Riccardo Petrolo

Aikaterini Roukounaki

Valeria Loscrí

Nathalie Mitton

John Soldatos

Connecting physical things to a SmartCity-OS

Keywords: Smart Cities, Internet of Things, Sensor Networks

A Smart City can be seen as a system in which different Internet of Things (IoT) solutions coexist and cooperate. According with this vision, the number of IoT deployments is, nowadays, in continuous expansion and it involves disparate scenarios, from street lighting, waste management, etc. However those initiatives are standalone, based on different protocols and standards, while the Smart City concept requires, on the other hand, integration and interoperability among all its stakeholders. To face this problem, in this paper we introduce the VITAL-OS architecture, that can monitor, visualize, and control all the operations of a city. Then, we present a practical use case of connecting a Sensor Network to this OS and we describe eCACHACA, a ranking mechanism that facilitates the discovery of services provided by each sensor. Performance has been evaluated via experimentation on the FIT IoT-LAB, and results demonstrate the effectiveness in the discovery of resources.

I. INTRODUCTION

The Internet of Things (IoT) is in continuous expansion as a result of the huge interest raised in both academia and industry. The number of devices deployed nowadays is already massive -thanks also to the cost reduction of smart technology -and it will reach 50 billion according to CISCO white paper [START_REF] Evans | The Internet of Things -How the Next Evolution of the Internet is Changing Everything[END_REF]. Thanks to those devices, the IoT will change all the aspects in our lives, e.g., work, health, transport, etc. [START_REF] Vermesan | Internet of Things Strategic Research Roadmap[END_REF]. Looking at the bigger picture, the Smart City concept represents a clear example of coexistence and cooperation between different IoT ecosystems; it can be seen, indeed, as a system that integrates all the IoT solutions [START_REF] Libelium | 50 Sensor Applications for a Smarter World[END_REF], especially the ones that are crucial for a city scenario. To confirm this momentum, in the last years, the Smart City concept gained significant interest behind which there is a real need to make cities ready to face new challenges (e.g., waste management, traffic congestion, etc.). In this context, the IoT has a primary role since it represents the main "supplier" in terms of data streams and information. According with this vision, the number of IoT solutions is, nowadays, rising exponentially involving different scenarios, from street lighting, to traffic intersections management, etc. Nevertheless, those initiatives are standalone, based on different protocols and standards, while the need of integration and interoperability among all the Smart City stakeholders is clear [START_REF] Petrolo | Towards a smart city based on cloud of things, a survey on the smart city vision and paradigms[END_REF].

To face this problem, the European FP7 VITAL 1 project, introduces an abstract virtualized layer that operates across multiple IoT architectures and platforms. This layer allows the development, deployment and operation of IoT applications for 1 http://vital-iot.eu Smart Cities, thereby turning VITAL into an operating system that can monitor, visualize, and control all the operations of a city [START_REF] Serrano | The future of smart cities: A practical case of connecting cities with vital-os[END_REF].

In this paper we describe the VITAL-OS architecture and how it is designed to deal within different Smart City scenarios. We present a practical use case of monitoring in a Smart Building context; we first illustrate a discovery and ranking mechanism for Sensor Networks (SN), then, we show how to connect those sensors to VITAL-OS and how to use them. In order to evaluate the performance of the proposed algorithm, we performed experimentation on the FIT IoT-LAB testbed 2 .

The paper is structured as follows: in Section II we introduce the VITAL-OS architecture. In Section III we describe, in detail, how to connect physical "things" to VITAL-OS by using a Raspberry Pi 2. The performance is discussed in Section IV, while Section V shows how to use the VITAL-OS. Section VI browses the most influential initiatives towards IoT integration and compares them with the proposed VITAL; Section VII concludes the paper.

II. VITAL-OS

The VITAL-OS architecture, as shown in Figure 1, is organized in three main layers, each of which is made of different modules. In the following, we present the features of the fundamental modules:

• IoT Platforms and Data Sources. At this layer, different data sources stand. In order to be virtualized and integrated into VITAL, those systems have to expose an implementation of the well-defined PPI (Platform Provider Interface). • Complex Event Processing (CEP). It enables the processing of data streams in order to identify patterns and/or infer events. • Orchestration. It has been designed to combine and manage multiple services from the above-listed modules, in order to deliver new added-value services. The combinations of the various services are defined by the users as workflows. • Development Tools. This module is available at the Smart City Applications and Tools layer. Here, we support the development, integration, deployment and operation of Smart City applications [START_REF] Roukounaki | Visual Development Environment for Semantically Interoperable Smart Cities Applications[END_REF].

III. CONNECT "THINGS" TO VITAL-OS: DESIGN AND ANALYSIS

We next describe a practical example of connecting a Sensor Network (SN) to the VITAL-OS with the objective to monitor a Smart Building environment. In order to make this connection possible, it is fundamental to use a gateway that communicates, from one side, with the IoT Data Adapter module of the VITAL-OS, and on the other, acts as a sink for the SN. Figure 2 shows an example of interaction between the aforementioned players, while detailed aspects are listed in the following subsections.

A. The Sensor Network

In order to sense the physical environment, we chose Maxfor nodes (Figure 3). As shown in Table I, a node embeds a MSP430 as CPU and CC2420 as radio frequency module, and it is integrated with temperature and light sensors.

The sensor nodes use Contiki-OS 3 and in particular we flashed their firmware with eCACHACA, an extended version of the ranking mechanism CACHACA (Confidentbased Adaptable Connected objects discovery to HArmonize smart City Applications) that we proposed in [START_REF] Petrolo | Confident-based Adaptable Connected objects discovery to HArmonize smart City Applications[END_REF]. By running this algorithm, sensor nodes can evaluate and classify their neighborhood and the available services (e.g., temperature, light, humidity, etc); each node indeed, advertises itself and the services that it can observe. CACHACA is based on a rule-based fuzzy inference system and the use of parameters such as the Received Signal Strength Indication (RSSI) and the Timestamp of the last frame received from a neighbor in order to introduce two functions -Physical (ϕ) and Service (ω) Confidence -used to rank the nodes and services. In this work, we just consider the Physical confidence, since we assume that nodes are offering only one service, i.e., temperature.

IoT Data Adapter

Gateway

Sensor Node eCACHACA borrows its main features from its "ancestor" -nodes describe their services according to the standardized IPSO [START_REF] Shelby | The IPSO Application Framework draft-ipso-app-framework-04[END_REF] format, etc. -. The novelty introduced regards the frame format; as shown in Figure 4, when using eCACHACA, a node advertises also the measured value. This mechanism allows the gateway to have all the information required to publish sensor data to VITAL-OS.

Listing 1: PPI -Get system metadata. 1 { 2 "@context": "http://vital-iot.eu/contexts/system. jsonld",

3

"id": "http://example.com/rpi2_ppi",

4

"type": "vital:VitalSystem",

5

"name": "RPi2 PPI Implementation",

6

"description": "VITAL compliant system to retrieve data coming from RPi2",

B. The PPI to VITAL-OS

In order to be part of the VITAL-OS, the gateway should provide and expose a PPI implementation. Through that implementation, it is possible to retrieve:

• Information about the system (e.g., its status).

• Information about the services exposed and how to access them.

• Information about the sensors managed and what they observe.

• Observations made by the sensors. According to VITAL specifications [START_REF] Soldatos | Specification and Implementation of Virtualized Unified Access Interfaces V2[END_REF], the PPI is defined as a set of RESTful web services. Listing 1 shows an example of a response to the GET SYSTEM METADATA primitive, in which the gateway exposes information about the network (e.g., its type and description), as well as a list of the available services and the managed sensors.

C. The gateway

The gateway represents the adapter between the VITAL-OS and the SN; it allows IoT Data Adapter to access data produced by the underlying SN and, at the same time, it acts as a sink for the sensors. In this work we used a Raspberry Pi 2 Model B (Figure 5), which has a quad-core ARM Cortex-A7 CPU, with 1 GB of RAM, and is equipped with 4 USB ports, 1 Ethernet port, and 40 GPIO pins. As operating system we adopted Raspbian4 , a free version of Debian optimized for the Raspberry Pi hardware. We chose this device because of its hardware capabilities and physical size.

The main tasks of the gateway are:

• Managing the sensor network.

• Formatting the information received from sensor nodes based on the VITAL ontology. • Storing information into a local database.

