strong inuence on neighbouring countries.

• The areas of inuence between cores stress the places that have shared `core' inuences. The Mediterranean Sea has been a place of struggles between European countries and the Ottoman Empire 8 , as the Maltese history reminds us. Eastern Europe and the Balkan areas, both in recent times, but also in the past, have been inuenced by Europe and Russia, while some Turkish inuence can also be noted in this region. The Central Asian, embodied here by Azerbaijan, and the Turkish (linguistic and cultural) and Russian (political and historical) inuences have also been strong.

• The last category, `former European colonies' is a simplied grid of the colonial inuence of Europe. In South America, the inuence is high because large parts of the national population have a European origin, and the states were built on the European model by colonisers. But in those spaces independences occurred early: at the beginning of the 19th century for Brazil. In South Asia, the mainly English colonisation had rst commercial purposes. If the English intensively exploited Indian resources, they also built some ecient infrastructures (railways, telecommunications) and employed many locals in the administration. Independence occurred in 1947. In Africa, the exploitation of resources has been high too and in the early times of colonisation lots of indigenous peoples were exported as slaves to the Americas. Colonisers in Africa, (France, the UK, Belgium, Germany, Italy, Spain and Portugal) did not involve the local population as much as the English did in South Asia and independence has sometimes occurred very late: 1960 for both Cameroon and Senegal, the two countries in our sample.

The countries surveyed are represented by a star coloured according to their spatial and historical situations toward the European core. They have been then positioned on the `knowledge and appreciation' graph using the main results of the WP2 analysis on the vocabulary used to describe Europe (WP2 working papers). In the gure, we can observe more clearly what was stressed in the various analyses, and more precisely how the relative positions of countries are inuenced by the spatial and historical positions of countries. The spatial and historical position of China as regards to Europe implies a relatively low level of knowledge together with a relatively high level of appreciation. As far as former European colonies are concerned, the graphic is even more explicit. African countries are closer to Europe in spatial and historical terms, and in this space the inuence of Europe is still strong but not very well perceived. The knowledge level is roughly equivalent to the Indian and Brazilian one but the appreciation level is quite dierent: Cameroonian and Senegalese students have some negative representations of Europe that occur more rarely in India and Brazil. What is also striking, which should be analysed more in detail, is that the countries identied as `areas of inuence between cores' are grouped around the non-European core. For example, Eastern European countries are in a median position between Russia and Belgium and France, and Mediterranean countries are more or less grouped around Turkey. The use of this graph seems relevant in the analysis of the representation of Europe in dierent countries, and will be later used in the analysis of other part of the questionnaire, question B. China to the EU (February 2010): `. . . in China, many people are angry that the EU criticizes and attacks China on the issues of democracy and human rights despite the great progress China has made. Some are frustrated that the EU should take advantage of its unique mechanism to maximize benets at the bilateral level while playing bad guy at EU level. Some are disappointed by the EU's indecision and procrastination in lifting the arms embargo and granting full market economy status to China. Such gaps in mutual-perception, together with the negative moves on the EU side, have aected, to certain extent, the eorts in building greater mutual trust and impeded China-EU relations from moving towards a deeper and higher level.' (http://www.fmprc.gov.cn/eng/wjb/zwjg/zwbd/t656007.htm) Source: National political vision (WP4) [START_REF]3 Material and symbolic capital and the representation of Europe 23 4.4 Role of `Europe' individual experience[END_REF] The role of the socio-economic situation and individual characteristics

