domain: qfin stat shs

text:
Christophe Bontemps

Valérie Orozco
email: valerie.orozco@inrae.fr

Toward a FAIR Reproducible Research

Keywords: Reproducible Research, FAIR, Trusted Science, Confidential Data

Two major movements are actively at work to change the way research is done, shared and reproduced. The first is the reproducible research (RR) approach, which has never been easier to implement given the current availability of tools and DIY manuals. The second is the FAIR (Findable, Accessible, Interoperable, and Reusable) approach, which aims to support the availability and sharing of research materials. We show here that despite the efforts made by researchers to improve the reproducibility of their research, the initial goals of RR remain mostly unmet. There is great demand, both within the scientific community and from the general public, for greater transparency and for trusted published results. As a scientific community, we need to reorganize the diffusion of all materials used in a study and to rethink the publication process. Researchers and journal reviewers should be able to easily use research materials for reproducibility, replicability or reusability purposes or for exploration of new research paths. Here we present how the research process, from data collection to paper publication, could be reorganized and introduce some already available tools and initiatives. We show that even in cases in which data are confidential, journals and institutions can organize and promote "FAIR-like RR" solutions where not only the published paper but also all related materials can be used by any researcher..

| THE NEED FOR REPRODUCIBLE RESEARCH

During the last decade, a great number of papers have been published on the problem of irreproducibility of research [START_REF] Nature | Reducing our irreproducibility[END_REF][START_REF] Munafò | A manifesto for reproducible science[END_REF] and on the crisis in science due to errors [START_REF] Reinhart | Growth in a time of debt[END_REF] or fraud [START_REF] Ioannidis | Why most published research findings are false[END_REF], leading to a lack of trust in published results. One response of this credibility crisis has been a renewal of interest in the "reproducible research" (RR) approach, as defined initially by geologist John Claerbout as the possibility of the "replication [of a paper] by other scientists " [START_REF] Claerbout | Active documents and reproducible results[END_REF].

However, despite an apparent consensus on the general problem, the publication of papers exhorting the scientific community to publish reproducible results, and the dissemination of tools, good practices and courses [START_REF] Stodden | Setting the default to reproducible: Reproducibility in computational and experimental mathematics[END_REF][START_REF] Gentzkow | Nuts and bolts: Computing with large data[END_REF][START_REF] Sandve | Ten simple rules for reproducible computational research[END_REF]Orozco et al., Forthcoming 2021), we still observe considerable weaknesses in both researcher and journal practices, leading to the scarce dissemination of raw scientific materials.1 Many journals do not have a replication or data and code availability policy. Among those that do, there is a great diversity in practices, with many implementing a simple supplementary materials section on their website. Thus, a clear organization and precise guidelines on how to achieve the initial goals of reproducibility in science are still lacking.

Since science is based on the accumulation of verified results, its growth is limited if researchers cannot easily reproduce one another's results and verify them. To achieve verification, several conditions have to be fulfilled: First, the research has to be done in such a manner that it can easily be reproduced. Second, the materials used to produce the results have to be available to others. Finally, somebody, i.e., a referee for a journal or another researcher, has to reproduce and validate the published results using the materials available. These conditions may seem very strong, but we argue that they are necessary to prove the validity of any research. In mathematics, we would all agree that a paper with a new theorem should, first, be accompanied with its complete proof in a readable format. Second, all the elements of the proof (lemmas, other theorems) must be provided in the paper or easily available, and finally, someone must have checked-reproduced-the theorem using these elements. Our message here is that even in empirical work where we use data and code to produce a result, we have to prove our findings. We follow the idea of [START_REF] Leveque | Python tools for reproducible research on hyperbolic problems[END_REF] that "constructing a computer program isn't so different from constructing a formal proof" and claim that reproducing a result issued from a computer program should not be different from reproducing a formal proof. This paper is devoted to two practical problems that have received little attention in economics and statistics so far: How, in practice, can we ensure that the results published in a paper have been reproduced and verified? How are all the materials used to produce the results of that paper shared with the community? These are very complex questions that can be even more complex when materials are confidential or when certain technical expertise (on machine learning, big data, etc.) is required for storing and using them. We question here the overall organization of research leading to the publication of a paper. The workflow leading to publication is long, and many obstacles may limit the publication of anything else but the paper. The researcher has a great role in preparing not only the document to be submitted but also all the materials leading to the results. Thus, the focus has been on researchers' practices for a long time. However, other actors, in particular journals as well as data providers and research institutions, also have a role to play in facilitating the diffusion of science, not only through publications but also through the availability of all the materials necessary for science to be truly reproducible and trusted.