• Exposing a PPI implementation via the web.

IV. PERFORMANCE EVALUATION

To evaluate the performance of eCACHACA, we ran experiments on FIT (Future Internet of Things) IoT-LAB -a platform suitable for testing small wireless sensor devices over large scales. This choice allowed us to experiment with a realistic environment -. We used the following metrics (measured at the gateway): (I) the number of neighbors discovered, (II) the time required, and (III) the Physical confidence. In order to study the behavior of the network, we varied the number of nodes from 10 to 90.

Figure 6a shows the percentage of NEIGHBORS DISCOV-ERED by the gateway as a function of the NUMBER OF NODES. With 10 nodes deployed, the gateway discovers all of them; while when we increase the number of nodes, this performance downgrades but it is still acceptable, indeed 80% of nodes is discovered.

The time required to discover those nodes is represented in Figure 6b. When the network is not dense (10 nodes), the discovery process is fast; all the nodes are discovered in less then 15 seconds. However, even when increasing the number of nodes, the gateway can discover them in less than 70 seconds.

The last analysis (Figure 6c) provides information about the PHYSICAL CONFIDENCE. When 10 nodes are deployed, the physical aspects measured at the gateway are more close to "Excellent". While, when increasing the number of nodes, the Physical confidence is "Good". This is due to the interference that possibly occurs when the network is more dense.

V. USING VITAL-OS

VITAL-OS provides a development tool that integrates all VITAL-OS functionality and makes them accessible to smart city application developers. The fact that all functionality are exposed via virtualised interfaces (i.e. RESTful web services) facilitates the task of integrating them into a single tool.

The development tool is based on Node-RED 5 , an opensource tool for wiring the IoT that we have extended with nodes specific to the purposes and the needs of the VITAL-OS, as shown in Figure 7.

The development tool is used by developers that want to build and deploy smart city applications that involve multiple IoT platforms, architectures and business contexts. For that purpose, the tool enables them to access and compose the following VITAL-OS functionality:

• ICO and Service discovery.

• Complex Event Processing.

• Filtering.

• IoT system, ICO, data stream, security, configuration, SLA, and component management. • Business Process Management. The developers can even use the tool to directly access PPI primitive implementations, like the one we have provided for the SN.

Based on the above and in the context of our example, a developer can use the VITAL-OS development tool to build a website where users will be able to find out how each sensor has classified its neighbors.

VI. RELATED WORK

In the last decade, many middleware solutions have been proposed in literature with the objective to gather and integrate information from disparate data sources. In the following, we survey the most representative ones:

VII. CONCLUSIONS

There is nowadays, a real demand to make cities smarter in order to face challenges -i.e., waste management, traffic congestion, etc. -caused by the population growth. In this context, one key role is played by the Internet of Things and its data streams that can be converted into relevant information used to address the above issues. According with this vision, the number of IoT solutions is, nowadays, increasing, but on the other hand those initiatives are standalone and based on different protocols and standards. The VITAL-OS presented in this paper deals with this problematic, by introducing an abstract virtualized layer that operates across multiple IoT architectures and platforms. This layer represents the end-point thanks to which it is possible to monitor, visualize, and control all the operations of a city.

In order to validate the VITAL-OS architecture, we presented a practical example of monitoring in a Smart Building environment. We used a gateway that communicates, from one side, with the IoT Data Adapter of the VITAL-OS, and on the other, acts as a sink for the SN. The firmware of the nodes is flashed with eCACHACA, an algorithm that enables the discovery and the ranking of the neighbors and the available services. Performance has been evaluated via experimentation on the FIT IoT-LAB, and results demonstrate the effectiveness in the discovery of resources. Indeed, even when the network is highly dense, the gateway discovers 80% of the available nodes in less then 70 seconds.

In the future, we plan to improve the performance of our algorithm by introducing more sophisticated criteria for the evaluation of the neighborhood. At the same time, we also aim to analyze eCACHACA in more complex use cases in which nodes are mobile.

Fig. 1 :

 1 Fig. 1: The VITAL-OS architecture.

Fig. 2 :

 2 Fig. 2: Gateway -Example of interaction.

Fig. 3 :

 3 Fig. 3: Maxfor sensor node. (source http://www.maxfor.co.kr)

7 "services": [ 8 " 9 ], 10 "Fig. 4 :

 789104 Fig. 4: Frame format in eCACHACA.

Fig. 5 :

 5 Fig. 5: Raspberry Pi 2 -Model B. (source http://wikimedia.org)

  (a) Number of Nodes vs. Neighbors Discovered. (b) Neighbors Discovered -temporal trend. (c) Number of Nodes vs. Physical Confidence.

Fig. 6 :

 6 Fig. 6: eCACHACA performance.

Fig. 7 :

 7 Fig. 7: The VITAL-OS development tool.

TABLE I :

 I Sensor node specifications.

	P arameter	Specif ication
	CPU	MSP430
	RF Chip	Texas Instruments R CC2420
	Frequency Band	2.4 GHz -2.485 GHz
	Transfer Rate	250 Kbps
	RF Power	-25 dBm -0 dBm
	Range	120m [outdoor]; 20-30m [indoor]
	Sensor Temperature & Humidity	Sensirion R SHT11
	Sensor Light	600 nm peak

http://www.iot-lab.info

http://www.contiki-os.org

https://www.raspbian.org

http://nodered.org

https://xively.com

https://thingspeak.com

https://github.com/OpenIotOrg/openiot

ACKNOWLEDGMENTS

This work is partially supported by CPER Nord-Pas-de-Calais/FEDER DATA and by the European Community in the framework of the VITAL (Virtualized programmable InTerfAces for innovative cost-effective IoT depLoyments in smart cities) FP7 project under contract number FP7-SMARTCITIES-608662. The authors acknowledge help and contributions from all partners of the project.


Charline Sowa
email: sowac@bv.upmf-grenoble.fr

Phd

THE ROLE OF THE ARCHITECT AND HIS DECISION-MAKING POWER IN THE TRANSFORMATION PROCESS OF SHRINKING CITIES. LEARNING FROM TWO FRENCH EXPERIENCES

Keywords: France, shrinking cities, urban and architectural projects

d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The issues of urban transformations in shrinking cities: between urban policies and architectural and urban interventions.

At the beginning of the XXIth century, being interested in shrinking cities and their urban evolution participates in the improvement debates about the adaptability, the reversibility and the resilience of the city. How to continue to transform the city, growing or shrinking, when the global system is questioned after successive crisis (economic, social, political, environmental, etc.)? How urban planners and architects contribute?

The shrinkage phenomenon transforms the city spatially: lands, buildings and infrastructures, uses and landscapes. A diversity of abandoned spaces appears on the same territory: flats, buildings or plots, public spaces or urban infrastructures (Oswalt, 2005). Wastelands can be industrial, residential, commercial or still agricultural. They are in old (city centre) and suburban fabrics, in neighbourhood of blocks of flats, or in villages centres in rural spaces. It exists a new form of porosity in the city between the abandonment of spaces of big dimensions and spaces of small size, which are multiplying and integrated in the urban fabrics. It is particularly visible in Europe (Vigano, 2012). When the built, the plot and the public place are not occupied and maintained, their process of degradation tends to accelerate. The landscape is quickly transformed and the man has to Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015Prague, , pp. 1224Prague, -1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

"live" with these abandoned spaces (Anizon, 2010). The perception of empty can vary according to urban morphology. This distinction is perceptible between European and American cities (figure 1). The spatial impacts of this process accentuate or allow several urban issues (social, environmental, security, hygiene, etc.) to emerge. For example, abandoned spaces can become impassable, participating in the spatial fracture of the city and the isolation of individuals. Abandoned buildings often become place of squat and traffic; and their fragility can threaten nearby inhabitants and the housing (Oswalt, 2005). In front of these numerous urban issues, urban planners and architects have to act. This new urban condition is an opportunity to think the city and urban environment differently. However, the climate (difficult and uncertain) and the constraints, linked to demographic, political, socioeconomic and spatial changes, might complicate the urban intervention. The state of the urban environment, -the quality and the degradation of existing building, plots and grounds-, might affect the choice of orientation of the project and its costs. The instability and the uncertainty of the socioeconomic context have to be integrated, but they can impact on the implementation of the project and its sustainability. The capacity of action is often limited because of the lack of human and financial means of the project ownership (public, private or inhabitants) and the public authorities (ex.: depts, bankrupt). It restricts possibilities of the project management to intervene.

