Victor Cazalis
email: victor.cazalis@laposte.net

Anne-Caroline Prévot

Are protected areas effective in conserving human connection with nature and enhancing pro-environmental behaviours?

Halting the on-going biodiversity crisis requires large individual behavioural changes through the implementation of more pro-environmental behaviours (PEBs) by every citizen. People's experiences of nature, such as outdoor activities, have been identified as great enhancers of such behaviours. Yet, these experiences of nature got scarcer in the last decades, due to an increased spatial segregation between human and nature, particularly in societies that follow a Western way of life. In this context, we wondered if protected areas (PAs), because they offer more opportunities for people to be in contact with natural landscapes and offer more ecological information and governance than other places, could enlarge the implementation of PEBs for people living in or close from them. We addressed this question by modelling the link between three types of PEBs in Metropolitan France (i.e., voting for Green party candidates, joining or donating to biodiversity conservation NGOs and participating in a biodiversity monitoring citizen science program) and the proximity to large PAs. Innovatively, we addressed this question at national level, with exhaustive data collected in more than 16,000 French municipalities with more than 500 inhabitants. All models controlled for difference in population size, average income and proportion of retired people between municipalities. We found that each of the studied PEBs decreased with distance of the municipality to PAs, even after having controlled by the naturalness of municipalities' surroundings. Our results suggest that, beyond their effect through exposure to natural landscapes, PAs affect PEBs by the institutional context they create. Additionally, PEBs were higher inside PAs than in close surroundings, suggesting that, besides restrictions brought by PAs on inhabitants, a fraction of the population responds positively to their implementation. Our results suggest that PAs can play a role in enhancing environmental friendly ways of life by conserving human's connection with nature.

Introduction

We are currently facing the sixth mass extinction of biodiversity, with thousands of species vanishing and the decline of many species' populations, described as a time of biodiversity annihilation [START_REF] Ceballos | Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines[END_REF]. This crisis is mainly due to the human domination of Earth's ecosystems [START_REF] Balmford | Trends in the state of nature and their implications for human well-being: Trends in the state of nature[END_REF][START_REF] Dirzo | Defaunation in the Anthropocene[END_REF], and threatens ecosystem services and human well-being [START_REF] Cardinale | Biodiversity loss and its impact on humanity[END_REF][START_REF] Rockström | Planetary Boundaries: Exploring the Safe Operating Space for Humanity[END_REF].

Simultaneously with this decline in biodiversity, most societies are moving away from nature and biodiversity. Indeed, the proportion of people living in cities increased in the last centuries and decades, reaching 81.5% in high-income countries in 2018, a number that keeps increasing (United Nations, 2018). This spatial segregation of human and nature, together with a reduction of nature recreation activities [START_REF] Soga | Extinction of experience: the loss of human-nature Front[END_REF] dramatically reduced both desire and opportunities to directly experience nature [START_REF] Turner | Global Urbanization and the Separation of Humans from Nature[END_REF][START_REF] Clayton | Transformation of Experience: Toward a New Relationship with Nature: New experiences of nature[END_REF]. [START_REF] Pyle | Nature matrix: reconnecting people and nature[END_REF] characterised this on-going trend as the extinction of experience and defined it as an "inexorable cycle of disconnection, apathy, and progressive depletion".

Nonetheless, significant life experiences of nature are important to create sensitivity, concern and knowledge about environmental issues [START_REF] Prévot | Routine experiences of nature in cities can increase personal commitment toward biodiversity conservation[END_REF][START_REF] Chawla | Significant Life Experiences Revisited: A Review of Research on Sources of Environmental Sensitivity[END_REF]. Indeed, numerous studies have shown that they can increase concern about environmental issues and willingness to take action against them (Clayton and Myers, 2015a;[START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF][START_REF] Prévot | Routine experiences of nature in cities can increase personal commitment toward biodiversity conservation[END_REF]). Yet, changes in human behaviours and way of life are needed in order to reduce human impact on biodiversity [START_REF] Martin | The need to respect nature and its limits challenges society and conservation science[END_REF]. Consequently, proenvironmental behaviours (PEBs) have been of main interest in the field of conservation psychology, in order to understand which factors can enhance them and therefore reduce human's impact (Clayton and Myers, 2015b). This term of PEB includes a wide variety of environmental-friendly human behaviours, with different impact levels, from voting for Green party candidates or feeding birds in the winter, to environmental activism or adopting of environment-friendly consumption [START_REF] Larson | Understanding the multidimensional structure of pro-environmental behavior[END_REF]. Some of them have direct impacts on biodiversity, some have indirect impacts and someconsidered sometimes as symbolic -, are seen by some authors as a "foot in the door" of environmental-friendly way of life, leading potentially to PEBs with bigger impact [START_REF] Burger | The Foot-in-the-Door Compliance Procedure: A Multiple-Process Analysis and Review[END_REF][START_REF] Truelove | Positive and negative spillover of pro-environmental behavior: An integrative review and theoretical framework[END_REF].

One of the main tools used in conservation to halt biodiversity decline, is to define areas where human activities are restricted and controlled: that is protected areas (PAs), which can have very different protection levels. PAs currently represent about 15% of worldwide land area and should reach 17% by 2020 (UNEP-WCMC, IUCN and NGS, 2018). Even if increasing in importance, PAs alone cannot address the biodiversity crisis [START_REF] Prévot-Julliard | The Need for Flexibility in Conservation Practices: Exotic Species as an Example[END_REF]. However, aside from their direct conservation impact, we can expect PAs to have an effect on the environmental concern of nearby inhabitants. First, PAs are more natural than the average [START_REF] Joppa | Global protected area impacts[END_REF], which allows nearby inhabitants to have more opportunities to experience nature than other people do. Second, as PAs' governance systems are particularly dedicated to biodiversity (UNEP-WCMC, IUCN and NGS, 2018), inhabitants can be in contact with ecological information through education initiatives of PAs (e.g., signs, activities, conferences, green tourism [START_REF] Cetas | A systematic review of motivational values and conservation success in and around protected areas: Cetas & Yasué[END_REF][START_REF] Laurens | Les Parcs naturels, du concept à la pratique d'une agriculture environnementale[END_REF]). Hence, PAs inhabitants and neighbours can be directly affected by PAs, for instance by being more exposed to pro-biodiversity discourses in their daily lives than other people are; we refer to this effect in the manuscript by "PAs' institutional context". With these two processes, PAs may increase inhabitants opportunities to experience nature, knowledge and awareness of environmental problems, and therefore their motivations to implement some PEBs [START_REF] Hinds | Engaging with the natural environment: The role of affective connection and identity[END_REF][START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF]. Conversely, PAs are often known to raise opposition preceding implementation (e.g., [START_REF] Stoll-Kleemann | Opposition to the Designation of Protected Areas in Germany[END_REF][START_REF] Stern | The Power of Trust: Toward a Theory of Local Opposition to Neighboring Protected Areas[END_REF][START_REF] Cadoret | Des conflits territoriaux révélateurs d'efforts différenciés de protection de l'environnement : le cas du Parc National des Ca-lanques[END_REF]. Therefore, we could expect people living inside PAs to adopt fewer PEBs than people living outside but close to PAs, as this former group will benefit from greater opportunities to experience nature while they will not be subject to restrictions in their living location.

To our knowledge, few studies investigated the relationships between PAs and PEBs. [START_REF] Halpenny | Pro-environmental behaviours and park visitors: The effect of place attachment[END_REF] conducted a survey study in Canada and showed that the place-attachment expressed by PAs visitors enhanced their PEBs intentions. [START_REF] Ramkissoon | Place attachment and pro-environmental behaviour in national parks: the development of a conceptual framework[END_REF] developed a conceptual framework providing rationale for this relationship, splitting placeattachment in four items: place dependence, place identity, place affect and place social bonding. [START_REF] Cetas | A systematic review of motivational values and conservation success in and around protected areas: Cetas & Yasué[END_REF] reviewed cases where policy instruments were used in PAs to promote conservation behaviours in local people. They found numerous papers studying such policies and found they were more efficient when they targeted intrinsic motivations of PAs' inhabitants (i.e., arisen directly from an individual because of spontaneous interest in a particular activity) rather than extrinsic motivations such as rewards or punishment. However, to our knowledge, no study has compared PEBs between protected and unprotected areas, which is a way to address PAs impact on PEBs.

Here, we investigated the relationship between PEBs of French inhabitants and the distance between their living location and PAs. To do so, we considered three types of behaviours, as follows. First, we considered people's implication in a biodiversity monitoring citizen science program, which reflects a local interest in biodiversity and can be linked to concern about biodiversity issues and the implementation of PEB [START_REF] Cosquer | Observations of Everyday Biodiversity: a New Perspective for Conservation[END_REF][START_REF] Prévot | Routine experiences of nature in cities can increase personal commitment toward biodiversity conservation[END_REF]. Second, we considered donations or membership to wildlife NGOs, which shows a specific concern about biodiversity issues at national or global scales, and constitute a tangible contribution to its conservation [START_REF] Larson | Understanding the multidimensional structure of pro-environmental behavior[END_REF]. Finally, we considered voting for Green parties in elections, which reflects people's willingness to act on environmental problems by a broader, transversal, societal transformation [START_REF] Gill | Ecological Concern, Attitudes, and Social Norms in Voting Behavior[END_REF][START_REF] Larson | Understanding the multidimensional structure of pro-environmental behavior[END_REF]. We gathered exhaustive data for these three types of PEBs in each municipality in metropolitan France, and modelled how they varied with distance to large French PAs (national parks and regional parks). As PEB levels are known to differ between rural and urban populations [START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF], to vary with people age and to depend on social variables such as income [START_REF] Hines | Analysis and Synthesis of Research on Responsible Environmental Behavior: A Meta-Analysis[END_REF][START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF], we controlled in the models for municipalities' average income, proportion of retired people and population size (in first approximation, we assumed a direct negative link between population sizes and rurality level of the municipalities, but see [START_REF] Hart | Rural definitions for health policy and research[END_REF]. In order to discriminate the effect PAs have by increasing opportunities to experience nature from the effect of the institutional context, we have run all models with and without controlling for exposure to nature. Indeed, as PAs surroundings are on average more natural, when we added a control for exposure to nature in our models, the measured effect of PAs only included institutional context, allowing us to discriminate both parts of the effect. In a second time, we compared the difference in PEBs between municipalities located inside PAs and the ones close to PAs, expecting lower levels of PEBs inside PAs because of restrictions applied on inhabitants.

