Mena Lafkioui

IDENTITY CONSTRUCTION THROUGH BILINGUAL AMAZIGH-DUTCH DIGITAL DISCOURSE *

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

Introduction

Despite the precarious and marginal socio-political position of the Amazigh languages, an explosion of hybrid -in form and content -cultural expressions has been occurred in recent years. 1 Now more than ever, these languages function as a central source for constructing and reconstructing the Amazigh group identity, a process in which literacy and electronic media play a significant role. One of the most far-reaching and allencompassing media is the Internet. It allows individuals and groups to create new discourses and contexts: digital interactions. 2 Therefore, I will examine how identity is (re)constructed in digital interactions on Amazigh websites. I have chosen to examine Dutch-based Amazigh websites since they are most advanced and regularly updated. Moreover, these websites show a high level of creativity, related to the large presence of Amazigh people in the Netherlands who show a keen interest in the preservation and promotion of their cultural tradition and identity. The Dutch-based Amazigh * This publication is made possible by a Postdoctoral Fellowship grant from the Flemish Fund for Scientific Research (FWO). 1 However, the socio-political status of the Amazigh languages is changing in North Africa. They have recently acquired a national -but not "official" -status in Morocco (1994) and Algeria (2002). National institutions as the Algerian HCA (Haut Commissariat de la Culture Amazighe; 1995) and the Moroccan IRCAM (Institut Royal de la Culture Amazighe; 2001) were installed to maintain and develop the Amazigh cultural patrimony. The insertion of the Amazigh languages in the national education programme of these countries is an important outcome of this development, even though these languages are still considered constitutionally as "dialects" that serve to improve the proficiency of standard Arabic. This linguistic policy fits perfectly the linguistic-educational programmes for minority languages existing in the Diaspora, for instance, the LC2 programmes of the Netherlands.

websites considered in this study are most developed (see number and design of updated hyperlinks, subpages and items) and popular (see number of registered members and hits): www.amazigh.nl (7446 registered members on 25/06/08; 7912 forum topics) and www.tawiza.nl (1255 registered members on 25/06/08; 2652 forum topics). 3 The most appropriate paradigm for a thorough understanding of the complex relationship between language and identity in a multicultural and multilingual computer-mediated context, such as the Dutch-based Amazigh websites, is the interactional sociolinguistic approach (Goffman 1974, 1981, 1983; Gumperz 1982; Gumperz & Hymes 1972; Kerbrat-Orecchioni 1990, 1992, 1994, 2001; Rampton 1995; among others), mainly because of its conceptualisation of identity as dynamic. 4 Identities are permanently constructed and reconstructed by interactants during digital interactions. A central position is attributed to the 'interactants', rather than disembodied language, who jointly construct and reconstruct meaning, and produce and reproduce cultural values, such as identities. With regard to the multiplicity (age, race, class, gender, ethnicity, geopolitical setting, social status, sexual orientation, religion...) and the hybridity of identity, this perspective permits in-depth analyses of an unlimited scale of variables by correlating social variables with linguistic variables in a multidimensional frame. The approach is enriched by using notions from the poststructuralist perspective, which is founded on the interactional paradigm. Most notably the focus on the factor power (especially political power) is crucial for this study, in the sense that speech as a social process can be a source of gaining and exercising power, and thus is fundamental for the (re)construction of identities by minorised or oppressed groups and individuals (Bourdieu 1982, 1991; Gal 1989; Heller 1988, 1992, 1995a/b; Pavlenko & Blackledge 2004; Blommaert & Verschueren 1998, 2003). Unequal power relations can obstruct the 'right to speak' and can lead to a repositioning of the 'dominated' interlocutor in the interaction context and a reconstruction of his or her identities (Bourdieu 1991).

Digital resources and Dutch-based Amazigh websites

The Internet interactants visiting Dutch-based Amazigh websites use mainly Dutch and Tarifit (Amazigh language of North Morocco) for their digital interactions. 5 These are also the two basic languages in which these websites are assembled. Arabic (Moroccan or standard Arabic), English and French are generally employed if a written or multimodal text is inserted into the website in its original format. So, the interactants are constrained in their language choice for their digital interactions by their own language repertoire (linguistic competencies and interactive skills) as well as by the digital context in which the interactions occur. Digital context involves both the micro-context of a specific interaction instance in a precise timeframe (a chat forum interaction for example) and the macro-context of the transnational Amazigh website. Having access to these contexts and hence to their benefits and restrictions implies sharing the digital resources which the websites require; in this case, Dutch and Tarifit function as linguistic and interactive resources. Sharing these resources entails, however, the exclusion of others, such as Arabic and French, which may be motivated differently following the "argumentative" programme of the website. 6 Tarifit primarily accomplishes the function of symbolic marker of the Amazigh group identity in opposition to various other local and trans-local group identities, for instance the Turkish identity (local "ethno-linguistic" identity), the Dutch identity (local national identity) and the Arabic-Islamic identity (trans-local international identity). A more pragmatic and instrumental function is assigned to Dutch as a digital resource, even though it may indicate a Dutch group identity in contrast with other national identities, such as the French identity on French-based Amazigh websites. Different interactive functions and social categories (values) are associated with different resources, whether interactively performed or unperformed in online or offline contexts. Structures and functions of digital resources are layered and stratified (Hymes 1966, 1996; Fairclough 1992; Blommaert 5 In the Diaspora, national and local policies determine basically the sociolinguistic hierarchy of the languages used by the Amazigh speakers. Mother tongues as Tarifit (Amazigh language of more than 70% of North Africans in the Netherlands), with a non-official and minority status, cannot compete with the dominant languages: Dutch, the only official language in the Netherlands, and English, which is generally seen as the most international language. Moreover, no official education is given in the mother tongues in the Netherlands.