The paper is organized as follows. In the next section, we identify and illustrate the current problems that limit the reproducibility of research. We also clarify and illustrate the definitions of the terms and notions used in the RR and FAIR approaches and survey some important initiatives that have been proposed. In section 3, we introduce some recent initiatives and propose new schemes involving researchers, journals and the FAIR and reproducible research community. Some issues arising from the nature of the raw materials (big data) or of the analysis (machine learning) are also addressed in this section. We illustrate the problem of sharing research materials when they are confidential in section 4 and show that some solutions to this problem have already been implemented by some journals. Section 5 lists the incentives and impediments related to the proposed approach and concludes the paper.

| REPRODUCIBLE RESEARCH IN PRACTICE

The notion of reproducibility has been discussed lengthily in the literature, sometimes with conflicting terminologies [START_REF] Barba | Terminologies for reproducible research[END_REF][START_REF] Benureau | Re-run, repeat, reproduce, reuse, replicate: Transforming code into scientific contributions[END_REF][START_REF] Bollen | Social, behavioral, and economic sciences perspectives on robust and reliable science: Report of the subcommittee on replicability in science, advisory committee to the national science foundation directorate for social, behavioral, and economic sciences[END_REF]. We follow [START_REF] Barba | Terminologies for reproducible research[END_REF] who summarize it by the equation "same data + same method = same results".2 For Gentleman and Temple [START_REF] Gandrud | Reproducible Research with R and RStudio Second Edition. Chapman & Hall/CRC The R Series[END_REF], this idea means that the "data+code" compendium -or reproducibility package -used in a paper is made available to the readers so that they can first verify (reproduce) the results and second conduct alternative analyses of the work. The notion of reproducibility is thus related to the similar notion of verification or scientific proof.

In complement to RR, the Open Science movement emerged 10 years ago and aims at sharing data used in research as a patrimonial and cumulative goal. This movement has seen the involvement of many stakeholders, communities, and institutions (e.g., the Open Government Partnership comprising 70 countries, the Center for Open Science, the Research Data Alliance). 3 These initiatives have focused primarily on the big questions behind open science implementation (e.g., repository certification, reusability, data citation, data management plans). Many tools and platforms emerged from these discussions: e.g., the European Open Science Cloud, the GOFAIR initiative and the Transparency and Openness Promotion (TOP) guidelines [START_REF] Nosek | Promoting an open research culture[END_REF]. The FAIR principles (findable, accessible, interoperable, and reusable) proposed by [START_REF] Wilkinson | The fair guiding principles for scientific data management and stewardship[END_REF] recently emerged as a global template for sharing data. FAIR does not mean open but, in brief, requires some accessibility to findable elements (most often datasets or at least metadata). The principles call for materials to be shared in a format that others can use (interoperable) and reuse.

These two movements are very active and influence the way institutions, research centers and national statistical offices (NSOs) construct their infrastructures and datacenters. To illustrate how these movements may affect the research publication landscape, we propose to reduce all the materials needed to produce a paper to only three key elements: the data, the code and the workflow, even if elements such as the documentation and the computing environment are also of great importance for some papers. We use the pictograms presented in Figure 1 throughout the paper. In view of the RR approach as defined by [START_REF] Claerbout | Active documents and reproducible results[END_REF], all these elements, not only the research paper, should be shared with the scientific community.

F I G U R E 1 Pictograms of inputs and outputs of empirical research (simplified)

We also illustrate the process leading to the publication of a paper by focusing on 3 major actors: the researcher(s), the journal that handles the publication process and the scientific community that should benefit from a new publication. We represent these actors with the pictograms in Figure 2. Later in the paper, we will see that other actors, such as research institutions, data providers and funding agencies, may play an important role in the publication process and its outcome.