Methods

We collected data of pro-environmental behaviours (PEBs) and control variables in all metropolitan France (i.e., excluding overseas departments and territories), for each of the 36,528 municipalities. In France, a municipality ('Municipalité') consists in an administrative division, often including a village or a city and territories around the urban area, that extend to an invisible border with adjacent municipalities (i.e., every place in France belongs to a municipality).

Pro-environmental behaviour data

Vote data

We downloaded public vote data from a French government official website (République Française, 2018). We included in this study, only elections that have a unique clearly identified Green party candidate in each municipality. This was not the case in local elections, nor in the 2017 presidential election, as ecology was incorporated in several candidates' manifestos, while none presented ecology as the first focus. We used the 2012 presidential election data where Eva Joly was candidate for the Green party ('Europe Ecologie Les Verts'), and the 2014 European election data where there was a Green candidate in each of the seven constituency under the list 'Europe Ecologie Les Verts'. For both elections, we considered as PEB score the percentage of vote cast in favour of the Green party candidate, excluding blank and invalid votes.

NGO data

We used the number of supporters per municipality for the two main French wildlife protection NGOs, both doing tangible actions in favour of biodiversity: the WWF France and the LPO. These data are not public and were provided directly by the organisations. The WWF France gets money through either donations or purchases (e.g., books, textiles, goodies). Since its creation, 871,052 individuals have donated or purchased at least once to the organisation. We used as PEB score the number of inhabitants per municipality that made at least one donation or purchase to the WWF since its creation in 1973. The LPO ('Ligue pour la protection des oiseaux') is a NGO recognized as being of public utility, defending and promoting nature (all fauna and plant species), and is the official representative of BirdLife International in France. This association can count on a network of 44,986 members (who outnumber the 20,000 donators). We used as PEB score the number of members per municipality in 2016.

Citizen science data

We wanted to include data from a biodiversity monitoring citizen science program that was widespread in France, did not require any naturalist background and that encourages people to monitor biodiversity where they live. Among programs matching these criteria, the program 'Oiseaux des jardins', managed together by the 'Museum National d'Histoire Naturelle' and the LPO, is the most popular. It is the French equivalent of the UK Garden Birdwatch program, and monitors birds seen in gardens with a checklist system: each observer registers its garden and reports, opportunistically, a list of birds. No particular background in ornithology is required to participate in this program. Between the creation in March 2012 and the 28 th of February 2018, 30,233 gardens have been registered. We used as PEB score the number of gardens per municipality.

We did not pool PEBs by type in order to facilitate interpretation and enable comparisons between PEBs. Therefore, our dataset included five PEBs, of three types: voting for Eva Joly in the 2012 national presidential election, voting for EELV in 2014 European elections, donating or purchasing items to WWF France, being member of the LPO in 2016, participating in the French garden birdwatch program.

Protected area data

Our main explanatory variable was the distance to a PA. We integrated two types of PA into this study, national parks ('Parcs nationaux') and regional parks ('Parcs naturels régionaux'). Both of them cover fairly large areas and are well known to local people who are aware that they live in or near such PAs, unlike some of the smaller PAs in France. These two types of PA are nevertheless very different in terms of their objectives and means of nature conservation [START_REF] Laurens | Les Parcs naturels, du concept à la pratique d'une agriculture environnementale[END_REF][START_REF] Lepart | Des réserves de nature aux territoires de la biodiversité L'exemple de la France[END_REF]. The primary objective of national parks is to protect biodiversity, often concerning the presence of emblematic species. To achieve this objective, they are spatially organized with two different zones: a "core area" where human activities are highly restricted and regulated, i.e. PA category II in the IUCN classification, (UNEP-WCMC, IUCN and NGS, 2018)), and a peripheral "adhesion area" that allows for more human activities (category V). Because of their national status, their governance system includes nominated representatives from the state (France), representatives from local authorities in an administrative council with local stakeholders and experts (each park has a scientific commission). The 'Parc national des Cévennes' is an exception as the core area includes habitations and human activities such as hunting, the whole park is therefore considered as being a type V class by the IUCN. Regional parks allow for human activities, often they contain several villages or small towns, and they do not have a core area with regulatory control. Their primary aim is to protect both natural and cultural heritages (often categorised V by the IUCN, sometimes IV). Their governance system is composed of an administrative council with elected representatives of the local communities and stakeholders; they also have a scientific commission. National and regional parks are therefore different in their objectives, means and governances. However, peripheral adhesion areas in national parks are similar to regional parks in terms of objectives and restrictions (i.e., same IUCN category) and both follow a charter signed by all the local municipalities that adhere to the National Park, or which are within the boundaries of the regional park. Local governance is thus an important element of both types of PA, indeed local municipalities actually choose whether they want to be included in the peripheral adhesion area of a national park or within a regional park or not. As there are no inhabitants and villages inside core areas in all national parks, except in the 'Parc national des Cévennes', both types of parks might have similar effects on inhabitants.

There are 7 national parks and 51 regional parks in metropolitan France. We included all national parks except (1) the 'Parc national de Port-Cros', which is located on a small island and (2) the most recently created, the 'Parc national des Calanques', created in 2012, because we considered that its young age prevented any impact on most of the studied PEBs. In addition, the latter has the city of Marseille that fringes the core zone of the park making any study of distance from the PA difficult. We included all regional parks other than the 'Parc naturel régional de la Sainte-Baume' and the 'Parc naturel regional de l'Aubrac', because they were created very recently, respectively in 2017 and 2018. Selected parks are shown in Fig. 1.

Among the 36,528 municipalities located in metropolitan France, we only considered the 16,825 municipalities with more than 500 inhabitants (Fig. 1), in order to remove extreme values (e.g., vote score can be very high in small villages, as a single individual will affect strongly the municipality score). Among these selected municipalities, respectively 79 and 1,828 were located inside national and regional parks.

We calculated the distance of each French municipality to the closest national or regional park, as follows: we first calculated the coordinates of the barycentre of each municipality using the shapefile from OpenStreetMap (2015). We then used the parks shapefile provided by MNHN-INPN (2017) to determine the closest edge of the closest park for each municipality, considering peripheral areas of national parks as parts of the park. Finally, we calculated the distance between the municipality barycentre and the closest edge of this park; this distance was negative for municipalities located inside a park.

Control variables

In order to control for social differences, we controlled in our analyses for municipality population size, using municipality population size from 2014, available in a French official website (République Française, 2018). We also controlled for income declared to the tax office by households ('Revenu fiscal de reference'). We extracted from the same website the summed 'Revenu fiscal de reference' and the number of fiscal households of each municipality and calculated an income index as the quotient of these two variables (i.e., the average 'Revenu fiscal de reference' of a tax household in the municipality). We extracted from the same dataset, the number of retired inhabitants ('Retraites et pensions, nombre') and calculated the retirement proportion of municipalities as the number of retired inhabitants divided by the total number of inhabitants.

In order to discriminate the effect of exposure to nature from the effect of the institutional context, we have run models controlling for exposure to nature. Hence, in the first set of models (without exposure to nature), the measured effect of PAs includes both a greater exposure to nature and institutional context, while in the second set of models (with exposure to nature), the measured effect of PAs only includes institutional context. We estimated exposure to nature using the 2012 Corine Land Cover raster (CLC, 2012), calculating the proportion of pixels overlapping with the municipality limits that represent natural land uses. We considered as natural land use: pastures (CLC code = 231), forests , open natural habitats (321)(322)(323)(324)333), sandy areas (331), bare rocks (332), burnt areas (334), glaciers and perpetual snow (335), and wetlands (411-523).

Statistical analysis

All five PEBs were independently modelled against distance to PAs using General Additive Models (GAMs) with the 'mgcv' R package [START_REF] Wood | Fast stable restricted maximum likelihood and marginal likelihood estimation of semiparametric generalized linear models: Estimation of Semiparametric Generalized Linear Models[END_REF]. Vote data were modelled assuming a Gaussian distribution, after being log transformed (log(Vote)+1) in order to fit to this distribution. NGOs and citizen science data correspond to count data but were overdispersed compared to a Poisson distribution and were therefore modelled assuming negative binomial distributions.

All models assumed the link between PEBs and distance to PAs to be linear and included all control variables as smoothed terms, allowing non-linear relations. A first set of models (one per studied PEB) included as control variables logarithm of population size, logarithm of the income index, retirement proportion, together with longitude and latitude of the municipality barycentre in order to control for spatial autocorrelation in the country. Each PEB was then modelled with similar models but including also exposure to nature as smoothed term, in order to discriminate the effect of exposure to nature from the effect of the institutional context.

Because of national parks' scarcity and agglomeration in mountains (see Fig. 1), comparing the impact of national and regional parks was not statistically straightforward. Rather than a general quantitative comparison, we therefore decided to check that the effect of national and regional parks were qualitatively similar. To do so, we ran the same 10 models (5 PEBs with and without considering exposure to nature) but considering distance to regional parks only (see Supporting Information Table S1). Then, we compared the percentage of deviance explained by models considering distance to regional parks only with those considering distance to all types of park (both regional and national). A higher percentage of deviance explained by the model when all parks are considered would highlight that national and regional parks' effect are qualitatively similar (i.e., they affect PEBs in the same direction; see Supporting Information Table S2).

In order to test for the effect of living inside a PA rather than close to a PA, we made a subset of our dataset, keeping only municipalities inside a PA or close to a PA (< 20 km). This represents about half of our dataset with 1,907 municipalities inside a PA and 7,002 municipalities close to a PA. We ran GAMs modelling the five PEBs against a binary variable (inside or outside PA) and controlling for population size, income, retirement proportion, longitude and latitude as in previous models. We also ran the analyses controlling for exposure to nature.

Figure 1: Map of the studied area (Metropolitan France). Protected areas considered include national parks, or 'Parcs nationaux' (in green), and regional parks, or 'Parcs naturels régionaux' (in orange). Each dot represents the barycentre of a municipality with more than 500 inhabitants, which corresponds to the municipalities included in the analyses.

