Maud Poulin
email: maud.poulin@grenoble-inp.fr

Cédric Jean-François Boujut
email: jean-francois.boujut@grenoble-inp.fr

Cédric Masclet
email: cedric.masclet@gscop.eu

Analysis of the co-design activity: influence of a mixed artifact and contribution of the gestural function in a spatial augmented reality environment

Keywords: Co-design, activity analysis, augmented reality, intermediary objects, multimodal interactions, human system interaction

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Analysis of the co-design activity: influence of a mixed artifact and contribution of the gestural function in a spatial augmented reality environment

INTRODUCTION

The G-SCOP lab and six of its partners were involved in the European project SPARK H2020 (http://sparkproject.net/). The goal of the project is to facilitate interactions within co-design sessions involving designers and customers. The project has provided a responsive ICT platform based on Spatial Augmented Reality (SAR) technology. One of the objectives of the SPARK project was to study the influence of a mixed artifact (in a spatial augmented reality environment) on the interactions between designers and clients, and to determine if these influences are beneficial for the overall results from the codesign sessions. This allowed us to focus on gestures made during artifact-centric interactions. Thanks to the development of a real-time quantitative data collection tool and the constitution of an artifact-based interaction coding methodology, we were able to gather information on the type of artefact used by designers and clients during these interactions. Six real co-design sessions were conducted using three different technologies: spatial augmented reality (SAR), augmented reality (AR), and a standard session of tangible artifacts. The results obtained in this project showed that artifact-centric interactions (tangible, numerical, mixed) were more used than unsupported artifact interactions (about 70% of artifact-centric interactions against 30% of ephemeral interactions). Although we have collected results showing a major trend of artifact-centric interactions in contrary to gestures made in the air, we still know little on the use of these latest category. This is why we want to deepen our work on the influence of such a technology, involving a mixed artifact, on the co-design process. For this, we must proceed to an analysis of the co-design activity by the speech and the gesture of which we will strive to define the roles.

CONTEXT AND PRELIMINARY RESULTS

Co-designing is a large and complex human activity where the problem is still poorly defined, and involves several acceptable solutions at the end of the sessions [START_REF] Simon | The structure of ill-defined problems[END_REF]. Given the co-evolution of problem-solution in design [START_REF] Dorst | Creativity in the design process: Co-evolution of problem-solution[END_REF], many studies have been conducted to analyze and understand the cognitive activity underlying the design task. Ericsson and Simon [START_REF] Ericsson | Protocol analysis: Verbal reports as data[END_REF] are at the origin of the method of analysis of individual protocols whose objective is to understand the cognitive mechanisms and processes that produce relations between the stimulus and the response that appear during human activity. However, verbal interactions remain the most analyzed and traditionally used modality during protocol analysis. Indeed, Jiang and Yen [START_REF] Jiang | Protocol analysis in design research: a review[END_REF] have identified that the use of verbal protocol analysis has significantly increased since the Ericsson and Simon publications and that two types of studies coexist in the literature: the analysis of the individual design and group design analysis with a predominance for the method of "think-aloud" [START_REF] Eastman | Cognitive processes and ill-defined problems: a case study from design[END_REF]. Wishing to stay closer to the reality of the co-design sessions, think-aloud method does not appear to be relevant in our study because it is more relevant in an individual and experimental design situation.

A study conducted as part of the Eiffel project [START_REF] Darses | COMET: A method for Analysing Collective Design Processes[END_REF] has provided a method for analyzing the group design process. This method, called COMET, is based on units of sentences where each argument corresponds to a type of spoken action applied to an object to be conceived. The COMET method distinguishes a functional level that examines collaborative design from the point of view of actions and objects implemented in meetings. This method also makes it possible to distinguish a cooperative level showing sequences of actions corresponding to cooperative moves. The application of such a method in our study context seems relevant for its objective is to characterize the structure of functional communications.

Concerning the gestures coding and the functions associated to these gestures, a preliminary work has been carried out in the SPARK project by constituting a gesture coding framework. This coding framework is inspired by the work of McNeill [START_REF] Mcneill | Hand and Mind: What gestures reveal about thought[END_REF] classifying gestures in four different categories: iconic, metaphoric gestures, deictic and beats. In order to quantify and analyze artifact-centric interactions, we also identified deictic gestures (pointing) as relevant. Depending on the type of technology pointed by the participants, these artefact-based pointing gestures were related to the following categories: "tangible" for material artifacts, "digital" for digital artifacts (mainly screens and laptops) and "mixed" for the mixed artifact of the SAR system. Other types of non artefact-centric gestures have also been identified. These are gestures in the air that are not systematically meaningful and that accompany the speech. These gestures, we called ephemeral gestures, were divided into two categories: the gestures of "communication" accompanying simply the speech and the gestures "simulation of an artefact" being mimicry actions of a virtual artefact. These gestures were identified by McNeill as metaphorical and beat gestures (rhythmic) on the one hand, and iconic on the other hand. You will find below a comparative table of these two different coding: Thanks to an adaptation of the COMET coding scheme to our study as well as the refinement of the coding of the gestures coming from SPARK, we will study the influence of a mixed artefact, that is to say a spatial augmented reality technology, on the co-design activity.

SPARK

PROBLEMATIC AND HYPOTHESES

Based on a rich collection of qualitative information about co-design process in a Spatial Augmented Reality environment, our analysis will focus on the multimodal collaboration.

Then, our main research question focuses on a multimodal analysis method seeking to answer the following research questions:

-"What characterize the tangibility of an artifact on the co-design process ? -"What does tangibility transform in the collaborative activity ?"

This broad research question includes a subset of more specific questions concerning the specificity of design processes with SAR technology and also, the use and the function of gestures (artefact-centric interactions and ephemeral gestures) in design.

PROCEDURE

In order to answer the main research question, we will proceed with the following steps.

 In a first part of the thesis, we will analyze the 6 SPARK sessions in a multimodal way to bring out assumptions of tangibility effect of the artefact on the co-design process. For that, we will elaborate the new coding scheme of both speech and gestures. Based on the COMET method for the speech interactions in the one hand and the SPARK coding scheme for the gestures interactions in the other hand, we will work on the combination of these methods to our study. Being interested in the influence of the tangibility of an artifact on a SAR platform, we will compare design sessions on this platform with traditional design sessions. Then, after coding and comparison of the SAR and Standard sessions, activity patterns can be highlighted from both gestural and verbal point of view.

 In a second time, we will create another experimental stage where we will proceed as in the first step of the study but including postsession interviews. These individual post-session interviews based on the explanation interview [START_REF] Vermersch | L'entretien d'explicitation[END_REF] will allows professionals and researchers to have access to cognitive representation and expressed rationality of the participant through verbalization of his experience and what he perceived he has done during the session. It's not an interpretation of the researcher but what the participant really thought when he made a gesture or when he made an utterance about the artifact during the session. This method uses the work memory and linger on the participants' experience in a defined context, which will be here, the co-design session. The aim of these interviews are to find out what happened (real activity) according to the participant and make implicit knowledge explicit.

This second experimental stage will give us a new light from the ergonomics and cognitive psychology point of view, complementing the traditional protocol analysis methods, by accessing to the designers and clients' cognitive processes.

Comparing the design process with a mixed artifact and with a tangible artifact and thanks to the coding of multimodal interactions and the explanation interview, we hope to know if the tangibility of an artifact has an effect on the design activity.

EXPECTED RESULTS

By performing a succession of coding and analyses, we seek to understand the designers' activity from a collective standpoint.

Although the SAR and the standard sessions do not use the same technologies, we expect the steps of collaborative design activities [START_REF] Détienne | Characterization of Collaborative Design and Interaction Management Activities in a Distant Engineering Design Situation[END_REF] to be the same regardless of the tangibility of the artefact. However, some activities would be easier to achieve than others with a SAR technology, for example argue, convince and assess the product being designed.

All these co-design activities use different multimodal interaction categories. For example, we expect that the cognitive synchronisation use more gestures in the air than artefact-centric interactions. Whereas, the argue on a product should use more artefact-centric interactions than gestures in the air. The virtual artifact gestures, as for them, would be very used in cases of justification of ideas by the simulation of an action of a product. Hence, it could highlight privileged associations between activities and nature of artifacts in co-design sessions.

We wish to apply the explanation interview in order to solve the ambiguities of some interactions. Thus, we can adjust our analysis of the co-design process closer to the reality of designers.

CONCLUSION

Gestures and speech will be analyzed thanks to two methods: a traditional coding of gestures and speech as done in many protocol analysis researches and the explanation interview from the ergonomic psychology field. We hope to highlight the function of gestures in the co-design cognitive activity and make conclusions about the influence of a mixed artefact on the design process.

Table 1 :

 1 Comparison of coding scheme classifications between SPARK and McNeill

	coding scheme	McNeill coding scheme
	Virtual artefact	Iconic gestures
	Communication	Metaphoric gestures
		Beat gestures
	Tangible/Mixed/Digital	Deictic gestures
	None


THE SHADOW OF GOD IN POEMS OF THE PAST AND THE PRESENT

STÉPHANIE BERNARD

In his Preface to Poems of the Past and The Present 1 published in 1901, Thomas Hardy explains that the volume gathers "a series of feelings and fancies written down in widely differing moods and circumstances, and at various dates. It will probably be found, therefore, to possess little cohesion of thought or harmony of colouring" (CP 84).