F I G U R E 2 Main actors in the research and publishing process (simplified) Since the publication of the seminal paper by [START_REF] Claerbout | Active documents and reproducible results[END_REF], several authors have pointed out weaknesses in researchers' day-to-day practices and have proposed tools, solutions and advice. Many of these proposals underline existing ways of improving our practices toward RR, focusing on technical solutions. Applied statisticians and econometricians can now enjoy tools developed in R [START_REF] Leisch | Sweave: Dynamic generation of statistical reports using literate data analysis[END_REF][START_REF] Meredith | Towards reproducible econometric research: The sweave framework[END_REF][START_REF] Gandrud | Reproducible Research with R and RStudio Second Edition. Chapman & Hall/CRC The R Series[END_REF][START_REF] Xie | Dynamic Documents with R and knitr, Second Edition[END_REF][START_REF] Xie | R Markdown: The Definitive Guide[END_REF], Python [START_REF] Bilina | Python for Unified Research in Econometrics and Statistics[END_REF], Stata [START_REF] Gentzkow | Nuts and bolts: Computing with large data[END_REF][START_REF] Jann | Creating latex documents from within stata using texdoc[END_REF]Jann, , 2017)), SAS [START_REF] Lenth | Sasweave: Literate programming using sas[END_REF] and MATLAB [START_REF] Hunt | A Guide to MATLAB: For Beginners and Experienced Users Third Edition[END_REF][START_REF] Woodward | Automating communications measurement[END_REF].

Others [START_REF] Baiocchi | Reproducible research in computational economics: guidelines, integrated approaches, and open source software[END_REF]Orozco et al., Forthcoming 2021) have identified possible organizational improvements at the researcher level. These authors proposed principles to link a paper to its raw components, data and code through a clear workflow, following the original idea of reproducible research documents proposed by [START_REF] Knuth | Literate programming[END_REF]Knuth ( , 1992) ) and his literate programming approach. Other principles include a clear organization of work and files, greater attention to versioning, good documentation of the research workflow, good writing practices for code using layouts and naming conventions. Automating the whole workflow is also recommended and encouraged.

We have also seen the emergence of companion websites and "executable" papers allowing online code editing and execution [START_REF] Hurlin | Runmycode.org: a novel dissemination and collaboration platform for executing published computational results[END_REF][START_REF] Gorp | Share: a web portal for creating and sharing executable research papers[END_REF]. Platforms (e.g., Code Ocean, Exec&Share, SHARE) have been created to allow code to be run online using materials stored by other researchers. With this technology, researchers from around the world are able to rerun the exact same code as the author, change parameter values to see the impact on the results, or even replicate the code with another dataset. However, despite the efforts observed and all the tools and methods mentioned above, implementing RR has often been a challenge in practice. In a recent survey, [START_REF] Chang | A preanalysis plan to replicate sixty economics research papers that worked half of the time[END_REF] attempted to update the seminal work of [START_REF] Dewald | Replication in empirical economics: The journal of money, credit and banking project: Reply[END_REF] and successfully replicated only 33% of 67 papers published in economics journals. Other examples in other disciplines exhibit similar features (Miyakawa, 2020;[START_REF] Asendorpf | Recommendations for increasing replicability in psychology[END_REF]. This current situation, whereby journals do not ask for or check the raw materials used to produce a research paper, is represented in Figure

F I G U R E 3
The researcher (left) uses code and data following a (written) workflow and submits a (reproducible) paper to a journal (middle) that neither asks for nor checks the raw materials. The researcher then decides to share (or not) some materials (e.g., the code) with the community (right) online or "upon request".

3.

There are many reasons for the overall "irreproducibility" [START_REF] Nature | Reducing our irreproducibility[END_REF] of research. It is true that crafting reproducible papers may require more time and effort than that needed for papers with code that will be used only once. However, when researchers, especially young ones, invest in RR practices, habits and tools, they generally become more efficient in their day-to-day practices [START_REF] Stodden | Setting the default to reproducible: Reproducibility in computational and experimental mathematics[END_REF]. They are able to reuse their own materials, reproduce their own results, answer referees' questions more quickly and test various specifications of their models with little effect on the time spent reporting new results in a paper [START_REF] Mccullough | Open access economics journals and the market for reproducible economic research[END_REF]. There is also some evidence that papers that share their research materials are more likely to be cited [START_REF] Christensen | Transparent and Reproducible Social Science Research: How to Do Open Science[END_REF]. The case of the software industry has shown that open-source creations are likely to increase the reputation and hence the value of their authors in the labor market [START_REF] Lerner | Some simple economics of open source[END_REF].