Results

Models not controlling for exposure to nature showed a significant decrease in all five PEBs with distance to PAs (Fig. 2A, Table 1 first column). Thus, a municipality within or close to a PA showed greater PEBs than a municipality far from PAs, the effects of population size, income, retirement proportion and spatial autocorrelation being taken into account. In models controlling for exposure to nature, all PEBs were positively correlated with exposure to nature (Fig. 3D), leading to a decrease in regression coefficients between PEBs and distance to PAs (Fig. 2B, Table 1, second column) emphasizing that part of PAs effect on PEBs is due to their more natural landscapes than average. Yet, the negative effect of distance to PAs was still significant for all PEBs, meaning that municipalities with equal population sizes, incomes, retirement proportion and exposure to nature, still showed different PEB levels depending on their distance to a PA. This highlights that PAs have a direct effect, aside from providing higher exposure to nature.

Population size of the municipality was strongly and inconsistently correlated with PEBs (Fig. 3A). Both, voting scores for Green party candidates and WWF donation were higher in municipalities with larger population sizes. Conversely, participation in the French garden birdwatch program was higher in municipalities with small populations. LPO membership declined with population size -until ca. 10,000 inhabitants -before increasing for large cities. Income level was also strongly, and mainly positively, correlated with PEBs (Fig. 3B). The proportion of retired inhabitants of municipalities was positively correlated with NGOs and citizen science participation, but negatively with voting for Green parties (Fig. 3C). Longitude and latitude plots in Fig. S2 and Fig. S3 (Supplementary Information) show that spatial autocorrelation was rather high, especially for PEBs with limited data (i.e., LPO membership and French garden birdwatch), highlighting that these PEBs have not homogeneously spread across the country.

The covariates effects for models not including exposure to nature are similar to the effects for models including exposure to nature and are given in Supplementary Information (Fig. S1), together with all covariate effects on PEBs with confidence intervals (Fig. S2 and Fig. S3) .

All effects but one hold when we considered regional parks only (Table S1). However, these models had a smaller percentage of deviance explained, except for membership to the LPO (Table S2), than models considering distance to all parks (both national and regional). This suggests that the effects of national and regional parks were qualitatively similar.

All PEBs were significantly higher in municipalities inside PAs than in municipalities close to PAs (Fig. 4), refuting the hypothesis that PEBs decrease inside PAs because of restrictions applied on populations.

Table 1: Estimated effects of the distance to PAs for the five studied PEBs measured in French metropolitan municipalities with at least 500 inhabitants. The estimates were obtained using GAM models with smoothed terms controlling for log(population size), log(income), latitude and longitude. Regression coefficients for distance to PAs are given in the cTot column (for models not including exposure to nature) and cRed (for models including exposure to nature as a smoothed term). cRed / cTot is a measure of the relative importance of exposure to nature in the relationship between PEBs and distance to PAs. Deviance explained columns correspond to the percentage of deviance explained by the whole model. P-values are given following: 0.05 > * > 0.01 > ** > 0.001 > *** We predicted PEB values against one covariate, fixing all other covariates to their median values. In order to obtain comparable scales, we divided PEB predictions by their predicted level with the minimal value of the studied covariate (making the plot start at 1). NGO and citizen science PEB variables consisted in counts (of respectively people and gardens), but for the population plot (A), we divided the predicted level of PEBs by the population in order to obtain the proportion of the population adopting the given PEB (for interpretation purposes). Longitude and latitude effects and confidence intervals of each curve are presented in Supplementary Information (Fig. S2).

Figure 4: PEBs' levels differences between municipalities located inside a PA (dark green) and municipalities located outside but close to a PA (< 20 km; light green) in models without accounting for exposure to nature (left) and accounting for exposure to nature (right). The effect shown are predictions extracted from the model, with all covariates fixed to their median values. Bars represent 95% confidence intervals predicted from the models. In order to obtain comparable scales, we divided PEB predictions by their predicted value inside PAs, fixing all dark green dots to 1. The three stars illustrate p-value below 0.001.

Discussion

In this study, we have found a significant decrease in pro-environmental behaviours (PEBs) with distance to large French PAs (national and regional parks), consistently in all five studied PEBs (voting for Green party candidates in two elections, joining or donating to two biodiversity conservation NGOs, and participating in a bird monitoring citizen science program).

As expected, all PEBs were positively correlated with income. This is probably due to the well-known positive correlation between PEBs and both knowledge and education level [START_REF] Hines | Analysis and Synthesis of Research on Responsible Environmental Behavior: A Meta-Analysis[END_REF][START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF], which correlate with income [START_REF] Autor | Skills, education, and the rise of earnings inequality among the "other 99 percent[END_REF][START_REF] Van Winden | European Cities in the Knowledge Economy: Towards a Typology[END_REF]. Conversely, the relationship between PEBs and municipalities' population size (considering municipalities above 500 inhabitants only) differed between PEBs. Both WWF donation and votes for Green party candidates, which can be considered as the large-scale PEBs in our dataset, were higher in municipalities with high population sizes, consistently with French literature [START_REF] Bussi | Ecologistes des villes et écologistes des champs : analyse spatiale de l'implantation en France des partis écologistes et «Chasse Pêche Nature et Traditions[END_REF]. Conversely, the proportion of the population participating in the French garden birdwatch program decreased with municipalities' population size. LPO membership decreased with municipalities' population size before increasing for large cities; this increase is combined with a very large confidence interval, making this small increase hypothetical (see Fig. S2). To participate in the French garden birdwatch program, people are asked to count regularly birds in a garden, making people living in large cities less likely to participate in this program, as they may not have easy access to a garden and a biodiversity rich area [START_REF] Turner | Global Urbanization and the Separation of Humans from Nature[END_REF]. The same is probably true for LPO membership, which could be associated with ordering bird-feeding equipment to the organisation. These differences in municipalities' population size relationship with PEBs are consistent with literature, which suggests that PEB differences between rural and urban areas are inconsistent across places and PEBs measured [START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF].

Similarly, the correlation between retirement proportion and PEBs is different according to PEBs, being positive for NGOs donation and citizen science participation and negative for vote behaviours. In their review, [START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF] found that PEBs were generally higher in elders, while younger people showed a greater concern about environmental issues. This could explain why active behaviours were positively correlated with retirement proportion, while votes -which appear as weekly related to active participation but more related to global environmental concerns -are more represented in municipalities with lower proportions of retired people. Moreover, LPO membership and participation to citizen science could be enhanced by the fact that elders live more in rural areas and have greater access to private gardens [START_REF] Stockdale | Pre-retirement age migration to remote rural areas[END_REF].

For all PEBs, models including exposure to nature emphasized a positive correlation between nature exposure and PEBs, and consequently decreased the coefficient between PEBs and distance to PAs. This result is consistent with Joppa and Pfaff (2011)'s study, who showed that PAs presented more natural land uses than unprotected areas. In our case, we propose that living close to a PA offers more opportunities to be in contact with nature, which in turn encourages individuals to implement more PEBs. However, distance to PAs effect was still strongly significant after exposure to nature was taken into account. This suggests that exposure to nature was not the only factor explaining the negative correlation between PEBs and distance to PAs and, hence, that protection itself has a direct effect on PEBs. This effect could include for instance environmental education, institutional communication implemented in the parks, as well as governance systems or even social contexts and relationships. However, our control for exposure to nature could be improved. Indeed, this control considers only municipalities' landscape; landscapes from nearby towns are not included in this control while they may also affect people. Moreover, our exposure to nature index is based on a binary vision of land use (natural versus non-natural), which is a simplification from reality and does not consider the diversity of natural landscapes people can experience [START_REF] Clayton | Transformation of Experience: Toward a New Relationship with Nature: New experiences of nature[END_REF]. Therefore, we cannot entirely exclude the fact that our correlation between PEBs and PAs is only due to a higher exposure to nature near PAs. Moreover, we cannot specify how protection affects PEBs through what we call "institutional context", as no data on environmental education or access to ecological information are available at the scale considered.

The strong negative correlation between PEBs and distance to PAs arisen from our models could be explained by several processes, that we cannot discriminate from our quantitative and correlative study. First, this correlation could have arisen if PAs have been implemented in areas where people already had a strong environmental concern. However, based on the strength of our results, their consistency between PEBs and across all the distance gradient, and the fact that most of the PAs included in the analyses were implemented decades ago (1963)(1964)(1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979) for national parks and from 1969 for regional parks), we can reasonably assume that the correlation between PEBs and distance to PAs is posterior to PAs' implementation.

Second, PAs might have attracted and concentrated people with high level of PEBs. Several geographic studies showed that some people, particularly among elders, move toward rural areas, searching a higher quality of life through more natural and rural lifestyles [START_REF] Cadieux | Amenity migration, exurbia, and emerging rural landscapes: global natural amenity as place and as process[END_REF][START_REF] Stockdale | The role of a 'retirement transition' in the repopulation of rural areas[END_REF][START_REF] Stockdale | Pre-retirement age migration to remote rural areas[END_REF]. It is possible that people with high environmental concern were more likely to move toward more natural areas, and that they were attracted by the protection status of PAs. To our knowledge, no study investigated the link between environmental concern and life movements, and this hypothesis would be very interesting to explore.