To Hardy, though, this is no defect. Conversely, it allows for a wider expression of the thoughts and sentiments of the poet. The contradictions inherent in such a loose mode of writing and publishing give way to the rich and varied rendering of life: "I do not greatly regret this. Unadjusted impressions have their value, and the road to a true philosophy of life seems to lie in humbly recording diverse readings of its phenomena as they are forced upon us by chance and change" (CP 84). Philip Larkin seemed to share this point of view for he wrote: "One can read him for years and years and still be surprised". 2 Hardy's poetry is characterized indeed by "its resistance to belongingness". [START_REF]The Ashgate Research Companion to Thomas Hardy[END_REF] There is "a sense of the lyric's placelessness in his poetry, of its ability to unsettle and disorient both its speakers and readers, and to achieve […] a music of wondrous strangeness". 4 Hardy's treatment of the question of faith and religious belief contributes to the unsettling strangeness of the writing. As Timothy Hands puts it in his work entitled Thomas Hardy: Distracted Preacher?: "Though stridently anti-Christian on the one hand, Hardy's religious impulse is also a more complex mixture of conflicting viewpoints, a war between intellect and emotion which necessitates an artistically fructifying indecision." [START_REF] Hands | Distracted Preacher?[END_REF] A metaphorical war takes place under the reader's eyes as soon as he or she tries to trace a coherent system of ideas in Hardy's thought as it is expressed in the poems, especially in Poems of the Past and the Present.

The collection creates a feeling of indeterminacy, not only in so far as style, form and subject-matter are concerned -Hardy's "little cohesion of thought or harmony of colouring"but also as regards the notion of the passing of time, of the now and then contained in the title.

The conjoined evocation of the past and the present suggests a blurring of limits and a need to turn towards the past in order to be, or speak, in the present. Is the past the origin, the cause that gives life to the present? Or is it the shadow that darkens the present and tints every moment with the hues of loss and withering? These questions are also those Hardy seems to ask about God. Is he the Creator, the Cause?

Or the Destructor? Is God really God? In asking such questions, Hardy baffles the Victorian reader, challenges religious dogmas and undermines the notion of sacredness. But how daring is the poet? How far does he travel on that road of human self-reliance in a rejection of transcendence?

The refusal of the sacred The themes of the poems inside the collection confirm the impression of strangeness and tension which is characteristic of Hardy's poetry: some texts are about the disasters of war ("Embarcation", "The Colonel's Soliloquy"), others about the disillusions of lovers ("The Well-Beloved", "A Broken Appointment", "The Supplanter"). Others at last, like "The Mother Mourns", "The Subalterns", "To an Unborn Pauper Child", tend to evoke a bleak vision of life in general, and to convey a disenchanted philosophical outlook, derived from a loss of faith.

The reading of most poems begets an overall impression of nostalgia, i.e. a feeling that the text insists on what is lost but still longed for (whereas elegy would notify the loss as irrecoverable and definitive). In the very same manner, Thomas Hardy's loss of faith when he was a young man in London was never a thing of the past, so that most of his writings are haunted by the Scriptures and the question of belief. As Claire Tomalin explains: "He could no longer believe, but he cherished the memory of belief […]." [START_REF] Tomalin | The Time-torn Man[END_REF] Brought up in a Christian family, Hardy read the Bible and sang Christian hymns. He went to church regularly and was well aware of the differences that existed within the Anglican Church. Indeed, the parish of Stinsford to which Hardy belonged was High Church, so that he was accustomed to the ceremonial of the service there. But the rest of Dorset was chiefly Low Church, that is to say Evangelical: this meant a close reading of the Scriptures and rituals being brought to a minimum. As an apprentice in architecture in Dorchester, Hardy met Henry Robert Bastow who was a staunch Evangelical; the correspondence they kept with each other allowed for discussions on Christian dogmas, and rites such as baptism.

Hardy fluctuated between the edges of Anglicanism: in London, he would "attend a strangely polarized mixture of churches allied to established religious extremes". [START_REF] Hands | The Ashgate Research Companion to Thomas Hardy[END_REF] It may have been a foreshadowing of his later abandonment of faith and church attendance. Yet, at the same time, the hesitation can signal renewed attempts to find a suitable church and show how significant religion was to him; it suggests what impact the rejection of belief could have on his life and artwhat a void it could have left.

As for the writings, they are imbued with contradictory feelings of rejection and nostalgia as regards Christian belief. Indeterminacy pervades the whole of Hardy's creation. His lyrics notably oscillate between a rendering of prosaic reality and epiphanic "moments of vision", 8 between the despondency of loss and the joy of past regained.

An example of that oscillation can be found in the poem "The Self-Unseeing". The first stanza emphatically opposes the past and the present, to underline what used to be in the place described and consequently what has been lost.

Here is the ancient floor, Footworn and hollowed and thin, Here was the former door Where the dead feet walked in. (CP 166) Yet this vision of death allows for a revival of the past, a nostalgic re-enactment of youth's innocence and joy in the rest of the poem: She sat there in her chair, Smiling into the fire; He who played stood there, Bowing it higher and higher Childlike, I danced in a dream; Blessings emblazoned that day; Everything glowed with a gleam; Yet we were looking away! (CP 166-167) This revival can be interpreted as a moment of vision. The "dream" gives life to phantoms of the past: we see a smile, a dancing child, a violin player. Suddenly, through the melodious rhythm of the first two lines in the last stanza, one can hear the music, the footsteps of the child (/t/, /d/ and /b/ sounds), and the vibrations of the violin (/s/ sound): "Childlike, I danced in a dream; / Blessings emblazoned that day". 9 The plain reality depictedthe floor, the fireplaceallows for some sort of revelation and almost preternatural recreation of what no longer exists.

Hardy's vision, therefore, does not exclude the spiritual or the supernatural. The short story "The Withered Arm", for instance, illustrates the intrusion of the supernatural into the harsh reality of plain rural life. Several poems, too, evoke the manifestation of something that is normally invisible or ungraspable. However those manifestations are emptied of any sacredness: they have to do with "A Dream" (in "The Dream-Follower" CP 143) or a "Shape" (in "The Well-Beloved" CP 96), with "Shades" (in "I have lived with Shades" CP 184) and "Memory" (in "Memory and I" CP 185), but not with God's presence or faith.

What exists beyond grasp and beyond sight resurfaces in Hardy's writing. The movements in nature, the coming and passing of life, the presence of light and shade, the recurrent evocation of the past and memory, constitute means of representing, or at least suggesting, that not all that exists can be seen, touched or depicted. But to Hardy the ungraspable is not of God, it is of nature rather. It is not transcendent but immanent.

The consequence of immanence rather than transcendence as the origin of life is that death is no hope at all. In the poem entitled "To Life", nothing is to be expected outside life itself.

There is no hope to foster on any account, except the illusory one "That Earth is Paradise" (CP 118). The dead therefore haunt those who survive. They haunt the only space that can be haunted. This could be the reason why the figure of the spectre is recurrent in Hardy's writing. 10 In the poem "The Self-Unseeing" quoted above, "the mind's ear hears the absent footfall at the end, the last, emphatic, ghostly tread" 11 through the evocation of the "dead feet" in the first stanza. In the poem "The Well-Beloved", the speaker falls in love with a sprite who is the very ghost of his bride. When he meets the latter again, it seems that "her soul had shrunk and died, / And left a waste within." (CP 135) She has become the unsubstantial spectre.

Paul Volsik stresses that ghosts are central to the poetry of Thomas Hardy. He argues that on the one hand the ghost shows that Hardy belongs to the nineteenth century, his art appearing under the influence of the Romantics. But "the ghost is powerful also in that heor especially shegives direct access to the psychological, the dimension that the twentieth century will insist upon in several ways". 12 This psychological approach to the spectre can be traced in the poem entitled "His Immortality". Here, the poet envisions after-life as the continuation of a man's existence through the traits and memory of those he has left: I saw a dead man's finer part Shining within each faithful heart Of those bereft: Then I said: "This must be His immortality." (CP 143) But as the descendants grow old and die, the man disappears into oblivion, which could be the true meaning of death in Hardy's sense, 13 his own version of "the second death" mentioned in the Book of Revelation (2:11; 20:6,14; 21:8), but here emptied of its sacred, Christian meaning.

The death of God

Hardy empties the Christian religion of its message of hope. He often discredits or mocks the priests who may appear in his texts: to him they cannot cure the soul. Religion cannot soothe suffering mankind because it is cut off from the reality of human life. In fact, Hardy negates the foundation of Christian theology: Jesus-Christ, the Son of God. The Encyclopaedia Britannica first defines Christianity as "stemming from the life, teachings, and death of Jesus of Nazareth (the Christ, or the Anointed One of God)", then adding that:

[f]ew Christians, however, would be content to keep this reference merely historical. Although their faith tradition is historicali.e., they believe that transactions with the divine do not occur in the realm of timeless ideas but among ordinary humans through the agesthe vast majority of Christians focus their faith in Jesus Christ as someone who is also a present reality 14 .

Accordingly the Church of England insists on the relationship with Jesus Christ in its definition of "Being a Christian": Christian life is lived in relationship with God through Jesus Christ and, in common with other Christians, seeking to deepen that relationship and to follow the way that Jesus taught. […].

How do we know that 'God is for us'? Because Jesus Christ, the one human being who is completely in tune with Godwith what God wants and what God is doinghas carried the burden of our human betrayals of God and running away from goodness. He has let himself be betrayed and rejected, executed in a humiliating and agonising way, and yet has not turned his back on us. Death did not succeed in silencing him or removing him from the world. He is alive; and that means that his love is alive, having survived the worst we can do [START_REF] Williams | Being a Christian[END_REF] ." (my italics)

In his approach to religion, Hardy does seem to silence Jesus Christ by not mentioning the Resurrection and by obliterating the notions of hope, life, and communion that are characteristics of Christian faith. As an example, "The Bedridden Peasant" (CP 124), who is agonizing on his death bed, addresses God, "the Maker". He sounds submissive and reverent in the end: "I'll praise Thee as were shown to me / The mercies Thou wouldst show" (CP 125). However he does not mention the very core of orthodox Christian faith, never alluding to Jesus, the Saviour.