2005) and consequently identities -considered as semiotic interactive processes -too. The Internet as an instrument of globalisation allows people to complete functions of linguistic resources trans-locally. Accordingly, it repositions these functions in the interactive (substantial and cognitive) space. The Amazigh languages, which in North Africa are officially still considered as "dialects" of "minorities" with a low socio-cultural status, may gain prestige through the trans-local transfer by the Internet. On the trans-local level, these languages may symbolise highly esteemed cultural values that may be entrenched in specific local contexts (Amazigh Diaspora in the Netherlands for instance) to create specific group identities. Moreover, the Internet may enhance their semiotic flexibility. One same sentence may be used in different online contexts consisting of diverse interactive positions from which various identities can be constructed.

Reconstructing Amazigh identity by reconstructing Amazigh oral genres on the Internet

The following example shows how a trans-local transfer of an oral text by means of the Internet deeply affects its very nature and structure and sometimes even its functions.

Example 1:

Tmazight -DV on 11-09-2003 (20.42) on Tawiza (http://www.tawiza.nl/content/awid.php?id=87&sid=1&andra=artikel)

This example is an excerpt of a narrative written text that "retells", mainly in Dutch, a traditional oral Amazigh folktale the author calls Oom Ooievaar (Dutch) or 3emmi Bheleizh (Tarifit), which means "Uncle Stork". Because it provides the clue to the narration, focus is placed on the utterance wallah ma ath fathgegh 3emmi Bheleizh thayit yinnan (By God, I shall not betray him, Uncle Stork, he told me!) by expressing it in Tarifit and thus codeswitching it with the Dutch text. Besides the function of narrative contrast, an emblematic and expressive function is related to this utterance by means of its highly marked morphological-syntactic structure (expressive sermon) sustained by a well-defined expressive intonation, though not represented in the transcript. The expression tfoe is an interesting orality marker because it literally stands for the act of spitting, which is usually produced orally (verbally and non-verbally) in the Amazigh interactions. The parts in Dutch also have an oral character indicated mainly by their direct and simple style and the large presence of expressive and short locutions. The originally oral narration, performed in Tarifit in specific offline contexts 7 , has been drastically reconstructed in order to meet the linguistic and interactive criteria which the website "Tawiza" demands. 8 Its digital recontextualisation (reframing) engages different dimensions (linguistic, social, cultural, and historical dimensions) that are all synchronised toward one signified feature: the digital folktale. Digital recontextualisation has changed the creative potential of the oral narration but not without altering the social and cultural categories associated with it. Compared with the original text, which is usually considered as normative, the digital version may be perceived as "non-literary", "non-authentic", "non-Amazigh"… in sum "wrong-footed".9

Most of the Amazigh websites offer under the hyperlink "Taal" (Language) "traditional" riddles and idiomatic expressions in Tarifit, written in Latin transcript and translated into Dutch (see samples of riddles in example 2). Interestingly, the transfer of these literary genres from an oral 7 Traditional Amazigh folktales are mostly narrated by women, usually of a certain age. They are only allowed to be performed at night because of the ancestral belief that the magical power of these narratives could inflict the audience with baldness if they were told by daylight. Even if this ancestral belief has lost its meaning to the younger Amazigh generations, it still has its function as an interaction framework, a specific ritualised setting in which ancient and modern narratives are located.

8

The website operates here as a kind of "system of contextualisation conventions" as to speak in Gumperz' terms (1992).

local interactive context to a digital trans-local one has not affected their primary social and cultural function: the transmission and exchange of Amazigh cultural tradition. Part of this literary tradition is also the complex of symbolic imaginary that these riddles evoke and require in order to be comprehended. Example 2:

Extract of riddles on Tawiza (http://www.tawiza.nl/content/sectie.php?cid=48&secties=cat)

Examples 1 and 2 illustrate how certain literary genres and productions from the Amazigh oral tradition serve as a representative basis for constructing and claiming trans-local Amazigh identities. Bilingualism (or multilingualism) is a significant aspect of this identity creating-process for several reasons. For one thing, it expands the semiotic potential and hence the interactive capacity of the interactants. For another, it is an important indicator of how they project themselves in their digital discourse. The bilingual composition of the riddles of example 2, for instance, points to different functions and values that the website editors/designers have allocated to Tarifit and Dutch. Tarifit occupies a central position in the display of these riddles, which are written in two different Latin-based orthographic systems. The first and main transcript (first line of the riddle) is written in an orthographic system that the editors of the website Tawiza generally use adequately, though without giving any information about it. This lack of information might explain why most submitted texts are written in the interactants' own orthography, as shown in the Tarifit expressions of example 1. The second transcript (fifth line of the riddle) is presented as the "standard" Amazigh orthography (Standaard tamazight), although in fact no unified or 'standard' Amazigh orthographic system -whether based on Latin, Arabic or Tifinagh (ancient Amazigh graphemes) alphabet -has yet been agreed, either for Tarifit as a single language or for the Amazigh language group as a whole. Its labelling as "standard" expresses the aspiration of the website editors to transmit these riddles -originally produced orally -in a 'modern' cultural format embodied in literacy and language homogeneity. The presentation of Tarifit as a 'written' and 'standardised' language not only responds to the ubiquitous demands and pressure for 'modernity' but also empowers it interactively by increasing its social and cultural status. The choice of a Latin-based orthographic system reinforces this status because this alphabet is commonly considered, both in the academic world and in activist circles, the most viable and 'modern' option for the writing of the Amazigh languages. Nonetheless, the Tifinagh alphabet is a significant contender in the Amazigh orthography debate (Lafkioui 2002). 10 As measured both by the number of offered items and also by the number of hits these receive, narration (example 1) and poetry are the most productive genres of Amazigh literary productions on Dutch-based Amazigh websites.11 Some of the most dynamic and popular Amazigh websites on which these genres function as symbolic cultural transmitters are "www.amazigh.nl", "www.timazighen.nl" and "www.tawiza.nl".