Individual perspective in representations

Some of the results from the WP4 `national political vision', which provides a synthesis of countries' ocial diplomatic positions toward Europe, have great dierences, if not contradictions. For example, one extract from the Chinese national political vision (Box 2) pointed out that in China people are not happy with Europe's position vis-à-vis human rights in China, when the students' words used to describe Europe (Box 3) do not evoke this problem at all. The personal visions of students can be explicitly found in the regionalisation of the world (C2 question in the WP2 survey). If the large majority of students seem to perceive the world in continents, a small proportion of them develop personal views. The most original visions of the world are maybe the `One world' maps, where students decided to make only one world region (2.3% of the sample) and the `Ego world' maps, where students used mainly the personal pronoun `I' to describe the world region (1.3%). The students creating these maps do not seem to be inuenced by global world visions but rather by their personal perspectives. The inuence of the students' socioeconomic backgrounds and family histories should thus be analysed more in detail in order to check how much the personal parameters inuence the vision of the world and the vision of Europe. Europe gives Chinese students a strong impression of its powerful economy: `developed'(31.0%) `rich' (21.4%) `advanced'(8.4%). Chinese students appreciate the culture of Europe a lot: `romantic' (17.9%) `civilized' `classical' `elegant' `civilization' etc. , which indicate that the diversity of the culture of Europe. Europe is mentioned many times by Chinese students as an `open' space or a place where people live with much `freedom'. It can be inferred Europe is considered to be a good place to live by Chinese students because of the good `environment', the `clean' circumstance and the social `welfare'. In Chinese students' eyes, Europe is a group of `small' `countries' but not a union. Source: Chinese country report As we have seen before, the representation of the world depends on the belonging of the individual. The global level provides a `general scheme' of perception, whereas the national level renes the representations by introducing elements shared by people at the national level that are dierent from one country to another. Other levels of the belonging of people can also have an inuence and the personal and familial perspective should not be forgotten. Individual spatial representations are strongly inuenced by the distance of the spatial object as explained by [START_REF] Moles | Psychologie de l'espace[END_REF]. However, one main factor in the shaping of representations (spatial or not) is the intentions [START_REF] Ponty | La Phénoménologie de la perception[END_REF] of the subject vis-à-vis the object considered. The representation of Europe as a spatial object is therefore `nal'. That means that an intention exists in the framework of representations and that representations are oriented by our projects (Dortier, 2002).

Gender perspective

As far as individual perspectives are concerned, it seems clear that the gender of an individual can have an inuence on his/her representation of the world. This is of course expressed in the project of students, and for example in the eld of study chosen. As shown in the Maltese country synthesis, there exist `ingrained gender schemas that inuence the choice of both men and women's life paths' inuencing the choice of eld of study (Figure 10) and, as far as we can imagine, the vision of the world. In at least two cases in our previous analysis, the role of gender in the vision of Europe has been stressed. The rst is the one of Somali migrant women in Maltese camps. They perceive Europe as a haven of security because their lives are threatened in Somalia because they are women. They hardly know anything about Europe, except the fact that, as women, they will be safe there. Here, the role of dierence pointed The second example of the role of gender in the representation of Europe is the analysis of the words used to describe Europe as stressed in the nal report of the WP2: `Overall, the feminine vision of Europe is more positive and enjoyable, oriented on aesthetic issues and leisure, and sensitive to social inclusion goals. In opposition, the vision of men is imbued with a certain severity, as if Europe would be the result of a culture based on political domination and struggle for life'.

Material and symbolic capital and the representation of Europe

The rst part of the WP2 cross-country synthesis concluded that social and economic inequalities in the EuroBroadMap sample could have an inuence on the world representation. A factorial analysis was carried out, which shows clearly how much material (family income level) and symbolic (education level of both parents) capital are correlated with world experience, proxied by the number of languages spoken (Figure 11). The analysis of the vocabulary used to describe Europe shows clearly the existence of a signicant relation between material and symbolic capital and the representation of Europe9 .

Students declaring a `low' income level have a quite Manichean representation of Europe traducing the feeling of the students. Europe is perceived either as an attractive place of opportunities or as a land of imperialism Students declaring a `medium low' income level have a roughly similar ambivalent perception of Europe. They point out both the development level and the feeling of exclusion. However, the vocabulary used is more abstract and they use more geographical terms.

Students declaring a `medium high' income level have a consumerist vision of Europe. They quote famous tourist places and European luxury brands. Their knowledge of Europe seems more precise because of their experience of travelling in Europe. They also evoke some cultural and institutional aspects of Europe but do not use very negative or very positive vocabulary to describe Europe.

Students declaring a `high' income level have a neutral image of Europe characterised by the use of a territorial and institutional vocabulary.

Indeed, it seems that the lower is the material and symbolic capital of students, the lower is the level of knowledge and more Manichean it is (Figure 12). On the other side, the higher is the material and symbolic capital of students, the higher and more neutral is their knowledge of Europe. The relation between the material and symbolic capital level and the representation of Europe seems relatively easy to explain. On one hand, students from highest income/educational level families have better access to information Moreover, material and symbolic capital also has an inuence on how the individual perceives him/herself in the world: the analysis of the declaration of students on their scale of belonging (local, infra-national, national, supranational and global) shows a great inuence of parent education and family income. In all countries, low material and symbolic capital is associated with a low level of belonging (local, infra-national), whereas high material and symbolic capital is associated with a high level of belonging (supranational, global). Of course, the way an individual perceives him/herself in the world will inuence his/her world representation. This point should be deepened in the analysis of world maps. However, some analysis conducted in WP2 already showed that `global' students were more eager to make a low number of world regions on the world map, or even refused to divide the world into regions.