The way researchers apply RR methods and share their research materials may be another important reason for the prevalence of irreproducibility. When they share their materials, researchers do it in an unstructured manner, on their websites or on GitHub, and many do not link the materials to each other or to the associated publication [START_REF] Baker | Why scientists must share their research code[END_REF]. Even if available, the data may not be easily accessible. In their book, [START_REF] Christensen | Transparent and Reproducible Social Science Research: How to Do Open Science[END_REF] remark that when shared, submitted data were also frequently an "unlabeled and undocumented mess". Many authors cite only general source information but do not give enough precise information about the data used [START_REF] Dewald | Replication in empirical economics: The journal of money, credit and banking project[END_REF]. Many researchers focus on code and share their files without a clear document explaining the order of execution of each piece of code or the overall workflow. The readme files that serve as a workflow description are rarely structured to explain how to use the programs and often only describe the materials used and are far from a manual for reproduction. Some materials, mostly code, may be shared after acceptance in the journal's supplementary material section (if any), on the researcher's website or on GitHub. Most of the time, researchers decide on their own initiative to share (or not) their materials "upon request". Data availability and data accessibility are thus ubiquitous problems.4 These problems are not the sole responsibility of researchers. Many scientists currently do share code and data, but this takes time and effort. [START_REF] Wacharamanotham | Transparency of chi research artifacts: Results of a selfreported survey[END_REF] recently surveyed more than 1000 authors of papers in computer science, asking if they were sharing their materials and if not why. The results underline some "misunderstandings about the purpose of sharing and reliable hosting". We have to acknowledge that even if some researchers do share their research materials, others simply do not want to.

In other disciplines, data collection represents a substantial effort. Researchers may not want to loose their investment and do not want to share this rent with others after a first publication.

The lack of incentives to share and the lack of sharing solutions are thus two barriers to reproducibility. They exist either because no clear data and code-sharing policies are defined by journals or because the technical solutions proposed are not good ones.

In Figures 3 and4, we illustrate different unsatisfactory yet frequently observed situations in which the research community has no access to the original raw materials even when the paper was originally designed by the researcher to be reproducible. In Figure 4, only the code is finally shared with the research community, even if the journal has access to all the materials. The materials may be "available upon request", allowing the author the freedom to decide what to share. It is not guaranteed in either case that the paper was crafted to be reproducible nor that the referees were able to reproduce the results when reviewing and then accepting the paper for publication. Several examples of errors, such as the famous one in [START_REF] Reinhart | Growth in a time of debt[END_REF], cast doubt on the role of referees and their ability or willingness to ask for and use submitted materials to reproduce results during the referee process. This issue is not limited to applied research: even theoretical mathematics papers display the same types of problems, with some analyses failing to be reproduced during the referee process or with authors citing unpublished papers in their work. Recently, a mathematician discovered a basic error (an inversion of an inequality) in the proof of a published paper [START_REF] Shchur | A quantitative version of the morse lemma and quasi-isometries fixing the ideal boundary[END_REF] and published the correct version where all the proofs had been checked using an open-source computer proof checker, opening the way to a new type of computer-assisted referee process [START_REF] Gouëzel | A corrected quantitative version of the morse lemma[END_REF].

For journals, reproducing a submitted paper requires many combined conditions that are still rarely met. First,

F I G U R E 4
The researcher (left) sends all materials to the journal (middle) but in the end shares some material (e.g. code) directly online (e.g. GitHub). There is no indication that the shared materials are the ones used in the paper, that they have been checked, or that they are working. the journal's policy must require that all materials be sent before or during the referee process. This implies that the submitted paper must have been done in a reproducible manner by the researchers in the first place. Second, the referees must have the skills, the willingness and the incentives to check the empirical proofs. Finally, the paper has to be reproduced, which implies some technical requirements, time and resources. Even if a journal is willing to reproduce a paper, it may not be able to do so and such conditions are still rarely fulfilled. Since replicating others' work can be quite technical and time consuming, this burden could also be outsourced to specialized third-parties agencies (see section 4). The journal then has several options to organize the way that materials are shared or not with the community. In practice, many journals do not impose or specify a way for materials to be shared. The most popular way of sharing consists of a "supplementary materials" section on journal websites. In a poll, [START_REF] Science | Challenges and opportunities[END_REF] reports that less than half of data requests from researchers to authors lead to positive outcomes.

