Susan Molyneux-Hodgson

Morgan Meyer

Tales of Emergence-Synthetic Biology as a Scientific Community in the Making

Keywords: Community-making Devices, Emergence, Identity, Scientific Communities, Synthetic Biology

This article locates the beginnings of a synthetic biology network and thereby probes the formation of a potential disciplinary community. We consider the ways that ideas of community are mobilized, both by scientists and policy-makers in building an agenda for new forms of knowledge work, and by social scientists as an analytical device to understand new formations for knowledge production. As participants in, and analysts of, a network in synthetic biology, we describe our current understanding of synthetic biology by telling four tales of community making. The first tale tells of the mobilization of synthetic biology within a European context. The second tale describes the approach to synthetic biology community formation in the UK. The third narrates the creation of an institutionally based, funded ʻnetwork in synthetic biology'. The final tale de-localizes community-making efforts by focussing on ʻdevices' that make communities. In tying together these tales, our analysis suggests that the potential community can be understood in terms of ʻmovements'the (re)orientation and enrolment of people, stories, disciplines and policies; and of ʻstickiness'-the objects and glues that begin to bind together the various constitutive elements of community.

Interest in the area of synthetic biology is growing rapidly. Indeed, this article is a contribution to the ongoing debate in this journal about the emerging field [START_REF] Anonymous | Beyond the genome: The challenge of synthetic biology[END_REF][START_REF] Calvert | The commodification of emergence: Systems biology, synthetic biology and intellectual property[END_REF][START_REF] Lentzos | Visions and challenges in redesigning life[END_REF][START_REF] Pottage | Too much ownership: Bio-prospecting in the age of synthetic biology[END_REF]. The funding announcement in early 2008 from the BBSRC (the UK Biotechnology and Biological Sciences Research Council) of the establishment of seven networks in synthetic biology (NSBs), followed by the publication of a report on ethical and social aspects of synthetic biology [START_REF] Balmer | Synthetic biology: Social and ethical challenges[END_REF], appear to us to mark a symbolic starting point for synthetic biology in the UK context.

At an international level, the 4th synthetic biology conference took place in Hong Kong in October 2008 and articles on synthetic biology have been appearing in journals such as Nature and Nature Review Genetics (e.g. [START_REF] Benner | Synthetic biology[END_REF][START_REF] Endy | Foundations for engineering biology[END_REF]. The current situation prefaces what appears to be a long-term research agenda for scientists and social scientists alike. Ongoing work on the reproduction of scientific communities [START_REF] Hodgson | Narrating community: History and absence in scientific texts[END_REF][START_REF] Molyneux-Hodgson | The textbook as cultural artefact: Reproducing the culture of science[END_REF], and on the practices and boundaries of communities [START_REF] Meyer | Increasing the frame: Interdisciplinarity, transdisciplinarity and representativity[END_REF][START_REF] Meyer | On the boundaries and partial connections between amateurs and professionals[END_REF] has led to our current interest in the emergence of a potential community of synthetic biology practitioners. Synthetic biology is a prominent contender for the next ʻpromissory science' [START_REF] Hedgecoe | Terminology and the construction of scientific disciplines: The case of pharmacogenomics[END_REF]: a promising area of science, that has the right ʻlabel', that puts forward visions and is able to attract support. Leaving aside what the science may or may not deliver in the future, our focus here is on the work already under way to establish synthetic biology as a field. In particular, we wish to focus on how the formation of a synthetic biology community is being accomplished.

At the same time, we too are explicitly members of this emergent community due to the inclusion of so-called ELSI researchers (those that study Ethical, Legal, and Social Issues or Implications) in the NSBs that form part of the UK's approach to synthetic biology development. While we are uncomfortable with the ELSI label, we nevertheless need to situate ourselves in relation to the emerging field and a specific NSB, and so this article also represents an attempt to grasp our own location in the emerging field. Synthetic biology presents us, as sociologists of science, with an opportunity to engage with scientists involved in an emergent area of scientific practice and with the possibility of tracing the process of community building in actu (in ʻreal time'). Our article is structured as follows. We first review some of the ways in which scientific communities have been conceptualized previously and note the scarcity of work on ʻbeginnings' found within the field of social studies of science. Then, we will present four tales of emergence which give partial insights to the generation of the current situation. The first tale recounts how synthetic biology has materialized in the European Union (EU) over the past few years and some of the policy work involved in this process. Following this, tale two will explore how synthetic biology is forming in the UK context and the work that led to a call for, and establishment of, NSBs. Our third tale is about the creation of one such network, based at a UK university. Having traced through these tales the emergence of synthetic biology from a ʻglobal' to a ʻlocal' level, in our fourth tale we then look at how a sense of a universal, collective enterprise is recreated through what we term ʻcommunity-making devices', that is, entities such as journals, postdocs, conferences and success stories.

Theorizing scientific communities and their emergence

It is commonplace in the social studies of science, as well as other disciplines, to argue that scientists are not isolated individuals who work on their own but that they ʻdo things together' (see [START_REF] Becker | Doing things together: Selected papers[END_REF]. They are part of a collective of people who share forms of language, sets of theories, technologies, and so forth. In brief, scientists are part of a community. Over the years, sociologists of science have come to examine scientific communities through various theoretical approaches (see [START_REF] Dubois | Introduction à la sociologie des sciences et des connaissances scientifiques[END_REF] for a review): they have been understood as a ʻnormative' unit (Merton), as ʻinvisible colleges' (Crane), as ʻthought collectives' (Fleck), as a ʻparadigmatic' unit (Kuhn) and, more recently, as something more akin to ʻtransactional' units (e.g. Bourdieu; Latour and Woolgar; Hagstrom). As social studies of science began to leave behind the norms and the ethos of science as the focus of their study, sociology increasingly explored scientific communities ʻin action' [START_REF] Latour | Science in action: How to follow scientists and engineers through society[END_REF], looking at the practices and the cultures of science [START_REF] Pickering | Science as practice and culture[END_REF]. Scientific communities were not only organized around the things that they knew, but also around the way they worked together. The alleged unity of science was increasingly put under question, while its multiplicity and disunity became emphasized [START_REF] Dupre | The disorder of things: Metaphysical foundations of the disunity of science[END_REF][START_REF] Galison | The disunity of science: Boundaries, contexts, and power[END_REF][START_REF] Knorr-Cetina | Epistemic cultures: How the sciences make knowledge[END_REF]. Alongside, there has been a shift from analysing communities as self-referential organizations and as merely concerned with scientific knowledge, to an understanding of scientific communities as more heterogeneous assemblages that cut across the public and the private, the social and the technical, nature and culture, and so forth. Indeed, increasingly we see these ʻscientific' networks cut across and incorporate social science and humanities disciplines and concerns. Recent theorizing has also seen communities of scientists intrinsically as ʻcommunities of promise'. ʻWithin communities of promise, expectations structure and organize a whole network of mutually binding obligations between innovators, investors, consumers, regulators and so on' (Brown, 2003: 6). Scientists are, in this sense, members of ʻcommunities of hope' since their present actions are shaped by an imagined future. Central to understanding scientific communities is the need to consider how they reproduce and change over time. In particular we need to consider what processes are involved, what kinds of events, social formations and political conditions, may lead to new communities emerging. [START_REF] Mody | Corporations, universities, and instrumental communities: Commercializing probe microscopy, 1981-1996[END_REF] has described the interactions between instrument development and various interested groups in the evolution of nanotechnologies. [START_REF] Gingras | Physics and the rise of scientific research in Canada, trans[END_REF] has explicitly focused on aspects of emergence in his consideration of physics as a case in Canada. He offers an analytical model for examining the formation of identifiable communities, a process that he describes along three overlapping dimensions: emergence, institutionalization and the creation of a clear social identity (1991: 4-6). The first phase consists of the development of a research practice, either through the importation of know-how or through the reconstruction of individual trajectories which have yet to be institutionalized. Then, after the conditions for the generation of research practice have been established, individual and institutional identities are aligned: we see the institutionalization of research, a crucial step in the formation of a scientific community. Gingras writes:

It is, in effect, the condition for the growth and survival of a community, for only by setting up institutional structures which favour the production of knowledge and the reproduction of agents endowed with the necessary dispositions for this activity can scientists reproduce themselves as a group and participate in activities that constitute a scientific field. (1991: 5) The third step consists in the formation of a social identity, be it disciplinary or professional (e.g. ʻphysicist'). So, Gingras lays out potential ways in which we could track the genesis of a synthetic biology community. However, his work considered the development of a community at the beginnings of the twentieth century and, while emphasizing the production and reproduction of community and the means through which institutionalization can be accomplished (departments, curricula, funding, scholarships, etc.), Gingras did not consider the external forces shaping this emergence [START_REF] Conway | Physics and the rise of scientific research in Canada by Yves Gingras[END_REF]. Nor did he offer any concepts to describe the structures and conditions that come before community. Hence, we need to give further thought to conceptualizing the emergence of synthetic biology as a collective activity. In particular, we should be mindful of the potential multiplicity of approaches that the term ʻsynthetic biology' encompasses [START_REF] O'malley | Knowledge-making distinctions in synthetic biology[END_REF] and the range of possible communities that could emerge.