Role of `Europe' individual experience

As far as the individual perspective is considered, special focus has been placed on the evolving vision of Europe of people through European experience. Indeed, the time span for changing the presentation of Europe can be quite short from the individual perspective. The variation in the representation of Europe of students according to the number of places visited should be analysed in order to check how much the experience of Europe shapes its representation. Unfortunately, this has not been done yet. Anyway, some material can be found in the WP3 report. The analysis of Indian migrants in Italy shows clearly how much the perception of Europe varies in the migration path. During the formulation of the migration project, Europe is perceived by Indians as a rich, clean, prosperous and modern place of opportunities: the level of knowledge seems rather low and more expressed in an idealistic perspective. After migration, the Indians surveyed in Italy stress the diculties nding jobs and the legal problems. They developed a more faded vision of Europe -still perceived as a place of opportunities, but with diculties.

It seems important to stress that the socio-economic positions of individuals play an important role in the evolution of the representations of migrants because their material and symbolic capital has an inuence on their capabilities to full their projects of mobility toward Europe. When people have a high social position, they have possibilities to go to Europe legally (travel or study). When they have a low social position, European borders are closed, which leads them to develop bad feelings together with a growing wish to defy.

Indeed, the vision trajectory in the `knowledge/appreciation graph' of an individual in particular and a social group considered at the national level can be dierent depending both on the national and personal history and on perspectives. For example, the general knowledge of Europe in a country can theoretically decrease and become more positive (if the level of inuence decreases and Europe is only perceived as a nice place for tourism instead of a rival economic power for example), when the general knowledge of one individual from that country can increase. However, it becomes negative through the dierent stages of the experience of migration (as stressed by some of the results of the WP3) (Figure 13). However, it is dicult to make such an analysis in this project because the majority of the surveys and analyses were carried out once.

Conclusion

This attempt to analyse the representation of Europe conrmed that spatial representation can be considered largely as normal social representations. It is possible that they may be less stable over time and that the inuence of the position of the subject surveyed in space has a greater inuence. Anyway, the world scale perspective produces a kind of `average vision' of Europe (as a free medium declining world economic power made of `attractive' countries in the west and `non-attractive' countries in the east) that is Figure 13: Theoretical co-evolution of national and individual perceptions of Europe quite well dened in the south and with fuzzy borders in the west. This is a long-term perspective of Europe, built by the history of Europe and its own identity construction. The national visions of Europe are determined by the national historical relations with Europe but also by the place of Europe in the national perspective (rival power, helpful associate, selsh and unfair exploiter etc.). One should be aware that at this level, representations are quite linked with propaganda and that this propaganda orientation can evolve rather quickly. At the individual level, the representation of Europe is shaped by the cognitive capabilities that are partly determined by material and symbolic capital. However, the issues at the individual level are not only cognitive as the individual level implies the intentionality of the subject vis-à-vis Europe and its probability of succeeding. These representations are then mobilised in the individual project in order to justify it as in the dialectic couple rich/poor, endangered/secured, lack of hope/opportunity.

To conclude, the representation of Europe is organised at dierent levels of the social frameworks of spatial representations and, depending on the level considered, it is easy (or not) and rapid (or not) to act to modify them. The EU, in its communication strategy, must be careful because it is dicult to modify the representation at some levels and sympathy capital can erode quite quickly at others.

Figure 2 :

 2 Figure 2: Four social frameworks for spatial representations

Figure 3 :Figure 4 :

 34 Figure 3: Repartition of students according to the number of world regions made

Figure 5 :

 5 Figure 5: Vision of undergraduate student's vision of world states

Figure 6 :

 6 Figure 6: Extension and limits of Europe

Figure 7 :

 7 Figure 7: Grouping of places of survey in countries in the analysis of drawings of Europe

Figure 8 :

 8 Figure 8: Dierence between all students and students from Cameroon

Figure 9 :

 9 Figure 9: Position of countries toward Europe and position in knowledge appreciation

Figure 10 :

 10 Figure 10: Gender repartition by eld of study

Figure 11 :

 11 Figure 11: Material and symbolic capital variation in the EBM survey sample

Figure 12 :

 12 Figure 12: Knowledge and appreciation of Europe variation according to social variation

Table 3 :

 3 Chinese country report on survey part 1 (WP2)

The nightmare before Christmas, 1993, Tim Burton, Henry Selick, Walt Disney Pictures

.6 I take the opportunity here to warmly thank all the partners involved in the project. It is impossible to add all their names on the report cover, but this synthesis would not have been possible without their eorts.