Chat-in-interaction: constructing the Self through digital interactions on Amazigh websites

The language representations of the interactants as expressed through their digital interactions on Amazigh websites are strongly connected to their social and individual histories and ideologies. The next excerpt demonstrates this by means of a digital forum discussion between Yidir (male) and Drifa (female), two names that are most likely pseudonyms. 12 Example 3:

Extract of a chat forum interaction on Tawiza Drifa opens the discussion by expressing her astonishment at the lack of knowledge of and proficiency in Tarifit among Imazighen youngsters in the Netherlands. 13 It is apparent that her parents monitor strictly her performance, and consequently also her proficiency, in Tarifit. She also utters her disapproval of the use of Dutch or Arabic in interactions between Imazighen, even though she uses herself Dutch for digital interaction with a fellow Amazigh: 14 12 The use of pseudonyms is a common practice on chat sites (Bechar-Israeli 1995). 13 The reference to The Netherlands is implicitly present in the semantic content of her discourse and its contextualisation on a Dutch-based website. 14 The fact that Drifa does here the very thing she disapproves of suggests a discrepancy between her representations of Tarifit and her in vivo language practices. Tarifit as a digital resource accomplishes here the interactive function of symbolic marker -the icon -of the Amazigh group identity. In contrast, the instrumental function of language Erger nog, zij praten Nederlands of Arabisch met elkaar… sad emoticon Even worse, they speak Dutch or Arabic with each other… sad emoticon Her negative attitude to this state of affairs is displayed by the expression erger nog (even worse) and the sad emoticon she has chosen to close her assessment with. The lexical choices she has made imply a recategorisation of the discourse object (forum topic), which is Wie praat er Thmazight met z'n/haar ouders? (Who speaks Tamazight with his/her parents?). By her lexical choices, Drifa strongly commits herself to her discourse and so increases the potential for interactional tension between her and her digital interactant, Yidir. However, the expression of this stance does not in fact entail a great risk of conflict between the interactants because a basic consensus is assured by the Amazigh website which functions as an attributive centring institution (Silverstein 1998) and gate-keeping apparatus (Gumperz 1982), regulating to some degree the language features, functions and contextualisation. 15 Most people who participate in the forum discussions on these websites adhere more or less to Amazigh activist ideologies (group-specific ideologies), a stance which is confirmed by the use of the emblematic expressions of Azul (Hello), D wenni nta (Goodbye), and in particular the expression Tawmat N Imazighen (The Amazigh brotherhood) employed by Yidir as a kind of signature at the end of his response. The component Tawmat (Brotherhood) of this latter expression reveals an implicit semantic and pragmatic reference to the trans-local but sub-cultural values embedded in the strongly mediated concept of "Afro-American Brotherhood".

In his response, Yidir agrees with Drifa's observation about Amazigh language "loss" among youngsters but attempts to provide excuses for it: Dat heeft een oorzaak (There is a cause for this). With a kind of authority accorded by himself to his discourse he attributes it to social, historical and political factors. In his opinion, the ones who are also to blame for this particular situation are the parents who prefer to teach darija (Moroccan Arabic) to their children for religious ("taal" van religie -"language" of -usually completed by interactive 'dominant' languages in offline contexts -is allocated to Dutch. 15 The digital context also avoids, to a certain degree, the risk of loss of face of the interactants (see Goffmann 1967 for the concept of 'face'). religion), ideological ("taal" van land -"language" of country) 16 and/or economic ("kan er geen brood mee verdienen" -"you cannot make a living of it") reasons. It is them he considers responsible for the identity crisis they have inflicted upon themselves and their children.

Drifa replies in the third paragraph that she regrets this diminution of onze mooie en unieke taal en identiteit (our beautiful and unique language and identity). The deictic marker onze (our) of this excerpt indicates that Drifa identifies with the orthodox Amazigh group identity involving representations of language, culture and history. 17 Her adoption of this identity entails a certain rejection of the use of non-Amazigh languages in the presence of Amazigh-speaking people. To Drifa, embracing Amazigh identity means the assimilation of its language and history, as indicated in the following excerpt:

Het is eigenlijk het verlochenen afstand doen van jouw afkomst als je het niet spreekt en niet op de hoogte bent van het rijke en emotionele historische verleden van onze voorouders. Ik zal mijn kinderen het thmazight letterlijk en figuurlijk met de paplepen inbrengen… inschaAllah. It is actually refuting (and) relinquishing your birthright if you do not speak it and are not aware of the rich and emotional historical past of our ancestors. I will feed thmazight to my children with a spoon literally and figuratively… God willing.

In ways like this, the Amazigh language is an essential defining aspect of Amazigh group identity, constructed in opposition to state hegemony, whether in North Africa or in the Diaspora. The concept of "Tamazight community" is strongly present in actual Amazigh activist offline and online discourses because the idea of "language community" increases the capacity to create group identities (Silverstein 1998). 18 And yet, this oppositional 16 The notion of "country" refers here to the meaning of "country of origin" and so "homeland". 17 Drifa strongly commits herself to her discourse by using this deictic expression. In fact, the whole extract reveals a high degree of discursive commitment by the interactant. 18 However, the in vivo digital interactions of the interactants on Dutch-based Amazigh websites, and hence their interrelated identity-constructing practices too, are mostly bilingual or multilingual. People who participate in these interactions by sharing the required digital resources constitute a "speech community", a concept which contrasts language-ideological alternative matches the hegemonic ideologies of linguistic and cultural exclusivity and modernity.

Chatting also allows for (meta-)discursive recontextualisation of Amazigh interactional instances, such as oral and written texts, through the reflexive nature of language (Rampton 2001; Verschueren 2001) with that of "language community", which indexes the interactants' belief that they speak/write the same language (Silverstein 1998).

Têttf ay i tuccentt deg ûdâr

Literally: A female jackal is holding my leg. ⇒ Expression used when someone feels a sudden cramp in his foot.