Locating an emerging community

To conceptualize an emerging community, and begin to study empirically the processes involved, we need to tie the genesis into ongoing, broad movements occurring at many levels beyond our location within a UK synthetic biology network. [START_REF] Fujimura | Transnational genomics in Japan: Transgressing the boundary between the ʻmodern/West' and the ʻpremodern/East'[END_REF] has argued, using the case of translational genomics, that national context is significant in that such context changes the production of knowledge in biology in important ways. Thus our study of the way in which a potential scientific discipline emerges needs to maintain a sense of place, as evolving structures depend on local and national contingencies [START_REF] Collins | Innovation systems in the European periphery: The policy approaches of Ireland and Greece[END_REF]. The emergence of a community of practices is not a global process (even though it can be made to become a global process). Although the study of laboratory science from ethnographic perspectives is well established, usually the laboratories to study and the communities that occupy them already exist, whereas our initial interest is rooted in what happens prior to the establishment of physical working spaces and fixed identities of occupants. Thus, in order to examine the emergence of synthetic biology we need to look to a variety of places where community can be made and articulated. We propose considering devices as mundane as a workshop and a grant funding proposal, and things as ʻhigh brow' as an EU policy document and a UK policy initiative as equally relevant. In other words, we aim to be symmetrical in our approach [START_REF] Callon | Some elements of a sociology of translation: Domestication of the scallops and the fishermen of Saint Brieuc Bay[END_REF] and not a priori concerned whether the factors that shape communities are local or global, texts or talks, bottom-up or top-down, internal or external. We start with the assumption that all these are entwined in the emergence of scientific communities and that each needs to be taken into (our) account. The empirical materials we will draw upon for this article include: transcripts of interviews with lead participants in the local NSB; policy documents, reports and statements from scientific institutions in the UK; research documents; and reflective diaries of the two authors based on attendance at meetings, seminars and workshops from mid-September 2007 onwards. In this sense, we are undertaking a multi-sited ethnography (Marcus, 1998: 79), an ethnography that ʻmoves out from the single sites and local situations of conventional ethnographic research designs to examine the circulation of cultural meanings, objects, and identities in diffuse time-space'. Given that our main concern is in ʻhow'-How does a community appear to materialize, become global, become ʻtextured'? How is a community ʻheterogeneously engineered' (see [START_REF] Law | On the methods of long distance control: Vessels, navigation and the Portuguese route to India[END_REF])?-we want to find a way to talk about scientific communities that is neither too general, and thus unable to focus on practices and contents, nor too narrowly focused on a single field site and blind to what takes place beyond this site (Vinck, 1999: 390). To start this project then, we will recount four tales of emergence that present a ʻsnapshot' of the story of synthetic biology so far.

Tale one: mobilizing synthetic biology in Europe

On entering the ʻfield' of synthetic biology, we found the need to look East (to Brussels) and West (to the US), and to the past eight years, to locate some origins of community. The last eight years can be identified as seeing important developments in terms of policy work around the notion of convergence, that is, the idea of the bringing and coming together of different scientific fields. A particular US research and technology policy initiative from 2001 is often cited as the starting point for discussions about the idea of converging technologies. This initiative, shortened to NBIC, aims to bring together the fields of nanotechnology, biotechnology, information and communication technologies and the cognitive sciences in order to ʻimprove' human performance (Roco and Bainbridge, 2003). Despite reservations from various quarters, and the strong military focus of the original initiative, it had an important impact on the European Commission. In response to NBIC, the European Commission has developed its own approach titled ʻConverging Technologies for the European Knowledge Society' (CTEKS), which aims to be a more demand driven approach in which converging technologies respond to societal needs and demands.

Initiatives like NBIC and CTEKS present optimistic futures and a range of utopian promises. New terms come to the fore in these policy statements, blurring the boundaries between technology and nature, inanimate and animate-terms such as ʻnanobiotechnology', ʻsynthetic biology', and ʻnew bionics'. These terms can be taken as signs of the spreading of NBIC-type convergences (Coenen, 2008: 61). So let us now turn specifically to policy work in the domain of synthetic biology, which was identified as one of eight key areas of convergence in the EU policy arena [START_REF] Andler | ʻConverging technologies' and the social sciences and humanities-An analysis of critical issues and a suggestion for a future research agenda[END_REF]. In 2005, the EU NEST (New and Emerging Science and Technology) programme published a report entitled Synthetic Biology-Applying Engineering to Biology. The report states that: Synthetic biology is a nascent field, and there is currently no systematic, global effort to coordinate the developments in this field. [. . .] What is needed [. . .] is a framework for coordinating the current research, fostering a community of researchers (particularly among young researchers) and creating a forum for the establishment of clear goals, shared tools and agreed standards. (European Communities, 2005: 7, emphasis added) The report further asserted that what was needed was funding, intellectual and physical infrastructures, education and training activities, conferences, and human resources-ʻsynthetic biology is a young discipline that needs some nurturing to flourish' (European Communities, 2005: 20). In addition to the NEST report, the ʻTowards a European Strategy for Synthetic Biology' initiative was launched, which had as its core a series of workshops, and also the EMERGENCE initiative, which aims ʻto provide a communication and working platform for the emerging European synthetic biology community in order to strengthen the organizational and conceptual basis of synthetic biology as a true engineering discipline in biological engineering' (http://www.emergence.ethz.ch/home.htm, emphasis added; see also [START_REF] Greener | Is the grass greener on the other side? Encouraging the development of synthetic biology in Europe[END_REF]. The European vision for synthetic biology involves using the science to resolve ʻsocietal challenges'; for example, finding replacements for fossil fuels; developing novel medical diagnostics, and microbial approaches to cleaning water. Incited by these reports and initiatives, and perhaps the perceived leadership of the US in synthetic biology developments-and the consequent risks of ʻlagging behind'-things started to happen in the UK national context. As one of the principal investigators of an NSB described the situation: the UK has seen that this field is starting to grow [. . .] that it could be something that's important for UK science, UK industry, UK plc, however you want to describe it. And so they've decided [. . .] to put money in to get people to work together to see what the field should be and how to shape the field and how to get to various end points. (R1) An integral part of ʻwhat the field should be' is a coming together of existing communities; not just from large, amorphous areas of science (like nanotechnology and ICT) as suggested by convergence-speak, but also specific, named disciplines. The Royal Society (2007: 1) writes: ʻSynthetic biology has developed from the convergence of knowledge and tools from other disciplines.' The field of synthetic biology is conceived as drawing on various disciplines: molecular biology, engineering, physics, computer modelling, etc. and so specific administrative techniques are needed to bring about the meeting of the communities involved. Commenting on the launch of the UK networks, the Minister for Science and Innovation Ian Pearson stated:

By developing this emerging science, the UK will continue to keep its leading edge. [...] This initiative [the NSBs] is aimed at raising UK profile and capability in this area to put the country at the forefront of the field. (in BBSRC, 2008a) While this story is clearly a partial one, we see here evidence of a policy accomplishment process [START_REF] Hodgson | Policy and its exploration[END_REF]. Synthetic biology, as a strategic policy object and an arena in which it is allegedly important not to ʻfall further behind' (both for the EU and the UK) has been translated into concrete communitybuilding efforts. Finally, synthetic biology has also been on the agenda in discussions within the Royal Society, the Royal Academy of Engineering and the Royal Society of Chemistry (Lentzos et al., 2008: 311). Institutional awareness of the emerging science and support for its development appears widespread, even concerted.

In 2006, the BBSRC established a working group on synthetic biology in order to reflect on the important issues that may arise in the field and on how to shape future research. An outcome of the recommendations of this working group was the organization of a Synthetic Biology Workshop which took place in February 2007.

The workshop aimed to: ʻassist in the development of an interdisciplinary synthetic biology research community'; identify ʻcommunity-support needs' and to devise research programme agendas (BBSRC, 2007: n.p.). The workshop brought together researchers from a variety of disciplines as well as representatives from several other research councils. ʻ[I]t was agreed that building a community was vital',(1) and that this was deemed necessary due to the perceived large gap between the disciplines involved. Ideas generated by the workshop participants, in order to build this community, included: using generic methods for new community development such as ʻsand-pits';

(2) the funding of networks to enable the ʻforging of multi-disciplinary collaborations'; using discipline-hopping schemes to enable ʻfostering (of) disciplinary cohesion'; feasibility studies and grant applications that would follow from networks.