Translation from French.

One main ambiguity here lies in the fact that the Ottoman Empire has been perceived as `European ' in the Modern Age by the European power implied in the European geopolitical game.

The results presented here should be analysed with caution. The country of survey variable was not controlled for and some of the vocabulary variation seems to be inuenced by national context.


Anu Jagannathan
email: jagannathan@lps.u-psud.fr

Benjamin Motz

Elena Vedmedenko

Novel properties of frustrated low dimensional magnets with pentagonal symmetry

Keywords: aperiodic materials, low-dimensional structures, magnetic films, magnetic structure, nanosized clusters, theoretical frustrated antiferromagnet, quasiperiodic magnetic thin film, fractals quasiperiodicity, frustration, antiferromagnetism, fractals

We consider a new type of frustrated spin networks with pentagonal loops and long range quasiperiodic structural order. Five-fold loops can be expected to occur naturally in quasicrystals, and experimental studies of icosahedral alloys show manifestations of local five-fold symmetry in a variety of different physical contexts. Our model considers classical spins placed on vertices of a subtiling of the two dimensional Penrose tiling, and interacting with nearest neighbors via antiferromagnetic bonds. The ground state of this fractal system has a complex magnetic structure, and is studied analytically as well by Monte Carlo simulation on finite clusters.

Frustrated magnetic models have been a subject of much interest over the years, due to the new types of behaviors that can arise as a result of the frustration. Spin glasses are one well-known example of frustrated magnets. In these materials, the magnetic moments (spins) interact via exchange interactions that are random in sign and, in most cases, in magnitude as well. As a consequence, any given spin is typically unable to find an orientation that can satisfy all of the bonds that join it to its neighbors, whence the idea of frustration. Spins freeze below a certain transition temperature, with randomly oriented moments, forming a disordered magnetic glassy phase, with complex dynamical and thermodynamical properties. Periodic frustrated systems include the Ising antiferromagnet on a triangular lattice, whose interesting zero temperature properties were considered by Wannier in 1950 [1].

In the triangular antiferromagnet, the frustration has a geometric origin, due to the fact that one cannot place three vectors on the three vertices of a triangle so as to satisfy simultaneously all of the antiferromagnetic bonds. Similarly, in three dimensions, the presence of triangular loops in the face-centered cubic lattice leads to frustration. In recent years much interest has been shown in the quantum states of such frustrated antiferromagnets, and much work has been done on frustrated systems such as the Kagome lattice [2], the pyrochlore lattice and many other interesting lattices in two and three dimensions (for a review see [START_REF]Frustrated Spin Systems[END_REF]).

In this report, we will introduce a new type of frustrated model which is based on five-fold symmetry, present in many quasicrystals. Motivation for considering such a quasiperiodic magnet comes from the experimental progress in recent years in producing quasiperiodic atomic layers on the surfaces of quasicrystals. Many different atomic species have been shown to form pseudomorphic films with a connectivity that reflects the underlying quasiperiodic organisation as can be seen in Fig. 1 which shows an STM image of adsorbed Pb atoms on the surface of AlPdMn (for more details see the review in [START_REF] Smerdon | [END_REF]). It is thus likely that magnetic structures could eventually be obtained as such techniques are refined and extended. We note in passing that three-dimensional antiferromagnetic quasicrystals with antiferromagnetic interactions have been investigated in many preceding works [5].

As a simple theoreticians model of a frustrated two dimensional quasiperiodic magnetic layer, we consider antiferromagnetically coupled vector classical spins on vertices of a subtiling of the Penrose tiling. We find that the resulting structure is frustrated on an infinity of length scales, with, as the starting point the elementary pentagonal five-fold rings. The frustration leads naturally to a macroscopic entropy of the ground states of this system, as has been shown for the six-fold symmetric Kagome lattice antiferromagnet, which is based on the triangular elementary unit. This quasiperiodic antiferromagnet provides a new playground for exploration of the physics of frustrated systems, and is of course expected to have different properties compared to unfrustrated quasiperiodic antiferromagnets (such as the quantum spin models on the Penrose and Ammann Beenker tilings considered in [6]).