Identity work is displayed here by the code-switching practices between Tarifit and Dutch. More explicit identity statements in this excerpt are the following signature-expressions:

Asermed di temzi am tira deg wezru (Tarifit) Learning young is like carving in stone. 19 De enige oplossing voor Arif is op zijn minste Autonomie (Dutch) The only solution for the Rif is at least its autonomy.

Both stances are highly emotive but the Tarifit stance contains a greater symbolic and expressive load due to the linguistic code used.

During such bilingual chat forum interactions, a general consensus is reached between the interactants on the content of their discourses as well as on the interactional positions from which they express themselves. The digital context permits this negotiation of jointly (re)created identitiesrepresentations of the Self and the Other -from a symmetrical and relatively more convenient interaction position.

However, the Amazigh websites are institutionalised contexts which regroup different institutionalised genres within a wider trans-local "institutional discursive regime" (Fairclough 1992). Amazigh websites are flourishing discursive fora hosting group-specific-ideologies, some of them visible as symbolic group identity markers, others invisible because of their all-embracing features. The internet is a power-instrument with powerful symbols. The transfer of these multifaceted symbols over the Internet provides a huge semiotic potential for the construction and reconstruction of group identities.

  . The interaction in example 4 -which has Vertaling van Tmazight naar Nederlands (Translation from Tamazight into Dutch) as the forum topicillustrates this phenomenon. Example 4: Extract of a chat forum interaction on Tawiza In this excerpt, Ilizi asks how to translate two Amazigh expressions into Dutch: Tennûrzm ay i tawwûrt deg ûârûr Literally: A door has been opened in my back. ⇒ Expression used when someone feels a sudden sharp pain in his back.

The expression 'digital interactions' denotes all kind of computer-mediated interactions.

For a general iconographic examination of these Dutch-based Amazigh websites, see[START_REF] Merolla | Migrant Websites, WebArt, and Digital Imagination[END_REF].

Little attention has been paid to sociolinguistic and pragmatic topics of computermediated communication, with exception of some notable references such as[START_REF] Herring | Gender and democracy in computer-mediated communication[END_REF][START_REF] Herring | Computer-Mediated Communication[END_REF][START_REF] Herring | Interactional coherence in CMC[END_REF],[START_REF] Georgakopoulou | Self-presentation and interactional alignments in e-mail discourse: The style and code-switches of Greek messages[END_REF][START_REF] Georgakopoulou | Computer-mediated communication[END_REF] andAndroutsopoulos (2006a/b).

The argumentative programme contains the interactive objectives and functions of the website.

See[START_REF] Goffman | Frame Analysis: An Essay on the Organization of Experience[END_REF] for the concept of "footing".

The fact that the IRCAM (Institut Royal de la Culture Amazighe) has opted for the Tifinagh alphabet for their literacy practices has had a certain impact on the direction of the orthography dynamics of the Amazigh languages in Morocco.

See also[START_REF] Lafkioui | Oralité et nouvelles dimensions de l'oralité[END_REF].


Anne Humeau-Heurtier

Guillaume Mahé

Pierre Abraham

Microvascular blood flow monitoring with laser speckle contrast imaging using the generalized differences algorithm

Keywords: Medical and biological imaging, Laser speckle, Image analysis, Blood flow, Microcirculation

come

Microvascular blood flow monitoring with laser speckle

contrast imaging using the generalized differences algorithm

Introduction

The monitoring of microvascular blood flow can be performed with several optical techniques, among which laser Doppler flowmetry (LDF) and laser speckle contrast imaging (LSCI) are now currently used [START_REF] Humeau-Heurtier | Relevance of laser Doppler and laser speckle techniques for assessing vascular function: state of the art and future trends[END_REF]. In LDF, the tissue under study (skin for example) is illuminated with a low-power laser light.

The backscattered light is transmitted to a photodetector. LDF relies on the Doppler frequency shift that appears when light is scattered by moving blood cells (mainly red blood cells). The LDF perfusion is defined from the first moment of the power spectrum of the photocurrent fluctuations (see, e.g., [START_REF] Stern | In vivo evaluation of microcirculation by coherent light scattering[END_REF][START_REF] Humeau | Laser Doppler perfusion monitoring and imaging: novel approaches[END_REF]).

LDF signals have been the subject of many works (see, e.g., Refs. [START_REF] Stefanovska | Wavelet analysis of oscillations in the peripheral blood circulation measured by laser Doppler technique[END_REF][START_REF] Bernjak | Basal sympathetic activity to the microcirculation in tetraplegic man revealed by wavelet transform of laser Doppler flowmetry[END_REF]), but one of the major drawbacks of LDF is that it is a single-point measurement technique. Due to the spatial variations of the microvascular blood flow [START_REF] Wardell | Spatial[END_REF][START_REF] Braverman | The cutaneous microcirculation[END_REF], the reproducibility of the measure is poor [START_REF] Roustit | Reproducibility and methodological issues of skin post-occlusive and thermal hyperemia assessed by single-point laser Doppler flowmetry[END_REF][START_REF] Roustit | Excellent reproducibility of laser speckle contrast imaging to assess skin microvascular reactivity[END_REF]. Laser Doppler imaging (LDI) has been designed to prevent this drawback [START_REF] Wardell | Laser Doppler perfusion imaging by dynamic light scattering[END_REF]. However, for most of imagers, the image is computed by scanning the area under study which entails long recording times and prevents the monitoring of rapid physiological phenomena.