Practitioners have to confront with another difficulty: the capacity to think the project and its process. Current tools and methods were developed to answer urban growth and not to this specific phenomenon of shrinkage. Constraints and problems due to the shrinkage ask to adapt themselves and new tools are necessary (Oswald, n.d;Rienets, 2006;Ryan, 2012). For example, the big scale of the vacancy asks to requestion the land management and its tools especially when owners left or when public authorities are little means. It is an essential aspect for the transformation and the reorganisation of shrinking cities, but it is a real difficulty for local authorities.

Today, urban planners and architects with public stakeholders think together about the future of their cities and alternatives approaches to the classic system. The relation between various stakeholders seems essential to find solutions and to realise projects. This paper will focus on the role of the architect in the definition of new tools to adapt the shrinking cities and his influence on the decision-making power of local authorities. How does the architect participate into thinking of urban strategies ? How does he make the connection between urban policies, the urban strategy and the architectural intervention? Has he a particular influence? How does he lead the project? Three hypotheses will be explored: -The architect would highlight the architectural and urban qualities, the potentialities of the territory which was until now depreciated. Like for "urban design theory for the shrinking city ideal", he "will, by necessity, have to value and incorporate these attributes" (Ryan, 2012). He would allow to change the look of local stakeholders and inhabitants with his specific analysis and knowledge on the site; -In front of difficulties to lead the project, the architect would propose new forms of collaboration between local stakeholders and inhabitants to facilitate the realisation of project, in short and long term; -With his operational approach, the architect is capable to think about new ways and tools to manage lands, but also to test it in situ. This approach would help owners and project ownerships for the evolution of the city and to anticipate complex situation. Furthermore, it is an opportunity to develop new options for enriching documents and tools of urban planning. The architect give an essential support of the project ownership at the between the urban strategy and the urban and architectural interventions.

Case studies and method

To explore these questions, the context of France is interesting. The first remark is that it exists more and more studies and projects treating of issues of shrinkage, in urban and rural region. The second element is that there is a participation and an investment of public authorities in most cases. This choice is also due to my knowledge of the project practice in France, further to my training of architect and urban planner. This work has allowed myself to initiate a reflexion on the condition of the architect and the development of specific roles in front of current cyclical crisis in the profession. We will analyse two experiences in cities declared in shrinkage by European researchers and statistical datas when projects were started. We have the urban project, the Îlot-test Franche-Amitié at Saint-Etienne, and the study Habiter les centres-bourgs (Living in center-villages) proposed by the Parc Naturel Régional of Livradois-Forez. For the analysis, they exist research documents for understanding the process of shrinkage and to explain urban policies in this context. About the project, the analysis made with documents of project presentation (websites, brochures, etc.) and with interviews of architects, teams of project management and local stakeholders when it was possible. These discussions helped to have information, which is not accessible or visible in the communication of initiatives, by the architect or by the municipality. It does not exist currently scientific documents about projects presented here.

Firstly we shall see the current positioning of the architect in reflections on the shrinkage in the international research and in the practice of the project. Then, we shall observe the role of the architect in the passage between the urban strategy and the architectural intervention. We will try to understand why he takes a more and more important place in the assistance for the project ownership and the community project management. This evolution is particular in the case of shrinking cities. To finish, we will explore this question in the specific case of France.

2. The architect, stakeholder involved in the reflection about the urban shrinkage since the 2000s.

A noted involvement in the international research.

Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015Prague, , pp. 1224Prague, -1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

Works of research and scientific debates about the phenomenon shrinkage are linked in general to the fields of geography, sociology, urban planning or political sciences. Many studies interpret mechanisms of shrinkage, but they analyse urban politics too (Großmann and al., 2013;Cunningham-Sabot and al., 2014) like: the governance, the economic development, the management of urban infrastructures (water network, public road network, etc.) or programs of housing and urban renewal.

Architecture, as urban design, is little visible in the international researches until now, in proposed topics in symposium and research networks. The architect can give however a specific vision of space. It is an element on which the architect is presently called to intervene (Corboz et al., 2009). The relation is different from the one of the geographer, be it in methods of analysis, tools or the way of intervening. Even if the architect is trained to intervene in contexts of growth, he is also in capacity to analyse the urban shrinkage. He leans on concrete data, in particular from his field experiences, for formulating the project and imagining the future. Another track of the research is the capacity to reflect on the transformation of shrinking cities through the process of project and its analysis. To conclude, the architect is able to bring complementary knowledge in definitions, in descriptions of cases studies, in the way to intervene at the scale of plot or block, or in prospective approaches.

One of the first to take an interest in urban and architectural aspects was the research team of the architect Philipp Oswalt, in the framework of the German program Shrinking City. One part of their work was to collect experiences in the world, which dealt with the management of the urban shrinkage, as well in term of urban policies and urban actions by the architects, as initiatives of inhabitants. All the work was mediatized between 2004 and 2006. Further to the study, a web site, a set of books and an exhibition was created. This exhibition was presented in Germany, in Europe and in the United States. A striking event was its installation at the 10th International Biennial of Architecture at Venice in 2006. In the fame of this event, numerous practitioners (architects, landscape-architects, urban designers, urban planners, etc.) were able to discover this work and became aware of the urban phenomenon. Today, the interest for this topic among young researchers in architecture is also to underline and is beginning to distinguish. This assessment is perceptible with PhD students of the network SCRIN 1 , and during training schools organized in 2011, 2012 and 2013 by the European program EU-COST action: TU0803 Cities Regrowing Smaller (Wiechmann, 2009) and the University of Dortmund (Germany). For the last workshop in 2013 entitled Scenarios 2030 -Possible Intendeds of Shrinking Cities in Europe, there were 5 architects and 1 landscape-architect among 14 invited students.

In the architectural research in France, the shrinkage in all dimensions still little is object of research, even if some interventions and cases of study are submitted to the debate in specialized French periodicals such as Ecologik, D'A, Archiscopie, AMC, Les cahiers thématiques : architecture, histoire, conception, or Urbanisme and Traits urbains. The case of Detroit is become one of the inescapable grounds for these five last years. Research programs, studies and thesis are developing in different laboratories of architecture schools (ex. : Nantes, Versailles, Grenoble). Works are about questions of ambiances, inhabitant initiatives, architectural projects and masterplans or the urban agriculture and the landscape evolution. Even if this context is interesting, Detroit should not to become the support for generalities on the debate and the research on the urban shrinkage. The multiplicity and the diversity of spaces in shrinkage ask to the architect to adapt in every situation.

1 SCRIN : Shrinking Cities Research International Network Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015Prague, , pp. 1224Prague, -1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

A fertile ground for experimental reflections about the architectural and urban project.

For more than ten years, at the international scale, shrinking cities has become new playgrounds for architects, urban planners, artists or inhabitants for exploring and testing alternative urban experiments. It exists a diversity of projects at various scales and we can see that in some specific books as: Shrinking cities 1,International research (2005),Shrinking cities 2,Interventions (2006), The unreal estate guide to Detroit (2012) and Urban catalyst: the power of temporary use (2013). Some projects and calls of ideas are open to debate.