We present the model in the following section 2. The first subsection outlines some details regarding the geometrical properties of the model. The following subsection outlines the methods of analysis that we have used. Section 3 presents results, along with a discussion and conclusions.

A model of a frustrated quasiperiodic antiferromagnet

We consider two-component vector spins (XY spins) S i placed on vertices, labeled by the index i, of a subtiling of the Penrose rhombus tiling (PT), as shown in Fig. 2. The Hamiltonian is where J is the strength of the spin-spin interactions. All the couplings are antiferromagnetic (J > 0), they are of equal strength and act along the short diagonals of the fat rhombuses, indicated by blue bonds in Fig. 2.

H = J i,j S i • S j (1)
Spins are clearly frustrated due to the presence of the pentagonal rings. The ground state degeneracy is easily calculated. In the case of Ising variables, it is five, since there are five ways to have one frustrated bond in a given pentagon. For the vector spin case, the degeneracy is reduced to just two, as we explain below. However, the frustration is also present at larger length scales, and this is a consequence of the geometrical properties of the structure, some of which we outline in the next subsection. This in turn is reflected in the ground state entropy of this frustrated antiferromagnet.

Geometrical properties of the pentagonal cluster model (PCM)

The system illustrated in Fig. 2 can be obtained from the Penrose rhombus tiling by retaining only those pairs of sites which are linked by the diagonals of the fat rhombuses. It can also be obtained very simply by the cut and project method (which will not be described here). A two-component -or XY -spin is attached to each of these sites . Figure2 shows the resulting sites and bonds of length τ = ( √ 5 + 1)/2 (in units in which the edge length of a rhombus is equal to 1). All bonds have the same strength and are antiferromagnetic.

The PCM is an assembly of interpenetrating clusters of increasing size, which are five-fold symmetric and fractal. They are labeled C n , where n is the "generation" of the cluster. The smallest clusters are isolated pentagons (C 0 and C 1 , which have opposite orientations and occur with different frequencies). Next, there are clusters of five pentagons arranged around a decagonal ring (C 2 ). C 3 has five pairs of pentagons arranged around a decagon, as will be illustrated further below. Each cluster can be constituted recursively from three preceding ones.

The properties of the infinite cluster, which percolates through the system can thus be calculated to great accuracy by a recursive method. We thus find the fractal dimension of the infinite cluster to be 1.799. The probability of occurrence of each type of cluster, p n , falls off with the cluster linear size l n = τ n (the length of the side of the pentagonal cluster) as a power law. Fig. 3 shows the distribution obtained numerically for the PCM for large finite samples obtained using the method of cutand-projection. The slope gives the exponent of the power law dependence p ∝ l -γ with γ = 2.089.

Magnetic ground states

For XY spins on the vertices of a pentagon, the minimal energy states correspond to configurations in which the spins angles are rotated by ±4π/5 as one passes from one vertex to the next. The bond energies are all equal, and have the value b = J cos(4π/5). For a given pentagon, we can define χ = bonds (φ i -φ i+1 )/4π where is the sum of changes of angle around the five bonds of the pentagon. The overall change of angle is thus ±4π and there is a two-fold chiral degeneracy of the ground state, χ = ±1. The next biggest cluster is composed of 25 spins arranged in five linked pentagons. The minimal energy configurations for two of the clusters are shown in Fig. 4. The resulting structure is frustrated, both at the level of the pentagonal rings and, as a result, at the level of the decagonal loop as well. One can distinguish three types of bonds: b 1 , bonds belonging to the pentagons, b 2 , the bonds that belong both to a pentagon and the decagon and b 3 , the bonds of the decagon that connect two different neighboring pentagons. By a direct minimization of the cluster Hamiltonian, we can easily determine the optimal values of each of the bond energies. b 1 and b 2 correspond to a difference of angles close to 4π/5, while b 3 is close to the optimal value of -J, or equivalently to a difference of angles close to π. These last are the least frustrated bonds in the cluster. Bigger clusters have a greater number of inequivalent bonds, but one finds that the values of bonds belong in one of three main groups. This is shown in fig. 5 which shows a color coded representation of the main classes of bond energies expected in the ground state of a large cluster.