He praises "an Unknowing God", as the subtitle indicates, which heightens the tragedy and hopelessness of his situation: But Thou, Lord, giv'st us men our day In helpless bondage thus To time and Chance, and seem'st straightaway To think no more of us! (CP 125) There are indirect echoes of the Gospel in the poem. "But Thou, Lord, giv'st us men our day" recalls Jesus's prayer in Luke 11.3: "Give us day by day our daily bread". The expression "For Thou art mild of heart" that appears line 16 alludes to Matthew 11.29: "I am gentle and humble in heart". But these occurrences tend to heighten the subversive and even provocative irony of the painful whimper. The poor peasant seems culturally imbued with Christian teachings without being personally convinced or truly grasped by the essence of the belief, so that his conventional Christianity makes him feel abandoned by the powerful God who should be all-loving and all-knowing.

Similarly, "The Respectable Burgher" who decides to "sit on Sundays in [his] chair, / And read that moderate man Voltaire" (CP 159), rejects the contents of the Old and New Testaments: he expresses doubts about the veracity of the stories of several prophets and Biblical characters; more strikingly he refuses to name Jesus Christ. Although the speaker pretends to omit the name for the sake of respect ("but for shame I must forbear" CP 160), the effect of the two long dashes that signal the place left vacant by the omission is to empty the Biblical message of its substance. Christianity is hollowed out of its gospel of love: the absence of the moment when God offers his son to save humanity (John 3:16)in other words, the negation of incarnationmeans depriving the Gospel of its meaning and denying its historical and human dimension.

Logically, therefore, God appears as a distant and potentially cruel entity, cut off from the humanity he has made. In the last line of the poem entitled "The Sick Battle-God" the poet declares: "The Battle-god is god no more" (CP 99). On first reading, the "Deity" may recall the God of the Old Testament, especially in the first stanza:

In days when men found joy in war, A God of Battle sped each mortal jar; The peoples pledged him heart and hand, From Israel's land to isles afar. (CP 97) This last line, however, shows that Hardy does not refer narrowly to a Judeo-Christian context. The "isles afar" designate other religious traditions and Hardy's thought underlines the universality of the urge to oppose, destroy and dominate. The author denounces man's idolatry more than the god in question.

The Battle-God, who is "god no more", announces "the Monarch" of "God's Funeral" in the later collection of poems entitled Satires of Circumstances. The said Monarch is a "manprojected Figure" described as "jealous, fierce, at first" and who was then given "justice as the ages rolled" (CP 327). The story of that god is in reality the history of humanity. Hence, each poem deprives its god of any sacredness or grandeur, and suggests that men are the creators of the divinity, urged by a need to revere and believe.

On the one hand, both poems could be read as daring, revolutionary, even blasphemous pieces. On the other hand, the displacement of the focus onto man and his idolatry undermines the argument and relocates the core of the subject: the absence of transcendence results in human tragedy. Man is mistaken and errs in a universe that surpasses him. The poet himself is mistaken: the hope for a better world and for the weakening of the war spirit expressed in "The Sick Battle-God" acquires a tragic and pessimistic dimension in the light of later events, such as the two World Wars. The irony which is so typical of Hardy now turns against the poet himself.

These several aspects could leave the reader with the impression of a desperate philosophical thought, of a nihilistic and pessimistic vision of life. The impact of Nietzsche's thought can be discerned in the description of a crowd weeping over the death of God as well as in the title "God's Funeral". The poem could be read as a rewriting of the so-called "parable of the madman" in Nietzsche's The Gay Science published in 1882: "Have you not heard of that madman who lit a lantern in the bright morning hours, ran to the market-place, and cried incessantly: "I am looking for God! I am looking for God!" As many of those who did not believe in God were standing together there, he excited considerable laughter. "Have you lost him, then?" said one. "Did he lose his way like a child?" said another. "Or is he hiding? Is he afraid of us? Has he gone on a voyage? or emigrated?" Thus they shouted and laughed. The madman sprang into their midst and pierced them with his glances. "Where has God gone?" he cried. "I shall tell you. We have killed himyou and I. We are his murderers." [START_REF] Nietzsche | The Gay Science, Book III[END_REF] Both texts enact the death of God and denounce man's foolishness in revering an idol.

They also express man's distress after losing his way and his points of reference with the disappearance of God. Indeed, the parable ends up with a series of questions: "Whither are we moving now? Away from all suns? Are we not perpetually falling? Backward, sideward, forward, in all directions? Is there any up or down left? Are we not straying as through an infinite nothing?" 17 These questions are echoed by stanza XII in Hardy's poem: "And who or what shall fill his place? Wither will wanderers turn distracted eyes For some fixed star to stimulate their pace Towards the goal of their enterprise?"… (CP 328) Nevertheless the feeling of disillusion and disorientation is not equivalent in both texts.

While in Nietzsche's story the laughter of the people standing in the market-place resounds, deriding the madman and stressing the ridicule of the situation, Hardy's speaker insists on the memory of what has been lost and cannot be regained. There is no notion of radical nihilism [START_REF]That is, "God is dead" because the timeless and universal standpoint of God has led to "nihilism"the viewpoint that there is essentially nothing meaningful to our world beyond a set of true facts." (Adrian Samuel, 'Nietzsche and God' (Part I)[END_REF] in Hardy who found him "incoherent" [START_REF] Bridgewater | English writers and Nietzsche[END_REF] and had "an unfavorable opinion of Nietzsche, which paralleled that of a greater part of the English community in the early twentieth century". [START_REF] Demille | Nietzsche, Conrad, Hardy, and the "Shadowy Ideal[END_REF] So that, even in "God's Funeral", a feeling of doubt and sadness gradually replaces the intimation of blasphemy that can be derived from the reading at first, for the speaker eventually joins the procession of mourners, "'twixt the gleam and gloom" (CP 329).

Blasphemy or disenchantment?

This movement that takes poet and reader away from philosophical considerations and cold irony, and closer to the condition and moods of man, appears clearly in the poem entitled "The Church-Builder" (CP 170) published in Poems of the Past and the Present. The vision is no longer that of an anonymous "I", but of the dismayed church-builder, arousing and encouraging the reader's empathy.

The denunciation of religion is conveyed through the personal testimony, the intimate story of pain and failure of one particular man. The general effect is much closer to blasphemy than in the two previous poems. The mise en scène of his suicide in this place of communal worshipsuicide being condemned by the church and Christianity at large as a transgression of the sixth commandment "Thou shalt not kill" -is "mockery" (CP 172) in the face of society and religion.

The Church-Builder's abandonment of faith is complete and definitive, but it also has undertones of tragedy. The man spent all his money, neglected his family, and wasted his strength in order to realise the dream of his life. But, like the dream of Jude the Obscure, "[...] the whole scheme had burst up, like an iridescent soap-bubble, under the touch of a reasoned inquiry". 21 The new awareness has undertones of the absurd: My gift to God seems futile, quite; The world moves as erstwhile; And powerful Wrong on feeble Right Tramples in olden style. My faith burns down, I see no crown; But Cares, and Griefs, and Guile. (CP 171)

The story of that man turns out to be a tale of self-destruction. The irony of the situation is extreme as all his efforts and "stintless pains" (stanza I) to build an incredible edifice of "ashlared masonry" (stanza II) and "ivoried Rood" (stanza IV), "emblazoned glass" and "jewels" (stanza III) attract the others' scorn and deprive him of all hope and faith. The last stanza, dramatizing the probable reactions of those who will find the dead man's body in the church, sums up his predicament in poignant terms:

Well: Here at morn they'll light on one Dangling in mockery Of what he spent his substance on Blindly and uselessly!... "He might," they'll say, "Have built, some way, A cheaper gallows-tree!" (CP 172)

The ending of the poem is all the more ironical as the church-builder turns the mockery against those who used to laugh at him. He is now the one to "sneer and smirk" (stanza VII), very like the Conrad character of Kayerts who, in An Outpost of Progress, "was hanging by a leather strap from the cross" and "irreverently […] putting out a swollen tongue". [START_REF] Conrad | An Outpost of Progress[END_REF] By writing his own end in advance, he defies God, becoming the creator of his own story. Yet the denunciation targets men and society again, as much as it targets God who is not addressed directly but appears to be absent and uncaring.

The individualization of the outlook humanizes the rebellion and de-rationalizes the argument. The doubt so common in Hardy's texts and which recalls his agnosticism, the insistence on the particularity of an individual's vision, as well as the numerous versions of the representation of God in the poetry, do not allow for a systematic discourse on religion, or for a clear-cut and methodical denunciation of God on scientific grounds. So, the poet continues his quest. He does not announce, after all, the death of God but the disappearance of man's belief in God or in a man-created image of God. He asserts the coming of a new, godless and disenchanted age, in an orphan world. Hardy's writings, in other words, resist the diktats of philosophy, relying more on impressions and intimations that emphasize the tragedy of loss and endow the poems with nostalgia.

The absent keeps returning in Hardy's texts through the memory of those who are still presentoften through the voice and gaze of a solitary figure that can be that of the poet himself. "The dominant figure for his art is the voice of the absent person, lost or dead", [START_REF] Harrison | The Ashgate Research Companion to Thomas Hardy[END_REF] and so is it with God whose absence is enigmatic and does not allow for a final answer to the question of his existence and his attributes.

Is God absent or unconscious? Is he malevolent or simply not caring? Senseless or merely clumsy? The obsession with the question of God, of the origin of life, of suffering, makes it impossible for Hardy to be satisfied with a monolithic answer. This accounts for what could appear as incoherence in the discourse but allows for the never-ending quest of the poet whose imagination seems to be inhabited by the spectre of the ungraspable divine.