One can note that shrinking cities became a veritable fertile ground for numerous architectural projects since the last crisis of 2008. The highlighting of more and more cities in shrinkage 2 and the images of empty plots indeed had an effect of electric shock in the profession. This event also accelerated an already present process where "many young architects, themselves affected by the crisis in the building sector, have taken on this new role and turned their misery into a professional challenge, exploiting the possibilities of low rents and empty spaces to set up small enterprises or cultural initiatives" (Rienets, 2006). Shrinking cities, like all territories in crisis, the post-disaster reconstruction ask the architect to "include the ability to do more with less"(Aquilino, 2011) and to define the construction neither "as the goal of architectural/urban planning action" but as "the starting point" (oswalt, n.d.). All kind of vacant spaces become the base of the intervention before favouring the artificialisation of new grounds and are questioned: do you need to preserve, to transform, to deconstruct or to recycle? Which reflection to have on plot pattern? etc. This interest is perceptible through two examples. There is a multiplication of student works in architecture and urban design. The researcher Brent Ryan organized with the MIT different workshops on Buffalo in 2010 and Baltimore in 2011 and 2013. In France, more and more students work for their diploma in architecture about the urban shrinkage. They choose study grounds in France (Thiers), in Germany (Leipzig, Essen), in Japan or in the United States (Detroit, Saint-Louis). By the innovative dimension of propositions, some of the projects are published or awarded. This year, the topic of the European workshop Oikodomos 3 is about "contemporary living patterns: growth / shrinkage", with cases of Berlin and Cottbus (Germany). This trend is also noted for the Europan competition which is recognized by the profession of architect at the international scale. For the two last sessions, Europan 12 (2013) and Europan 13 (2015), the topic is "the adaptable city: inserting the urban rhythms" and it is the occasion to highlight potentials of territories in favour of the urban innovation. The concept of shrinking city was presented (Rebois, 2011) in the edition 2013, and there are some selected cities are considered in shrinkage: Vichy and Moulins (France); Wittenberge, Bitterfeld-Wolfen and Gera (Allemagne); or Seraing (Belgique). All experiences around the world contribute to reflections and debates on the practice of project in territories in crisis and the research in architecture. Some aspects and questions are recurring and we can note for example: the evolution of uses of vacant lands; the reduction of costs to realise the project at different levels (participation of inhabitants; the recycling of materials; the construction site, etc.); the place of architect in the project process.

An opportunity to rethink our urban model?

2 In the media as in the scientific literature, like Leipzig in Germany or in United States (Detroit, Pittsburgh, Buffalo, Cleveland, etc.). 3 Oikodomos is a virtual campus to promote the study of dwelling in contemporary Europe. Different european schools and universities of architecture, urban planning and urban design work together. website : http://www.oikodomos.org Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015, pp. 1224-1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

The urban condition of shrinking cities re-questions our current urban models (Mateo, 2011) and the approach of development by growth. The evolution of the urban form, of the uses and of the landscape is in the heart of debates. Besides ecological issues and the ambition to reduce the human impact on the territory, to think about these questions in context of shrinkage is an opportunity: everything can be newly define. Some cities use it to think the city more "green" from the demolition of the unused and unhealthy built, and the renaturation of spaces, but these approaches are sometimes distorted for purposes of "urban marketing" by municipalities (Baron and al., 2010).

In more theoretical approaches in specific contexts, the architect contributes at the exploration of new urban models in proposing radical urban strategies. The team of architects, composed of Rem Koohlaas, Oswald Mathias Ungers, Peter Riemann, Hans Kollhoff and Arthur Ovaska, were the first ones to explore new urban models with the case of Berlin, in the 1970s. For them, the demographic decline is an opportunity to identify vacant spaces and to determine spaces which have to be protected and those to be renatured for forming a cityarchipelago. This theoretical project was re-communicated in 2013 with the research work of Florian Hertweck and Sébastien Marot in the book The City in the City. Berlin: A Green Archipelago. It still is current. Since, more and more cities experiment new forms of urban strategies and urban policies for engaging the mutation of the city. They can be quoted in different plans and programs. In Germany, the city of Halle is exploring the compact city (De Gasperin, 2009;Roth, 2011). They are also the tool International Architecture Exhibition4 which was used twice by authorities to think the transformation of cities and regions in shrinkage. The first experience was the IBA Emscher Park during 1990s in the Ruhr region. An important part of work was the improvement of the environmental frame and the renaturation of brownfields with the creation of cultural and sports facilities. Between 2002 and 2010, the urban shrinkage was at the heart of the IBA Urban Redevelopment Saxony-Anhalt in East Germany5 . Selected cities served as experimental territories to find alternatives in their re-energization and re-organization. Dessau was the exploration territory to try the concept of urban archipelago through the project Urban Cores -Landscape Zones (Wiechmann et al., 2013). In the United States, the rightsizing of the city is more often experimented and especially for "greening" vacant spaces (Schwarz, 2012). Perspective projects like Youngtstown 20106 and the Detroit Future City Strategic Framework Plan7 are two characteristic examples. In Japan, the project of Fiber City 20508 for the metropolis of Tokyo proposes a different approach of American cities in focusing on the urban development and the concentration of inhabitants on urban fibers as existing green armatures and railways.

On the short term, these examples offer various ways to adapt the city of human (demography) and urban realities (vacancy). It is an opportunity to think about to have a better urban management, to reduce artificial spaces and to renature grounds, or still to preserve the proximity and the social links between inhabitants which are scattered on the territory. In long-term, it might be a veritable impact of way of life. Nevertheless, these urban strategies still have not much impact in the documents of town planning (Ryan, 2012), or in the architectural and urban projects lead by the local authorities.

3. From urban strategy to urban intervention: a role of assistance for the architect with different stakeholders more and more marked in shrinking cities.

Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015, pp. 1224-1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

An evolution of the public commission which re-questions the role of the architect in projects.

Even if the shrinkage are being accepted as a "decisive factor of the evolution to come from territories, societies and activities" by local stakeholders (Baron and al., 2010), alternative urban strategies which integrates this situation (as seen previously -part 2.3.) still are exceptional. In some cities in Europe, the architect until now answered requests which integrated in urban policies for revitalizing the territory, transforming the image of the city and attracting new populations and new investors (Baron and al., 2010;Cunningham-Sabot, Fol, 2010). The urban strategy was to recapture important brownfields and developed flagship projects (urban projects and public buildings), often linked with the culture (Grésillon, 2011) and with the invitation of a "starchitect". The Guggenheim museum of Bilbao by Frank Gehry was the first example. The "choice of architectural and design about a cultural policy of international scale" and " a new communication of the project on the outside scene"(Nicolas, 2014) made a deep impression on people and the concept was took again. Thereafter, were built: "la Cité du Design" (agency LIN with Finn Geipel) at Saint-Etienne; the Louvre-Lens museum (SANAA); the University Library of Cottbus (Herzog & De Meuron); the Riverside Museum of Glasgow and the Phaeno Science Center of Wolfsburg by Zaha Hadid, etc. In parallel of these initiatives, there are often projects of urban renewal on the existing urban fabric, treating problems of the housing and the management properties and buildings. Architects are generally in front of commissions asking to maintain, to demolish, to recycle building or to product new constructions.

Since the beginning of 2000s, other projects have been emerging outside these important and mediatised urban and architectural projects. With more knowledge of the process and their capacities, local stakeholders searched new urban strategies and alternatives to transform the urban environment for maintaining inhabitants and improving their wellbeing (Baron et al., 2010). It allows architects to have more liberties and to experiment new ways of thinking the process of project. The architect and the team of project management are important stakeholders on the territory and its transformation. The model of urban strategy marked by cultural policies has begun to be criticized as these architectural flagship projects which can be characterised of "machines célibataires" (single machine). Olivier Mongin took over this concept of Marcel Duchamps illustrating architectural objects which are not in relation with its environment (Mongin, 2005). There is a "standardisation" of architectural production. In this continuity of these argument, Jean-Louis Violeau remind that "to design a project (of architecture) means to open a space, and no to try systematically to fill it as try to make it these single buildings" (Violeau, 2013, p.19). In shrinking cities, the analysis shows us that flagship projects are currently disconnected of the obsolete urban fabric and they are not accessible to all the population. It is "disembodied, on the scale of "consciousness" collective, by the construction of a "city branding" (Baron et al., 2010, p. 293).

Actual trend in shrinking cities: more and more architects with a role of assistance.

The current trend in Europe is an evolution of the role of the architect towards the council and the mediation "in interaction with a multitude of partners (State, local authorities, society of planning and developers)" (Bonetti, 2004). We can note this evolution especially in shrinking cities like in Germany or in France. For example, public project-ownerships (ex.: municipalities, regional structures) have little ways to act on their territories. Consequently they will lauch calls for ideas to have several possibilities to act. In France, it is very common in rural regions. In this situation, the architect as project manager might become project ownership supporter. The result is not the Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015, pp. 1224-1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015. finalised project but the development of tools for accompanying public authorities and inhabitants in the definition of new urban strategies and urban projects. In this continuity, we have the international competition, Future Ground9 , organized by the Van Alen Institute in collaboration with the municipality of the New Orleans. Three multidisciplinary teams were invited to think about the transformation of landscapes and the reuse vacant lands through the experimentation of flexible designs and policy strategies. It is more frequent to see the architect becoming "project manager supporter". His assistance is more and more asking from a specific project-ownerships, particularly present in shrinking cities : the community groups composed of inhabitants, non profit organization or association, etc. In United State, it is very visible where the State and local authorities are not any more invested (Detroit, Buffalo, Philadelphia, etc.). These community groups are the project-ownerships but also the project manager. They are themselves who think and realise projects of urban renewal at the scale of their neighbourhood. At Detroit, we have the example of the transformation of Old Redford district by the non-profit organisation Motor City Blight Busters (MCBB) and the One Mile Project in the New Center district.