Coming now to the question of degeneracy, we have shown that the C 2 clusters have many degenerate states, one of which is illustrated in 6, and that the degeneracy grows with cluster size. The calculation of the configurational entropy of the entire system is in progress will be reported elsewhere. We note here simply that this feature is an consequence of the chiral degeneracy already mentioned for the C 0 and C 1 elementary pentagons.

Results and Conclusions

Figs. 6 and7 show some results of a Monte Carlo simulation of a cluster of 1515 spins. The spin orientations for this sample follow the theoretically predicted schema. Deviations occur because of the low dimensionality of the system despite the low temperature (T=0.05 in units of J) used for the simulation. There is a good accord between the analytically and numerically determined states. magnets. Problems we would like to address in the near future concern the spin dynamics and magnetic response of this type of magnetic material. The quantum version of this model, similar to what was discussed for the unfrustrated Penrose tiling case in [6] will be an interesting theoretical challenge. Studies of the low energy magnetic states for the long range dipolar spin-spin interactions considered in [7] are also in progress, and results will be reported elsewhere.

F

Figure 1 .

 1 Figure 1. STM image of Pb atoms deposited on a AgInSb surface showing the presence of five and ten-fold atomic rings (figure reproduced with permission, courtesy of the Liverpool and Nancy groups)

3 Figure 2 .

 32 Figure 2. The vertices of the subtiling, along with the couplings are shown in blue, with the original Penrose tiling shown in light gray for comparison.

Figure 3 .

 3 Figure3. A log-log plot of the probability p of each cluster plotted against its linear size l, showing the power law dependence. The slope is equal to -2.089.

Figure 4 .Figure 5 .

 45 Figure 4. One of the ground state spin configurations for the clusters C 2 and C 3 containing 25 and 40 spins respectively

http://mc.manuscriptcentral.com/pm-pml Philosophical Magazine & Philosophical Magazine Letters

Taylor & Francis and I.T. Consultant

Acknowledgements

We would like to thank Pavel Kalugin for useful discussions. Benjamin Motz was supported by a CNRS contract for the duration of this work.

A small region of a large cluster, representing one of the possible low energy spin configurations, with the chirality indices shown for each of the pentagons (Nb. one defect is present in this figure.) Figure 7. A portion of a large cluster showing the local spin orientations as obtained by Monte Carlo simulation (T=0.05J). The agreement between theory (fig. 5) and calculations is found to be good.

Conclusions

We have presented a new class of frustrated antiferromagnet based on five-fold frustrated units. The structure is fractal, and has characteristic scaling properties in real space as well as perpendicular that follow from the algebraic properties of the underlying Penrose tiling. On the theoretical side, the subtiling is an interesting geometrical object in its own right, as it forms a percolating subsystem. It is conceivable that this type of structure could be realized by atomic deposition on quasiperiodic substrates, in which the adsorbate atoms sit on preferential sites. This would provide an exciting opportunity for exploring the physics of frustrated


Johan Forsgren

Ulrika Brohede

Maria Strømme

Håkan Engqvist
email: hakan.engqvist@angstrom.uu.se

Co-loading of bisphosphonates and antibiotics to a biomimetic hydroxyapatite coating

Keywords: Antibiotics, bisphosphonates, hydroxyapatite, sustained release

We have incorporated bisphosphonates and antibiotics simultaneously into a biomimetic hydroxyapatite implant coating aiming to use the interaction between drug-molecules and hydroxyapatite to enable local release of the two different substances to obtain a dual biological effect. A sustained release over for 43 h of antibiotics (cephalothin) was achieved without negative interference from the presence of the bisphosphonate (clodronate) which, in turn, successfully bonded to the coating surface. To our knowledge, this is the first study that indicates the possibility to simultaneously incorporate both antibiotics and bisphosphonates to an implant coating, a strategy that is believed to improve implant stability and reduce implant-related infections.

Introduction

Post-surgical infections and insufficient bone growth around prosthetic implants are two concerns within orthopedics that need to be addressed to improve the clinical outcome for the increasing number of patients receiving implants annually. Revision surgery due to infection and/or implant failure imposes considerable strain on both afflicted patients and the health care system, where the procedure in most cases is substantially more complicated and costly compared with the index 2 surgery [START_REF] Lavernia | Revision and Primary Hip and Knee Arthroplasty -a Cost-Analysis[END_REF]. In the U.S., almost 40% of all nosocomial infections are due to surgical site infections [START_REF] Mangram | Guideline for Prevention of Surgical Site Infection, 1999[END_REF]) and the incident rate can be as high as 10% for some procedures (spinal surgery) [START_REF] Carreon | Perioperative complications of posterior lumbar decompression and arthrodesis in older adults[END_REF]. In a recent retrospective study, of 9245 patients undergoing primary hip or knee arthroplasty 65% of the developed infections appeared within the first year [START_REF] Pulido | Periprosthetic joint infection: The incidence, timing, and predisposing factors[END_REF], indicating that perioperative infections associated with the open procedure accounts for the majority of infections.