One of the answers offered by the poet in response to this endless questioning is that humanity has been abandoned and is now "God-forgotten" (CP 123):

-"The Earth, sayest thou? The human race? By Me created? Sad its lot? Nay: I have no remembrance of such place: Such world I fashioned not." -(CP 123)

In the poem God's forgetfulness is almost wish-fulfillment. The poet's hope for a creator who would suddenly remember his creatures is but a "childish thought" (CP 124), for God remains, as in James Joyce's Portrait of the Artist as a Young Man, "invisible, refined out of existence, indifferent, paring his fingernails [START_REF] Joyce | A Portrait of the Artist as a Young Man[END_REF] ".

The absent creator in Joyce's meaning is God, but also the artist himself. Irony surges if we apply the quotation to Hardy, for while he reproaches God with creating a world he abandons, he does the same in his fiction from which he seems absent and in which the characters are the victims of fate. The narrator is what Nathalie Bantz calls "a figure of the absent" in the short stories. [START_REF] Bantz | Les Nouvelles de Thomas Hardy, Stratégies narratives d'une écriture sous contrainte[END_REF] In the novels, the narrator is more intrusive, often infusing the text with his own view of event and character. Yet the narrative voice fades further away with each new novel. In the poems, the first person is more present, revealing itself through a mosaic of personae and stances, making the ambivalence of the position toward God even more blatant. A doubt remains, which is inscribed in the fluctuating narrative standpoint in the various works and in the artistic commitment of the author. This suggests that Hardy cannot go as far as Joyce in his denunciation of God. Hardy's craft largely amounts to counter the disappearance of meaning and the absence of form that characterize the universe and human existence in his eyes, and to make up for that loss through artistic creation. While Joyce or Conrad attempt to say the unspeakable, Hardy depicts what can be represented in order to suggest what is hidden and ungraspable.

Hesitating between the Victorian age and the dawn of modernity, he offers a multiple vision that gives birth to numerous images of God in Poems of the Past and the Present.

A ghostly presence

Sometimes God is presented as a careless weaver or clumsy mother. The effect is that God is repeatedly feminized and deprived of the unlimited power conferred to him by the traditional view of an omniscient, all-powerful masculine presence. The poem "The Sleep-Worker", for instance, delineates a mother-god who has "unwittingly" (CP 121) blundered in her creative gesture. The world she has created is a mixture of joy and pain, of "right enmeshed with wrong", "of ache and ecstasy" (CP 121), that seems beyond all comprehension. The poet's perplexity is reinforced by the absence of an answer, the silence of the "Sleep-Worker".

The same idea of the unconsciousness of God informs the poem "Doom and She", in which the creator is represented as a blind "Matron": "Unlit with sight is she" (CP 119).

Deprived of one of her senses, she is nonetheless full of empathy for her "clay-made creatures" and wishes she could see what she has done. She addresses her male companion, who personifies the very Hardyan concept of "Doom", asking him to be her vision: "The fate of those I bear, Dear Lord, pray turn and view, And notify me true; Shapings that eyelessly I dare Maybe I would undo.

Sometimes from lairs of life Methinks I catch a groan, Or multitudinous moan, As though I had schemed a world of strife, Working by touch alone." "World-Weaver!" he replies, "I scan all thy domain; But since nor joy nor pain It lies in me to recognize, Thy questionings are vain." (CP 119)

Unfortunately "Doom" is blind at heart: "Vacant of feeling he" reads the text. This heartless lord cannot fulfil the "World-Weaver"'s wish:

-Unanswered, curious, meek, She broods in sad surmise….

-Some say they have heard her sighs On Alpine height or Polar peak When the night tempests rise. (CP 120)

The last stanza with the repetition of the sound /ai/ allows us to hear her sincere and heartbreaking "sighs" as they are echoed by the "Alpine height" and the tempests that "rise".

The pair here depicted give a strange image of the creator and this undermines the notion of a powerful and omniscient God. This tale of a blind, vulnerable mother and a heartless, unfeeling father as the origin and cause of humanity leaves an impression of powerlessness and, indeed, doom. The image of the couple is all the more sarcastic as one may think of Hardy's conception of marriage as a mere contract rather than as a sacred union or at least a love match 26 .

In the last one of the Poems of the Past and The Present, whose Greek title is "ΆΓΝΩΣΤΩΙ ΘΕΩΙ", the character named "Doom" is echoed by the "Willer masked and dumb", Who makest Life become, -As though by labouring all-unknowingly, Like one whom reveries numb.

How much of consciousness informs Thy will, Thy biddings, as if blind, Of death-inducing kind, Nought shows to us ephemeral ones who fill But moments in Thy mind. (CP 186)

These personae lead us back to the notion of immanence for they are alternative versions of the universal cause that, in the later poem "The Convergence of the Twain", Hardy will reduce to the senselessness of the "Immanent Will that stirs and urges everything" (CP 306). [START_REF]The Convergence of the Twain[END_REF] The Will is initially alluded to in the opening of the Dynasts, Hardy's epic drama about the Napoleonic Wars (1904-1908). One character of the tragic chorus says:

[…] like a knitter drowsed, Whose fingers play in skilled unmindfulness, The Will has woven with an absent heed Since life first was; and ever will so weave.

To counter this "skilled unmindfulness" that gives birth to a cruel reality torn apart by antagonistic forces, Hardy uses his own artistic will, his visionary power to shape a sensible rather than a senseless world. The life he creates becomes meaningful in an artistic way, as opposed to the meaninglessness of real life. So that through writing Hardy infuses consciousness and form into creationat least into his creations, and more particularly in the poetry, with its insistence on sound, rhythm and structure. For, to him, "[t]o find beauty in ugliness is the province of the poet". [START_REF] Florence | The Life of Thomas Hardy[END_REF] The fabric of the universe has been loosely knitted, while it should have been the work of a delicate embroiderer. This is what Joseph Conrad will suggest some years later in a letter to R. B. Cunninghame Graham in which he develops the concept of the knitting machine:

There islet us saya machine. It evolved itself (I am severely scientific) out of a chaos of scraps of iron and behold!it knits. I am horrified at the horrible work and stand appalled. I feel it ought to embroiderbut it goes on knitting. […] And the most withering thought is that the infamous thing has made itself: made itself without thought, without conscience, without foresight, without eyes, without heart. It is a tragic accident -and it has happened… It knits us in and it knits us out. It has knitted space, time, pain, death, corruption, despair and all the illusionsand nothing matters. [START_REF]Joseph Conrad's Letters to R. B. Cunninghame Graham[END_REF] The echoes between this quotation and the extract from The Dynasts hint at the modernity of Thomas Hardy. The terms chosen by each writer suggest a strange connection with Joseph Conrad, one of the fathers of modern fiction. Besides, the correlation highlights the fact that Hardy's stance, as stated above, is that of the poet and not that of the philosopher. If Schopenhauer's influence can be traced in the notion of the Will, it is the never-ending quest and the need to turn it into words and worlds that prevailsthe need for the poet and novelist to "embroider" where the senseless machine "knits". Moreover, it is necessary to bear in mind that, at the time of the writing of Poems of the Past and the Present, the notion of the Immanent Will was not yet defined. Several texts give rise to philosophical or metaphysical questions. Nevertheless, most poems in the collection convey an impression rather than assert a theory: they convey the impression that something

The Complete Poems, 83-187. The Complete Poems will hereafter be referred to as CP.

Philip Larkin is quoted by James Gibbon in his "Introduction" to The Complete Poems, CP xxxv.

is happening beyond the veil of words, outside the reality described or the story told, as if word after word the vision "is turning ghost" (CP 115).

The texts are inhabited by an indefinable force that seems to infuse every line. Most poems reveal an invisible but powerful presence, the ghostly shadow of God. In "God-Forgotten" (CP 123), for instance, the speaker is addressing God while denying His existence. The poem even opens on the image of the narrator standing "within / The presence of the Lord Most High". The image may well be a mirage; it nevertheless initiates a dialogue between himself and his creator. The latter's answers are imagined only and unheard in reality; however they are printed on the page.

In the same way, the three sad and meditative poems that make up "In Tenebris" are headed by quotations from the Book of Psalms. Each of the three extracts from the Psalms expresses alienation and despair, instead of offering hope and relief. The epigraph to "In Tenebris III" reads: "Heu mihi, quia incolatus meus prolongatus est! Habitavi cum habitantibus Cedar. Multum incola fuit anima mea." (Psalm 120:5, CP 169) The translation in the King's James Version is the following: "Woe is me, that I sojourn in Mesech, that I dwell in the tents of Kedar! My soul hath long dwelt with him that hateth peace."

The verse casts a gloomy and woeful shadow on every remembered scene in the poem, in the very same manner as the repeated evocation of "the ending" that might "have come" places the spectre of death at the heart of the text. The reader, therefore, seems to be the witness of inverted moments of vision. The potentially blissful episodes turn out to be sad and pale; the atmosphere is growing darker as on "a winter-wild night" (CP 169): those moments blind rather than reveal. God's words quoted in the epigraph no longer bring light, yet they remain "'Written indelibly", as the Lord says in "By the Earth's Corpse" (CP 126).