In fact, the situations depicted in Figure 4 In Figures 5 to 7, we illustrate different types of observed situations where the community has access to a verified paper. 5 These solutions assume that journals have a clear data and code availability policy that is enforced. This requires that the raw materials provided by the researchers closely follow the RR principles. The whole workflow, including the curation of the original (raw) dataset collected either by the researcher or through a data provider, should be written in a readable form for humans and computers, following the literate programming ideas proposed by Knuth (1992).

If these mandatory conditions are fulfilled by researchers, journals may implement two different strategies. They could try to reproduce the results and then signal or certify that the results are correct (Figures 5 and6). This is what is expected from any scientific journal willing to maintain a reputation as a trusted publication. Alternatively, if a journal lacks sufficient human or financial resources to achieve this task, it should at least organize the diffusion of the materials and leave the verification process to the community, as in Figure 7. 6 The best solution is illustrated in Figure 6, where the journal or a trusted third party reproduces and checks the paper's results and then organizes the sharing of the materials they have used for the benefit of the community. Such transparent organization may seem difficult to establish in practice, but it is in fact already implemented by some journals.

F I G U R E 6

The researcher (left) sends all materials to the journal (middle). The journal or a trusted third party certifies that the materials used in the paper actually reproduce the results. The journal also shares all the materials (code-data-workflow) online for the community (right), which can also check, reproduce and reuse the materials.

F I G U R E 7
The researcher (left) sends all materials to the journal (middle). The journal shares all the materials (code-data-workflow) online for the community (right), which may check the results.

| IMPLEMENTING FAIR AND RR PRINCIPLES IN PRACTICE

In an empirical study examining 346 journals in economics and business studies, [START_REF] Vlaeminck | Data policies and data archives: A new paradigm for academic publishing in economic sciences?[END_REF] showed that only 20% of the journals have a data policy. In Table 1, we compile the data and code availability policies for statistics and economics journals as published on their websites in 2020. We can observe a great heterogeneity of practices. From this nonexhaustive list, we confirm that many journals still do not publish any policy at all. Even if the publication of erroneous results has probably helped journals improve their referee process, the vast majority only "encourage" authors to share their materials, sometimes without any guidance on how or where to put the materials.

Until very recently, very few (e.g., JSS, AJPS) checked that the code runs and reproduces the key results [START_REF] Christian | Operationalizing the replication standard: A case study of the data curation and verification workflow for scholarly journals[END_REF]. Moreover, [START_REF] Duvendack | What is meant by "replication" and why does it encounter resistance in economics[END_REF] showed that in only 28 economic journals (out of 333) do a majority of the empirical papers supply their data and code. This suggests that even when data and code policies are written, their enforcement is lax.

Nevertheless, there are some very good examples that should be inspiring. The JASA, for example, has an "associate editor for reproducibility", responsible for the technical review of manuscripts before, during or after the usual review process [START_REF] Fuentes | Reproducible research in jasa[END_REF]. The Journal of Statistical Software (JSS) asks for a standalone replication script that must enable reproducibility. The materials are checked and then stored on the journal website, following the scheme of Figure 6. Since July 2019, all journals published by the American Economic Association require that authors share their data and code, which are systematically checked "within reasonable limits of time and computing resources". These verification's can be costly for journals, but we may expect that the costs should decrease over time with the improvement of researchers ' and reviewers' practices. 7 This process can also be outsourced to specialists. 8 An example is given by the American Journal of Political Science (AJPS), which contracted the Odum Institute for Research in Social Science to systematically check that research materials confirm the results of submissions [START_REF] Crabtree | Odum institute user study: Exploring the applicability of the dataverse network[END_REF].