Thirdly, this correlation result could reflect behavioural changes in people leaving in or close to PAs. This interpretation is strongly supported by literature. First, there are increasing evidences that people disconnection with nature is related to reduced direct experiences of nature [START_REF] Clayton | Transformation of Experience: Toward a New Relationship with Nature: New experiences of nature[END_REF][START_REF] Turner | Global Urbanization and the Separation of Humans from Nature[END_REF][START_REF] Soga | Extinction of experience: the loss of human-nature Front[END_REF]. This disconnection is supposed to lead to an increased psychological distance with biodiversity and environmental issues, which can further lead to a decrease in willingness to actively address these issues (Clayton and Myers, 2015b;[START_REF] Gifford | Personal and social factors that influence pro-environmental concern and behaviour: A review: Personal and social factors that influence pro-environmental behaviour[END_REF][START_REF] Spence | The Psychological Distance of Climate Change: Psychological Distance of Climate Change[END_REF]. For instance, [START_REF] Prévot | Routine experiences of nature in cities can increase personal commitment toward biodiversity conservation[END_REF] showed with a survey study in an urban area that five out of the six studied PEBs (including buying organic and seasonal food, enhancing biodiversity in private garden or voting for candidates with conservation concerns) were more implemented by people involved in experiences of nature. Secondly, PAs offer specific institutional contexts that could make PEBs easier to appear, for instance by increasing knowledge, which has been shown to be important to promote PEBs. Hence, environmental education programs can increase ecological knowledge and further encourage PEB's (e.g., [START_REF] Kruse | Effects of a Conservation Education Camp Program on Campers' Self-Reported Knowledge, Attitude, and Behavior[END_REF]). Yet, individuals anchor their behaviours in different forms of knowledge, including actionrelated knowledge (i.e. "which behaviours can be implemented and how") and effectiveness knowledge (i.e., "is this behaviour efficient", [START_REF] Frick | Environmental knowledge and conservation behavior: exploring prevalence and structure in a representative sample[END_REF]. In addition, a diversity of media and contexts for knowledge acquisition permits individuals to learn freely and to informally increase their knowledge [START_REF] Falk | Investigating public science interest and understanding: evidence for the importance of free-choice learning[END_REF]. Besides knowledge, PEBs have been shown to be encouraged by social norms regarding these behaviours (e.g., on energy consumption, [START_REF] Schultz | The Constructive, Destructive, and Reconstructive Power of Social Norms[END_REF]; in private gardening: [START_REF] Uren | Exploring social and cultural norms to promote ecologically sensitive residential garden design[END_REF]). These norms can be constructed and made salient by neighbourhood [START_REF] Schultz | The Constructive, Destructive, and Reconstructive Power of Social Norms[END_REF], but also by personalities living in the places [START_REF] Uren | Exploring social and cultural norms to promote ecologically sensitive residential garden design[END_REF], or by discourses and actions of local authorities (e.g., [START_REF] Skandrani | On Public Influence on People's Interactions with Ordinary Biodiversity[END_REF]. Based on this literature support, our results therefore suggest that PAs, through the increase in opportunities to experience nature they provide and the effect of institutional context, can reduce the disconnection of their inhabitants with nature and their psychological distance with biodiversity and environmental issues. This can involve environmental educationexposing inhabitants to ecological information (e.g., through popularisation activities or signs)-, and making people feel they live in a biodiversity rich area [START_REF] Laurens | Les Parcs naturels, du concept à la pratique d'une agriculture environnementale[END_REF][START_REF] Hinds | Engaging with the natural environment: The role of affective connection and identity[END_REF][START_REF] Halpenny | Pro-environmental behaviours and park visitors: The effect of place attachment[END_REF]. In addition, the concepts of biodiversity and sustainable development are more prone to be present in formal communication from the PAs' institutions; this could produce normative messages about environment, which may warrant individual implementation of PEBs. As our study is correlative, we cannot definitively conclude that these behavioural changes caused the described pattern. However, the statistical strength of our results, combined with pre-defined hypotheses regarding the causal relationships on abundant existing literature, together give high credit to this assumption. Only conducting survey experiments could allow to identify more clearly the underlying processes of these correlations.

This effect of PAs on PEBs held when we zoomed in around PAs and compared municipalities inside PAs with municipalities close to PAs. This result was not necessarily expected as PAs are well-known to provoke opposition about inhabitants before implementation [START_REF] Stoll-Kleemann | Opposition to the Designation of Protected Areas in Germany[END_REF][START_REF] Stern | The Power of Trust: Toward a Theory of Local Opposition to Neighboring Protected Areas[END_REF][START_REF] Cadoret | Des conflits territoriaux révélateurs d'efforts différenciés de protection de l'environnement : le cas du Parc National des Ca-lanques[END_REF]. Therefore, we could have expected PAs to have a negative impact on environmental concern of inhabitants, or at least to prevent people from being receptive to the PAs' institutional context. Yet, our analyses showed that PEBs were significantly higher for municipalities inside PAs than municipalities close to PAs. This does not imply that PAs are well received by all people, but rather that, beside restrictions, a part of the population is receptive to PAs environment quality and discourses.

In this study, we gathered two types of natural parks that present relatively different objectives [START_REF] Lepart | Des réserves de nature aux territoires de la biodiversité L'exemple de la France[END_REF][START_REF] Laurens | Les Parcs naturels, du concept à la pratique d'une agriculture environnementale[END_REF]. Indeed, national parks are mainly dedicated to biodiversity and landscape protection, excluding people from their core area. Regional parks' objectives rather include social aspects, promoting the coexistence of human and nature, and are therefore less restrictive of human activities. However, national parks have a peripheral area, which is less restrictive in terms of human activities than the core area and are therefore classified by the IUCN in the same category as most regional parks (V). Moreover, municipalities decide whether they want to be part of this peripheral area and, if so, sign a charter established by the park. In all studied national parks but the 'Parc national des Cévennes', villages are only present in these peripheral areas. This implies that the municipalities that we considered inside national parks are only in this peripheral area, except for the 'Parc national des Cévennes', which includes municipalities in the core area (18 municipalities, including two with more than 500 inhabitants have their barycentre inside the core area). Although we could not compare their impact quantitatively, our analyses suggest that both national and regional parks enhance PEBs of nearby municipalities' inhabitants.

The studied PEBs have only indirect impacts on biodiversity and are implemented by only 0.05 % (French garden birdwatch) to 2.6 % (European elections) of the French population.

Despite their high internal consistency, our results cannot thus pretend to be generalized without any caution. However, they open perspectives for further research at this national scale, which would concern behaviours with more direct or bigger impacts on biodiversity, such as designing private lands in order to favour biodiversity, changing consumption habits, or become an activist for biodiversity NGOs or Green parties.

The correlations between PEBs and covariates could have been more precise if we had access to individual data, which would have allow us to link geographical, social variables to PEBs directly. Here, we used data with resolution at the municipality level, which is the best scale available for the PEBs data we gathered, as well as income and retirement data. It is also important to remind that we excluded municipalities with less than 500 inhabitants in order to limit extreme values in PEBs, and therefore, we potentially excluded the most rural municipalities. The distribution of these small municipalities is slightly biased toward PAs as 13.4% of municipalities with population sizes below or equal to 500 are located inside PAs, against 11.3% for municipalities above 500 inhabitants.

Conclusion

With our study, we enlarged the potential roles of protected areas: besides the direct protection of biodiversity through reservation, PAs can provide opportunities to experience nature through different ways (e.g., by living in there, by visiting, but also by being exposed to natural settings or ecological information). In addition, they provide local context where being involved in biodiversity conservation could be socially encouraged and accepted. Therefore, even if this is not the main objective of PAs, we suggest here that they can play a role in conserving human's connection with nature, and lead local inhabitants toward a higher care for nature and biodiversity. We encourage the local governance system of protected areas to enlarge their objectives by including social outcomes, notably by being aware of the social norms they support. In these conditions, implementing new PAs would not only cause inhabitants' opposition and frustration, but could be positively received by other, potentially more discrete, inhabitants.

Figure 2 :

 2 Figure2: Effect of distance to PAs on Pro-Environmental Behaviours in models without accounting for exposure to nature (A) and accounting for exposure to nature (B). All covariates are fixed to their median values. In order to obtain comparable scales, we divided PEB predictions by their predicted level for the minimal value of distance to PAs (making the plot start at 1). Confidence intervals of each curve are presented in Fig.S2 and S3.

Figure 3 :

 3 Figure 3: Covariates effects on Pro-Environmental Behaviours in models including exposure to nature.We predicted PEB values against one covariate, fixing all other covariates to their median values. In order to obtain comparable scales, we divided PEB predictions by their predicted level with the minimal value of the studied covariate (making the plot start at 1). NGO and citizen science PEB variables consisted in counts (of respectively people and gardens), but for the population plot (A), we divided the predicted level of PEBs by the population in order to obtain the proportion of the population adopting the given PEB (for interpretation purposes). Longitude and latitude effects and confidence intervals of each curve are presented in Supplementary Information (Fig.S2).


Lucian Trupina

Liviu Nedelcu

Marian Gabriel Banciu

Aurelian Crunteanu

Laure Huitema

Catalin Constantinescu

Alexandre Boulle

Cătălin Constantinescu

Texture and interface characterization of iridium thin films grown on MgO substrates with different orientations

Keywords: iridium, thin film, epitaxy, texturation, interface, lattice distortion, mosaicity

Introduction

The crystallographic orientation of a metal thin film affects its surface energy and structure. Surface chemical reactions and interface engineering, which are important in applications including optoelectronic devices and catalysis, as well as understanding crystalline growth, are therefore of paramount importance [START_REF] Tolstova | Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering[END_REF][START_REF] Ohtake | Structure and Magnetic Properties of CoPt, CoPd, FePt, and FePd Alloy Thin Films Formed on MgO(111) Substrates[END_REF][START_REF] Tanaka | Microstructure of NiFe Epitaxial Thin Films Grown on MgO Single-Crystal Substrates[END_REF][4][START_REF] Wandelt | Surface and Interface Science[END_REF]. In this respect, iridium layers that are crystallographically oriented, exhibit low stress, yet high density and low surface roughness, find widespread use in various high-end technological applications, such as diffusion barrier material in ferroelectric random access memories, gate electrode in field effect transistors, template layer for diamond hetero-epitaxy, active layers in gas sensors, hydrogen separation membranes or materials for electro-catalyst [START_REF] Bensalah | Mosaicity, dislocations and strain in heteroepitaxial diamond grown on iridium[END_REF][START_REF] Okada | Reactivity of gold thin films grown on iridium: Hydrogen dissociation[END_REF][START_REF] Kúš | Magnetron sputtered Ir thin film on TiC-based support sublayer as low-loading anode catalyst for proton exchange membrane water electrolysis[END_REF][START_REF] Wesselmark | The impact of iridium on the stability of platinum on carbon thin-film model electrodes[END_REF], and even in ultrahigh quality grazing incidence configuration mirror elements of the Advanced X-ray Astrophysics Facility -Imaging (AXAF-I), a space-based X-ray observatory of NASA [START_REF] Bessey | Sputtered iridium coatings for grazing incidence X-ray reflectance[END_REF][START_REF] Broadway | Achieving zero stress in iridium, chromium, and nickel thin films[END_REF].