The interface between prosthetic implant and tissue is a region of local immune depression with reduced resistance to microbes, often referred to as an immune-incompetent fibro-inflammatory zone [START_REF] Gristina | Implant Failure and the Immune-Incompetent Fibro-Inflammatory Zone[END_REF]. Also, implant migration due instability in the interface between bone and implant can damage the tissues and almost completely deplete the immune defenses [START_REF] Campoccia | The significance of infection related to orthopedic devices and issues of antibiotic resistance[END_REF]). Thus, these peri-prosthetic regions are highly sensitive for bacteria colonization and biofilm formation. By using an implant coating as carrier for antibiotics, a bactericidal effect can be obtained directly where it is needed, namely in the direct vicinity of the implant [START_REF] Schmidmaier | Prophylaxis and treatment of implant-related infections by antibiotic-coated implants: a review[END_REF]). This is believed to reduce the number of early infections associated with bacteria entering the incision wound as it prevents immediate bacteria adhesion on the implant following surgery [START_REF] Stigter | Incorporation of different antibiotics into carbonated hydroxyapatite coatings on titanium implants, release and antibiotic efficacy[END_REF]. By letting the implant surface deliver bisphosphonates as well, a more dense bone formation is expected around the implant, which will increase the implant stability [START_REF] Mcleod | XPS and bioactivity study of the bisphosphonate pamidronate adsorbed onto plasma sprayed hydroxyapatite coatings[END_REF][START_REF] Gao | The effect of surface immobilized bisphosphonates on the fixation of hydroxyapatite-coated titanium implants in ovariectomized rats[END_REF]. This dual effect is proposed to reduce the infection rate and at the same time increase the implant stability.

Biomimetic hydroxyapatite (BHA) is a suitable interface between bone and implant due to its close resemblance with the apatic mineral in bone [START_REF] Barrere | Osteointegration of biomimetic apatite coating applied onto dense and porous metal implants in femurs of goats[END_REF]. BHA-coatings can carry antibiotics [START_REF] Stigter | Incorporation of different antibiotics into carbonated hydroxyapatite coatings on titanium implants, release and antibiotic efficacy[END_REF]Brohede et al. 2009a) and bisphosphonates (Åberg et al. 2009) individually but, to our knowledge, have these substances never been loaded simultaneously to a BHA-coating, which would promote a beneficial dual effect as described above. Thus, the present study was carried out to investigate the possibility to perform such a co-loading.

Materials and Methods

Drugs

The drugs used in the present study were the antibiotic Cephalothin (Sigma, art. nr: C3050) and the bisphosphonate, clodronate (Sigma).

Coating deposition and drug loading

Circular substrates of titanium grade 2 (diam.=14mm) were coated with biomimetic hydroxyapatite (BHA) as described earlier (Brohede et al. 2009b). Briefly, a thin coating comprised mainly of crystalline anatase TiO 2 was deposited on the substrates by physical vapor deposition. Subsequently, each of the coated substrates were immersed in 40 ml Dulbecco's phosphate buffered saline with for 7 days at 60°C for precipitation of a BHA layer on the surface.

Thereafter, the coated samples where subjected to a loading procedure where they were placed in individual plastic tubes containing 40 ml PBS and either 1 mg cephalothin, 1 mg clodronate or 1 mg of both, see Table 1. The samples were left in the tubes for 1 day at 40°C before taken out and gently rinsed in distilled water.

Analysis

Clodronate contains two Cl that are bonded to C which makes it possible to detect clodronate at the surfaces of the BHA coating by analyzing the presence of Cl. This was done with X-ray photoelectron spectroscopy (XPS, Quantum 2000, Physical Instruments). The atomic concentration of Cl in both co-loaded and single loaded samples was measured and compared to the presence in reference BHA samples. The analyses were performed on quadratic areas of the BHA coatings with the dimensions 200 μm x 200 μm. The surface charges were neutralized with argon ions during the analysis.