With constraints of shrinking cities, architects envisage also in the process or project to give a part of project of inhabitants and became "project manager supporter". One of most significant project is "Urban cores, Landscape zone" at Dessau (Germany). The pluridisciplinary team of project management defined important axes of the urban strategy. The choice was to offer inhabitants (citizen, family, company, group of young people, etc.) the possibility of defining, producing, managing and controlling these spaces freely. The objective was to make inhabitants aware of their responsibilities in front of their environment, and also to reduce cost of project on short and long term, to maintain public spaces (Br ckner, Stein, 2007;Wiechmann and al., 2013).

We can analyse that the architect and the team of project management have an important role to assist these stakeholders, public as private, to defend this new position and to succeed the urban intervention. It is important to take into account (Ryan, 2012). Exchanges and interactions allow to feed into the knowledge on the common territory and to bring new looks on its future. They accompany also stakeholders and inhabitants in the re-appropriation of their space by thinking about new ways of life, with proposals, which are short-term and long-term, ephemeral, as lasting.

The study of the French case: example of two experimental projects.

The phenomenon of shrinkage in urban context like rural: two potential sources of reflection.

The research work of Emmanuèle Cunningham-Sabot, Sylvie Fol, Hélène Roth, Daniel Florentin and Manuel Wolff in France introduce us with a diversity of shrinking cities. There are more particularly old industrial cities, small cities and villages in rural regions (Cunningham-Sabot and Fol, 2009;Wolff and al., 2013). Even if the question of the shrinkage is not directly highlighted in political speeches, there is generally a good knowledge of spatial realities by practitioners (architect and urban planner) and local stakeholders. This multiplicity of contexts offers architects and urban planners the possibility to explore all dimensions of shrinkage. Today, these territories know an increasing interest by these professions, be it for brownfields, small vacant plots in city center or the reconquest of public spaces. We were able to see it previously with works of students, the Europan competition or the multiplication of call for ideas. Saint-Etienne is one of the cities which explores most of Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015Prague, , pp. 1224Prague, -1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015. possibilities, between flagship projects (building and urban project) on brownfield and alternatives projects on the existing urban fabric. The public space was also a ground of experimental initiatives in Saint-Etienne. We have for example: the transformation of the site of the cardboard industry in temporary public spaces (since 2010); the competition «Défrichez-là» (2011) to occupied a vacant plot; a competition for urban furniture for the last biennale in 2015. Concerning policies of the urban renewal, the shrinkage is not always affirmed. We have maybe an exception with the international consultation organized to Saint-Dizier for the transformation and the extension of its historic center (Scoffier, 2011). But there is a research to have solution concerning the unhealthy and vacant habitat in shrinking cities. Since 2003, these cities are very often helped by a financial support of the State to lead their projects, through the Agence Nationale pour la Rénovation Urbaine10 (ANRU) in charge of the Programme National pour la Rénovation Urbaine (PNRU). Among 600 neighbourhoods which received of the PNRU, about fifty cases are in shrinking regions (Kacza et al., 2013). In 2014, the State decided to help villages centres in escheat in rural regions, further to a demographical decline or a weakening of their functions of centrality, sometimes accompanied by the development of peripheral suburban zones11 . 300 villages centres was eligible the call of manifestation of interest "Centres-bourgs", but only 50 were chosen to try this an experimental tool.

The French context is very regulated. How to lead the project when this framework can force or limit the action between specific constraints of the shrinkage and the regulatory system? Both two examples presented then, the urban project Îlot-test Franche-Amitié and the study Habiter les centres-bourgs, we will observe how the project try to surpass these constraints. We will analyse : the role and the place of architect in the process of project and between different stakeholders; the spirit of initiative of architect in the arranging of alternatives solutions for allowing the realisation of project; the awareness of different components of urban fabric (plot, build, uses) to act an urban renewal of quality.

Assuming the dedensification: Saint-Etienne and the project Îlot-test Franche-Amitié

Saint-Etienne lost between 1968 and 2010 around 23 % of its population. The departure of the activities and the inhabitants for the first urban rings and for other regions engendered a vacancy in the city centre and an advanced degradation of the urban fabric. From 1990s, the municipality became aware of its state and have been trying to revitalize (Miot, 2009). Architectural and urban projects punctuate from now on the landscape as the "Cité du Design" or the requalification of the site of the Manufacture-Plaine Achille entrusted to Alexandre Chemetoff's team. In parallel, the municipality searched also other approaches for its urban renewal with the priority objective: the improvement of the environment built in the unhealthy neighbourhood. It began an experimental initiative which aimed to acquire plots and building for acting on the urban fabric and for reducing the vacancy by the creation of quality public places12 . The project of the Square Hauptmann designed by the local agency YES Architectes (now, A-MAS) was the first experimentation (2000)(2001)(2002) of this kind. In the continuity, it is interesting to look more specifically at the project Îlot-test Franche Amitié, because the approach of plots repurchase was applied on the scale of a block. Realised between 2006 and 2014 by the team of project management composed of Eric Clavier (architect), François Chomienne (landscape-architect) and Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015, pp. 1224-1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015. the BET 13 Gépral, the site is integrated into the perimeter ANRU program in the Tarentaize-Beaubrun-Séverine neighbourhood. This block was chosen because it was the most degraded of the district and had to serve as model for a process of larger-scale urban renewal14 . The objective of the tender was to de-densify of the heart of the block, to regenerate obsolete buildings and to create public and private places with collective management for maintaining the local population. One of the major difficulties was to act on the block. The population living in the neighbourhood is essentially poor and owners had few financial means for acting. The municipality had no stranglehold (land) on the site. The choice by local authorities was to acquire plots to intervene and to lead a global action. Before the project begun, the SEDL 15 started to acquire some plots and buildings by anticipation on the future urban renewal. But to continue this process, the solution was to do a "déclaration d'utilité public" (DUP -declaration of public utilities) by the creation of a road and 20 garages. This axis had to allow the deconstruction of unhealthy buildings and the connection between the site and the rest of the district. The Etablissement Public Foncier de l'Ouest Rhône-Alpes (EPORA) helped the team of project ownership ( SEDL and the municipality of Saint-Etienne) to acquire and manage all plots with the obligation to restore some plots to the owners after the arrangements of private open spaces (gardens). It was a complicated assembly work in order to make the project feasible. The project proposed an intervention in the inside of the block, without affecting directly the building situated at the outside. The team of project management had a real role of assistance with the project ownership composed with local authorities to succeed in an urban project of quality. They were stakeholders of decisions and took part in the operational arrangement of project. They worked and negotiated more than 3 years with the team of project ownership to adapt the project; on one hand to answer budgets and regulatory requirements, and on the other hand to allow the production of a quality public place for transforming the road into pedestrian alley. In the work of the project definition, the qualities of the existing (plot pattern, situation of buildings) helped to define buildings to preserve or to deconstruct, as well as spaces opened to clear (Horticulture et Paysage, 2012).

Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015Prague, , pp. 1224Prague, -1238;; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015. The architect knew how to highlight his capacity to have a global vision on the project, allowing him to be: the interface between the complex project ownership and the spatial realities; an important stakeholder throughout the project : from the definition of the operational frame of the constructive details, with the period of construction site. The thinking of all steps of project process allowed to limit expenses and to remain in the projected budget. Until now, reflections and projects on the territory answered approaches one by one, without a long-term vision, according to needs and opportunities (Bernard et al., 2014). This approach was questioned since and abandoned spaces in villages centres are beginning to be envisaged as real of equipped and serviced land-reserves. The compact form of the urban fabric also tends to facilitate exchanges between individuals. To re-adapt villages centres would so offer an alternative to the urban sprawl. With this analysis, the PNR of Livradois-Forez went into an invitation to tender in 2011 for a study about the question of the living in village centre, with the financial support of the DATAR. 6 sites of study (Cunlhat, Châteldon, Courpière, La Monnerie-le-Montel, Saint-Germainl'Herm, Saint-Dier-d'Auvergne) served as support of reflection which were divided between three teams of project management, mainly consisted of architects, and two school of architecture. Through this study, one of questions was the land management by municipalities and inhabitants.