The lattice parameter of iridium is 0.38386 nm at 270 K [START_REF] Owen | Precision measurements of crystal parameters[END_REF][START_REF] Arblaster | Crystallographic Properties of Iridium. Assessment of properties from absolute zero to the melting point[END_REF]. The surface morphology and the crystallographic orientation of such thin films have a significant influence on their electrical and optical properties, as well as the rate of chemical reactions at the film surface, and hence on the foreseen applications. Growth of thin films with high-energy surface are extremely important especially in catalysts, because such surfaces exhibit a high density of active sites [START_REF] Zhuang | Surface Energy as a Descriptor of Catalytic Activity[END_REF][START_REF] Somorjai | Impact of surface chemistry[END_REF]. Chemisorption can lead to not only the restructuring of adsorbates but also a significant reconstruction of single crystal surfaces [START_REF] Lang | LEED intensity analysis of the (1 × 5) reconstruction of Ir(100)[END_REF][START_REF] Van Hove | The surface reconstructions of the (100) crystal faces of iridium, platinum and gold: I. Experimental observations and possible structural models[END_REF]. In many cases, massive reconstruction on clean surfaces can lead to a surface structure totally different from that projected from bulk structure. This is the case for reconstructed Ir(100) or Ir(110) surfaces [START_REF] Grant | A LEED study of the Ir(100) surface[END_REF][START_REF] Christmann | Interactions of CO and 0 2 with Ir(110) Surfaces[END_REF]. The dissociative chemisorption of O 2 and the properties of chemisorbed oxygen atoms on Ir(111) have also been studied in detail and are generally well understood [START_REF] Rai | Growth and termination of a rutile IrO 2 (100) layer on Ir(111)[END_REF].

These effects are very important in applications such as thin films and multi-layered structures [START_REF] Büttner | Influence of sputtering pressure on microstructure and layer properties of iridium thin films[END_REF], e.g. in metal-insulator-metal (MIM) capacitive applications [START_REF] Ghalem | Electrical transport properties and modelling of electrostrictive resonance phenomena in Ba 2/3 Sr 1/3 TiO 3 thin films[END_REF]. The use of iridium as bottom electrode in MIM-type devices was also found to influence the preferred orientation and microstructure, as well as the surface morphology, of para-/ferro-electric films grown on Ir [START_REF] Büttner | Influence of sputtering pressure on microstructure and layer properties of iridium thin films[END_REF][START_REF] Ghalem | Electrical transport properties and modelling of electrostrictive resonance phenomena in Ba 2/3 Sr 1/3 TiO 3 thin films[END_REF][START_REF] Nadaud | Domain wall motions in BST ferroelectric thin films in the microwave frequency range[END_REF][24][START_REF] Nadaud | Diffuse phase transition of BST thin films in the microwave domain[END_REF].

Single crystal MgO with various crystallographic cuts is commonly used as a substrate for the deposition of a wide range of thin film materials, in many different areas of research such as superconductors, and other types of oxides, metal and nitride films, multilayers and superlattices. In particular, highly lattice-mismatched metals with a controlled orientation can be developed, since the substrate lattice acts as a template for growth [1-3, 22, 26-28].

Growth of hetero-epitaxial (100) iridium thin films on (100) MgO single crystal [START_REF] Ishikawa | Epitaxial Ir Thin Film on (001) MgO Single Crystal Prepared by Sputtering[END_REF] or on MgO-buffered Si(100) [START_REF] Chen | Comparative study of epitaxial growth of Pt and Ir electrode films grown on MgO-buffered Si(100) by PLD[END_REF] substrate has been reported by pulsed laser deposition (PLD) and radiofrequency (RF)-powered plasma magnetron sputtering, while (111) oriented iridium films have been obtained by electron-beam evaporation (EBE) on yttria-stabilized zirconiabuffered silicon substrate [START_REF] Gsell | Epitaxial films of metals from the platinum group (Ir, Rh, Pt and Ru) on YSZ-buffered Si(111)[END_REF] or by direct-current (DC) magnetron sputtering technique on TiO 2 buffered silicon substrate [START_REF] Trupina | Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere[END_REF].

In this study, we present and discuss results on the growth of hetero-epitaxial iridium thin films with (100), (111), and (110) crystallographic orientations, respectively, grown on single crystal MgO substrates with the corresponding crystallographic orientation. A comparison of the crystalline properties and the morphology of the films is performed. For all three orientations, the level of residual strain, the interface structures and the overall structural quality are discussed with regard to growth mechanism and the surface energies of the corresponding orientations.

Experimental

The Ir thin films have been fabricated by DC-magnetron sputtering using a pure (99.9%) iridium target in a Gamma 1000C sputtering system with a base pressure of ~3 x 10 -5

Pa. The chosen substrates, i.e. single side polished MgO (100), ( 110) and (111) oriented single crystals (flux melt crystal growth, 10 x 10 mm square samples, 500 µm in thickness, one side polished, R q <1.0 nm), have been heat-treated at 1050 °C for 5 hours in air and at atmospheric pressure. This procedure has proven effective in obtaining clean MgO surfaces with regular atomic step-and-terrace structures. The thin films have been deposited at 600 °C substrate temperature and 0.66 Pa, in argon atmosphere. The applied density power on the iridium target was 1 W/cm², corresponding to a deposition rate of ~0.5 nm/min. Various thin film thicknesses have been obtained. Further details on the deposition procedure are presented elsewhere [START_REF] Trupina | Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere[END_REF]. The epitaxial relationships and the microstructural properties of the films (thickness, roughness, lattice distortions and lattice strain) have been investigated using X-ray diffraction (XRD). All measurements have been performed on a Bruker D8 Discover diffractometer, equipped with Cu target (λ = 1.5406 Å), and a parabolic mirror associated with a two-reflection Ge monochromator. Diffracted X-rays are collected using a 1D (LynxEye) detector covering a 2° 2θ range with an angular resolution of 0.01°. The film lattice parameters and residual strains have been determined by the analysis of reciprocal space maps (RSMs) of reflections with hkl indices containing both in-plane and out-of-plane components (i.e. asymmetrical RSMs). The surface morphology and roughness of the films have been investigated by atomic force microscopy (AFM), by using a MFP 3D SA microscope. Scanning electron microscopy (SEM) surface investigations, cross-section thickness measurements, and further sample processing, have been performed on a ZEISS Crossbeam 550 focused ion beam scanning electron microscope (FIB-SEM) equipped with a nanomanipulator for 3D analytics and sample preparation. This device was used in preparing transmission electron microscopy (TEM) samples, by using the low voltage capabilities of the FIB ion-sculptor to get ultra-thin samples while keeping amorphization damage at a minimum. Finally, the high-resolution (HR) TEM investigations of the iridium films and MgO substrates / thin films interfacial properties have been assessed on a Jeol JEM-2100F, 200 kV FE (field emission) analytical electron microscope.

Results and discussion

The growth of (100) or (110)-oriented iridium thin films is challenging because the {111} close packed planes have the lowest surface free energy of 2.59 J/m², followed by the {100} planes with 2.95 J/m², and by the {110} planes with 3.19 J/m² [START_REF] Mehl | Applications of a tight-binding total-energy method for transition and noble metals: Elastic constants, vacancies, and surfaces of monatomic metals[END_REF]. For this reason, the (111) crystalline orientation is preferred when the growth is governed by the low surface energy of the film. For instance, in the case of iridium films grown on silicon substrates under various deposition conditions, a preferential (111)-orientation has been systematically observed [START_REF] Trupina | Growth of highly textured iridium thin films and their stability at high temperature in oxygen atmosphere[END_REF]. However, changing the nature and the structure of the substrate might yield to favourable interface energies, allowing the epitaxial growth of different orientations, as it is observed in the present work.

As previously stated, at room temperature iridium has a face centred cubic (fcc) structure with a unit cell edge length of 0.38386 nm. MgO substrate has a fcc-type lattice of Mg ions with O ions occupying all the octahedral sites (and vice versa) with a unit cell edge length of 0.4211 nm. The possible hetero-epitaxial relations between iridium films and MgO (001), ( 111) and (110) substrates are schematically shown in Figure 1. The substrate-film misfit strain is defined as:

e= a s -a f a f ,
where a (s/f) represent the lattice constants of the substrate and the film. Since the film and the substrate exhibit the same orientations regardless of the substrates cut, the misfit strain is constant for all films and equals 9.7% (tensile). In the case of large lattice mismatch, hetero-epitaxial growth is possible via rotation domains hetero-epitaxy or domain matching hetero-epitaxy, and the associated formation of "geometrical" misfit dislocations [1-3, 33, 34]. The adjective "geometrical" is here used to indicate that these dislocations are directly formed at the interface during growth and do not require the glide of dislocations from the surface, as it is usually the case for lower lattice mismatch [START_REF] Birkholz | Thin Film Analysis by X Ray Scattering -Ray Sca[END_REF]. Interestingly, this potentially leads to high quality films to due to the lack of threading dislocation segments. The dislocation spacing is given by b/e (with "b" being the magnitude of the Burgers vector of the dislocations) which, with the above strain value, gives an average of 2.8 nm. This value has been obtained assuming the Burgers vector b = ½<110>, which, in the case of fcc metals, corresponds to perfect dislocations with the lowest energy. strain, e // , as well as the bulk (strain-free) lattice parameter, a (bulk) , of the film from the coordinates of the reflections of iridium and MgO. For this purpose, we follow the approach detailed in reference [START_REF] Boulle | Role of nanostructure on the optical waveguiding properties of epitaxial LiNbO 3 films[END_REF], where a (bulk) and e // can be deduced from the in-plane, d // = 2π/Q // , and out-of-plane, d  = 2π/Q  , lattice spacing determined from the RSM:

In the case of the (100) orientation and the 311 reflection,

Q // = Q [011] , Q  = Q [100]
, Φ is the angle between the (100) and the (311) planes and d // (bulk) = a (bulk) / 2 1/2 . For a (100) oriented film, the bi-axial Poisson ratio, υ 2 , is given in Table 1. The peak coordinates (Q // and Q  ) have been obtained by fitting the RSM with 2-dimensional Gaussian functions using the DxTools program [START_REF] Boulle | DxTools: processing large data files recorded with the Bruker D8 diffractometer[END_REF]. The in-plane strain, e// = [d// -d// (bulk) ]/d// (bulk) , is found to be compressive, with e// = -0.353(9)%. Although the theoretical misfit strain is tensile (9.7%), this apparent discrepancy can be explained by the fact that such a high misfit strain cannot be sustained by the film which therefore grows in a strain-relaxed state (with, as mentioned earlier, the formation of geometrical misfit dislocations with a spacing of 2.8 nm ̴ in the present case).