There was debate at the workshop over whether a fixed definition for synthetic biology was needed or not. Some participants viewed synthetic biology as not a new science, but rather as an ʻextension of what has already been done', an extension of existing biotechnology (similar arguments to this appear in the field of nanotechnology, see Pottage, 2006: 144). Other participants were keener on establishing sameness, continuity, a seamless change. The participants expressed the need for care in defining synthetic biology in the sense of how much work already existed in this area. Interestingly, one of the keynote speakers said in his abstract that he had used ʻa form of synthetic biology'-i.e. undertaken a series of steps to cut, paste and manipulate at the genomic level, to create a specific form of an organism, from which other things were done. Questions over whether current practice is, or is not, synthetic biology, have yet to be resolved.

The seemingly mundane task of defining a field and settling on a name is a difficult exercise, that is, definitional arguments point to something interesting. It has been argued that the ʻprocess of naming also sets in place the concept of borders to a community' (Molyneux- Hodgson and Facer, 2003: 156). Naming something ʻsynthetic biology' is not an innocent exercise, for it delimits, renders more visible, more powerful, and increases the potential to attract funding for, certain forms of work. Further, naming creates an order (see Hetherington, 1997: 191); to designate scientists as synthetic biologists produces a homogeneous and bounded discursive space. Yet, while participants at the workshop expressed the need for synthetic biology to ʻmature', including defining the area and bringing together the disciplines, it was also stressed that ʻResearch Councils should be careful to avoid premature ʻʻprofessionalization'' of this area. [. . .] If a thematic programme were launched, it would be important not to be restrictive or prescriptive, since synthetic biology was still developing.' The workshop report further stated: ʻthere was agreement that a thematic programme/research initiative was premature, for synthetic biology, at this stage, in the UK'. Hence, while there was a perceived need to discursively stabilize synthetic biology, and to find a common vocabulary and bounded arena of operation, there was also resistance towards rigidifying it too far. Part of the reticence regarding a specified research programme appears to arise from a desire to let things emerge from the ground-perhaps programmes are seen as too prescriptive, and, as synthetic biology is still developing, it requires research that includes ʻbottom-up approaches'. While this tale can be understood as part of larger debates on the balance of funding for research between ʻtop-down' governmental initiatives and ʻbottom-up' or ʻblue-skies' scientist-driven work, it is also suggestive of the notion of ʻinterpretive flexibility' [START_REF] Pinch | The social construction of facts and artifacts: or, How the sociology of science and the sociology of technology might benefit each other[END_REF]) that describes the multiple, culturally constructed understandings of phenomena.

Networks in synthetic biology. The call for networks prompted scientists from various universities in the UK to put together proposals and apply for funding. A requirement of the funding stream was the inclusion of ELSI researchers, indeed additional material was requested from these participants as part of the funding decision making process, whereby ELSI workers had to specifically state their objectives for participation in the networks.(3) Seven network projects were eventually successful. The networks were announced in a press release given by the BBSRC in June 2008 in which it was stated that the networks should ʻallow UK researchers [. . .] to form a true synthetic biology community' (BBSRC, 2008b: n.p.).

Tale three: making a synthetic biology network

When the call came out for network proposals, I thought that this is something that the university ought to do. (R2)

A scientist and an engineer from one university had attended the BBSRC workshop in 2007. When the call for networks was posted by the BBSRC, the two academics first called on collaborators from their existing projects-mostly projects on ʻsystems biology'-and recalled the work of other researchers in the university to generate ideas towards a proposal. Brainstorming sessions and meetings were held and draft documents were circulated.

I gazed at a sheet of paper for a while. [. . .] I thought that it would be rather interesting to be able to synthesize the kinds of molecules that are of use in the tissue engineering field. [. . .] I'd heard X [a name] give a talk, so I just went to see X and spoke to her and some of her colleagues [. . .] we decided more or less there and then that this would be worth trying. (R2)

In the final network proposal, tissue engineering-and specifically ʻmaking glues in microbes' (R2)-is put forward as a potential key area in which future research might take place, claiming that synthetic biology: ʻwill have major benefits for providing materials for tissue engineering, stem cell therapies and regenerative medicine, both with replacing current therapies and developing new ones not possible with current technology' (M.A., 2007: 1). Yet, like other NSBs funded by the BBSRC, the focus is not on research per se but on creating networks, a fact that the proposal repeats ʻThis is a network to develop ideas, not a research project' (M.A., 2007: 1, underlined in original). ʻThe aim is to generate more debate and drive the field forward' (ELSI text from proposal).

In the proposal, apart from a discussion about the specific area of scientific research envisaged in the future, a lot of text is devoted to research management matters. For instance:

The overall objective [. . .] is to build, within 3 years, a Network with the critical mass and skills-set necessary to tackle this challenging project in synthetic biology and thereby allow the network to become self-sustaining and contribute to new technologies and materials derived from breakthroughs in the synbio field. (M.A., 2007: 1)

Consequently, the outcome and success of the network is not to be measured in terms of direct research outputs, but in terms of infrastructural achievements and proposals for future work: ʻWe will know we have succeeded in the network's overall goal if a significant proposal or set of proposals in applying synthetic biology to biomaterials problems arises [. . .] and a formal centre has been created' (M.A., 2007: 6, emphasis added). Apart from articulating a number of visions and setting out promises, the proposal is notable for its emphasis on the structure of the network, which has to be sustained, developed, formalized. The kind of network being described in the proposal resembles what have been called ʻforums'. Vinck (1999: 394), who distinguishes five forms of networks, defines forums as: networks [that] organise the exchange of ideas and the constitution of a community of interest. They lead to the emergence of cooperation [. . .] and to the structuration of a collective problem. The most important intermediary objects here are of a textual nature (invitations, programmes, conference proceedings). Over time, Vinck argues, forums will evolve into different kinds of networks that become increasingly structured, productive and stable. At the time of writing this article the local network is organizing a kick-off retreat to ʻofficially' begin operation, but it already does exist and operates in various ways: it has been funded, it has brought together a range of people who agreed to work together, it has been written down, it has a draft website-i.e. it has been ʻinscribed' in multiple forms. The participants in the network are materialized in a table at the end of the proposal, a table that contains a list of people and partners, including their affiliations and research interests. The proposal further lists activities such as inviting ʻkey' international visitors, travel to conferences and the organizing of an international meeting.

Identity-work

It is important, at this point, to stress that something is also absent from the proposal and the other inscriptions outlined above: missing, are scientists who are ʻsynthetic biologists'. While there is some evidence in the literature for scientists naming themselves ʻsynthetic biologists', or as is more often the case, being labelled by others as such, this is primarily done in relation to long-established disciplinary communities. For example, two key papers describing the character of synthetic biology by scientists working in the area, [START_REF] Endy | Foundations for engineering biology[END_REF], and [START_REF] Benner | Synthetic biology[END_REF] draw explicit links between the existing collectives of biological engineering and chemistry, respectively, and the future activity of synthetic biologists. Indeed in 2005 Benner and Sismour already classified synthetic biologists as coming in two broad classes, separated by their end goals and means of achieving them. In our interviews we have asked questions about existing community affiliations and disciplinary identities of the people involved in the synthetic biology network. As one of the principal investigators explained: it's like a Venn diagram. [. . .] Some people are obviously members of a synthetic biology community, but they may also be members of a molecular biology community and so there is some sort of intersection between communities. (R1) This quotation is suggestive of a transition period for individual scientists. We have asked individual investigators how they describe themselves. Responses include:

Oh I'm a microbiologist. [. . .] My own research is very much on the interface of biochemistry and microbiology. So a lot of my academic life has been spent in biochemistry departments. [. . .] This is more or less a biochemistry department we're in now, although it doesn't quite have that name. But, I was trained as a microbiologist, so that's how I normally identify myself. (R2) I think the broadest term that I describe myself is probably a bio-chemical engineer. I probably don't describe myself as a synthetic biologist [but] if you ask me the same question in five years time, I might. (R1) My main community of reference is the bio-informatics systems biology community. A synthetic biology community [. . .]? I don't think that exists yet. (R3)

In the NSB, the people who do synthetic biology do not describe themselves as synthetic biologists. Yet, as the second quotation reveals, this is potentially due to change. The network proposal suggested that there may be ʻnew lecturer posts [. . .] to be picked up by the university beyond the terms of the grant. One of these is earmarked as a synthetic biology lectureship' (M. A., 2007: 4, underlined in original). Evident here is a sense of identity that is an ongoing project; that still needs to be negotiated and further institutionalized. The difference between a synthetic biologist and, say, a microbiologist is, at the current time, one of identity as ʻbecoming' rather than identity as ʻbeing' (see Simpson and Carroll, 2008: 31). All of the respondents above were already working together on systems biology projects prior to the synthetic biology network funding, so they are concurrently holding links to disciplines, research collectives and multiple fields of interest. The fluidity of identity within the network clearly requires further analysis and is beyond the scope of the current article. However, it seems apparent that the network will perform an important role in structuring the emerging synthetic biology community at a localized scale. The ongoing identity work brings us back to the beginning of our first tale of mobilizing synthetic biology on an EU level, where the lack of synthetic biologists is portrayed as follows: ʻin the long term it would be desirable to create a new breed of researchers who are familiar both with fundamental biology and with the methodology of engineering, as well as having requisite skills in areas such as computational sciences and chemistry' (European Communities, 2005: 7). What is particular about this ʻnew breed of researchers' in terms of identity formation? We see a bringing together of knowledge from various domains; this new ʻbreed' is described and positioned as being an identity in-between other, already existing identities. At the same time, this identity is on a trajectory, that is, the articulation of identity is based on two elements: imagination and alignment-the envisioning of possible futures and the doing what it takes to get there (Wenger, 2000: 241).