To overcome the latter point, full-field laser Doppler imagers have recently been proposed [START_REF] Serov | Laser Doppler perfusion imaging with a complimentary metal oxide semiconductor image sensor[END_REF][START_REF] Serov | Full-field laser Doppler perfusion imaging and monitoring with an intelligent CMOS camera[END_REF][START_REF] Serov | High-speed laser Doppler perfusion imaging using an integrating CMOS image sensor[END_REF][START_REF] Draijer | Twente optical perfusion camera: system overview and performance for video rate laser Doppler perfusion imaging[END_REF][START_REF] Leutenegger | Real-time full field laser Doppler imaging[END_REF][START_REF] He | 64×64 pixel smart sensor array for laser Doppler blood flow imaging[END_REF][START_REF] He | Laser doppler blood flow imaging using a CMOS imaging sensor with on-chip signal processing[END_REF][START_REF] Harbi | Body mapping of human cutaneous microcirculatory perfusion using a real-time laser Doppler imager[END_REF], but require high-speed cameras.

LSCI is another full-field optical technique for the monitoring of microvascular blood flow. It is a real-time method that does not need any scan and uses a normal CCD or CMOS camera [START_REF] Ponticorvo | How to build a Laser Speckle Contrast Imaging (LSCI) system to monitor blood flow[END_REF]. LSCI relies on the following prin- ciple [START_REF] Fercher | Flow visualization by means of singleexposure speckle photography[END_REF][START_REF] Briers | Laser speckle contrast analysis (LASCA): a nonscanning, full-field technique for monitoring capillary blood flow[END_REF][START_REF] Briers | Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging[END_REF][START_REF] Forrester | A laser speckle imaging technique for measuring tissue perfusion[END_REF][START_REF] Briers | Laser speckle contrast imaging for measuring blood flow[END_REF][START_REF] Draijer | Review of laser speckle contrast techniques for visualizing tissue perfusion[END_REF][START_REF] Boas | Laser speckle contrast imaging in biomedical optics[END_REF][START_REF] Basak | Review of laser speckle-based analysis in medical imaging[END_REF][START_REF] Senarathna | Laser Speckle Contrast Imaging: theory, instrumentation and applications[END_REF][START_REF] Briers | Laser speckle contrast imaging: theoretical and practical limitations[END_REF]: when the tissue under study is illuminated by a laser with an expanded beam, the backscattered light forms an interference pattern on the detector (a camera). Due to phase difference involved in the backscattered light, there are constructive and destructive interferences. The latter produce a pattern composed of bright and dark areas on the camera. This pattern is known as a speckle pattern. When particles move in the tissue under study, the speckle pattern changes. In LSCI, the changing speckle pattern is recorded with a camera that has an integration time in the millisecond range. Due to the long integration time compared to the typical decorrelation time of the speckle pattern, the speckle pattern is blurred in the image. The level of blurring is quantified by the speckle contrast K that is inversely related to blood flow (see an example in Fig. 1). In the laser speckle contrast imager used in our work, the perfusion is computed from

A C C E P T E D M A N U S C R I P T

1/K -1[ 3 0 ] .
It has been shown that the power spectral density measurements of the light fluctuations derived using LSCI and LDF techniques are equivalent [START_REF] Thompson | Tissue perfusion measurements: multiple-exposure laser speckle analysis generates laser Doppler-like spectra[END_REF].

LSCI data have shown to have excellent reproducibility [START_REF] Roustit | Excellent reproducibility of laser speckle contrast imaging to assess skin microvascular reactivity[END_REF][START_REF] Rousseau | Increasing the "region of interest" and "time of interest", both reduce the variability of blood flow measurements using laser speckle contrast imaging[END_REF][START_REF] Puissant | Reproducibility of non-invasive assessment of skin endothelial function using laser Doppler flowmetry and laser speckle contrast imaging[END_REF][START_REF] Humeau-Heurtier | Excellent inter-and intra-observer reproducibility of microvascular tests using laser speckle contrast imaging[END_REF]. The rapid adoption of LSCI in clinical research is also probably due to the relative ease and low cost of building an instrument, compared to other techniques such

A C C E P T E D M A N U S C R I P T

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as MRI or CT [START_REF] Ponticorvo | How to build a Laser Speckle Contrast Imaging (LSCI) system to monitor blood flow[END_REF][START_REF] Mehrabian | Calculation of intravascular signal in dynamic contrast enhanced-MRI using adaptive complex independent component analysis[END_REF]. The developments of the technique are again the subject of many studies (see, e.g., [START_REF] Duncan | Spatio-temporal algorithms for processing laser speckle imaging data[END_REF], [START_REF] Parthasarathy | Robust flow measurement with multi-exposure speckle imaging[END_REF], [START_REF] Miao | Imaging the cerebral blood flow with enhanced laser speckle contrast analysis (eLASCA) by monotonic point transformation[END_REF][START_REF] Duncan | The copula: a tool for simulating speckle dynamics[END_REF][START_REF] Duncan | Statistics of local speckle contrast[END_REF], [START_REF] Domoki | Evaluation of laser-speckle contrast image analysis techniques in the cortical microcirculation of piglets[END_REF], [START_REF] Yang | Laser speckle imaging using a consumer-grade color camera[END_REF][START_REF] He | Lateral laser speckle contrast analysis combined with line beam scanning illumination to improve the sampling depth of blood flow imaging[END_REF][START_REF] Wang | Dualwavelength laser speckle imaging to simultaneously access blood flow, blood volume, and oxygenation using a color CCD camera[END_REF][START_REF] Binzoni | Blood perfusion values of laser speckle contrast imaging and laser Doppler flowmetry: is a direct comparison possible?[END_REF][START_REF] Richards | Low-cost laser speckle contrast imaging of blood flow using a webcam[END_REF][START_REF] Humeau-Heurtier | Linguistic analysis of laser speckle contrast images recorded at rest and during biological zero: comparison with laser Doppler flowmetry data[END_REF], [START_REF] Kazmi | Optimization of camera exposure durations for multi-exposure speckle imaging of the microcirculation[END_REF]).