Strain is subsequently stored upon cooling down from the growth temperature. Since the coefficient of thermal expansion (CTE) of magnesium oxide, i.e. 12.6 x 10 ̴ -6 K -1 in the RT-700

°C range [START_REF] Madhusudhan Rao | Studies on Thermophysical Properties of CaO and MgO by γ-Ray Attenuation[END_REF], is higher that the CTE of iridium, i.e. 7.29 x 10 ̴ -6 K -1 in the RT-700 °C range [START_REF] Arblaster | Crystallographic Properties of Iridium. Assessment of properties from absolute zero to the melting point[END_REF],

this gives rise to a theoretical compressive strain of e = (α f -α s )(T growth -RT) = -0.31%. This value is in good agreement with the value of e // determined above. As shown below, a similar value is found for all films. Finally, it is worth considering the strain-free lattice parameter. Surprisingly, a (bulk) is not equal to the theoretical value of iridium, but it exhibits a -3.58% shrinkage, i.e. 3.8254 Å instead of 3.8392 Å. This might indicate the presence of iridium vacancies introduced during growth. A similar value is found for the (111) oriented films which seems to indicate that this is a process-dependent phenomenon. A reliable value could not be determined for the (110) orientation because of the mosaic nature of this particular MgO substrate (see discussion below).

The same procedure has been used in the case of iridium grown on MgO(111) substrate. All numerical results are also presented in Table 1. From the θ-2θ and φ-scans shown in Figure 3a and As mentioned earlier, it is noteworthy that, within experimental uncertainty, all films exhibit the same level of strain, which can be solely explained by the CTE mismatch between iridium and MgO. Interestingly, although the (111)-oriented iridium thin film has a thickness 3 times larger than the other orientations, this does not seem to induce any strain relaxation. Therefore, this leads us to conclude that the differences in the structural characteristics between the different films cannot be attributed to interfacial strain, but solely to the interface energy of the different orientations. Being the lowest energy orientation, the (111)-oriented films exhibit the best structural quality with a mosaicity 4 times lower than (100) and ( 110), and a vanishingly small level of lattice distortions. On the other hand, the surface energies of the (100) and (110) orientation are similar which leads to similar mosaicities and distortions, namely 1.26° and 0.012, and 1.3° and 0.011, respectively.

The AFM investigations, as presented in Figure 5, as well as the SEM analysis of the iridium thin films (not presented here), show that not only the crystalline orientation of iridium thin films depends on the crystalline orientation of MgO substrate but also their Although some dislocations can be observed at the film/substrate interface, it is important to note that the film is almost defect free, in particular no threading segments of dislocations are to be observed. This observation is in good agreement with the abovementioned domain-matching growth mechanism. In order to enhance the contrast of the zone axis, the apparent dislocation spacing is increased by a factor of 2 ½ . However, since both sets of dislocations contribute to the image, the overall dislocation density is actually overestimated by a factor of 2 ½ . With 18 visible dislocations, the average spacing, corrected for the above-mentioned 2 ½ factor, is 2.94 nm, in relatively good agreement with the value expected from the domain-matching interface model (2.8 nm). Figure 7a and Figure 7b show the same images for the (111) orientation. Unfortunately, the quality of the sample preparation here is not sufficient to get a highly resolved image, so that even the Fourier filtered image is difficult to interpret. Nonetheless, by compressing the image along the selected {00l} planes (Figure 7c) it is possible to resolve some misfit dislocations. Six dislocations can be distinguished with a computed spacing of 2.91 nm. Finally, the (110) orientation is depicted in Figure 8. The most striking feature is the peculiar morphology of the MgO surface which exhibits trenches perpendicular to the zone axis. Although the origin of those trenches is not yet determined, it might be due to a roughening transition occurring during the heat treatment to which the MgO substrates are submitted before deposition.

Despite these substrate surface features, one may observe that the iridium thin film surface roughness was improved compared with substrate surface roughness. This phenomenon of smoothing was also observed by de Assis et al. [START_REF] De Assis | Smoothening in thin-film deposition on rough substrates[END_REF], i.e. the surface roughness reduction of deposited thin films depends on initial substrate surface roughness, on the growth method and the used material and is strongly correlated with the mobility of the sputtered adatoms.

Another distinctive feature of this observation is the presence of defects (stacking faults) in the bulk of the Ir film. As a final point, repeating the same procedure as for the other films, 14 dislocations can be observed, which yields an average 2.68 nm of dislocation spacing. It should be mentioned that in this calculation the right hand side of the TEM image has been disregarded. Indeed, since the interface is poorly defined, the resulting FFT cannot be reliably analysed.

To conclude, the HR-TEM observations corroborate the film growth mechanism deduced from the XRD analysis of the residual strain: the film grows in a strain-relaxed state with the formation of geometrical misfit dislocations with an average spacing in the 10.5 -10.9 range, in excellent agreement with the value derived by assuming a complete strain relaxation during growth (10.3 unit-cells). Thermal strain is subsequently stored within the film upon cooling down from the growth temperature, as a result of the film/substrate thermal expansion mismatch.

Conclusion

We report on the epitaxial growth of atomically smooth iridium films grown on single crystal substrates, i.e. MgO(001), (111), and (110), respectively, by DC-magnetron sputtering.

Despite the fact that the growth of thin films with fcc-type structure generally is governed by the minimization of the surface energy, and thus the (111) crystalline direction is often preferred, hetero-epitaxial iridium thin films with (100), ( 111) and (110) crystallographic orientations is successfully achieved. The hetero-epitaxial relations between iridium thin films and MgO substrates can be attributed to the fact that the substrate acts as a crystallographic template for the growth of oriented Ir. It should be noted though that the surface energy still plays an important role, in particular by determining the overall crystalline quality of the films. In all cases, however, the iridium films exhibit flat topography with sub-nanometric surface roughness, making them a potential candidate for the template growth functional thin films.

  The XRD characterizations corresponding to iridium films grown onto MgO(100),MgO(110) andMgO(111) substrates are given in Figure2, Figure3and Figure4, respectively. Let us first discuss the case of MgO(100) in detail.In Figure2a, only the h00 reflections of iridium are visible, together with the h00 reflections of MgO, which indicates the (100) planes of iridium are parallel to the (100) planes of MgO. In this data, as well as in the following θ-2θ scans, additional peaks, labelled "*", are visible. Those peaks actually correspond to a residual of K β radiation. Although a two-reflection monochromator is used, a fraction of this radiation escapes the monochromator. Such radiations are usually cut out using a slit at the output of the monochromator, which was not the case for these experiments. However, this has no consequences on the results presented below. The in-plane orientation has been determined by φ-scan measurement using the (420) reflection plane of both MgO and iridium, as presented in Figure 2b. The reflections occur at the same azimuthal angle which demonstrates that the [010] direction of iridium is parallel to the [010] of MgO. The four symmetric peaks of the φ-scan indicate that the iridium film is grown cube-on-cube, with epitaxial relationship to MgO(100), exhibiting the (100) Ir || (100) MgO out-of-plane orientation and [001] Ir || [001] MgO in-plane orientation. The inset in Figure2ashows the simulation of the 200 reflection of iridium with a thin film scattering model from which were calculated the film thickness t, the roughness r (root-mean-squared (RMS) thickness fluctuations, <(t -<t>) 2 > ½ ), and the lattice distortions ε (RMS lattice plane distortions, <d-<d>) 2 > ½ / d). The obtained values are t = 23.2 nm, r = 0.7 nm, and ε = 0.012, respectively. Details regarding the scattering model can be found in reference[START_REF] Boulle | Recent advances in high-resolution X-ray diffractometry applied to nanostructured oxide thin films: The case of yttria stabilized zirconia epitaxially grown on sapphire[END_REF], equation[START_REF] Wandelt | Surface and Interface Science[END_REF]. Further information regarding thin film quality can be obtained from the rocking curves recorded through the h00 reflections of iridium, presented in Figure2c. The rocking curves have been simulated with a Pearson VII function; the full-width at half-maximum (FWHM) gives the mosaicity, which is 1.26 and 1.22° for the 200 and 400, respectively. Finally, the state of strain of the film was obtained from the analysis of 311 RSMs. Such a RSM is shown in Figure2d. Knowing the films orientation and the elastic constants of iridium, it is possible to compute the state of