Tale four: creating a sense of a global collective

In the tales above, we have encountered a number of devices that we will call here ʻcommunity-making devices'. Policy initiatives, workshops, calls for proposals and networks are all devices that help make, or at least articulate the need for, community. While occasioning community-building effort, the tales are dominated by movements of various kinds, e.g. shifts in individual definitions of belonging; the seeping of policy from macro to micro locales; (the) reorientation of resources, etc. Also, the devices we have described so far are attached to specific arenas: the EU, the UK, the university. In what follows, we want to discuss briefly a few ʻcommunitymaking devices' that are less bound to distinct spaces and are less about movement than providing ʻglue' to capture and begin to sustain emerging links. First, there are events and associations. One example is the annual, worldwide International Genetically Engineered Machines (iGEM) competition that primarily involves undergraduate students in synthetic biology, the first of which took place in 2004. The aim is to engineer biological devices using a library of standardized parts (called BioBricks) made available to the students entering the competition. On the iGEM's website we find ʻcommunity news', the annual competitions are called ʻjamborees'. One association is http://syntheticbiology.org which also includes a ʻCommunity News' section, with the first news item dating back to 1 November 2002. It includes: calls for conferences, workshops, competitions; information about the launch of new journals or new publications; declarations; lectures; information about mailing lists. Second, there are new journals being set up. IET Synthetic Biology, first issued in 2007, states that it ʻwill aim to support this growing new community. [. . .] In particular, we wish to support the activities of young workers entering the synthetic biology field.' Another journal is Systems and Synthetic Biology: ʻa new biomedical journal to publish original papers and articles on all aspects of Systems and Synthetic Biology'. The participants of the local NSB currently express ambivalence towards these journals:

There are some journals that are starting to emerge, but obviously they're quite new so time will tell as to whether they're successful and people do support them by publishing directly in there or still go for the, maybe the highimpact The ambiguity about these journals can be taken as a sign of emergence. In general, conferences are one of the traditional channels-alongside journals-for scientific dissemination of knowledge [START_REF] Lamb | Information and communication technology challenges to scientific professional identity[END_REF]. The international synthetic biology conference is a far more prominent and visible forum than the journals just mentioned. It has attracted an increasing number of participants and takes place in different locations across the globe. It produces stickiness through being able to bring together the main players in the field.(4) It has become, in other words, a knowledge maker [START_REF] Collins | Conferences as knowledge makers[END_REF], an institutionalized space where findings are communicated and knowledge is exchanged, and, above all, where identities can be shaped.

Finally, synthetic biology has its prominent success story: the development of a cheap anti-malaria drug through creating a new bacterial strain able to produce amorphadiene. This story is omnipresent in the material we have analysed: it has been mentioned by the people we interviewed; it is referred to in reports, in articles, etc. While current work in the sociology of expectations and communities of promise rightly stresses the role of visions, hypes and futures, we want to press the point that the past is also mobilized in important ways when constructing the future. In particular, it is through (re)telling ʻsuccess stories' (i.e. the anti-malaria drug) that the past becomes enrolled as a sort of guarantor for future developments in synthetic biology. It has been argued elsewhere that: ʻScientists need stories to support their work-stories they tell to funding bodies, governments, venture capitalists and the general public. Without the right story, their research cannot survive' (Anonymous, 2008: 12). Success stories have the further advantage that, unlike heavy equipment, they can travel faster and without much (financial) cost. A success story like the antimalaria drug thus has several functions: it travels within the community and thereby strengthens its interconnectedness, it becomes part of the shared repertoire of that community giving it a sense and purpose, and it enables future work (see also [START_REF] Felt | Fabricating scientific success stories[END_REF].( 5) Even though this particular success story has highly localized origins (a research team at the University of California, Berkeley headed by scientist Jay Keasling) it has already become a rather global story, a widely shared memory of a whole (and still emerging) community.

The devices described above have in common not only that they shape an emerging community of practice with a ʻshared repertoire of communal resources-language, routines, sensibilities, artifacts, tools, stories, styles, etc.' (Wenger, 2000: 229, emphasis in original); but they act as initial sticking points in that they are also able to ʻbring together the collective' [START_REF] Latour | Politics of nature: How to bring the sciences into democracy[END_REF] in particular ways; they provide opportunities to do community within the melee of shifts and movements that are required to create a space for a potential new community.

Discussion

So far, we have presented four tales: a tale about the mobilization of synthetic biology as a project within Europe; a tale about capacity building in the UK; a tale of the creation of a synthetic biology network at an institutional level; and promotion of a sense of global, collective endeavour. There are, of course, more tales that could be told about synthetic biology: tales about the creation of research groups or departments, tales about the relationship between synthetic biology and other disciplines, tales about instruments and techniques, tales about regulation, tales that begin in different places, tales about ʻembedded' sociologists, tales about emerging and changing metaphors,(6) and so on and so forth. So there are, on the one hand, more stories to be told and more aspects of synthetic biology that future research needs to explore. On the other hand, there are interconnections between the tales we have just told.

The tales we have presented operate at multiple levels. Alongside the narratives of the development of the science, are tales of community building, of the emergence of the scientists who will do the old/new science. Here, we have identified techniques of community building at different levels and that operate in different ways (including discursive, institutional, financial, etc.).

Overall, our aim was to map out the terrain of synthetic biology as we see it from our own institutional position within a network, as an initial step in understanding how to locate ourselves as members of an emergent synthetic biology community and toward the generation of a set of research questions for our ongoing study of an NSB in the UK. Toward this end, we sense the need to move beyond Collins and Evans' notion of ʻinteractional expertise' (2007) towards notions of legitimate peripheral participation [START_REF] Lave | Situated learning: Legitimate peripheral participation[END_REF]; whereby our engagement within the NSB perhaps allows us to both ʻrepresent and intervene' [START_REF] Hacking | Representing and intervening-Introductory topics in the philosophy of natural science[END_REF] in scientific knowledge production. Reflecting on the role of social scientists in synthetic biology, [START_REF] Calvert | The role of social scientists in synthetic biology[END_REF] propose a distinction between the role of the contributor, an ELSI expert ʻplugged in' after natural scientists have produced scientific knowledge, and that of the collaborator, who can genuinely influence and interact with knowledge production. We would tend toward the latter orientation but would further stress that our relationship with synthetic biology mirrors that of the identitiesin-the-making we have described above: it is a relationship in the making; it is uncertain, ambiguous and currently being negotiated; and we have yet to stabilize our roles and positions in relation to other identities. We believe that emerging communities can be analysed through identifying the mixture of movement and stickiness. A variety of movements have come to the fore: scientists getting enrolled, disciplines converging (in policy, if not yet practice), the mobilization of resources (such as money, equipment, etc.).

These movements consist, in other words, of the movements of the building blocks of a community and the convergence of these towards some central position. Such movements create a more or less homogeneous space in which it is possible, safe and fruitful to work together. Other movements are also visible: building upon past ʻsuccess stories', articulating future promises and expectations, using linguistic tools to emphasize a trajectory (ʻbuilding', ʻemergence', etc.). These more temporal movements are pointing towards a future state: the community itself is seemingly on a trajectory to evolve into a state that is more stable, better defined, more visible and, above all, able to deliver at least some of the promises. Apart from these movements, an emerging community is also trying to stop certain things from moving, to lock some entities into a fixed position. This has become evident through the perceived needs to develop a shared vocabulary, a common language, the efforts to clarify, to agree . . . in other words, to stabilize.