In that poem the irony becomes tragic nostalgia: the creator repents too late of what he has done. Life on earth has disappeared and he regrets Hardy reverses the traditional notion of hell: it is God who now repents for the wrongs he has done ("it still repenteth me!" CP 127). His own version of Christianity is subversive: because of his "eternal mind", God is doomed to remember and regret "that late earthly scene"what used to be and is no more. God becomes tragic. He is paradoxically presented in a very human way: the uncaring maker is now torn by a feeling of shame and regret. This strangely recalls Hardy's own experience after the loss of his wife Emma. The mixture of regret and desire that Hardy felt for the wife from whom he had been estranged so many years is quite similar to the nostalgia expressed in the poems about God. Besides, just as the Poems of 1912-13 are infused by Emma's ghost-like presence, so the Poems of the Past and Presentand many other poems tooare imbued with the ghost-like presence of God.

The reader, therefore, is invited to go beyond appearances. God's silence does not mean he is actually absent. On the contrary, most texts that seem to mock or at least question religion lead to "an irrefutable experience of transcendence even though the poet refuses to credit belief in any transcendent domain". [START_REF] Hughes | The Ashgate Research Companion to Thomas Hardy[END_REF] This is true of the poems that give voice to God in spite of Hardy's loss of faith, or that let the dead speak although nothing seems to be expected after this earthly life. This is true of other texts, as is suggested notably by the short story "The Withered Arm", in which the irrational and the supernatural gradually overpower the characters, the diegesis, and the text as a whole.

The shadowy, spectre-like presence of God haunts Hardy's writing. Even in his re-writing of the creation, he can never entirely get rid of the Biblical intertext. Hence, in "The Lacking Sense" which conjures up again the image of the blind mother weaving "her world-webs", the reference to an "angel fallen from grace" (CP 116) shows that the writer cannot get free of the influence of the Christian religion. The priest in "The Lost Pyx" must answer the call he has received and must look for the pyx he has lost. Similarly, Hardy must return incessantly to that call he received in his youth but rejected when he lost faith.

Religion is inescapable as Hardy himself knew. In the "Apology" he wrote in 1922 on the occasion of the publication of Late Lyrics, he contends "[…] poetry and religion touch each other, or rather modulate into each other; are, indeed, often but different names for the same thing" (CP 561). The amount of poems written suggests therefore their author's neverending quest for form and reasons to believerecalling the enduring hope of the narrator of "'The Oxen" (CP 468) in spite of "the gloom" -, and this until "He Resolve [d] to Say No More" (CP 929).


D A H Hanaor

Y Gan

M Revay

D Airey

I Einav
email: itai.einav@sydney.edu.au

3D Printable Geomaterials

Keywords: Granular media, 3D morphology, Shape generation, Surfaces

One of the many attributes of 3D printing is the ability to produce particles with independent control of morphology and material properties, parameters that are inexorably entwined in naturally occurring geomaterials. In this paper we describe the 3D printing of surrogate granular materials, show examples of the particles produced and present results showing their ability to capture real soil behaviour. Three approaches are demonstrated for the three dimensional generation of model grains. The first method involves the superimposition of a fractal surface with higher level stochastic features on the face of a closed volume such as a geodesic spheroid. The second method involves the use of Fourier descriptors or fractal geometry generated from 2D cross sections and their interpolation to produce simulated geomaterial particles in three dimensions. The third method involves the generation of complex particles by the aggregation of polyhedral elements such as cubes or octahedra which is suitable for the simulation and fabrication of porous or branching particles. Finally, we discuss applications of the fabrication of surrogate materials by 3D printing for use as standardised, printable geomaterials in future up-scaled geotechnical experiments and other geomechanical research.

Introduction

Understanding the micromechanical origins of the behaviour of granular materials is of increasing interest across multiple disciplines in science and engineering. In a broad range of naturally occurring granular materials, including soils, sediment particles, sand rocks and minerals, there is a need to establish better relationships between the multi-scale particle morphology of these geomaterials and their mechanical, hydrological, and rheological performance. This has the potential to enable more efficient utilisation of natural resources and improved reliability in geotechnical and environmental applications [START_REF] Scheel | Morphological clues to wet granular pile stability[END_REF][START_REF] Salot | Influence of relative density on granular materials behavior: DEM simulations of triaxial tests[END_REF]. Recent years have seen increasing research efforts aimed at gaining new insights into such relationships through computational and experimental methods [START_REF] Brisard | Morphological quantification of hierarchical geomaterials by X-ray nano-CT bridges the gap from nano to micro length scales[END_REF][START_REF] Cho | Particle shape effects on packing density, stiffness, and strength: natural and crushed sands[END_REF][START_REF] Cavarretta | The influence of particle characteristics on the behaviour of coarse grained soils[END_REF], Mollon and Zhao, 2013b).

The utility and significance of 3D printing techniques for the analysis of granular morphology was demonstrated recently in a study by [START_REF] Miskin | Adapting granular materials through artificial evolution[END_REF]. In this study idealised printed grains were constructed by joining 1 to 4 spherical units with minimum overlaps between the spheres. The growth in the capabilities and reducing cost of 3D printing technologies, combined with the availability of computational resources that permit high resolution, have made it possible to produce grain morphologies representative of real geomaterial particles in large quantities. Furthermore, the range of materials has expanded, facilitating the fabrication of complex grains with fixed morphology for different material properties. These capabilities now allow independent control of morphology and material properties.

The simulation of realistic geomaterial grain morphologies is of value, not only in 3D printing but also for discrete element method (DEM) models of granular materials [START_REF] Matsushima | Discrete element simulation of an assembly of irregularly-shaped grains: Quantitative comparison with experiments[END_REF]. Such methods have often assumed simplified geometries such as spherical or circular elements [START_REF] Persson | An experimental evaluation of the accuracy to simulate granule bed compression using the discrete element method[END_REF]Frenning, 2012, Cundall et al., 1979), clustered spheres or disks [START_REF] Thomas | Capturing nonspherical shape of granular media with disk clusters[END_REF], polygons [START_REF] Alonso-Marroquín | Micromechanical investigation of granular ratcheting using a discrete model of polygonal particles[END_REF] or spheropolygons (Alonso-Marroquin, 2008, Alonso-Marroquín and[START_REF] Alonso-Marroquín | An efficient algorithm for granular dynamics simulations with complexshaped objects[END_REF] and polyhedra [START_REF] Langston | Simple shear in 3D DEM polyhedral particles and in a simplified 2D continuum model[END_REF]. While these simplified geometries may be utilised effectively on a case by case basis, the hierarchical origins of surface-localised physical behaviour in geomaterials means that more complex approaches are necessary for the purposes of describing, predicting or explaining the morphological dependence of these characteristics [START_REF] Alonso-Marroquín | Experimental and numerical determination of mechanical properties of polygonal wood particles and their flow analysis in silos[END_REF], Hanaor et al., 2013).

In naturally occurring geomaterials macroscopically observed properties of friction and contact stiffness between grains are, in addition to bulk properties, governed by surface structures, which exhibit self-affine geometries showing features across a range of length-scales [START_REF] Russel | How water retention in fractal soils depends on particle and pore sizes, shapes, volumes and surface areas[END_REF][START_REF] Hanaor | Scalable surface area characterisation by electrokinetic analysis of complex anion adsorption[END_REF]. One can consider surface structures of granular material as an extension of hierarchical morphology exhibiting non-integer dimensionality [START_REF] Arasan | The relationship between the fractal dimension and shape properties of particles[END_REF][START_REF] Qin | Influence of particle shape on surface roughness: Dissimilar morphological structures formed by man-made and natural gravels[END_REF]. Additionally, cohesion and capillary forces between grains are also governed by surface structures [START_REF] Fraysse | Humidity effects on the stability of a sandpile[END_REF], further motivating the development of methods to characterise and model natural grain morphologies.

Methods to describe and classify the morphologies of naturally occurring grains predominantly invoke measures of sphericity, roundness, convexity and roughness. These parameters have been defined in a variety of manners, and have been the subject of multiple reviews [START_REF] Blott | Particle shape: a review and new methods of characterization and classification[END_REF][START_REF] Barrett | The shape of rock particles, a critical review[END_REF][START_REF] Pourghahramani | Review of applied particle shape descriptors and produced particle shapes in grinding environments. Part I: Particle shape descriptors[END_REF]. Charts put forward by Krumbein and Sloss have frequently been employed for the conventional classification of geomaterials over the past six decades [START_REF] Krumbein | Stratigraphy and sedimentation[END_REF]. However, the use of these morphological descriptors is driven primarily by convenience rather than physical meaning. Geomaterial grains are not uniquely defined by this type of descriptor and while these parameters can be extracted from image analysis with ever increasing ease [START_REF] Altuhafi | Analysis of an image-based method to quantify the size and shape of sand particles[END_REF][START_REF] Liao | On-line full scan inspection of particle size and shape using digital image processing[END_REF], they are insufficient for the computational generation and printing of simulated geomaterial particles.

Recent years have seen a growing interest in utilising Fourier descriptors to characterise particle shape on the basis of planar grain projections. This approach was first put forward in 1970 [START_REF] Ehrlich | An exact method for characterization of grain shape[END_REF] and utilises the Fourier spectrum of 2D contours to characterise grain morphology in terms of a series of numerical descriptors [START_REF] Bowman | Particle shape characterisation using Fourier descriptor analysis[END_REF][START_REF] Thomas | The use of Fourier descriptors in the classification of particle shape[END_REF]. The notable advantage to the use of Fourier descriptors is their applicability in grain simulation procedures as pioneered by Mollon and Zhao over recent years (Mollon and[START_REF] Mollon | Fourier-Voronoi-based generation of realistic samples for discrete modelling of granular materials[END_REF]Zhao, 2013a).