LSCI is now used in many medical fields such as dermatology, cardiology, vascular medicine, diabetology, neuroscience, ophthalmology [START_REF] Boas | Laser speckle contrast imaging in biomedical optics[END_REF], among others. In cardiovascular studies, LSCI can be used to analyze the impairment of tissue blood supply provoked by pathologies such as diabetes, Raynaud's phenomenon, or peripheral vascular diseases. Monitoring blood flow with LSCI can therefore allow early diagnoses or an evaluation of the evolution for such diseases. However, LSCI (as LDF and LDI) gives blood flow values in arbitrary units: no absolute values as ml.g -1 .min -1 tissue are possible [START_REF] Briers | Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging[END_REF][START_REF] Oberg | Laser-Doppler flowmetry[END_REF], as again pointed out recently (see, e.g., [START_REF] Briers | Laser speckle contrast imaging: theoretical and practical limitations[END_REF]). Another drawback of the LSCI technique is that it leads to a large amount of data: the frequency sampling of the images can be of several Hz (depending on the application) and the recordings usually last several minutes. In order to monitor the blood flow, the clinicians have therefore a stack containing many images (perfusion maps) reflecting the temporal evolution of the blood flow on the area under study. To analyze the data easily and rapidly, one or several regions of interest (ROIs) are often chosen on the first image of the image stack, and an average of the blood flow is performed in this ROI. The same ROI is chosen on the other images of the stack and thus an average of the blood flow can be studied in this ROI in time, at the rate of the image frequency acquisition [START_REF] Boas | Laser speckle contrast imaging in biomedical optics[END_REF][START_REF] Rousseau | Increasing the "region of interest" and "time of interest", both reduce the variability of blood flow measurements using laser speckle contrast imaging[END_REF]. This leads to a 1D-signal reflecting the time evolution of the average value for the blood flow in the ROI (see an example in Fig. 2). In the same time, algorithms or methods to obtain a higher spatial resolution for the images are still proposed (see, e.g., [START_REF] Cheng | Modified laser speckle imaging method with improved spatial resolution[END_REF][START_REF] Yu | High resolution mapping of cortical blood flow by mosaicing the laser speckle images[END_REF][START_REF] Liu | Fast blood flow visualization of high-resolution laser speckle imaging data using graphics processing unit[END_REF][START_REF] Miao | High resolution cerebral blood flow imaging by registered laser speckle contrast analysis[END_REF]).

However, this spatial resolution is "lost" by the averaging procedure performed in the ROIs, in clinical routine, to evaluate the evolution of the blood flow in a simple and rapid way. To get over this dilemma we propose herein a new way of visualizing LSCI perfusion data from commercialized imagers. Our procedure uses the so-called generalized differences (GD) algorithm. This leads to the age has the advantage of possessing the same spatial resolution as the original images. Our work therefore corresponds to a post-acquisition perfusion image processing procedure. Our goal is not to propose an imaging pre-processing method on raw speckle images. The problem raised by large volumes of data when imaging blood flow is of importance. Moreover, the visualization of blood flow data remains a challenging task (see, e.g., [START_REF] Borkin | Evaluation of artery visualizations for heart disease diagnosis[END_REF][START_REF] Ropinski | Multimodal vessel visualization of mouse aorta PET/CT scans[END_REF]).

Among the algorithms that are often used in the evaluation of the activity for laser speckle images we find the Fujii's method [START_REF] Fujii | Blood flow observed by time-varying laser speckle[END_REF][START_REF] Fujii | Evaluation of blood flow by laser speckle image sensing. Part 1[END_REF] and the temporal difference method [START_REF] Tekalp | Digital Video Processing[END_REF]. However, unlike the GD method (see below), the Fujii's algorithm does not take into account the difference between nonconsecutive images. This presents a drawback in the case of laser speckle perfusion evaluation as variations of perfusion are slow compared to the frequency of the image acquisition; the variations are therefore low between two consecutive images.

Comparisons between perfusion images differing by short times are not reliable because this prevents a salient analysis of slow phenomena when a relatively

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short duration is studied (a few seconds). Moreover, as for the Fujii's method, the temporal difference method is not appropriated for microvascular blood flow characterization with laser speckle perfusion data because the difference between nonconsecutive perfusion images are not taken into account. Moreover, the temporal difference method leads to a stack of N -1 difference images which does not correspond to our goal to obtain a new single image. These two methods have therefore been discarded from our work.

In what follows, we first present the GD algorithm. Afterwards, the proof of concept of our work and the measurement procedure used to acquire experimental laser speckle contrast images in different situations are described. The results obtained on simulated and experimental data with the GD algorithm are detailed and discussed. Moreover, the results are compared with those given by other algorithms.

Materials and Methods

Generalized differences

In the method called generalized differences, a new image PU GD is con-

structed from a sequence of N (perfusion) images PU k (1 ≤ k ≤ N ) as [59] PU GD (i, j)= N -1 k=1 N l=k+1 |PU k (i, j) -PU l (i, j)|, (1)
where PU k (i, j) is the perfusion value for the pixel situated at the coordinates (i, j)i nt h ek-th image of the perfusion sequence (a similar notation is used for PU l (i, j)). In the new image PU GD , regions differing in their activity are displayed as different gray levels. From Eq. 1, we observe that the GD algorithm does not depend on the order of the images. Moreover, the pixel (i, j) in image PU GD is zero (minimum value) when all the PU k (i, j) values are equal (no movement at this pixel).

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Another variant (denoted as GD*) considers not absolute values but square values of the difference [START_REF] Rabal | Dynamic Laser Speckle and Applications[END_REF]. The new image PU GD * is therefore computed as

PU GD * (i, j)= N -1 k=1 N l=k+1 (PU k (i, j) -PU l (i, j)) 2 . ( 2
)
It has been reported that one drawback of the methods based on GD is that they require many images and that the investigated phenomenon must be slow as compared with the sampling frequency [START_REF] Rabal | Dynamic Laser Speckle and Applications[END_REF]. However, for LSCI perfusion data, several seconds and even minutes are commonly recorded to monitor microvascular blood perfusion. Moreover, the frequency acquisition is usually more than 10 Hz and the phenomena of interest are often slow compared to this frequency acquisition. The above-mentioned drawback for the GD algorithm is therefore not a problem for studies like ours. Moreover, one of the advantages of the GD and GD* representations is that a range of times is encoded in a single frame.