The architect had to propose one or several adapted solutions. The analysis presented that very often, municipalities had no idea of the state of land, little information on plot and its uses. Even if it existed, it was not always updated.

The work of the Collectif ETC on municipalities of Cunlhat and Châteldon was interesting for this dimension. To develop new tools, the team was inspired by tools of agricultural-land management conceived by the French association Terre de liens. It established a protocol of actions to collect information and to develop an operating tool of land management. It was to allow then to define actions on plots which would be adjusted to needs and real practices of space. The objective was to engage a dynamics of the land observation and to integrate the inhabitants into this work. After the mass of data, the team proposed different options about the way to manage plots and especially to execute a land assembly. The first one is to connect inhabitants and to raise awareness among them.

The second one is in the longer term, to assist the municipality to take the role of mediator between owners for allowing the emergence of projects with a bigger scale.

Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences.

in AESOP -Definite space-fuzzy responsability, Prague, 2015, pp. 1224-1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015. The architect had an important role in this reflection. Many recommendations were given on the improvement of the offer of the housing and the image of villages and the attractiveness. It was proposed innovative and alternative tools for helping municipalities and inhabitants.

Another dimension is interesting to present: the place of the communication in the appropriation process of the study by differents stakeholders (inhabitants like municipalities and the PNR Livradois-Forez). For Cunlhat, Châteldon, Courpière and La Monnerie-le-Montel, there was an important place for a blog which became a veritable space of communication and exchange.

The objective was to test and to retranscribe transposable methods of work in other territories which know the same difficulties that the villages centres of the PNR. But today, there are not continuity with different teams on the territory or applications. But this initiative inspired other territories, in the PNR Livradois-Forez (Ambert, Chabreloche, Olliergues) or in France.

Conclusion: which lessons to learn of these French experiences?

Through these examples, we saw that through the process of project, it is looked for to exceed the constraints linked with the shrinkage and in regulations of town planning. They try to propose adapted solutions for the transformation of the urban fabric. Architects and the team of project management was the interface between temporal and spatial scales for local actors and inhabitants.

Whether it is with the work of demolition and recycling in Saint-Etienne or with the reflection on the land assembly for Châteldon, the architects managed to offer another image of these spaces which were pending. They revalue as well the qualities of the plot pattern as the built and they propose a new quality of the housing environment in reply with the new demands.

In both cases, the relation between the various stakeholders was essential for a good understanding of the commission and proposals. In these collaborations, we were able to note some trends. For Saint-Etienne, the project management did the interface with the project ownership in the redefining of the commission. The architect brought his expertise and was a stakeholder in negotiations between the double project ownership and the owners. Secondly, he had a role of advisor to the architects acting on the built that to owners who wished to invest on the project in asking advices on the arrangement of private gardens. In the Livradois-Forez, we were able to see that different local stakeholders were requested at various stages of the project process. The architects valued their capacity to be porter of knowledge on their territory. They then found solutions to help municipalities to manage the land, and in particular with the investment of the inhabitants. This method aimed to allow for the inhabitants to reinvest their village and for the public stakeholders to have a better knowledge of them inhabitants and of the urban environment.

In the Livradois-Forez, the commission was complex in front of land problems. The collective ETC. gave tools to help municipalities to manage the urban fabric (land, built, uses) and to adapt it to the demand. Among other reflections on sites of the call for ideas, the proposition for the village centre of Monnerie-le-Montel proposed keys for reading of issues and a prospective vision to allow

Figure 1 .

 1 Figure 1. The different perceptions of the vacancy. Detroit (Chalmers district), Liverpool (Anfield district) and Saint-Etienne (Tarentaize-Beaubrun-Severin district) between 2013 and 2014. Source : google street view / google.maps.com

Figure 2 .

 2 Figure 2. Explicative maps of the project Îlot-test Franche-Amitié. 1: Two project ownership / 2: Influence of the action of the project manager / 3: Orientations of project / 4: Current state of block Source : Charline Sowa, 2014

Figure 3 :

 3 Figure 3: Point of view in the interior of block. Source : Charline Sowa, 2014

  Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015, pp. 1224-1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

Figure 4 .

 4 Figure 4. Situation of cities participating to the study in the PNR of Livradois-Forez.Source: PNR Livradois-Forez, 2014.

Figure 5 .

 5 Figure 5. Tools of of analysis on Châteldon. Source: Collectif ETC.

Figure 6 .

 6 Figure 6. Theoretical reflections for Châteldon to test different possibilities for the land assembly and the land management by public authorities and inhabitants. Source: Collectif ETC.

  Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability,Prague, 2015Prague, , pp. 1224Prague, -1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

Translation of German Internationale Bauausstellung, more famous with the acronym IBA.

The topic was "less is future". 19 cities participated.

wedsite: http://www.cityofyoungstownoh.com/about_youngstown/youngstown_2010/

website : http://detroitfuturecity.com

website: http://www.fibercity2050.net

website: https://vanalen.org/projects/future-ground/#about

the website : http://www.anru.fr/

Presentation of the project on the link : http://www.territoires.gouv.fr/revitaliser-les-centres-bourgs-un-enjeu-majeurpour-l-egalite-des-territoires

 12 Remarks collected with Stéphanie David, architect to the agency A-MAS (20/03/2014) and with Lauranne Ponsonnet, director of the Mission Project Urbain of the municipality of Saint-Etienne (03/06/2014).

BET is the acronym for "bureau d'études techniques". It can be translated in english by "engineering department".

Remarks collected with Anne Lebeau and Jean-Paul Chartron, assignment managers of the housing, Municipality of Saint-Etienne(02/07/2014)

in AESOP -Definite space-fuzzy responsability, Prague, 2015Prague, , pp. 1224Prague, -1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015. to the municipality to organize into a hierarchy their actions according to their capacities in time. A good relation between different levels of stakeholders allows to experiment new tools of project. For Saint-Etienne, they succeed to manage the project by exploring all the regulatory possibilities and by facing the multiplicity of owners. It would be interesting to develop this analysis on other examples in France, in Europe or in United-States. For the American case, it is possible to see very often approaches in pro bono to help community groups to realise their project, from the program to the construction, in coproduction or as project management supporter. To conclude, projects were possible with invested local stakeholders and help of public authorities with specific funds by the ANRU or the DATAR. The position of assistance was integrated in the process of project and it is not annexe. While in the case of the commission of the PNR of Livradois-Forez, proposals might be a potential impact in the decision-making power of the municipality to develop a territorial strategy; in the case of Saint-Etienne, it is to nuance. Even the project was realised and it is a interesting urban project at different levels, the temporality of the process and this expansive cost reduced the ambition to continue this approach at the scale of neighbourhood.

Sowa Charline -The role of the architect and his decision-making power in the transformation process of shrinking cities. learning from two french experiences. in AESOP -Definite space-fuzzy responsability, Prague, 2015Prague, , pp. 1224Prague, -1238; actes du colloque international 29th Annual AESOP 2015 Congress, AESOP-FAČVUT-STU, 13-16/07/2015.

• Anizon, E., 2010. Detroit, la ville qui rétrécit. Télérama.

• Baron, M., Cunningham-Sabot, E., Grasland, C., Rivière, D., Van Hamme, G., 2010


H Boutayeb
email: halim.boutayeb@univ-rennes1.fr

K Mahdjoubi

A C Tarot

ANTENNA INSIDE PBG AND FABRY-PEROT CAVITIES

Photonic crystals are used quite frequently to enhance the antenna gain. To understand the origin of this enhancement we have assimilated the PBG-Antenna structure to a Fabry-Perot cavity, where the source of the incident plane wave is placed inside. The PBG reflecting surfaces are composed of periodic metallic wires. The Fabry-Perot interferometer is usually studied with an excitation source placed outside the cavity. Here we had to extract new formulas for the case of the sources positioned inside the cavity. These simple formulas are found to be very helpful and very precise compared to the exact FDTD simulation. In the second part of the paper a simple model of the antenna is proposed to take into account the interactions between the cavity waves and the antenna.