The ability to print surrogate granular material offers new research methods that can assist in establishing the micromechanical origins, and the role of morphology and material properties, on the behaviour of granular materials. Importantly, the concept of printable granular geomaterials offers an avenue to "standardise" soil for quality control and calibration in geotechnical testing. Currently standard materials in geotechnical laboratories are mineral sands and soils from particular geological sources, e.g. Ottawa sands [START_REF] Tarnawski | Thermal conductivity of standard sands. Part I. Dry-state conditions[END_REF]. This limitation could be overcome if the ability to fabricate uniform and consistent geomaterial specimens with controlled standardised properties can be attained.

In order to realise the opportunities afforded by 3D printing techniques in the study of granular materials, two identifiable criteria must be met: (i) simulated granular matter must be meaningful and realistic representations of the materials of interest; and (ii) parameters utilised in the generation of simulated granular matter should be readily acquirable from real materials.

In this paper we present and discuss methods for the three dimensional simulation of realistic granular materials for application in 3D printing of standardised surrogate geomaterials, and show examples of the 3D printed particles produced. We further present results showing the ability of a bulk quantity of the printable material to capture real sand behaviour under drained triaxial loading conditions, and examine issues relating to the utilisation of these methods in the study of micromechanical interactions in granular materials.

Materials and methodology:

For the different approaches presently reported, simulated grains were generated in a Matlab environment and, with all methods, individual grains were described by discrete sets of corresponding vertices and faces. Additionally, subsequent to scaling, single grains or sets of multiple grains were converted into a Standard Tessellation Language (STL) format suitable for visualisation by computed aided design (CAD) software and for fabrication by 3D printing methods. Using these methods, grains can be generated in alternative computational environments and alternate output formats can be used. Fabrication of the grains reported here was carried out using layer by layer photo-polymerisation by means of an Objet Eden 250 poly-jet type 3D printer with a spatial resolution of 32μm using Fullcure 720 resin (Stratasys, USA) in a layer by layer printing method. The cured polymer has a specific gravity of 1.19 and an elastic modulus of approximately 2 GPa.

Method 1. Fractal Surface Overlay (FSO)

Natural materials tend to exhibit multi-scale surface structures featuring statistical self-similarity or fractality. For interfaces this fractality is quantified by reference to macroscopically flat surfaces. The same approach can be applied to define the morphology of grains by their interface structure across multiple scales overlaid on a spheroidal or polygonal macrostructure.

The Ausloos-Berman type variants of the Weierstrass Mandelbrot function are used for the generation of fractal surfaces with stochastic highest level features. In macroscopically flat surfaces this can be used for the simulation of realistic surfaces. In such macroscopically planar surfaces the surface height function can be described in polar coordinates (ρ,θ) in the following form [START_REF] Yan | Contact analysis of elastic-plastic fractal surfaces[END_REF][START_REF] Ausloos | A multivariate Weierstrass-Mandelbrot function[END_REF][START_REF] Komvopoulos | Effects of multi-scale roughness and frictional heating on solid body contact deformation[END_REF][START_REF] Ciavarella | Inclusion of "interaction" in the Greenwood and Williamson contact theory[END_REF][START_REF] Hanaor | Contact mechanics of fractal surfaces by spline assisted discretization[END_REF] (1)

Here n corresponds to consecutive frequency exponents and, as with previous work, in this approach M and nmax define the number of superimposed ridges and frequencies used to construct the surface and it was found that a value of M = nmax = 40 gives a sufficiently random surface structure, such that parallel ridge networks are absent as observed in the present and prior work [START_REF] Hanaor | Effects of surface structure deformation on static friction at fractal interfaces[END_REF]. γ corresponds to a scaling factor relating to the density of frequencies used to construct the surface and is set at 1.5 similar to previous work (Ciavarella et al., 2006, Yan and[START_REF] Yan | Contact analysis of elastic-plastic fractal surfaces[END_REF], αm is an arbitrary angle used to offset asperity ridges in the azimuthal direction, D is the fractal dimension, and L is a stochastic length parameter.

In applying this method to the simulation of grain surfaces, varying the stochastic length parameter L, at lower values allows for the control of the nodularity, the number of highest scale nodes protruding from the grain, or at higher values (L>πr) allows for the control of grain elongation simulated, using a variant of Eq. 1. To implement this, a geodesic sphere is simulated at a desired resolution on the basis of an icosahedral primitive unit to yield evenly distributed () pairs where  [0 2π] is the coordinate azimuth and  [0 π] is the elevation. The vectors representing the surface coordinates are adjusted to give a fractal surface structure overlaid on the geodesic sphere. This is done separately for the two hemispheres to avoid symmetry about the equator. For vertices in the first hemisphere, having ≤π sphere radii are adjusted in the following form

    ( 3) 1 max 1 0 , , , , 1 1 2 2 ( , ) cos cos cos cos cos D n n Mn m n m n m m n m n m n R R K L L                                               (2)
where R0 is the radius of the initial geodesic spheroid,  is a random phase angle and K is an amplitude scaling parameter. For coordinates in the second hemisphere, having values of >π radii are adjusted as follows

  ( 3) 1 max 2 0 , , 11 2 2 ( ) ( , ) cos cos cos D nn Mn m n m m n mn R R K LL                                     (3)
To impart surface structure randomness, a set of randomised phase angles  of the size M × nmax is included, given by a uniform distribution

) 2 , 0 ( ,   U n m



. To avoid symmetry, for the surface of the lower hemisphere where ≤π a second phase angle ζ is included and multiplied by the term cos to give continuity of the surface across the equator (where = π A scaling factor K is included in order to normalise the amplitude of the surface features to a desired level relative to the initial geodesic spheroid radius R0.

The results of this grain generation method and the effects of varying the stochastic length parameter are shown in Figure 1. By varying the proportional size of L relative to the grain radius, it is possible to create grains with a varying number of highest level features which can yield oblong, nodular or rough grain morphologies as shown. It can be seen that low L/R values tend to yield unrealistic grains exhibiting a large number of protrusions. In the present work the precursor shape from which grains are created is a geodesic sphere. However, equivalent methodologies can be implemented using geodesic precursors generated by 3D Voronoi tessellation or other methods similar to previously reported approaches [START_REF] Mollon | Fourier-Voronoi-based generation of realistic samples for discrete modelling of granular materials[END_REF][START_REF] Mollon | 3D generation of realistic granular samples based on random fields theory and Fourier shape descriptors[END_REF][START_REF] Pena | Influence of particle shape on sheared dense granular media[END_REF]. By adjusting the magnitude of the barycentric vectors of the primitive geodesic object, particle morphologies are created such that all rays emanating from a definable central point within the particle intersect the particle surface exactly once. Such morphologies are also referred to as star-like [START_REF] Robertson | Analytic functions star-like in one direction[END_REF][START_REF] Natalini | The Dirichlet problem for the Laplace equation in a starlike domain of a Riemann surface[END_REF]. Owing to the complexity in fractal surface analysis of granular materials, with this method there are difficulties in simulating grains on the basis of parameters extracted from real geomaterials.

                               n m m n n m D n n n M m L L M Z , , ) 3 ( max 0 1 cos 2 cos cos 2 ln ) , (          

Method 2. Contour rotation interpolation (CRI)

The morphological characterisation of granular materials using image processing based methods, with initial data acquired through electron microscopy or optical methods, frequently yields 2-dimensional grain contours or polyhedra as output. These geometries describe planar projections of grains, as described by Cartesian or polar coordinates. Additionally, the computational simulation of geomaterial morphology is often conducted towards the generation of such 2D geometries owing to the greater speed with which such algorithms can be implemented relative to 3D grain generation.

A novel computational method for generating realistic 3D grain morphologies on the basis of the interpolation of three 2D grain contours was first developed and reported in a recent publication by Mollon and Zhao and has been described in greater detail elsewhere [START_REF] Mollon | Fourier-Voronoi-based generation of realistic samples for discrete modelling of granular materials[END_REF], Mollon and Zhao, 2013a[START_REF] Mollon | 3D generation of realistic granular samples based on random fields theory and Fourier shape descriptors[END_REF]. Generating particles by CRI relies in principal on the generation of three closed grain cross sections, like those shown in Figure 3, followed by processes of contour correction, revolution, stretching and morphing in order to render a morphology that amalgamates the three grain projections into a single 3D object. A variety of methods can be used to obtain realistic grain sections. In Figure 3 we show examples generated by a fractal surface profile, Fourier descriptors and from a sand grain micrograph.

This method generates 3D geometries where each surface point is defined by a distinct coordinate (ρ,θ,φ). Thus, as with grain generation by FSO, this method yields starlike objects and does not allow for the generation of branching or porous morphologies.

On the basis of Mollon and Zhao's methods, contours can be generated by means of a Fourier construction, with the modes of the amplitude spectrum, known as Fourier Descriptors (FDs). Fourier descriptors 2,3 and 8 have been shown to respectively relate to characteristics of elongation, irregularity and roughness, while the remaining descriptors are calculated following an assumed regression [START_REF] Mollon | Fourier-Voronoi-based generation of realistic samples for discrete modelling of granular materials[END_REF]. In order to generate a realistic population of non-uniform particles, a randomised set of phase angles, generated in Matlab, is included to decompose the Fourier descriptors into the elements of the Fourier spectrum which can then be used to generate a unique grain contour , such as that shown in Figure 3(b). The construction of a 3D grain by CRI of FD based contours can utilise contours generated with a constant set of descriptors, or may utilise three contours each of which is generated using divergent descriptors, to account for anisotropy effects.

It is important to note that these descriptors can be derived from the Fourier transform of the 2D grain contours which can be obtained from the analysis of grain micrographs by SEM or optical microscopy, such as that shown in Figure 3(c).