Proof of concept

In order to show the proof of the concept used in our work (from a stack of perfusion images, we want to generate a new single perfusion image with the same spatial resolution as the original images (perfusion maps) and this new image reflects perfusion changes) we apply the GD algorithm on deterministic examples: we first generated a stack of 15 images, 30 × 30 pixels 2 each. On these 15 images, all the pixel values were identical and equal to 10 (simulating blood flow with no variations at all, or no blood flow (biological zero)), except on images 5 to 9 where a square of 6 × 6 pixels 2 had higher values, simulating a transient increase of blood flow in this region of interest (see Fig. . varying from half to more than four times larger than the simulated transient increase of blood flow, simulating transient increases of pixel amplitude due to movement artefacts (see Fig. 4).

Experimental image acquisition

Three kinds of experimental LSCI recordings have been performed to evaluate the performance of the GD algorithm in the visualization of perfusion changes from real LSCI data. All the image acquisitions have been done in laser speckle perfusion units (LSP U ) with a PeriCam PSI System (Perimed, Sweden) having a laser wavelength of 785 nm and an exposure time of 6 ms.

The first recording has been performed on the two hemispheres of a mouse, recorded through the skull. The experiment has been performed in compliance with institutional guidelines and international standards on animal welfare and approved according to local and national regulation for animal care and use for research purposes [63]. The mouse was anesthetized with isoflurane (2.5%

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induction, 1.5-2% during surgery) in 70% N2O and 30% O2. After end of preparation isoflurane anesthesia was reduced to 1.1-1.2%. Temperature was continuously measured and maintained at 37.8 • C by use of an automatic controlled homeothermic blanket system. The mouse was placed in a stereotaxic frame and the skin was removed above both hemispheres to enable cerebral blood flow measurements by LSCI. At the parietal bone a small craniotomy (∼3 mm lateral from midline/lambda and rostral to the lambdoid suture; diameter: ∼1.2 mm) was made by use of a dental drill (SI-923 implantMED, W&H Deutschland GmbH, Laufen Germany) for spreading depression induction. The LSCI recordings have been performed with a sampling frequency of 0.1 Hz and the distance between the laser head to skull was set at 10.4 cm [START_REF] Mahe | Distance between laser head and skin does not influence skin blood flow values recorded by laser speckle imaging[END_REF] which gave images with a resolution around 0.02 mm. The provocation used to obtain perfusion variations was a pinprick in one of the hemispheres that induced a cortical spreading depression/depolarization (CSD). CSD is a self-propagating wave of depolarization which corresponds to a slow-moving ionic and metabolic disturbance that propagates in cortical brain tissue [START_REF] Chang | A mathematical model of the metabolic and perfusion effects on cortical spreading depression[END_REF]. The perfusion map stack processed was composed of 10 images.

The second experimental LSCI recordings have been performed on the forearm skin of a healthy subject. The variations of the perfusion have been induced

by a local heating. The latter leads to a vasodilation and therefore to an increase of the perfusion values [START_REF] Brunt | KCa channels and epoxyeicosatrienoic acids: Major contributors to thermal hyperaemia in human skin[END_REF][START_REF] Charkoudian | Skin blood flow in adult human thermoregulation: How it works, when it does not, and why[END_REF][START_REF] Minson | Nitric oxide and neurally mediated regulation of skin blood flow during local heating[END_REF]. The recordings have been performed with a sampling frequency of 5 Hz and the distance between the laser head to skin was set at 14.7 cm [START_REF] Mahe | Distance between laser head and skin does not influence skin blood flow values recorded by laser speckle imaging[END_REF] which gave images with a resolution around 0.14 mm.

The perfusion map stack processed was composed of 100 images. . frequency of 5 Hz and the distance between the laser head to skin was set at 15.9 cm [START_REF] Mahe | Distance between laser head and skin does not influence skin blood flow values recorded by laser speckle imaging[END_REF] which gave images with a resolution around 0.15 mm. The perfusion map stack processed was composed of 100 images.

Results and Discussion

Simulated images 205

The result of the GD algorithm for the simulated data shown in Fig. 3 is represented in Fig. 5. From the latter, we observe that the GD image is zero everywhere except in the square that was present in images 5 to 9 of the stack.

In the new image PU GD , the pixels are zero (minimum value) when all the pixel values are equal in the stack (no movement at this pixel) and regions differing 210 in their activity are displayed as different gray levels. This result is therefore a proof of our concept for the use of the GD algorithm to detect perfusion changes in LSCI data. .

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The results of the GD algorithm for the stack of 15 images containing movement artefacts (Fig. 4) is shown in Fig. 6. The results show that the image generated with the GD algorithm reflects all the variations: all the four squares are visible in the new image, the one due to the transient increase of blood flow and the three squares reflecting the movement artefacts. Therefore, the GD algorithm keeps the transient increase of blood flow visible, but also reflects pixel amplitude variations due to movement artefacts. However, LSCI is by definition very sensitive to movements. That is why LSCI experiments have to be performed with still subjects to avoid experimental noise.

Experimental images

The first perfusion image of the recordings for the three experimental cases is presented in Figs. part of the image. For case 2 (see Fig. 11), we observe that the variations of the perfusion due to the local heating mostly appear in the bottom left part of the image. Finally, for case 3 (see Fig. 12), the perfusion variations are globally localized on all the image. As mentioned above, Fig. 10 has been computed from 10 images and Figs. 11 and 12 have been computed from 100 images.