INTRODUCTION

Placing an antenna inside a PBG structure can allow to obtain an important enhancement of the antenna gain [START_REF] Telmulkuran | Resonant cavity enhanced detectors embedded in photonic crystal[END_REF][START_REF] Biswas | Exceptionally directional sources with Photonic Band-Gap crystals[END_REF][START_REF] Enoch | Study of photonic crystal based directive antennas[END_REF][START_REF] Thevenot | Directive Photonic Band-Gap Antennas[END_REF], but the origin of this improvement is not clearly explained. To better understand the mechanism that creates the gain enhancement, we have revisited the fundamentals of Fabry-Perot cavity by generating the incident wave inside the cavity and not outside of it, as it's usually done.

In the first part of this communication we will consider an ideal cavity with infinite length in one hand and no interaction (absorption and reflection) between the antenna and the cavity waves in other hand. In the second part, we will propose a simple model for the antenna, used in FDTD method, to take into account some elementary interactions between the cavity and the antenna. Research works are going on to improve the source antenna model and to treat the practical case of finite length PBG materials.

I-IDEAL STRUCTURE

Let us consider a TM plane wave propagating inside the cavity in both left and right sides (Figure 1). The cavity is, in many cases, made of two infinitely long reflecting surfaces composed of PBG materials [START_REF] Telmulkuran | Resonant cavity enhanced detectors embedded in photonic crystal[END_REF][START_REF] Smith | Experimental and theoretical results for a twodimensional metal Photonic Band-Gap cavity[END_REF][START_REF] Ozbay | Defect structures in metallic photonic crystals[END_REF]. Here, there are composed of single layers of metallic PBG (periodic infinitely long wires) (Figure 1a).

The periodic surfaces are characterized by the diameter "a" of the wires and the transversal period "P t ". Figure 2 shows the typical reflection and transmission coefficients (r, t) of these periodic surfaces with a/P t = 0.5%. P t is maintained smaller than λ to avoid the grating lobes. (  ) 1b), we obtain the transmission coefficient "T" (equation (1)) of "Antenna-Cavity" structure. The magnitude of this coefficient represents in fact the "gain Enhancement G = |T|", because it corresponds to the output wave E t created by the cavity, relative to the incident wave E inc due to the isolated source/antenna (i.e. without cavity).

inc 1 D 2 2 D 4 jk 2 2 1 1 E e r r t + - inc E inc E r1, t1 r 2, t2 (b)
( )

( )( )         + + = = ∑ ∞ = + - - - - - 1 n D D 1 n 2 jk 1 n 1 n 2 D 2 jk 1 D 2 jk 1 inc t 2 1 1 2 e r r e r 1 e 1 t E E T ; G= |T| (1)
(r1,t1) and (r2,t2) are the reflection and transmission coefficients of the cavity walls (periodic surfaces ) (see top of Figure 1b). When the two periodic surfaces are identical, the "T" expression is simplified to the relation :

D 2 jk re 1 t T - - = ; G = |T|, ( 2 )
This formula is valid as far as the distance D is larger than P t [START_REF] Boutayeb | Problème de caractérisation des matériaux à Bande Interdite Photonique de taille finie[END_REF].

In Figure 3 the analytical formula ( 2) is compared to the exact gain value obtained by a FDTD simulation. One can see that there is a perfect agreement between the results.

It is interesting to note that the maximum and minimum of G are given respectively by the envelop curves r 1 t and r 1 t + , as it is shown in Figure 4. Note that the gain value can theoretically become very large. Figure 6 illustrates the results obtained for a second example of periodic surface (D=41.7mm, P t =0.9mm, a=0.36mm) for which the maximum gain can reach 80. In practice, this maximum can be unreachable because of the interactions between cavity waves and the non ideal source (antenna). In section II of this communication a rudimentary source model is proposed to obtain a better approximation for the gain enhancement. We would like to mention at this point that this gain improvement is not associated to any "directivity improvement", because actually the incident and transmitted waves E inc and E t are both plane waves, having already the maximum directivity .

Furthermore, the pick frequency can be obtained by applying resonance condition ϕ r = 2kD-2nπ, where k=2πf/c; n=0, 1, 2, …and ϕ r is the phase of "r" (cf. Figure 5).

II-A SIMPLE MODEL OF THE ANTENNA

A real antenna interacts with cavity waves by diffracting and absorbing them partly. As the waves are plane the diffraction leads to reflection and transmission waves. Then we consider the reflection coefficient r a and the transmission coefficient t a due to the antenna itself (see Figure 7a). Note that the antenna absorption leads to the condition |r a | 2 + |t a | 2 <1. Using these parameters allows to obtain the new transmission coefficient taking into account the antenna presence :

( ) D 2 jk a a 2 e t r r 1 t T - + - = ; G 2 = |T 2 | (3)
|r a | 2 + |t a | 2 =1-α 2 (a) E inc r a t a Resistance (R) electric source ∞ ∞ ∞ ∞ x y z V V V V V V (b)

Figure 7 : (a) : Antenna interacting with cavity waves (b) : Antenna model composed of an infinite plane of point voltage sources in series with point resistances (R)

In FDTD method, the incident wave is created by an uniform distribution of ideal voltage sources placed all over the antenna plane and having no interaction with the cavity waves. To modelize the effect of the antenna we have added a resistance "R" in series with each ideal source (Figure 7b).

Figure 8 shows new gain results G 2 for the example of R=2 kΩ. We observe a very good agreement between the FDTD solution and the formula (3). We can also note the new maximum an minimum envelops in Figure 8b.

The magnitude of reflection (r a ) and transmission (t a ) coefficients of the new source (antenna) are given in Figure 9a. The phases of r a and t a (not shown here) are relatively constant and equals to π and 0, respectively. 9b,R=1Ω). In this case, the antenna itself becomes a perfect reflecting plane (r a ≅ -1), giving rise to a new cavity composed of only one periodic surface. For these extremum cases the gain maximum is limited by the same envelop as in Figure 4. The case of real antennae is somewhere in between the two extreme cases. One notes that the gain due to the real antenna is less than that of extremum cases.

CONCLUSION

Inserting an antenna inside a cavity allows to enhance largely its gain. However the gain improvement does not mean directivity improvement. Indeed, the wave front, with and without cavity, remains the same (i.e. plane wave). Hence, the directivity, with and without cavity, does not change.

We have first studied the gain improvement due to a Fabry-Perot cavity effect. Then we have proposed a more realistic source and compared the ideal and non ideal results. We continue to work on models for real sources and we consider treating real cavities where the physical dimensions are finite. We are also studying conformal cavities to replace the Fabry-Perot one.

Figure 1 :

 1 Figure 1 : Antenna inside a Fabry-Perot cavity. (a) : geometry (b): calculation of the transmitted wave By applying the principle of successive reflections and by superimposing the successive output waves (Figure1b), we obtain the transmission coefficient "T" (equation (1)) of "Antenna-Cavity" structure. The magnitude of this coefficient represents in fact the "gain Enhancement G = |T|", because it corresponds to the output wave E t created by the cavity, relative to the incident wave E inc due to the isolated source/antenna (i.e. without cavity).

Figure 2 :Figure 3 :Figure 4 :Figure 5 :Figure 6 :

 23456 Figure 2 : Magnitude of t and r coefficients for a periodic surface of metallic wires of a/P t =0.5%

Figure 9b gives G 2

 2 Figure 7 : (a) : Antenna interacting with cavity waves (b) : Antenna model composed of an infinite plane of point voltage sources in series with point resistances (R)In FDTD method, the incident wave is created by an uniform distribution of ideal voltage sources placed all over the antenna plane and having no interaction with the cavity waves. To modelize the effect of the antenna we have added a resistance "R" in series with each ideal source (Figure7b).Figure8shows new gain results G 2 for the example of R=2 kΩ. We observe a very good agreement between the FDTD solution and the formula (3). We can also note the new maximum an minimum envelops in Figure8b.The magnitude of reflection (r a ) and transmission (t a ) coefficients of the new source (antenna) are given in Figure9a. The phases of r a and t a (not shown here) are relatively constant and equals to π and 0, respectively. Figure 9b gives G 2 as a function of R. There are two extremum cases: small |r a | and large |r a |. For small |r a | (|t a | ≅ 1), G 2 has the same form as the ideal case (Figure 3& Figure 9b); When |r a | ≅ 1 (|t a | ≅ 0) the pick frequency is approximately twice that of the ideal case ( Figure9b, R=1Ω). In this case, the antenna itself becomes a perfect reflecting plane (r a ≅ -1), giving rise to a new cavity composed of only one periodic surface. For these extremum cases the gain maximum is limited by the same envelop as in Figure4. The case of real antennae is somewhere in between the two extreme cases. One notes that the gain due to the real antenna is less than that of extremum cases.