In order to create ʻstickiness', emerging communities of scientists tap into a repertoire of existing ʻcommunity-making devices'. Associations and events, conferences, journals and success stories are, we argue, such markers and makers of community. These devices help to create a sense of a global collective of people and practices enrolled in the project of synthetic biology. Like other, established communities that use these devices to reproduce their community, emerging communities use these to establish themselves, to create an initial sense of community, to create a visible, demarcated and powerful niche. In doing so, they use devices and ideas which are both ubiquitous-a sort of ʻideal type'-and are specifically shaped to meet the particular needs of their community. In addition to these, we would also argue that discourses of emergence and newness are significant structuring devices-used by social scientists and scientists alike-and not so dissimilar from the communitymaking devices just mentioned. These discourses about emergence enrol people, establish links and create a sense of community. They have an effect on the way scientists align their practices with other scientists. Perhaps what an emerging community lacks in history and foundations is compensated for through discourses about emergence that provide a sense of direction and future, and by getting people interested in a project. At the same time, much discussion and, above all, uncertainty about the definition of synthetic biology is evident in these early days-which, we can already surmise, will become black-boxed and taken for granted in the future.

Summary

Our work in this article has been to make a first attempt at articulating the early stages of a potential community in the making and to contribute to a growing body of work on synthetic biology. We aimed to elaborate some of the ways in which ideas of ʻcommunity' are being mobilized in the synthetic biology project across different scales and places. Our intent was to capture something of the complexity and multifaceted nature of the origins of a potential synthetic biology community.

We have proposed two key organizing ideas as a means of understanding the emergence of the field; namely ʻmovement' and ʻstickiness'. These notions are intended to capture some of the fluidity of the process of scientific change, in opposition to long-standing narratives of the progress of science that emphasize a more linear, progressive story, and as an alternative to studies of communities that are already fixed.

In tracing the emergence from our position of association with a funded network in synthetic biology, we follow Sarah Franklin's invocation to ʻbegin with the specific and the localised' when addressing the large questions relating to processes of scientific change (Anonymous, 2008: 13). A key question, of course, is the extent to which what we see happening from our position is something ʻnew'; hence our use of the term ʻemergence', in order to temper the sense of radicality and dislocation that can often be detected in debates between social scientists and natural scientists. It remains to be seen whether ʻsynthetic biology' will become a separate discipline with a delineated community of practitioners, a sub-field of one of its constituent parents, or segue into some other configuration.

  [journals]. (R1) It's too early to, to say [. . .] the top systems biology and synthetic biology results are not published in those journals, they are published in Nature or Science, Cell, Plant Biology, or, you know, these high-impact factor journals. (R3)

  There is a concurrent bringing together of existing communities and a differentiation and filtering of research activity, to guide the emerging community.In the UK, funding bodies have shown an increasing interest in synthetic biology(Lentzos et al., 2008: 312): two research councils currently ʻsignpost' it as a key area of funding interest and several specific committees are dealing with issues relating to this field. The BBSRC has an Engineering and Biological Systems committee and a Biomolecular Science committee that cover relevant issues. Both committees have standing arrangements with the EPSRC (the UK's Engineering and Physical Sciences Research Council) for co-funding if appropriate. And it is via its Bioscience for Society panel, that the BBSRC considers social and ethical issues within its remit. The BBSRC states that it was ʻgiving serious consideration to the potential ethical, moral and societal impacts' of synthetic biology and a working group had been set up to explore the area (resulting in the 2008 Balmer and Martin report). Within the EPSRC, synthetic biology has emerged as an important area for development in the Engineering Directorate. Several routes to getting support for synthetic biology projects are being made available, e.g. workshops, research projects, student bursaries for iGEM (the International Genetically Engineered Machines competition).

	Tale two: building capacity in the UK

The resources needed to build communities and do scientific research-funding, training, communications support, networks, etc.-are being made available or are in development. As

Vinck has argued (1999: 391)

, the creation of scientific networks has now become subject to political drives to organize scientific work. What we also see is the carving out of areas of interest and potential research focus; in part to differentiate the European synthetic biology project from other versions.

  Following from this workshop, a joint call for proposals or NSBs was issued by the BBSRC and the EPSRC later in 2007 (additional partners being the AHRC [Arts and Humanities Research Council] and the ESRC [Economic and Social Science

	Research Council]). The aims of the networks included: developing and establishing
	communication and networking, forming partnerships, and building ʻa cohesive,
	cross-disciplinary community' in synthetic biology (BBSRC, 2007: n.p.). The call was
	framed to include ethics and stressed the need to handle ʻsocial and natural issues'
	concurrently.

  They have not yet become, not yet stabilized, into key ʻcommunity outlets'. This uncertainty is in stark contrast to the major conference in the field. Synthetic Biology 1.0, the first international meeting on synthetic biology-the ʻinaugural' conference (European Communities, 2005: 19)-took place in 2004 in the US (Cambridge, Massachusetts). The 2008 meeting, the fourth one of its kind, took place in Hong Kong. One of the investigators in the NSB described this conference as:A proper recognized international meeting now. It's been in the United States and now it's been in Europe and [. . .] it's in Asia next year. [. . .] several hundred people go to it, it has got an official name, and it's moving between continents now, so that does give it [. . .] a stronger international foundation as a real emerging discipline. (R1, emphasis added)

Acknowledgements

We would like to thank participants in one of the BBSRC-funded Network in Synthetic Biology events for their cooperation, in particular our interview respondents R1, R2 and R3. Thanks also to Dave Phillips for his comments on an earlier draft and to three anonymous referees.

Notes

(1) All the quotations in this section are from the unpaged workshop report (BBSRC, 2007).

(2) Sand-pits are a kind of ʻclose encounter' and brainstorming approach-the rationale being that if you put people in close proximity to each other, and structure their activity over an intense period of time, you will generate a collective vision and/or agenda and/or project.

(3) Perhaps this is a key difference between synthetic biology and other communities: the fact that the social sciences are posited as not only a legitimate but also a constitutive element of the community. This ʻupstream' involvement of social scientists is commonly explained by the need to avoid controversies such as those around genetically modified organisms. Hence, it seems to us that, like other emerging communities, the synthetic biology community mobilizes hopes, expectations and promises, but unlike other communities, it has to a certain degree internalized a prominent fear and is thus institutionalizing and policing the involvement of social science in a rather novel way.

(4) Also worthy of being mentioned is the first synbiosafe conference, an e-conference which lasted about a month and focused on the ethical, safety, public, etc. issues arising with synthetic biology.

(5) Felt (1993: 375) lists six ingredients allowing the construction of a scientific success story: ʻpolitical and economic interest; the flair of ʻʻlittle'' science; the presence of hero scientists; the possibility of staging an international (6) Some authors have argued that ʻmetaphors begin to emerge, it seems, quite specifically in order to provide suitable analogies for the representation of the inner workings of synthetic biology' (Balmer and Herreman, 2009: 221) and that there is a shift from literary metaphors (i.e. ʻthe book of life') to computational metaphors (2009: 231).


Franc ¸ois Pascal Moucheront

Georg Bertrand

Koval

Laurent Tocquer

Stéphane Rodts

Jean-Noël Roux

Alain Corfdir

Franc ¸ois Chevoir

MRI investigation of granular interface rheology using a new cylinder shear apparatus

Keywords: velocimetry, granular material, annular shear, interface, roughness

The rheology of granular materials near an interface is investigated through proton magnetic resonance imaging. A new cylinder shear apparatus has been inserted in the MRI device, which allows the control of the radial confining pressure exerted by the outer wall on the grains and the measurement of the torque on the inner shearing cylinder. A multi-layer velocimetry sequence has been developed for the simultaneous measurement of velocity profiles in different sample zones, while the measurement of the solid fraction profile is based on static imaging of the sample. This study describes the influence of the roughness of the shearing interface and of the transverse confining walls on the granular interface rheology.

Introduction

The interaction of a granular material with a solid interface is of interest in various engineering problems, such as industrial conducts [START_REF] Nedderman | Statics and kinematics of granular materials[END_REF], geotechnics [START_REF] Schlosser | Friction in reinforced earth[END_REF][START_REF] Tubacanon | Pile skin friction in sands from constant normal stiffness tests[END_REF], and in geophysical situations, such as tectonophysics [START_REF] Chambon | Frictional response of a thick gouge sample: 2. friction law and implications for faults[END_REF] or gravity flows [START_REF] Chevoir | Granular flows[END_REF].

At the immediate vicinity of the shearing interface, a thin granular layer, where the shear and dilation is localized, plays a significant role in the stress transmission between the solid interface and the bulk granular material. This rheology is influenced by the roughness of the shearing surface [START_REF] Dejong | Interface load transfer degradation during cyclic loading: a microscale investigation[END_REF][START_REF] Koval | Interface behavior of granular materials[END_REF][START_REF] Oumarou | Cyclic behaviour of a sand-steel plate interface[END_REF][START_REF] Uesugi | Influential factors of friction between steel and dry sands[END_REF][START_REF] Uesugi | Frictional resistance at yield between dry sands and steel[END_REF][START_REF] Uesugi | Behavior of sand particules in sand-steel friction[END_REF][START_REF] Vardoulakis | Interfacial localisation in simple shear tests on a granular medium modelled as a cosserat continuum[END_REF].