To succeed in organizing the way materials are shared while preserving the link with the results included in the paper, journals could extend the FAIR principles, developed primarily for datasets, as proposed by [START_REF] Wilkinson | The fair guiding principles for scientific data management and stewardship[END_REF]. In practice, sharing data and other materials together can be quite complicated. Individual solutions such as GitHub or even Dropbox may seem convenient for researchers but are not adapted or recommended as sharing solutions for published papers [START_REF] Gandrud | Reproducible Research with R and RStudio Second Edition. Chapman & Hall/CRC The R Series[END_REF]. There are risks that some elements in the code evolve (functions), that the data used are not explicitly identified (increments, versions) or that the links among all the research materials may be fuzzy or lost. Moreover, we believe that researchers should not organize the sharing themselves and that journals should align a strict mandatory policy with a clear organization and resources. In this regard, the Journal of Applied Econometrics (JAE) was a sort of pioneer, implementing its own data archive from the late 1980s. One satisfying technical solution is now offered by the Dataverse Network, developed at Harvard University. The network hosts collections of studies, embedding all materials for a paper in a single object, called a dataverse [START_REF] King | An introduction to the dataverse network as an infrastructure for data sharing[END_REF][START_REF] Leeper | Archiving reproducible research with r and dataverse[END_REF]. This solution is recommended by some journals (e.g., JASA, AJPS, QJE, PLOS, Nature). Other journals, following the recommendations of research institutions (NSF, ERC), use Figshare, Zenodo, Mendeley or ICPSR (see Table 1). 9

Following the FAIR principles implies not only that the materials should be shared, or accessible, but also that they should be interoperable and findable. The interoperability principle can be interpreted here as the ability for any reader to have access to materials stored in a readable format. 10 It should also be easy to find the materials without any ambiguity. We agree with the American Sociological Review that "citing datasets used in published research is just as important as citing journal articles, books, and other sources that contributed to the research". This means that the data and other materials should be identified in a consistent way. To precisely identify datasets and code, journals or institutions may request that a digital object identifier (DOI) be attached to each element described in the paper. 7 In a recent analysis, Jacoby William G. (2017) analyzed the AJPS verification policy and reported an average of 8 person-hours per manuscript to replicate the analyses and curate the materials. The publication workflow, involving more rounds and resubmissions, is also much longer. 8 There are already some useful resources and checklists that should facilitate the process for authors and replicators (see https://social-science-dataeditors.github.io/guidance/Verification_guidance.html) or the TOP proposing varying levels of replication policies for journals [START_REF] Nosek | Promoting an open research culture[END_REF]. 9 A complete list of solutions is detailed in The Registry of Research Data Repositories (http://re3data.org) a service of DataCite. In addition, CoreTrustSeal provides certification to repositories and lists the certified ones. 10 For datasets, the FAIR interoperability principle suggests the use of open formats such as CSV files instead of proprietary formats (.xls). For code and other materials, open-source software should be preferred to avoid exclusive access (Vilhuber, 2019). The metadata should also follow relevant standards (Dublin core or DDI) and ontologies. References and links to other related data should also be provided [START_REF] Jones | How fair are your data[END_REF].

DOIs are the backbones of the findable component of the FAIR principles. Even for data with constrained access (e.g., proprietary or confidential data), a DOI should provide enough elements, at least the metadata, to retrieve enough information describing the data (or other materials) used. 11 Several papers explain how to cite data repositories in a paper [START_REF] Fenner | A data citation roadmap for scholarly data repositories[END_REF].

In the context of big data or machine learning (ML) analysis, sharing the materials and the analysis are important issues that can be challenging [START_REF] Crosas | Automating open science for big data[END_REF]. The Zelig package, initially developed for R users, may offer a solution. Zelig provides a unified framework for statistical analysis allowing exploration, estimation and interpretation of any type of statistical model [START_REF] Choirat | Zelig: everyone's statistical software[END_REF]. An important feature in the context of ML is that the Zelig package automatically creates a workflow embedding all the procedures and algorithms used in the analysis into a single object that may then be exported and shared. The analysis can then be used by others, even if they do not know R [START_REF] King | An introduction to the dataverse network as an infrastructure for data sharing[END_REF]. In a recent paper, [START_REF] Crosas | Automating open science for big data[END_REF] proposed extending the architecture of Zelig to other tools and languages (Python) to provide a framework suitable for big data analysis. The NSF-funded Whole Tale (https://wholetale.org/) may also be a scalable solution enabling the creation, publication, and execution of "tales" or executable objects embedding data (potentially big data), code, and the complete software environment used to produce research findings [START_REF] Chard | Toward enabling reproducibility for data-intensive research sing the whole tale platform[END_REF].