Figure 8 :Figure 9 :

 89 Figure 9 : (a) : Magnitude of reflection (r a ) and transmission (t a ) coefficients of the plane antenna for various values of R (b) : Gain G 2 for various values of series resistance R (D=40mm, P t =40mm, a=2mm)


H Boutayeb

K Mahdjoubi

A-C Tarot

T Denidni

CONTROLLABLE CONFORMAL ELECTROMAGNETIC BAND GAP ANTENNA FOR BASE STATION

The structure is characterized by the number of cylindrical layers, the inner radius C, the radial period P r , the angular periods P θi (for layer i), the transversal P t =P θ1 *C (which we keep constant) and the diameter of the wires a (P r =C=40mm, P θ1 =30°, a=2mm)

INTRODUCTION

This work is a French Industry and Research project, called RNRT "BIP" (see ref. [START_REF] Boutayeb | A Reconfigurable electromagnetic bandgap structure for a beam steering base station antenna[END_REF] for a presentation) and concern three University laboratories (IETR, IEF, GEA) and two societies (France Télécom, Adventen). The purpose of the RNRT project "BIP" is to design a beam steering multi-band (GSM/DCS/UMTS) base station antenna.

We call T the transmission coefficient of the structure obtained by calculating the transversal electric field outside the structure normalized by the electric field obtained without the structure. Fig. 2 presents the |T| coefficient of the structure of Fig. 1. The curve show a band gap (or stop band) in low frequencies and a passband in high frequencies. In the band gap, the wave going out of the structure is strongly attenuated. The structure has been designed so that the band gap contains the frequency bands of interest (GSM/DCS/UMTS). Note that the value of |T| is not limited by one and that in the pass band the number of picks corresponds to the number of layers. More details in the |T| coefficient (forms and values greater than one) are given in ref. [7].

Electromagnetic band gap structures are periodic structures which take there origin from optical frequencies works [START_REF] Joannopoulos | Photonic crystals: molding the flow of light[END_REF]. To design our antenna we use a new geometry of Electromagnetic Band Gap structures, a cylindrical EBG. In a previous work [START_REF] Boutayeb | Radially Periodic Cylindrical Structures[END_REF], we have shown how to characterize in transmission coefficient cylindrical periodic structures of metallic wires. These structures, associated with the EBG propriety of electronic controllability [START_REF] Poilasne | Active Metallic Photonic Band-Gap materials (MPBG): experimental results on beam shaper[END_REF] [START_REF] De | Numerical and experimental demonstration of an electronically controllable PBG in the frequency range 0 to 20 GHz[END_REF], are now used to realize a new type of beam-steering antenna. Our concept has been the object of a French patent [START_REF] Boutayeb | Antenne a diagramme de rayonnement d'émission/réception configurable et orientable, station de bas correspondante[END_REF].

We first interest on the characterization of cylindrical periodic structures. Then we show the effect of defects inserted in the structure. To finish we present the geometry and the simulation results (matching and radiation patterns) of a prototype.

CYLINDRICAL EBG STRUCTURES

Let us consider a structure composed of multiple periodic cylindrical surfaces of infinite long metallic wires, excited by an infinite long line source in its center (Fig. 1).

Metallic wire of diameter a

Infinite long line source

P r C P θ1

Fig. 1 -Cylindrical periodic structure with six layers C=P r =40mm, P θ1 =π/6, a=2mm.

CYLINDRICAL EBG STRUCTURES WITH DEFECTS

Now, in the periodic cylindrical structures, some metallic wires are removed, realizing by this way defects on the periodic structures. It will be seen that the defects create "authorized" bands in the band gap: this concept take its origin from optical frequencies works [START_REF] Joannopoulos | Photonic crystals: molding the flow of light[END_REF]. In these "authorized" bands the radiation patterns show directive diagrams in the direction of the defects.

We have studied different cylindrical structures with defects varying the number of layers (see Fig. 3). For these different structures, Fig. 4 gives the radiation patterns at 2.5GHz. We can see that as the number of layers increase the diagrams become more and more directive. But the enhancement of directivity decrease as the number of layers increase.

Fig.3 -Radiation patterns of different structures with multiple layers at 2.5GHz.

There diagrams are directive at UMTS frequencies. One can see that the structure don't allow a radiation at the low GSM frequencies (0.89-0.96GHz).

To overcome this inconvenient the two first layers have been removed to obtain the structure presented in Fig. 7. Let us consider now the six layers structure with defects presented in Fig. 4. An observation point is put in the direction of the defects. In this point we calculate the electric field (E tot ) normalized by the electric field obtained without the structure (E inc ).

The transmission coefficient of this structure (calculated by the same way than above) is plotted in Fig. 8. Note that there is an authorized band in low GSM frequencies. The radiation patterns of the structure of Fig. 7 are given in Fig. 9. Now the structure radiates in all the bands of interest. Note that the diagrams are fewer directives in the UMTS (along 2GHz) than those of the preceding structure. The transmission coefficient E tot /E inc is plotted in Fig. 5. One can observe the "authorized" band created in the band gap. Fig. 6 gives the radiation patterns of the structure of Fig. 4 at the different frequencies of interest.

The structure of Fig. 4 can be a good candidate for an antenna working only in the UMTS band.

PRINCIPLE OF THE CONTROLLABLE EBG BASE STATION ANTENNA

Point of observation Fig. 7 -Structure of Fig. 4 with the first two layers removed.

In practice defect wires are replaced by discontinuous wires; each wire is composed of diodes which allow passing from a continuous wire to a discontinuous wire thanks to an electric command. Fig. 10 gives the principle of the controllable base station EBG Antenna: the control by diodes allows beaming the radiation in the direction of the mobiles.

FIRST PROTOTYPE

To test the concept of the controllable cylindrical EBG-Antenna, a first prototype is considered. This prototype consists on only on cylindrical layer. The excitation source is now a monopole whose parameters are given in Fig. 11. Fig. 12 gives the geometry of the EBG-Antenna prototype. The monopole of Fig. 11 is put inside a one layer cylindrical EBG. The parameters of the periodic structure are P θ =15°, C=100mm and a=2mm. Continuous wires have the length L w =166mm. Discontinuous wires are composed of segments spaced by s=2mm with the period P z =22mm: these parameters have been optimized to reduce the number of discontinuities. The monopole is embedded in a foam of dielectric constant ε=2mm. In Fig. 12, we see that the EBG-antenna is matched on the first GSM Band (0.89-0.96GHz). Fig. 14 and Fig. 15 gives the radiation patterns at 0.94GHz, respectively, in the horizontal and the vertical planes.

CONCLUSION

To conclude, we have shown in this paper a new type of beam steering antenna. We have given the results in matching and radiation pattern of a prototype working in the first GSM band. We will give later the parameters and the measures of the complete structure working in the GSM/DCS/UMTS bands.

Fig. 2 -

 2 Fig.2 -Transmission coefficient |T| of the structure of Fig.1 (FDTD result).

Fig. 3 -Fig. 5 -

 35 Fig.3 -Cylindrical structures with defects with (a) one, (b) two and (c) three layers, C=40mm, P θ1 =π/6, a=2mm. P r =40mm.

Fig. 6 -Fig. 9 -

 69 Fig.6 -Radiation pattern of the structure of Fig.4 at GSM/DCS/UMTS frequencies.

Fig. 10 -Fig. 8 -

 108 Fig.10 -Base Station controllable EBG-Antenna.

Fig. 11 -

 11 Fig.11 -Parameters of the monopole (excitation source).

Fig. 14 -

 14 Fig.14 -Simulated radiation patterns in the H plan at 0.94GHz.

Fig. 15 -

 15 Fig.15 -Simulated radiation patterns in the E plan at 0.94GHz.

[7] H. BOUTAYEB, Ph. D thesis, University of Rennes, France, December 2003.