Additionally, CRI based grain generation can be carried out using fractal surface profiles as input 2D contours. These contours, such as that shown in Figure 3(a), can be generated by adjusting radii of a circle following 2D variants of Eq. 1, where θ is held constant. The integration of three scaled grain contours following the interpolation procedure of Mollon and Zhao results in the simulation of 3D grains such as those shown in Figure 4. This figure shows grains each of which were generated from three FD defined contours. In Figure 4(a) contours are generated from three different FD sets while in Figures 4(b) and 4(c) all three contours are generated using the same FD set. The grains thus produced exhibit irregularity typical of natural particles, however the interpolation method currently employed yields some unrealistic parallel ridges. Naturally occurring geomaterials occasionally exhibit morphologies that are not star-like or fully dense and thus cannot be described by a unique set of (ρ,θ,φ) coordinates. In soils, sediments, organic matter and precipitates, branching and porous forms are often encountered and the morphologies of these particles, which can be described as fractal structures are of growing interest in numerous applications [START_REF] Hanaor | Scalable surface area characterisation by electrokinetic analysis of complex anion adsorption[END_REF]. The ability to meaningfully simulate this type of particle is of value in enabling the study of the morphological dependence of hydrodynamics, mechanics, interfacial interactions and transport phenomena in granular media dominated by non star-like particles (surface points are not described by a unique set of vectors). Additionally tools for the simulation of porous and/or branching aggregates are of value for the study of particle formation in processes of aggregation, precipitation and agglomeration and the dependence of these processes on environmental conditions and system parameters (e.g. pH, temperature or surface charge).

In contrast to methods, such as FSO and CRI, that generate particles by varying the surface structure of initial primitive geodesic spheroids or Voronoi type cells, the DPA method employs an aggregation algorithm to construct particles of varied porosity and volume fractality from many convex polyhedral primary particles. Comparable algorithms for the simulation of 3D and 2D aggregates from spheroidal and cubic primary particles have been reported in earlier works [START_REF] Maggi | Method for computing the three-dimensional capacity dimension from twodimensional projections of fractal aggregates[END_REF][START_REF] Schmid | Monte Carlo simulation of aggregate morphology for simultaneous coagulation and sintering[END_REF][START_REF] Erlebacher | Computer simulations of dense-branching patterns[END_REF].

In the presently reported DPA method the morphology of aggregate geomaterial particles was controlled using Matlab by the probability for the n-th primary particle to attach to an existing polyhedron with index i (1 ≤ i ≤ n-1 ) with respect to the history of primary particle addition, where n-1 is the existing number of primary particles. Thus, the probability that an existing particle with index a ≤ i ≤ b is chosen to receive a newly placed n-th primary polyhedral particle is The n-th primary particle, described by face/vertex data is then added to one of the unoccupied faces of primary particle i . The probability Pr[a ≤ i ≤ b] is a function of the exponent ε; low exponent values result in preferential addition onto older primary particles yielding closed sphere-like aggregates, with little or no porosity (zero volume porosity is only possible when primary particles are cubic); high exponent values result in preferential addition of primary particles onto faces of recently added particles, which are likely away from the aggregated centre of mass yielding branching aggregates. This approach is readily achieved in a Matlab environment by applying the exponent ε to a uniformly distributed pseudorandom selection from existing indices.

(4)                b a di i n b i a 1 1 ) 1 ( ] Pr[
The techniques explored here can be applied using various Platonic polyhedral elements (geometries where all faces are identical polygons) or Archimedean polyhedra (faces are of two or more types of regular polygon meeting at identical vertices) (Torquato and Jiao, 2009a). In the present work we demonstrate the application of this method using cubic and octahedral primary particles, shown respectively in Figures 5 and6. Smoothing of sharp corners can be carried out by interpolation of the face-vertex data as illustrated for the aggregates shown in Figure 5. For the case of aggregation of octahedral primary particles, illustrated in Figure 6, in addition to the selection of a face on which to attach each new particle, the aggregation algorithm includes a step to select one of three possible rotational orientations for the newly attached octahedron. Moreover, while cubic aggregation occurs in a regular lattice, where sites are either occupied or vacant, for construction from octahedral elements, a further step is necessary to ensure that no intrusion into existing particles occurs. The simulation of fully dense aggregates is only possible with cubic elements as other Platonic or Archimedean solids do not allow fully dense spatial tiling (Torquato andJiao, 2009b, Torquato andJiao, 2009a). The use of octahedral or other non-cubic elements yields more porous aggregates even at high exponent values.

Particle simulation and fabrication

The morphologies obtained by the three methods can be fabricated using 3D printing methods and are further utilisable in DEM models. Here we show the 3D printer output from the poly-jet fabrication of particles alongside computer renderings of the morphologies.

Figure 7 shows the results of the 3D printing based fabrication of simulated grains generated by the FSO method. All features present in the simulated grain object are captured by the fabrication process employed. With less regular smaller scale features some distortion is found to occur about the grain equator for grains where the amplitude of roughness features is large relative to the grain radius. The generation of realistic surface morphologies necessitates the use of appropriate parameters of fractal dimension (D), stochastic length scale (L) and amplitude scaling (K) in the application of Eqs. 2 and 3. Simulated grains can be obtained using the FSO method with similitude to many rock and sand geomaterial particles in traditional terms of sphericity, surface roughness, convexity/concavity and elongation. However, anisotropic roughness, faceted surface regions, open pores and angular vertices are not achievable with this approach. Grains simulated and fabricated using the CRI approach are shown in Figure 8. Similar to previously reported results obtained from this method, grains show anisotropic features in the form of tangentially parallel surface ridges. As with the FSO method this approach shares the disadvantage of not being able to readily facilitate the generation of grains with faceted regions and/or angular vertices, frequently encountered in natural geomaterial systems. Figures 8(a) and 8(d) were generated on the basis of the mean FDs extracted from the morphological characterisation of over 1000 grains of quartz sand. Figures 8(b) and 8(e) were obtained from Garnet sand derived FDs while Figures 8(c) and (f) show the CRI generated grain on the basis of 2D contours defined by fractal surface profiles. Examination of these objects shows that the particles produced are not representative of the original material, lacking facets and angularity and further suggests that the implementation of fractal surface structure generation is more appropriately carried out using methods of the FSO type. It should be noted that more recent published studies applying random field theory on a 3D grain surface have been shown to facilitate the application of grain FDs to generate more realistic grains featuring faceted geometries without the occurrence of parallel surface ridges [START_REF] Mollon | 3D generation of realistic granular samples based on random fields theory and Fourier shape descriptors[END_REF].

Figure 8. Comparison of printed and simulated grains obtained by the CRI method

Computer rendered and printed aggregate particles generated by the DPA methods described here are shown in Figure 9. While a wide range of realistic aggregate particles are obtainable from these methods, printed specimens exhibiting a highly branching or fractal structure are found to be fragile, particularly if a small primary particle size is employed.

The morphologies that can be generated by DPA algorithms are applicable in the study of fractal aggregates such as the type often encountered in sedimentology. By constructing a calibration curve, it is possible to control the value of the exponent ε to yield a desired aggregate fractal dimension (DA) which corresponds to a term of the type:

(5) where V corresponds to the true particle volume and A relates to the mean linear size of the smallest bounding box possible. The evaluation of the fractality of aggregate particles in air, soils or aqueous media and the study of the physical and mechanical behaviour of such materials in a range of applications has motivated numerous studies in recent years [START_REF] Tang | Limitation of determination of surface fractal dimension using N2 adsorption isotherms and modified Frenkel-Halsey-Hill theory[END_REF], Tang et al., 2002, Tang and Raper, 2002[START_REF] Tang | Modelling the mechanical strength of fractal aggregates[END_REF][START_REF] Sorensen | The mobility of fractal aggregates: a review[END_REF] [START_REF] Ahmadi | Fractal dimension of soil aggregates as an index of soil erodibility[END_REF]. The ability to fabricate representative particles of controlled morphology and fractal dimension can facilitate the development and implementation of new integrated experimental and computational studies into the significance of particle morphology on mechanical properties, reactivity and mobility. Moreover DPA algorithms of the type demonstrated here can be adapted to simulate and study the heterogeneous precipitation and growth of particles from solute species through chemical and biological processes [START_REF] Chekroun | Precipitation and growth morphology of calcium carbonate induced by Myxococcus xanthus: implications for recognition of bacterial carbonates[END_REF][START_REF] Cölfen | Precipitation of carbonates: recent progress in controlled production of complex shapes[END_REF][START_REF] Hanaor | Single and mixed phase TiO2 powders prepared by excess hydrolysis of titanium alkoxide[END_REF] and also the surface chemistry dependant growth of fractal particles from suspended solid elements through processes of attraction, aggregation, cementation and sedimentation [START_REF] Kranenburg | The fractal structure of cohesive sediment aggregates[END_REF][START_REF] Markus | Modeling aggregation and sedimentation of nanoparticles in the aquatic environment[END_REF].

, A V D A log log 

Bulk material response

Grains produced by the CRI method have been subjected to geomechanical testing in a triaxial apparatus to investigate their response during compression and shear. The CRI method was chosen to produce grains for this study as it allows the input of grain parameters obtained from natural geomaterials. Figure 10 shows a bulk print of 8,000 grains of mean diameter 2mm, which is sufficient for a triaxial specimen with dimensions of 38 mm diameter by 76 mm high. The grains are produced in one print with the same parameters so that they all have the same size but some variability in surface roughness. The process of printing and etching out this number of particles takes about 1 week. Triaxial tests have been performed using two grain shapes. These have been produced using Fourier Descriptors (0,0,0.02) referred to as rough spheres, and FDs (0.15, 0.10, 0.03) referred to as rough and angular and shown in the inset to Figure 10.