  Figure3b, the following epitaxial relations are obtained: i) out-of-plane: (111) Ir || (111) MgO , ii) in-plane variant 1:[START_REF] Tolstova | Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering[END_REF][START_REF] Ohtake | Structure and Magnetic Properties of CoPt, CoPd, FePt, and FePd Alloy Thin Films Formed on MgO(111) Substrates[END_REF][START_REF] Tanaka | Microstructure of NiFe Epitaxial Thin Films Grown on MgO Single-Crystal Substrates[END_REF][4][START_REF] Wandelt | Surface and Interface Science[END_REF][START_REF] Bensalah | Mosaicity, dislocations and strain in heteroepitaxial diamond grown on iridium[END_REF][START_REF] Okada | Reactivity of gold thin films grown on iridium: Hydrogen dissociation[END_REF][START_REF] Kúš | Magnetron sputtered Ir thin film on TiC-based support sublayer as low-loading anode catalyst for proton exchange membrane water electrolysis[END_REF][START_REF] Wesselmark | The impact of iridium on the stability of platinum on carbon thin-film model electrodes[END_REF][START_REF] Bessey | Sputtered iridium coatings for grazing incidence X-ray reflectance[END_REF] Ir ||[START_REF] Tolstova | Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering[END_REF][START_REF] Ohtake | Structure and Magnetic Properties of CoPt, CoPd, FePt, and FePd Alloy Thin Films Formed on MgO(111) Substrates[END_REF][START_REF] Tanaka | Microstructure of NiFe Epitaxial Thin Films Grown on MgO Single-Crystal Substrates[END_REF][4][START_REF] Wandelt | Surface and Interface Science[END_REF][START_REF] Bensalah | Mosaicity, dislocations and strain in heteroepitaxial diamond grown on iridium[END_REF][START_REF] Okada | Reactivity of gold thin films grown on iridium: Hydrogen dissociation[END_REF][START_REF] Kúš | Magnetron sputtered Ir thin film on TiC-based support sublayer as low-loading anode catalyst for proton exchange membrane water electrolysis[END_REF][START_REF] Wesselmark | The impact of iridium on the stability of platinum on carbon thin-film model electrodes[END_REF][START_REF] Bessey | Sputtered iridium coatings for grazing incidence X-ray reflectance[END_REF] MgO (180 and ± 60°) and variant 2:[START_REF] Tolstova | Heteroepitaxial growth of Pt and Au thin films on MgO single crystals by bias-assisted sputtering[END_REF][START_REF] Ohtake | Structure and Magnetic Properties of CoPt, CoPd, FePt, and FePd Alloy Thin Films Formed on MgO(111) Substrates[END_REF][START_REF] Tanaka | Microstructure of NiFe Epitaxial Thin Films Grown on MgO Single-Crystal Substrates[END_REF][4][START_REF] Wandelt | Surface and Interface Science[END_REF][START_REF] Bensalah | Mosaicity, dislocations and strain in heteroepitaxial diamond grown on iridium[END_REF][START_REF] Okada | Reactivity of gold thin films grown on iridium: Hydrogen dissociation[END_REF][START_REF] Kúš | Magnetron sputtered Ir thin film on TiC-based support sublayer as low-loading anode catalyst for proton exchange membrane water electrolysis[END_REF][START_REF] Wesselmark | The impact of iridium on the stability of platinum on carbon thin-film model electrodes[END_REF][START_REF] Bessey | Sputtered iridium coatings for grazing incidence X-ray reflectance[END_REF] Ir || MgO (0 and ± 120°). The existence of two epitaxial variants comes from the fact that there are two possibilities (related by a 180° rotation) to position the iridium unit-cell on the MgO unit-cell: the iridium triangle points either "upwards", or "downwards", as one may conclude from the schematic in Figure 1b. From a structural point of view, variant 1 preserves the fcc ABC|ABC stacking across the interface (the interface being represented with the "|"), whereas variant 2 corresponds to: ABC|BCA, i.e. a stacking fault is formed at the interface. The energetic cost associated with the stacking fault probably explains why variant 2 is less likely to occur ( 100× weaker intensity in the φ-scan). ̴ Hetero-epitaxial iridium thin films have also been achieved on MgO(110) substrates, although it was more difficult to determine the state of strain and the unit-cell shrinkage do to the poor quality of the MgO crystals. It should be noted that this is a fairly general characteristic of MgO single crystals which are often "multi-crystalline" (or twinned) instead of purely single-crystalline. Indeed, more than 70% of the MgO substrates from six different vendors that have been tested for "single crystal" characteristics by Schroeder et al were demonstrated to be of less than the claimed single crystal quality [40]. Here, in the case of the (100)-and (111)-oriented ones, it was experimentally possible to select regions of the MgO crystals where the amounts of twins were low enough to perform a reliable characterization. Unfortunately, regions of sufficiently high quality could not be found for the (110)-oriented crystals. Nonetheless, from the θ-2θ scan, only (220) reflection peaks appear for both iridium and MgO, which corresponds to the (110) Ir || (110) MgO out-of-plane orientation. Φ-scans results on the (400) reflections of iridium reveal that the film had a [1-10] Ir || [1-10] MgO in-plane crystalline orientation with a twofold symmetry indicated by the peak separation of 180 o , as presented in Figure 4.

  surface morphology. Hetero-epitaxial growth and morphology of iridium thin films are directly influenced by surface step-terraces periodicity, corner sites and other substrate surface defects which may act as nucleation sites. The surface morphology of iridium thin films grown on MgO(001) substrates has a homogenous microstructure represented by rectangular grain shape arranged regularly and compactly with a RMS surface roughness of approximately 5.8 Å, as presented in Figure 5a. In case of the Ir(111) thin films grown on MgO(111) substrates, the surface morphology shows formations of triangular pyramidalshaped grains. This reflects strong (111) orientation of fcc iridium structure and a surface roughness of approximately 8.5 Å, as presented in Figure 5b. Elongated rectangular grain shapes oriented along the same direction with lateral dimensions close to the width of the substrate terraces have been observed on Ir(110) grown on MgO(110), as shown by the AFM image presented in Figure 5c. The Ir(110) film exhibits a roughness of approximately 7.4 Å. It can be noted that, although different, these roughness values are of the same order of magnitude as those derived by XRD, i.e. 6.8 Å, 3.8 Å and 10 Å. The differences are most likely due to the fact that the AFM determination is local (with only a few µm² probed), whereas XRD probes several mm².In order to assess the quality and structure of the iridium thin films and the corresponding MgO substrates, TEM sample slides ( 20 ̴ × 7 µm) are cut by FIB and then soldered to the TEM holders with Pt, as shown in Supplementary Material. Samples are finally refined and thinned by FIB and with the help of a nanomanipulator are further transported and investigated. HR-TEM investigations of the iridium thin films vs. MgO substrates have been acquired at different magnifications and in several zones for all three crystalline orientations. Selected area electron diffraction (SAED) patterns have been recorded on the iridium thin film, the substrate, as well as on the substrate -thin film interfacial region for all samples, as shown in Supplementary Material (electron beam with a 1 nm diameter, at 200 kV acceleration voltage). Unsurprisingly, these measurements correspond to the epitaxial orientation determined by XRD. In Figure6a, the HR-TEM image of Ir(001) grown on MgO-(001) is presented. One may observe the crystallographic orientation and the neat interfacial continuity between the substrate and the thin film.

  interface misfit, a digital dark-field image of the interface has been generated by selecting the 002 and 00-2 reflections in the Fourier transformed image. The corresponding filtered image is displayed in Figure 6b. It can be noted that the in-plane lattice spacing can be computed from the plane period (far from the distorted region at the interface), which yields d 200 = 1.915 Å, i.e. a = 2×d 200 = 3.83 Å (in very good agreement with the strain-free lattice parameter obtained by XRD, 3.8254 Å). In this image, the geometrical misfit dislocations are now clearly observed (red circles), from which the dislocation spacing can be computed. Before proceeding, it should be emphasized that, since the Burger vector of the dislocation is of ½<110> type, with the (001) film orientation, two sets of dislocations are actually formed at the interface with Burgers vector ½[011] and ½[011], and dislocations lines extending along [011] and [011], respectively. Since the TEM image has been taken along the [010]

Figure 1 .Figure 2 .Figure 3 .Figure 4 .Figure 5 .

 12345 Figure 1. Schematic of the possible hetero-epitaxial relations between (a) Ir(001) on MgO(001), (b) Ir(111) on MgO(111), and (c) Ir(110) on MgO(110) planes

Figure 6 .Figure 7 .Figure 8 .Figure 1 .Figure 2 .

 67812 Figure 6. HR-TEM image of Ir(001) grown on MgO-(001) (a), and the corresponding filtered image (b)

Table 1 .

 1 Structural parameters obtained from the XRD analysis

	Tables & Figures (with captions)
	hkl	Thicknes s (nm)	Roughnes s (Å)	Distortion s	Mosaicit y ( o )	In-plane (%) strain	Cell e (%) shrinkag	Bi-axial Poisson ratio
	(100 )	23	6.8	0.012	1.26	-0.353(9) -3.586(5)	2 C 12 /C 11 (0.8441)
	(111 )	65	3.8	0	0.30	-0.36(1)	-3.10(2)	(2C 11 + 4C 12 -4C 44 ) / (C 11 + 2C 12 + 4C 44 ) (0.5281)
	(110 )	20	10	0.011	1.30	-0.30(6)	-6	(C 11 + 3C 12 -2C 44 ) / (C 11 + C 12 + 2C 44 ) (0.5965)

Electronic mail: lucian.trupina@infim.ro, catalin.constantinescu@unilim.fr

Electronic mail: lucian.trupina@infim.ro, catalin.constantinescu@unilim.fr

Acknowledgements

This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CCCDI -UEFISCDI project number 61/2016 within PNCDI III, Core Program PN19-03 (contract no. 21 N/08.02.2019) and by the H2020 European project "MASTERS" within the M-ERA.NET call (http://www.unilim.fr/h2020_masters).

The authors gratefully acknowledge the help of Pierre CARLES and thank the CARMALIM team at the "Centre Européen de la Céramique" in Limoges, for their support in investigating the structure and morphology of the thin film samples.

Texture and interface characterization of iridium thin films grown on MgO substrates with different orientations

Lucian TRUPINA 1 , Liviu NEDELCU

Supplementary Material

In order to assess the quality and structure of the iridium thin films and the corresponding MgO substrates, TEM sample slides (~20 × 7 µm) are cut by FIB and then soldered to the TEM holders with Pt, as shown in Figure 1 of this Supplementary Material. Samples are finally refined and thinned by FIB and with the help of a nanomanipulator are further transported and investigated. HR-TEM investigations of the iridium thin films vs. MgO substrates have been acquired at different magnifications and in several zones for all three crystalline orientations.

Selected area electron diffraction (SAED) patterns have been recorded from the film, the substrate as well as from the interfacial region for all films, as shown in Figure 2 of this Supplementary Material (electron beam: 1 nm in diameter).