In this paper, we focus our attention on the annular (Couette) shear geometry, where the material is confined between two cylinders and sheared by the rotation of the inner rough one (see [START_REF] Koval | Annular shear of cohesionless granular materials: From the inertial to quasistatic regime[END_REF] for a recent review). This geometry has been used to measure the rheological properties of granular materials, both in two dimensions [START_REF] Howell | Stress fluctuations in a 2D granular Couette experiment : a continuum transition[END_REF][START_REF] Latzel | Comparing simulation and experiment of a 2D granular Couette shear device[END_REF][START_REF] Miller | Stress fluctuations for continuously sheared granular materials[END_REF][START_REF] Veje | Kinematics of two -dimensional granular Couette experiment at the transition to shearing[END_REF] and three dimensions [START_REF] Bocquet | Granular shear flow dynamics and forces : Experiment and continuous theory[END_REF][START_REF] Chambon | Shear with comminution of a granular material: Microscopic deformations outside the shear band[END_REF][START_REF] Cruz | Flow of dry grains : Friction and jamming[END_REF][START_REF] Da Cruz | Viscosity bifurcation in granular materials, foams, and emulsions[END_REF][START_REF] Daniel | Vane rheology of cohesionless glass beads[END_REF][START_REF] Losert | Transition and steady-state dynamics of granular shear flows[END_REF][START_REF] Mueth | Mesurement of particule dynamics in slow, dense granular Couette flow[END_REF][START_REF] Mueth | Signature of granular microstructure in dense shear flows[END_REF][START_REF] Tardos | Forces on a slowly rotating, rough cylinder in a Couette device containing a dry, frictional powder[END_REF][START_REF] Tardos | Slow and intermediate flow of a frictional bulk powder in the Couette geometry[END_REF][START_REF] Wang | Particle dynamics and effective temperature of jammed granular matter in a slowly sheared 3D Couette cell[END_REF]. However, the visualization of the granular interface is usually limited to the upper (free surface) or bottom layers (through a transparent glass window) [START_REF] Chambon | Shear with comminution of a granular material: Microscopic deformations outside the shear band[END_REF][START_REF] Koval | Interface behavior of granular materials[END_REF][START_REF] Koval | Slow annular shear of granular-continuum interfaces: macroscopic and mesoscopic observations[END_REF]. Following previous magnetic resonance imaging investigation of granular rheology [START_REF] Fukushima | Nuclear magnetic resonance as a tool to study flow[END_REF][START_REF] Fukushima | NMR Imaging in Chemical Engineering, chapter Granular flow[END_REF][START_REF] Kuperman | Nuclear magnetic resonance measurements of diffusion in granular media[END_REF][START_REF] Nakagawa | Non-invasive measurements of granular flow by magnetic resonance imaging[END_REF]: flows in rotating drum [START_REF] Caprihan | Correlation time and diffusion coefficient imaging : application to granular flow system[END_REF][START_REF] Ristow | Shape dynamics of interfacial front in rotating cylinders[END_REF][START_REF] Seymour | Pulsed gradient spin echo nuclear magnetic resonance imaging of diffusion in granular flow[END_REF][START_REF] Yamane | Steady particulate flows in a horizontal rotating cylinder[END_REF], vertical chute [START_REF] Chevoir | Dense granular flows in a vertical chute[END_REF], annular shear cell [START_REF] Cheng | Three-dimensional shear in granular flow[END_REF][START_REF] Cruz | Flow of dry grains : Friction and jamming[END_REF][START_REF] Mueth | Signature of granular microstructure in dense shear flows[END_REF], segregation and convection under vibration [START_REF] Caprihan | Magnetic resonance imaging of vibrating granular beds by spatial scanning[END_REF][START_REF] Ehrichs | Granular convection observed by magnetic resonance imaging[END_REF][START_REF] Hill | Bulk segregation in ro-tated granular material measured by magnetic resonance imaging[END_REF][START_REF] Knight | Experimental study of granular convection[END_REF][START_REF] Kuperman | A new technique for differentiating between diffusion and flow in granular media using magnetic resonance imaging[END_REF][START_REF] Metcalfe | Pattern formation during mixing and segregation of flowing granular materials[END_REF][START_REF] Yang | Potential energy in a three-dimensional vibrated granular medium measured by NMR imaging[END_REF][START_REF] Yang | Measurement of grain motion in a dense, three-dimensional granular fluid[END_REF], we have used MRI to measure the granular rheology (velocity and solid fraction profiles) well inside the sample.

Sec. 2 is devoted to the description of a new annular shear cell, specially designed to be inserted in a MRI device. Based on a geotechnical cylinder shear apparatus [START_REF] Chambon | Shear with comminution of a granular material: Microscopic deformations outside the shear band[END_REF][START_REF] Corfdir | A cylinder shear apparatus[END_REF][START_REF] Dumitrescu | Experimental study of the interface behavior between a structure and a granular soil[END_REF][START_REF] Koval | Interface behavior of granular materials[END_REF][START_REF] Koval | Slow annular shear of granular-continuum interfaces: macroscopic and mesoscopic observations[END_REF][START_REF] Lerat | Study of the soil -structure interface in granular media by using a new ring shear apparatus[END_REF][START_REF] Lerat | Experimental study of the soil -structure interface in granular media[END_REF], its originality relies on the control of the radial confining pressure exerted by the outer wall on the grains and on the measurement of the torque on the inner shearing cylinder.

Sec. 3 explains the multi-layer MRI velocimetry. MRI velocity measurements were performed using a spin-warp / phase encoding technique previously adapted from [START_REF] Hanlon | Rapid MRI and velocimetry of cylindrical Couette flow[END_REF] and used for routine liquid rheology in annular Couette cells (see for instance [START_REF] Bonn | Some applications of magnetic resonance imaging in fluid mechanics: Complex flows and complex fluids[END_REF][START_REF] Huang | Flow of wet granular materials[END_REF][START_REF] Jarny | Rheological behavior of cement pastes from MRI velocimetry[END_REF][START_REF] Ovarlez | Local determination of the constitutive law of a dense suspension on noncolloidal particles through magnetic resonance imaging[END_REF][START_REF] Ovarlez | Wide-gap couette flows of dense emulsions: Local concentration measurements, and comparison between macroscopic and local constitutive law measurements through magnetic resonance imaging[END_REF]). It was here further modified on purpose of quasisimultaneous assessment of different regions in the sample.

Sec. 4 describes the measurement of the velocity and solid fraction profiles, as well as the shear stress on the shearing wall, from which we deduce the influence of the roughness of the shearing interface and of the trans-verse confining walls on the granular interface rheology. Our study is restricted to the quasi-static regime (small shear velocity and/or high confining pressure).

Preliminary and complementary results are presented in [START_REF] Koval | Interface behavior of granular materials[END_REF].

Annular shear cell

The annular shear cell is inserted in the MRI device through an external support. The figure 1 shows a schematic view of the cell, which components are made of PMMA. The sample has a hollow cylinder shape. The granular material is confined between two fixed horizontal (bottom and upper) plates (height H = 10 cm), an internal rotating cylinder (radius R i = 3 cm) and an external latex homemade dip molded membrane (radius R e = 6 cm) filled with water. A pressure-volume controller (GDS ) applies a radial confining pressure P to the sample, in the range 0 -15 kPa. An optical fiber sensor (FOP MEMS 1000 kPa -Fiso Technologies ) precisely measures this pressure close to the membrane.

The internal rotating cylinder is guided by two journal bearings set in the external support, while the main cell (membrane, bottom and upper plates) is only connected to the external support through the torque sensor, which measures the whole torsion effort.

An aluminum-alloy torque sensor was specially designed, based on resistive strain gages, in the range ±10 Nm. This measurement was not possible during MRI experiment, but when displacing the cell bellow the MRI device. This prototype is a first step toward the realization of a torque sensor working inside the MRI device.

Depending on the way upper and bottom plates are mounted, it is possible to measure the whole torsion effort or only the fraction transmitted to the lateral membrane (the difference between those two measurements provides the torque transmitted by the horizontal walls).

The cell is connected to the transmission axis of a rheometer previously designed to be inserted within the MRI facility [START_REF] Møller | Shear banding and yield stress in soft glassy materials[END_REF][START_REF] Ovarlez | Local determination of the constitutive law of a dense suspension on noncolloidal particles through magnetic resonance imaging[END_REF][START_REF] Raynaud | Direct determination by nmr of the thixotropic and yielding behavior of suspensions[END_REF][START_REF] Rodts | Recent developments in MRI applications to rheology and fluid mechanics[END_REF], through a gearbox. This two-stage, timing-belt and pulley system is placed close to the cell and far from the motor. Its reduction factor of 10 provides a rotation range 1/600 ≤ Ω ≤ 1/6 RPS.