Due to the spatial heterogeneity of the microcirculation [START_REF] Wardell | Spatial[END_REF][START_REF] Braverman | The cutaneous microcirculation[END_REF] and because clinical cases require perfusion analyses with a high spatial resolution (see, e.g.,

Ref. [START_REF] Lu | Automatic segmentation of scaling in 2-D psoriasis skin images[END_REF]), LSCI is an interesting optical technology. However, the visualization of LSCI perfusion images should be easy and rapid. Due to the high amount of images generated by several minutes of recordings, the GD image is an interesting way to visualize the variations of the perfusion (post-acquisition procedure) with a spatial resolution as high as the original perfusion maps.

As shown in Fig. 6, the GD image reflects perfusion changes but also movement artefacts. This is also shown in Fig. 13 where the GD image has been computed from perfusion data recorded on the forearm of a healthy subject during a local heating while movements were performed by the subject. We the subject is totally still.

We also compared our results given by the GD algorithm on the experimental LSCI data with the ones given by the GD ⋆ algorithm and by the Fujii's method.

The results given by the GD ⋆ algorithm are shown in Figs.

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x Laser speckle contrast imaging (LSCI) enables to monitor microvascular perfusion x Large amount of data are often recorded leading to a long process of analysis x Spatial averaging is therefore often performed in regions of interest (ROI)

x The spatial averaging reduces the spatial resolution of the images x We propose a new visual representation of LSCI data using generalized differences Highlights

Figure 1 :

 1 Figure 1: Perfusion image (151 rows and 61 columns) from LSCI technique of a zone on the forearm of a healthy subject.

Figure 2 :

 2 Figure 2: Laser speckle contrast signal (perfusion signal) of a zone on the forearm of a healthy subject, at rest, during vascular occlusion and post-occlusive reactive hyperaemia, computed from spatial averaging on a region of interest of 7 × 7p i x e l s 2 in laser speckle contrast images (perfusion images).

Figure 3 :Figure 4 :

 34 Figure 3: Representation of images 1, 5, 6, 7, 8, and 9 of the simulated images (see text for details).

Figure 5 :

 5 Figure 5: Image computed with the generalized differences algorithm from 15 simulated images (see Fig.3).

Figure 6 :

 6 Figure 6: Image computed with the generalized differences algorithm from 15 simulated images (see Fig.4).

7 to 9 .Figure 7 :

 97 Figure 7: Perfusion map (623 rows and 623 columns) representing the two hemispheres of a mouse, recorded through the skull [63].

Figure 8 :Figure 9 :Figure 10 :

 8910 Figure 8: Perfusion map (201 rows and 201 columns) representing the forearm skin at the very beginning of a local heating.

Figure 11 :

 11 Figure 11: Image (201 rows and 201 columns) computed with the generalized differences algorithm from 100 perfusion images recorded during and after a local heating (see text for details).

Figure 12 :Figure 13 :

 1213 Figure 12: Image (501 rows and 301 columns) computed with the generalized differences algorithm from 100 perfusion images recorded just after a local pinching (see text for details).

Figure 14 :Figure 15 :Figure 16 :

 141516 Figure 14: Image (623 rows and 623 columns) computed with the modified generalized differences algorithm (GD ⋆ ) from 10 perfusion images recorded during a pinprick in one of the hemispheres that induces a wave of ischemia (see text for details).

Figure 17 :

 17 Figure 17: Image (623 rows and 623 columns) computed with the Fujii's method from 10 perfusion images recorded during a pinprick in one of the hemispheres that induces a wave of ischemia (see text for details).

Figure 18 :Figure 19 :

 1819 Figure 18: Image (201 rows and 201 columns) computed with the Fujii's method from 100 perfusion images recorded during and after a local heating (see text for details).

changes and movement artefacts, the acquisitions have to be performed when

Acknowledgment

The authors would like to thank N. Offenhauser and J. Dreier for the record-285 ings performed on the mouse.


Soulier Coralie

Berho Catherine

Togola Anne

Analytical and statistical approaches to preselect relevant organic compoundsin the non-target screening by coupling passive sampling and high resolution mass spectrometry: application to groundwater

One of ongoing challenge is to protect and preserve water resources. This involves an increased monitoring and the characterization of micropollutants, emerging substances and their metabolites or transformation products. Emerging compounds are mostly released by wastewaters discharge into surface waters and then into other environmental compartment. All these compounds are present in complex mixture at low concentration, implying the need of specific analytical methodology to identify them.

The aim is to support public policy development of highlighting and identifying compounds of interest present in groundwater. The main difficulties for the implementation of monitoring are low concentration levels and mix of pollutants from various sources. No therefore there is a strong interest to combine passive sampling and high resolution mass spectrometry (HRMS). On the one hand passive sampling tools allow accumulating compounds during exposure and improving the sensitivity by their integration abilities. The Polar Organic Chemical Integrative Sampler (POCIS) were used to sampling polar and semi-polar compounds. On the other hand HRMS allows detecting and identifying organic compounds. The high resolving power, mass accuracy and the sensitive full spectrum acquisition of this technique are the key points for organic compounds screening.

Different groundwater impacted by agricultural, urban or rural pressures were investigated and sampled during several months. Grab and passive sampling were deployed and analyzed by LC-QTof. To process data different approaches were investigated. The first approach is based on research from compounds listed on homemade database (around 450 with experimental data on our system as retention time, exact masses for molecular and fragment ions). The non-targeted screening wasappliedusingstatistical tools such as principal components analysis (PCA) with direct connections between original chromatograms and ion intensity.Trend plots are used to preselect relevant compounds for their identification. This approach allows making comparison of samples and giving multidimensional visualization of chemical patterns as molecular fingerprint and highlighting recurrent or specific peaks of each site. The identification of relevant signal was partially succeeded by using different database such as Norman Mass Bank or Chemspider. The workflow used allows identifying compounds never revealed in these sampling sites. Keywords: non-target screening, passive sampling, POCIS, high resolution mass spectrometry