The release of cephalothin was analyzed at 238nm. Four plates were placed in 10 ml deionized water that was circulated through the measuring cell using a peristaltic pump and the absorption was measured regularly until a plateau was reached.

Results and discussion

The elemental composition on the different surfaces is given in Table 2. The amount of Cl was higher for the samples immersed in the clodronate-containing liquids, indicating an incorporation of clodronate into those surfaces. The Cl content of the other sample surfaces is due to incorporation of Cl from the PBS during the precipitation of BHA. The Cl 2p peak for the different surfaces is shown in Figure 1, from which it is clear that the binding energy is slightly higher for the Cl in the clodronate containing samples. This indicates a difference in binding state of the Cl due to a different atomic environment and supports the statement that clodronate is incorporated in the surfaces. The amount of Cl is low but shorter loading times promote more efficient loading with an optimum at 1 h of soaking [START_REF] Mcleod | XPS and bioactivity study of the bisphosphonate pamidronate adsorbed onto plasma sprayed hydroxyapatite coatings[END_REF]). Yet, since Cl only constitutes 13.3% of the clodronate molecule, the concentration of Cl at the surface is not a direct measure of the amount of incorporated clodronate, which in reality, is higher. The incorporation of clodronate was unaffected or even improved by the presence of cephalothin in the PBS during loading.

A continuous diffusion controlled release of cephalothin for 43 h was achieved for both the co-loaded samples and the samples loaded with cephalothin alone, see Figure 1. The release rate was found to be somewhat faster for the co-loaded samples during the first 5 hours of release and almost identical during the remaining release period.

The release rate of cephalothin was faster from the co-loaded samples during the first 5 h of release and approximately the same from both sample types for the remaining release period. The co-loaded samples also proved to release the highest amount of cephalothin. The results show that it is possible to load both antibiotics and bisphosphonates simultaneously to a BHA coating on a titanium substrate by a simple soaking procedure. The incorporation of the two different molecules seems to be unaffected or even improved by the presence of the other. The release rate of cephalothin is in agreement with previous studies where it was sufficient for bacteria inhibition in the vicinity of the implant (Brohede et al. 2009a).

The findings in this study show that it is possible to simultaneously incorporate antibiotics and bisphosphonates to implant coatings comprised of BHA by a simple soaking procedure. To improve the loading procedure, it is suggested to decrease the soaking time as this has been shown to be beneficial for incorporation of bisphosphonates [START_REF] Mcleod | XPS and bioactivity study of the bisphosphonate pamidronate adsorbed onto plasma sprayed hydroxyapatite coatings[END_REF]) and successful incorporation of antibiotics can be achieved already after 15 minutes (Brohede et al. 2009a). The proposed strategy with the dual biological effect is believed to decrease the number of postsurgical infections. With the proposed concept, the antibiotic will act during the first few days following surgery to inhibit bacteria adhesion on the implant surface whereas the bisphosphonate is expected to induce more dense bone formation, thus reducing the risk for immune depression at the interface between bone and implant associated with implant migration.

Conclusions

A successful incorporation of both the antibiotic cephalothin and the bisphosphonate clodronate to a BHA implant coating was achieved via a simple soaking procedure. No negative effects on the incorporation of each substance by the presence of the other was observed and a controlled release of cephalothin was obtained for 43 h, which is believed to prevent immediate adsorption of bacteria on the surface during the crucial first days following surgery. The study proves that the concept of co-loaded hydroxyapatite is a potential strategy to reduce the number of post-surgical infections related with biofilm formation and implant migration.

Figure captions

Tables

Fig 1 .

 1 Fig 1. The left panel displays release profiles of Cephalothin from the co-loaded samples (upper curve) and the samples loaded with Cephalothin alone (lower curve). The solid lines are incorporated as guides for the eye.

Table 1 .

 1 The number of samples used for each analysis

	Sample	XPS	UV/vis
	BHA	2	-
	BHA+Cephalothin	2	4
	BHA+Clodronate	2	-
	Co-loaded	2	4

Table 2 .

 2 Concentration table (at%) of the different elements in the surfaces of each type of sample.The results are displayed as the average concentration in two samples.

	Sample	Cl	P	Ca	O	C
	BHA	0.3	12.7	17.0	62.9	7.0
	BHA+Cephalothin	0.3	13.5	17.9	64.9	3.0
	BHA+Clodronate	0.8	13.5	17.9	64.9	3.0
	Co-loaded	0.9	13.6	18.0	63.2	4.3