This configuration allows to place down the cell (out of the MRI tunnel) during the sample preparation and torque measurement and then move it up to the observation position.

The complete cell has a total diameter of ≈ 19.5 cm and a total height, without gearbox, of 28 cm, which fits inside the RF coil.

Multi-layer MRI velocimetry

MRI experiments were carried out on a Bruker Biospec 24/80 MRI facility operating at 0.5 T (21 MHz proton frequency). The MRI magnet is a vertical superconducting prototype (Magnex Scientific, Oxford), with a 40 cm bore. These characteristics are particularly suited for the study of large and inhomogeneous samples, exhibiting strong internal susceptibility contrasts. The magnet is equipped with a birdcage RF coil (height: 20 cm, inner diameter: 20 cm, hard π/2 pulse duration: 100µs), and a BGA26 shielded gradient system (Bruker), delivering a 0.05 T/m gradient strength with a rising time of 500µs.

MRI methodology for radial velocimetry inside the cell was that of [START_REF] Hanlon | Rapid MRI and velocimetry of cylindrical Couette flow[END_REF] as further modified by [START_REF] Raynaud | Direct determination by nmr of the thixotropic and yielding behavior of suspensions[END_REF] and [START_REF] Rodts | Recent developments in MRI applications to rheology and fluid mechanics[END_REF]. It is based on a two-pulse spin echo sequence (Fig. 2a), in which the two pulses are made space-selective in z and y direction respectively so as to virtually cut a beam along one cell diameter (Fig. 2b). A read-out gradient in x directions permits to get after Fourier transform of the signal a 1D magnetization profile along the beam. An additional pair of gradient pulses in y direction (in black) induces on the magnetization profile an x dependent phase shift reading:

ϕ(x) = γGδ∆v y (x), ( 1
)
where γ is the gyromagnetic ratio of proton, G the strength of these 'velocity' pulses, δ and ∆ are timing components of the sequence as described in Fig. 2, and v y (x) is the y velocity component along the selected diameter. In order to get a velocity profile, one performs two MRI measurements with respectively positive and negative velocity gradients, and then compares in each pixel the phase of the two magnetization profiles. When the thickness of the beam in y direction is small enough as compared with the cell diameter, such measurement may be regarded as a direct measurement of the orthoradial velocity component v θ versus the radial coordinate r (Fig. 2b). In this sequence, only the phase of NMR signal bears relevant information. It is then safe to use recycling times T R equal or even shorter than T 1 values. Indeed, an incomplete spin-lattice relaxation between two successive sequences may only affect the signal to noise ratio, but is not prone to introduce any bias, provided that the magnetization be correctly cleaned from past solicitations before each sequence. Such cleaning was here performed with a saturation module at the beginning of the T R delay.

spoil spoil /2 /2 TR sat (a) 0 1 -1 G z G y G x (b) t h v (r) r R i R o H z y x
Thanks to saturation, T R may even be chosen so as to optimize the signal to noise ratio of the experiment. Let's imagine that, because of experimental constraints, one has a fixed delay T exp to perform a velocity measurement. If some T R delay is used, then it will be possible to repeat the sequence N = T exp /T R times. Granted that the available magnetization at the beginning of each sequence scales as 1 -exp(-T R/T 1 ), and that the improvement of signal to noise ratio when repeating sequences scales as √ N, the signal to noise ratio S NR of the whole measurement process scales as:

S NR(T R) ∝ 1 -exp - T R T 1 T exp T R . ( 2
)
This quantity is maximum for:

T R opt = 1.26T 1 , (3)
and fairly stays above 90% of this maximum in the range 0.57T 1 ≤ T R ≤ 2.59T 1 . Saturation then turns out a useful tool for signal optimization.

For the assessment of the velocity profiles at different height in z direction, sequences were repeated while systematically shifting the vertical position of the beam. In order to study unsteady granular flows, it was important to make these multi-layer measurements as simultaneous as possible.

First of all, looking back at the NMR sequence, the measurement of one beam at a given position clearly affects all the magnetization of a larger region in the cell, composed of the sum of the two slices selected by each RF pulse. This, together with the use of the saturation module, prevents considering measurements at different z positions as independent: it is not possible to run the sequence at one height immediately after running the sequence at another height, even if the two associated beams are well separated. Real simultaneous measurements of velocity in multiple layers were then not possible.

We proceeded instead as follows (Fig 3). The whole measurement consisted in two nested loops. In the first loop the vertical location of the beam was shifted after each single sequence, so as to go through all necessary beam positions. The procedure was then just repeated with inverted velocity gradient strength. This first loop was inserted in a second one consisting in standard phase cycling and signal accumulation. One could get this way velocity profiles at different height measured over exactly the same period of time.

In the present work, the thickness t of the beam in y direction was 10 mm, and the recycling time T R was 3 taken as 100 ms. The typical echo-time was about 20 ms. Strong enough velocity gradients were here sufficient to select the proper coherence pathway. Our MRI system did not suffer any visible acquisition quadrature defect, so that the phase cycling procedure simply consisted here in a base-line correction, and could be completed in two steps. The minimal value of the height h of the beams was 1.5 mm. The maximum relevant value was the cell size. Thinner layers are well adapted to study regions with a strong vertical gradient of velocity, like the zone close to the horizontal walls. Because of hardware constraints, the maximum number of layers was 10. The total experimental time was 13 minutes for three layers of 1.5 mm width, 104 minutes for five layers of 0.4 mm width and 208 minutes for five layers of 0.15 mm width.

Experimental results

Three roughness levels of the rotating cylinder are tested: the first one corresponds to a vertically corrugated surface (triangular shape with thickness equal to depth of 1 mm), the second one to a glued seeds surface and the third one to sandpaper (medium grain -80). The horizontal walls (upper and bottom) are originally smooth. To modify their roughness we have sticked sandpaper and glass beads with the same diameter as the seeds (for practical reasons the beads are glued to sandpaper and not directly over the plate surface).

Mustard seeds are used as model granular material (mean diameter d = 1.5 mm, quite monodisperse, mass density of 1200 kg/m 3 ). The relaxation times are T 1 ≈ 100 ms and T 2 ≈ 40 ms.

The granular material is poured inside the cell with a funnel from the top and then levelled off (see Fig. 4). After closing the cell, the sample is confined by the application of the radial pressure through the membrane. Then, the material is pre-sheared (at least 15 rotations of the cylinder, corresponding to ≈ 2800 mm of tangential displacement of the wall) to drive it in a steady-state. Then data acquisition starts. Internal stresses associated to gravity (of the order of 0,7 kPa) can be considered to be dominated by the applied confining pressures.

The maximum value of the inertial number [START_REF] Koval | Annular shear of cohesionless granular materials: From the inertial to quasistatic regime[END_REF], used to qualify the granular flow regime, can be estimated around 3 • 10 -4 , indicating that the granular material is in the quasi-static regime.

We now discuss the radial profiles of velocity and solid fraction. They are presented as a function of r -R i , normalized by the diameter d of the grains.

Velocity profiles

We have first measured the profiles of the orthoradial velocity v θ (r), normalized by V θ , far from the horizontal walls, comparing three layers 15 mm thick separated by 10 mm (Fig. 5). Fig. 6 shows that v θ (R i ) < V θ , which signifies that there is significant sliding at the wall. Fig. 6 also shows that there is no influence of the roughness of the horizontal walls in the central zone. An approximately exponential decay of the orthoradial velocity profiles v θ (r) is measured, with a maximum value at the shearing wall, consistently with previous studies [START_REF] Bocquet | Granular shear flow dynamics and forces : Experiment and continuous theory[END_REF][START_REF] Chambon | Shear with comminution of a granular material: Microscopic deformations outside the shear band[END_REF][START_REF] Cruz | Flow of dry grains : Friction and jamming[END_REF][START_REF] Howell | Stress fluctuations in a 2D granular Couette experiment : a continuum transition[END_REF][START_REF] Koval | Slow annular shear of granular-continuum interfaces: macroscopic and mesoscopic observations[END_REF][START_REF] Koval | Annular shear of cohesionless granular materials: From the inertial to quasistatic regime[END_REF][START_REF] Latzel | Comparing simulation and experiment of a 2D granular Couette shear device[END_REF][START_REF] Mueth | Signature of granular microstructure in dense shear flows[END_REF]. Qualitatively, this shear localization is explained by the strong decrease of the shear stress away from the inner wall, while the normal stress remains approximately constant. As expected in the quasi-static regime, no influence of the velocity at the wall V θ nor of the confining pressure P has been observed.