The particles were placed dry, loosely and were tamped to form the triaxial specimens, which were then subjected to a small confining stress before being saturated by percolation of water followed by back pressure saturation. The specimens were then subjected to an effective confining stress of 20 kPa before performing conventional drained shearing tests. Figure 11(a) shows the evolution of stress ratio and Figure 11(b) the associated volume strains. Values of the void ratios at the start of shearing are indicated on the figures. The results for the rough spheres demonstrate shear behaviour typical of sand. The stress ratio (q/p) of the denser specimen rises to a peak, before reducing, with associated dilation, towards an ultimate state, while the stress ratio of the looser specimen rises gradually and the specimen compresses throughout. An ultimate state with a stress ratio of about 1.5 (friction angle of 37 o ) is suggested by these responses. This may be compared with an ultimate angle of about 38 o indicated by tilt table tests. Two tests are shown for the rough angular particles and in each the material compressed and the stress ratio rose steadily until the tests were terminated at large strain where the specimens were highly distorted. The second test was a repeat test using the same particles to confirm the high resistance and also to investigate whether changes in shape of the soft particles could be influencing the shear behaviour. Although a few particles were noticeably changed, it can be seen that the bulk response is not significantly affected. The friction angle implied at the test termination was 55 o . While this is unusually high, tilt table tests indicated an ultimate friction angle of 43-48 o , significantly higher than for the rough spheres and suggesting that larger strains than can be applied in the triaxial test are required for this angular material to reach an ultimate state. Although the shear responses are typical of geomaterials, during compression time dependent compressibility was observed as a result of the soft polymer comprising the grains, and further advances in material are needed to fully reproduce geomaterial properties.

Conclusions

The generation of geomaterial grain morphologies by techniques such as those described here, facilitates the fabrication of surrogate geomaterials by 3D printing. Such materials are utilisable in experimental parametric studies where morphology and material can be decoupled. Here we have focused on methods that can be applied to generate realistic and printable grain morphologies. Preliminary triaxial tests have confirmed that the printed grains are capable of reproducing aspects of shear behaviour and the significant effect that shape can have on the bulk material behaviour.

The relative advantages and drawbacks of the different grain generation methods applied here are outlined in table 2: There are two geotechnical research directions that will significantly benefit from the ability to decouple morphology and material by means of 3D printing techniques: (i) the variation of bulk constitutive behaviour with grain morphology can be studied for constant material properties; and (ii) the variation of constitutive behaviour with material properties can be studied while maintaining constant realistic geomorphology. The first direction is restricted by printing resolution, which was 32μm in the present work, while the second direction is limited by the available range of printing materials. However, we anticipate that rapid progress in 3D printing technology in terms of printing resolution, rapidity and material versatility will address these concerns. The capabilities of ceramic-material printers is continuously increasing lending to the prediction that rather than just surrogate geomaterials, future research involving the synthesis of artificial mineral geomaterials will be made possible allowing the fabrication of standardised reference geomaterials for quality control in geotechnical testing with further potential applications as a supplementary material in construction and ground improvement.

Figure 1 .

 1 Figure 1. Grains simulated using the FSO method with the stochastic length parameter (L) varied relative to grain radius from 0.1R to 10R. Fractal Dimension is maintained constant at 2.4.For a given value of L/R, the fractal dimension D can be varied to yield controlled surface-structure scaling behaviour illustrated in Figure2. As with the stochastic length parameter excessively high or low fractality values leads to unrealistic grain structures in the simulated geomaterials.

Figure 2 .

 2 Figure 2. Grains simulated using the FSO method with the applied fractal dimension (D) varied from 2 to 2.8. Stochastic length parameter is constant at L=7R.

Figure 3 .

 3 Figure 3. Sample grain contours from three sources, a simulated fractal grain profile, Fourier descriptors based contour simulation and a grain micrograph obtained by optical microscopy.

Figure 4 .

 4 Figure 4. Sample grains simulated by the CRI method using Fourier descriptor derived contours 2.3. Method 3. Directed Polyhedra Aggregation (DPA)

Figure 5 .

 5 Figure 5. Grains simulated using the DPA method with cubes, showing varied values of the exponent ε resulting in particles with controllable fractality

Figure 7 .

 7 Figure 7. Comparison of printed (left) and simulated grains (right) obtained by the FSO method

Figure 9 .

 9 Figure 9. Comparison of printed (left) and simulated grains (right) obtained by the DPA method

Figure 10 .

 10 Figure 10. Bulk printed granular material with inset showing rough angular particle

Hanaor, D. A. H., Gan, Y., Revay, M., Airey, D. W., & Einav, I. (2016). 3D printable geomaterials. Géotechnique, 66(4), 323-332.

Table 2 : Summary of grain generation methodologies investigated in the present work. FSO: Superimposition of a simulated fractal surface on a 3D geodesic spheroid

 2 Benefits:  Reproduction of natural isotropic multi-scale grain surfaces  Grain elongation control by varying highest level wavelength Drawbacks: Extraction of input parameters from real materials is challenging  Absence of smooth facets, angularity and pores  Branching morphologies cannot be simulated  Computationally intensive CRI

: Interpolation and morphing of three 2D contours to generate a 3D surface

  Benefits: Input parameters can be readily extracted from 2D grain data  Captures properties of elongation, roughness and irregularities  Appropriate for studying the effect of varying morphology Drawbacks:  Absence of smooth facets, angularity and pores  Anisotropic features in the form of parallel ridges  Branching morphologies are not represented DPA

: Controlled assembly of polyhedral elements to yield branching aggregates

  Benefits:  Reproduction of sediment particles and branching aggregates  Control of aggregate fractality by particle selection exponent  Input parameters can be extracted from particle characterisation Drawbacks:  Surface roughness is not meaningfully represented  Cannot simulate solid monolithic particles  Computationally intensive


Romain David
email: romain.david@inra.fr

Jean-Eudes Hollebecq

Llorenç Cabrera-Bosquet

Hanna Ćwiek-Kupczyńska

François Tardieu

Pascal Neveu

Identifying, naming and interoperating data in a phenotyping platform network: the Good, the Bad and the Ugly

The Good if your authority is not persistent enough. • Provide multiple output format (.txt, .html, .csv, etc.) and link them together, so the user will have the choice. • Integrate/upgrade already existing identifiers in a URI. • Use persistent-URL with 303 redirect status.

• Associate creation date to help understanding.

The EPPN 2020 is a research project funded by Horizon 2020 Programme of the EU that will provide European public and private scientific sectors with access to a wide range of state-of-the-art plant phenotyping installations, techniques and methods. Specifically, EPPN 2020 includes access to 31 plant phenotyping installations, and joint research activities to develop novel technologies and methods for environmental and plant measurements.

Here we present the results of the discussions of the 2019 annual project meeting to adopt community-approved architectural choices. It focuses on persistent identification of data and real objects, the naming of variables and the priorities for increasing interoperability among phenotyping installations. We describe the main elements to prioritize (the good) in order to enhance Findable, Accessible, Interoperable and Reusable (FAIR) quality for each data management system with a pragmatic concern for all partners.

The Bad Focus on naming...

Next challenges that need to be addressed by the EPPN 2020 community are related to:

• the partial reuse of pre-existing ontologies,

• the persistence of long-term access to data,

• interoperation between all potential users of the phenotyping data.

The Ugly A common architecture for identifiers and variable names is being built in order to enable a first level of interoperation between Phenotyping Hybrid Informations Systems (PHIS). All instances are connected to a PHIS Resource center using ontologies and enabling sharing between each instance of PHIS.

R D A P 1 4 t e r s e s s i o n W I N N E R A W A R D

•

  Use non ambiguous and persistent identifier • Use minimal information, get rid of everything that may change. • Require external identifier (B2HANDLE, e-PIC...)

•

  Unnecessary metadata in the identifier • Ownership and other information that are likely to change over time, prefer nature of the resource • Unnecessary long identifiers with too much semantic • Entirely opaque identifier • Files extension in the URI (no .extension in the URI) • Query (no "?" in the URI) • Misleading characters such as O and 0 or I and l, etc. • URI that are not the best way to identify the object you are looking at The plant phenotyping community gathers different actors with various means and practices. Among all the recommendations, the community requests identification methods (including the use of ontologies) compatible with the 'local' pre-existing ones. The identification scheme being adopted is based on Uniform Resource Identifiers (URIs) with independant left and right parts for each identifier. (based on ePID recommendations) https://www.pidconsortium.eu/?page_id=122 Focus on identification... The Good • Look for "reference ontologies", first in the dataweb stacks • Be careful of needs and implementation capacities to manage ontology links on the long term • Look for concepts related to your phenotyping experiments available in "application ontologies" in your disciplinary domain first, before creating new ones. • Ontologies should never be developed isolated. Use SKOS to link as much data as possible to reference ontologies first, and to trade/application ontologies with "exact match" then "close match" SKOS predicates • If you need a new concept, try to do it in concertation with the larger community (as far as possible) The Bad • To create an ontology before prospecting an existing one • To create an ontology without a community approving process • To give a URI for an ontology with date or version in the persistent link • To use first a species specific ontology before considering concepts from general and recommended plant ontologies • To use approximated data type • To refer to approximated data concept in your specialized ontology Naming variables need to share a community approved vocabulary, and to build or reuse appropriate ontologies. Some questions like how to choose them, how to implement and update them and with which means are recurrent challenges in the EPPN 2020 Phenotyping network. First work focuses on the associated objects and variables common to all EPPN 2020 members, namely the scientific object (which can be a plant in a pot or a plot), sensors and variables.

Acknowledgements This work was supported by EPPN 2020 project (H2020 grant agreement No 731013) & PHENOME-EMPHASIS project (ANR-11-INBS-0012) funded by the National Research Agency and the 'Programme d'Investissements d'Avenir' (PIA) & EMPHASIS ESFRI.