Marie Tahon
email: marie.tahon@limsi.fr

Laurence Devillers
email: laurence.devillers@limsi.fr

LAUGHTER DETECTION FOR ON-LINE HUMAN-ROBOT INTERACTION

Keywords: Laughter detection, acoustic features, laughter emotional valence

This paper presents a study of laugh classification using a cross-corpus protocol. It aims at the automatic detection of laughs in a real-time human-machine interaction. Positive and negative laughs are tested with different classification tasks and different acoustic feature sets. F.measure results show an improvement on positive laughs classification from 59.5% to 64.5% and negative laughs recognition from 10.3% to 28.5%. In the context of the Chist-Era JOKER project, positive and negative laugh detection drives the policies of the robot Nao. A measure of engagement will be provided using also the number of positive laughs detected during the interaction.

INTRODUCTION

The authors focus on laughter detection in humanmachine interactions. During real-life affective interactions, many different sounds are collected by the acoustic sensors: neutral and emotional speech, human and non-human sounds. Among human-sounds there are affect bursts: laughs, coughs, cries, etc. In the present study, the authors focus on laughter detection only. In the framework of the Chist-Era JOKER 1 project leaded by the LIMSI-CNRS, positive and negative laugh detection drives the policies of the robot Nao.

Analyzing laughter is a rather complex task because there exists many different types of laughter. In spontaneous speech, most of the laughs overlap speech, so-called "speech-laughs" [START_REF] Trouvain | Phonetics aspects of "speech-laughs[END_REF]. Affect bursts detection and particularly laughs detection are of importance for emotion recognition in spontaneous interactions [START_REF] Devillers | Real-life emotions detection with lexical and paralinguistic cues on human-human call center dialogs[END_REF] and specifically in interaction using humor strategies like in the JOKER project. Laughs can support positive feelings (joy, amusement, etc.) but also negative affective states (such as contempt [START_REF] Schröder | Experimental study of affect bursts[END_REF], sadness or embarrassment). A perceptive test carried on almost 50 isolated laughs have shown a clear difference between laughs perceived as positive or negative in a call center corpus [START_REF] Devillers | Positive and negative emotional states behind laughs in spontaneous spoken dialogs[END_REF]. Several studies [START_REF] Bachorowski | The acoustic features of human laughter[END_REF][START_REF] Campbell | Perception of affect in speech -towards an automatic processing of paralinguistic information in spoken conversation[END_REF] found that fundamental frequency, instance duration energy and formants are relevant for clear and well-identified laughs (i.e. "sounds which would be characterized as laughs by an ordinary person if hears in everyday circumstances"). Gaussian Mixture Models have been used for training PLP features [START_REF] Truong | Evaluating automatic laughter segmentation in meetings using acoustic and acoustic-phonetic features[END_REF]. More recently, 13 MFCC trained with HMM have been used for filler/laughter/speech/silence segmentation [START_REF] Salamin | Automatic detection of laughters and fillers in spontaneous mobile phone conversations[END_REF]. At the present time, very few real-life laughs databases are available. In the SEMAINE emotional database [START_REF] Mckeown | The semaine database: annotated multimodal records of emotionally coloured conversations between a person and a limited agent[END_REF] and the SSPNet Vocalization Corpus [START_REF] Vinciarelli | From nonverbal cues to perception: personality and social attractiveness[END_REF], laughter information have been extracted. In a previous study, clear laughs have also been extracted from a spontaneous child-robot interaction [START_REF] Tahon | Corpus of children voices for mid-level social markers and affect bursts analysis[END_REF]. In the JOKER project, an emotional and affect bursts corpora was collected with the aim to train affective models which are described in this paper. The models for detecting laughs are tested in different contexts with data collected in two previous projects ARMEN [START_REF] Chastagnol | Collecting spontaneous emotional data for a social assistive robot[END_REF] and JOKER [START_REF] Bechade | Automatic construction of behavioral rules from traces of humanrobot interaction[END_REF]. Our main goal is to present a cross-corpus analysis of laugh.

In this paper, the authors present their study on positive and negative laughs recognition in spontaneous humanmachine affective interactions. The section 2 summarizes the databases used for training and testing laughter. Methodology and experimental protocols are presented in section 3. And section 4 presents the conclusions of the study and further works.

DATABASES

In this section, three emotional speech and affect bursts databases are presented: one for training and two for testing in cross-corpus conditions.

JOKER training database

The training database was collected with two scenarios -jokes and emotion game -which were written in order to elicit emotional speech and laughs. 8 speakers were recorded with a high-quality microphone during an interaction with the robot Nao. In the joke scenario, the robot tells jokes in the aim to elicit laugh. In the emotion game scenario, the speaker has to act emotions (anger, sadness, happiness or neutral state) so as to be recognized by the robot. The recordings collected during the interaction contains emotional speech and affect bursts: laughs but also noise (most of noise sounds being microphone noise or striking table), cough and blows (breathing or blowing). In order to have balanced classes, the robot were asking the speaker to act affect bursts at the end of each scenarios. Each recording has been segmented and transcribed, the number of segments per emotional class and affect bursts is summarized in table 1.

ARMEN test database:

The ARMEN corpus [START_REF] Chastagnol | Collecting spontaneous emotional data for a social assistive robot[END_REF] was collected in order to collect spontaneous emotional speech with dependent people interacting with a Virtual Agent. In a first phase, the subject was invited by the interviewer to act emotions on purpose, by exaggerating the emotional tone of his voice. In the second phase, the subject would interact with the dialog system designed to induce emotions by projection: a daily situation with an emotional potential. 77 French participants (48 men and 29 women) from 18 to 90 year-old were recorded for a total duration of about 70 min. of speech. Laughs have been perceptively annotated in context, the number of laugh segments is summarized in table 1.

JOKER test database:

The JOKER testing database [START_REF] Bechade | Automatic construction of behavioral rules from traces of humanrobot interaction[END_REF] have been collected during funny human-robot interactions. This database was collected to study correlations between Nao's jokes (social, excessive, selfderision jokes and serious questions) and the user's appreciation. 18 young adults were recorded. Only laughs have been segmented yet (see table 1).

METHODOLOGY

Automatic classification and tasks

Automatic classification is performed with the Weka platform 2 with SMO function, RBF kernel and non optimized parameters (c = 2 and γ = 0.125). The complete acoustic set Set294 contains 294 prosodic, spectral, cepstral, formants and voice quality features extracted on the full, voiced and unvoiced segment [START_REF] Devillers | Détection des états affectifs lors d'interactions parlées: robustesse des indices non verbaux[END_REF]. Because the number of acoustic features is more important than the number of instances per class (around 140), a feature selection is essential. Analyzing negative and positive laughs from the training database confirms the state-of-the-art acoustic characteristics: F 0 , formants, loudness and spectral features. Two subsets of features were perceptively selected from ANOVA analysis.

• Set93: extracted on full segment only • Set32: spectral, formants and F 0 based features Preliminary analysis on acoustic features show that negative laughs are often confused with positive laughs are blows, then it must be relevant to perform hierarchical binary classification tests. Two different configurations are tested (table 2) one is parallel, one is hierarchical.

Table 2: Parallel (up) and hierarchical (down) configurations.

Results

The results are given in terms of F.measure for positive and negative laughs classes only. Cross-validation (CV) and testing (TEST) results are given in table 3. The True (resp. False) Positive, TP (resp. FP) results for the Hierarchic configuration are obtained using the following equations where P(x|y) m corresponds to the proportion of y laughs classified as x laughs by the model m.

T P + = P(+|+) laugh × P(+|+) a f f ect × P(+|+) speech Since the CV results with the parallel configuration are slightly better with Set93 (pos:72.7%; neg: 63.0%) than with Set294 (pos: 67.8%; neg: 59.3%), our feature selection is validated (table 3). One of the advantage of the Hierarchic configuration is to adapt the feature set to the classification task. The last line (HieraMix) corresponds to a speech classification with Set94 and affect/blow/laugh classifications with Set32. This optimization may also helps to avoid over-fitting since the speech classes contain around 500 instances and the affect classes contain only 140 instances. The results obtained with all the laughs are best with the Set93, whereas they are better with the HieraMix with positive laughs only. The results obtained with different classification tasks are better since they significantly improve the negative laughs classification.

CONCLUSION

In this study, laugh classification is presented. The authors studied different configurations and different acoustic feature sets for classifying laughs. Experiments are carried in a cross-corpus protocol, which means that training and testing acoustic conditions, tasks, speakers are not similar. F.measure obtained results are promising: a combination of acoustic sets improved the recognition of positive laughs from 59.5% to 64.5% and negative laughs from 10.3% to 28.5%. Some technical improvements can be realized: normalization, feature selection, real-time experiments, etc. This experiment also shows that negative laugh are very difficult to detect, because annotations are usually done in context, because they are very often confused with either positive laughs or blows. Multi-modal classification could probably helps to improve recognition rates.

T

  P -= (P(-|-) laugh + P(-|-) blow ) × P(-|-) a f f ect × P(-|-) speech FP -= P(-|+) laugh × P(-|+) a f f ect × P(-|+) speech FP + = P(+|-) laugh + P(+|-) blow ) × P(+|-) a f f ect × P(+|-) speech

Table 1 :

 1 Number of segments per class for each database, total and mean duration in sec.

	Annotation	# inst.	total	mean
			duration duration
		training database
	Noise	128	240.7	1.88
	Pos. Laugh.	140	139.2	0.99
	Neg. Laugh.	117	60.9	0.52
	Blow	140	117.7	0.84
	Cough	85	65.0	0.77
	Anger	140	263.7	1.88
	Sadness	144	190.1	1.79
	Neutral	144	249.8	1.73
	Happiness	140	237.5	1.70
	testing laugh databases
	JOKER-pos	48	93.1	1.94
	JOKER-neg	27	33.2	1.23
	ARMEN-pos	226	252.9	1.12
	ARMEN-neg	27	20.4	0.76

Table 3 :

 3 Results of the classification test (F.measure in %)

		CV		TEST
		pos	neg	pos	neg
	Parallel/Set294	67.8 59.3 59.5 10.3
	Parallel/Set93	72.7 63.0 60.8	5.6
	Hierarchic/Set93			68.8 15.4
	Parallel/Set32	75.1 54.7 61.7 15.2
	Hierarchic/Set32			61.5 27.4
	HieraMix			64.5 28.5