Influence of the roughness of the horizontal walls

In a 2D system, the shear stress is entirely transmitted from the inner to the outer wall by the granular material [START_REF] Koval | Interface behavior of granular materials[END_REF][START_REF] Koval | Annular shear of cohesionless granular materials: From the inertial to quasistatic regime[END_REF]. In a 3D system, the granular material interacts with the horizontal walls, to which part of the torque is transmitted. This changes the stress distribution within the sample, and may consequently affect the 3D velocity profile. This influence of frictional lateral walls has been evidenced in granular surface flows between vertical walls [START_REF] Jop | Crucial role of sidewalls in granular surface flows: consequences for the rheology[END_REF], especially when they are rough [START_REF] Jop | A constitutive law for dense granular flows[END_REF]. We now wonder if such effect is observed close to the horizontal walls.

The analysis of the influence of the horizontal walls was based on a comparison of the profiles of 5 layers 1.5 mm thick separated by a distance of 1.75 mm (Fig. 7). The gap of 0.45 mm between the horizontal wall and the first layer ensured that only moving particles were considered in the measure. In the rough case, a similar gap was taken from the glued glass beads surface giving a total thickness of 2.5 mm. The horizontal roughness made of glass beads is not detectable by MRI, which provided a correct evaluation of the velocity of the grains in direct contact with this surface. The motion of the grains could be clearly distinguished from the motion of the cylinder, given the strong velocity gradient.

Fig. 8 shows a comparison between the profiles in the central zone and near the horizontal wall. In the case of a smooth horizontal wall, there is no significant influence. This result has practical applications, validating the measure of displacements of granular materials through transparent glass walls [START_REF] Chambon | Shear with comminution of a granular material: Microscopic deformations outside the shear band[END_REF][START_REF] Koval | Interface behavior of granular materials[END_REF][START_REF] Koval | Slow annular shear of granular-continuum interfaces: macroscopic and mesoscopic observations[END_REF]. Conversely, in the case of a rough horizontal wall, a signif-5 icant decrease is observed very close to the horizontal wall, particularly in the first layer. This indicates the transmission of shear stress between the granular material and the horizontal walls. However, the perturbation remains very localized, in contrast with granular surface flows [START_REF] Jop | A constitutive law for dense granular flows[END_REF]. The fluctuations of the velocity profiles in the first layers close to the horizontal wall is explained by the small thickness of those layers, which strongly decreases the signal to noise ratio.

Influence of the cylinder roughness

Fig. 9 shows that the cylinder roughness has a significant influence on the velocity v θ , causing offsets of the whole velocity profiles. Sliding, defined as the ratio between the maximum value of the particle velocity and the wall velocity V θ [START_REF] Koval | Slow annular shear of granular-continuum interfaces: macroscopic and mesoscopic observations[END_REF][START_REF] Koval | Annular shear of cohesionless granular materials: From the inertial to quasistatic regime[END_REF], decreases from sandpaper cylinder to the corrugated one, that is to say as the roughness increases.

Friction coefficient

The average shear stress at the inner cylinder is simply deduced from the measured torque C as S = C/(2πR 2 i H). Consistently with previous studies [START_REF] Coste | Shearing of a confined granular layer: Tangential stress and dilatancy[END_REF][START_REF] Lerat | Study of the soil -structure interface in granular media by using a new ring shear apparatus[END_REF][START_REF] Uesugi | Influential factors of friction between steel and dry sands[END_REF][START_REF] Uesugi | Frictional resistance at yield between dry sands and steel[END_REF], a linear relation between the shear stress S and the confining pressure P is observed (Fig. 10), from which an effective friction coefficient S /P is deduced (considering that the normal stress at the cylinder wall is approximately equal to P) for each of the three cylinders: 0.35 for sandpaper, 0.38 for glued seeds and 0.4 for corrugation. This increase seems consistent with the decrease of the particle sliding shown in Fig. 9. The roughness of the horizontal walls does not affect this value, which is consistent with the very localized influence of this roughness.

Solid fraction profile

In order to measure the influence of the shear on the radial distribution of grains, 3D spin density pictures (20 layers 5 mm thick in z direction, with a space resolution of 0.2 mm in both x and y directions) were performed at rest before and after shearing (at least 200 rotations, making ≈ 38 m of tangential displacement). 6 Fig. 11a and Fig. 11b show typical density pictures obtained before and after shearing respectively. For each radial coordinate, grayscale pictures were then integrated together in the orthoradial direction. Granted that the integrated spin density profile in radial direction provides a relative measurement of the solid fraction, these solid fractions ν(r) are normalized by the mean value ν m obtained before shearing, and shown in Fig. 12.

Before shearing, after the granular material has been poured in the cell, the solid fraction is relatively homogeneous, with a certain structuration (ν(r) oscillations) near the inner wall. After shearing, a much clearer structuration (already visible on the static images (Fig. 11)) together with a significant dilation is observed close to the shearing cylinder (r -R i 7d). However, the zone 7d r -R i 12d does not reveal significant solid fraction changes. This indicates that most of the volumetric variations are localized in the region near the cylinder, as reported by other experiments and simulations [START_REF] Koval | Interface behavior of granular materials[END_REF][START_REF] Koval | Slow annular shear of granular-continuum interfaces: macroscopic and mesoscopic observations[END_REF][START_REF] Koval | Annular shear of cohesionless granular materials: From the inertial to quasistatic regime[END_REF].

Conclusions

As a way to study the rheology of granular materials near an interface, we have developed a cylinder shear apparatus inserted in the MRI device, which allows the control of the radial confining pressure exerted by the outer wall on the grains and the measurement of the torque on the inner shearing cylinder. We have also developed a multi-layer velocimetry sequence for the simultaneous measurement of velocity profiles in different sample zones. This study shows that the roughness of the shearing interface significantly affects the granular interface rheology (sliding velocity and friction coefficient), while the influence of the roughness of the transverse confining walls remains localized in the very first layers. Moreover the measurement of the solid fraction profiles, based on static imaging of the sample, shows that, when starting to shear the material, its volumetric variations remains localized close to the shearing interface. Those data are useful to test models attempting to describe granular interface rheology [START_REF] Mohan | Frictional Cosserat model for slow shearing of granular materials[END_REF][START_REF] Latzel | Comparing simulation and experiment of a 2D granular Couette shear device[END_REF][START_REF] Artoni | Effective boundary conditions for dense granular flows[END_REF] for annular shear. Using this device together with the velocimetry sequence, work is under progress to study the transient behavior of the granular material, under

Figure 1 :

 1 Figure 1: Schematic view of the shear cell.

Figure 2 :

 2 Figure 2: (a) MRI sequence used for velocity measurements, and its coherence pathway. Velocity encoding gradients are shown in black. (b) Cell scheme and virtual beam cut.

1 Figure 3 :

 13 Figure 3: Organization of MRI velocimetry sequences for the quasisimultaneous assessment of n layers in the cell.

Figure 4 : 5 -

 45 Figure 4: (Color on line) Sample preparation.

Figure 5 :

 5 Figure 5: Scheme of layers in the central zone.

Figure 6 :

 6 Figure 6: (Color on line) Velocity profiles (glued seeds cylinder). (a) Smooth horizontal walls (layers 1, 2 and 3). (b) Influence of the roughness of the horizontal walls (layer 1): (•) smooth, (⊕) sandpaper, (•) glued glass beads. In inserts, the region closer to the shearing cylinder in semi-logarithmic scale.

Figure 7 :

 7 Figure 7: Scheme of layers close to the inferior plate.

Figure 8 :

 8 Figure 8: (Color on line) Velocity profiles near the bottom horizontal wall (semi-logarithmic scale, glued seeds cylinder). (a) Smooth horizontal wall (layers described in Fig.7a), (b) horizontal wall with glued glass beads (layers described in Fig.7b). ( ) layer 1, (•) layer 2, ( ) layer 3, ( ) layer 4, ( ) layer 5, ( ) central profile.

Figure 9 :

 9 Figure 9: (Color on line) Influence of the cylinder roughness on the velocity profiles: ( ) sandpaper, (•) glued seeds and ( ) corrugated. (a) Linear scale and (b) detail of the region near the shearing cylinder in semi-logarithmic scale.

Figure 10 :

 10 Figure 10: (Color on line) Average shear stress at the inner cylinder S as a function of the confining pressure P for different cylinder roughness: ( , ) sandpaper, (•) glued seeds and ( , △) corrugated. The full symbols indicate smooth horizontal walls, while hollow ones indicate rough horizontal walls (V θ = 3.14 mm/s)

Figure 11 :Figure 12 :

 1112 Figure 11: Static images used for the measurement of the solid fraction profile (sample quarter). Definition: 25 pixels/mm 2 . (a) Before and (b) after shear (corrugated cylinder).

Table 1 :

 1 List of velocimetry experiments.

Now at the National Institute of Applied Sciences (INSA), Strasbourg, France

[START_REF] Schlosser | Friction in reinforced earth[END_REF] Corresponding author. Email address: chevoir@lcpc.fr