Another difficulty may be due to the length of the publication process, which can be quite extensive. The reviewing process often requires additional tests or modifications. Thus, the code as well as the datasets and even the workflow may change with the evolution of the paper under review. Researchers following the RR approach and writing RR papers are already familiar with version control tools such as GitHub for their code. They should easily integrate their data and workflow in the same spirit. Both researchers and journals must integrate versioning in their organization. They should coordinate to be able to identify the exact version of each element used in the current version of the paper under review.

Another large step would be to question the access policies of publications, which are often paywalled, and to promote open-access publications such as PLOS (https://plos.org/) or arXiv (https://arxiv.org/) in our fields. 11 The DataCite project [START_REF] Brase | Datacite -a global registration agency for research data[END_REF] is a popular resource to locate and precisely identify data through a unique DOI.

| CONFIDENTIAL DATA

Confidential or proprietary data are often cited as an obstacle to reproducibility, mainly because of data accessibility restrictions such as those imposed by the European GDPR. 12 In economics, [START_REF] Christensen | Transparency, reproducibility, and the credibility of economics research[END_REF] observed that there has been a small increase in empirical papers (using data) published coinciding with a significant increase in data exemptions.They found that nearly half of the papers using data are not reproducible because the data are not available (see also [START_REF] Vilhuber | Reproducibility and replicability in economics[END_REF]). These exemptions may be due to the use of confidential data or to other restrictions limiting data availability.

Restrictions may also come from data providers' preservation policies or national statistical offices (NSOs) data management conditions allowing only remote and strictly controlled access to data through secure virtual terminals. 13 Journals and reviewers are then unable to access the data and cannot check the results, having access to the paper and the code only. 14 According to [START_REF] Lagoze | O privacy, where art thou? making confidential data part of reproducible research[END_REF], 50% of confidential data used in papers are from NSOs (approximately 60% in 2010 for top economic journals), and each NSO has its own data-sharing restriction and regulation. To handle the complexity of security-level restrictions and to allow third parties or reviewers to access confidential materials, [START_REF] Sweeney | Sharing sensitive data with confidence: The datatags system[END_REF] proposed a system of datatag repositories. Each datatag repository documents the way data and other sensitive materials can be shared, reducing the complexity of the situation to a small number of tags. Some authors propose altering original raw data into "safe data", potentially accessible by anybody, using blurring or aggregation techniques to remove sensitive details such as individual information [START_REF] Alter | Responsible practices for data sharing[END_REF].

Other methods include adding random noise or swapping individual responses between otherwise similar respondents while maintaining the same likelihood distribution [START_REF] Boker | Maintained individual data distributed likelihood estimation (middle)[END_REF]. In our view, these methods are limited to some specific cases and do not seem compatible with the principles of transparency used in the RR approach. Moreover, the transformation of raw data does not seem to solve the confidentiality issue, since the code used for these transformations must itself remain confidential, leading to a new sharing problem.

Nonetheless, solutions exist to preserve privacy while allowing other researchers to access and replicate results.

The principle is based on a trusted third-party having a secure access to confidential data and on an interactive platform 12 There are many sources of confidential and nonshareable data [START_REF] Christensen | Transparency, reproducibility, and the credibility of economics research[END_REF][START_REF] Lagoze | O privacy, where art thou? making confidential data part of reproducible research[END_REF]. 13 In France, the CASD (https://www.casd.eu/) is a single-access portal to many public data providers (INSEE, ministries, etc.). Researchers are not allowed to copy all the materials locally on their machine, and only some type of outputs can be extracted. 14 The code may also contain some confidential elements. In particular, the code used for the initial data curation may contain, e.g., brand or city names, addresses, etc.

F I G U R E 8

The researcher (left) shares all materials (code-data-workflow) privately with the trusted third-party. Access may be contracted with the journal (middle). A certification of reproducibility is sent to the journal together with the paper. The paper is published with the reproducibility certification, but only nonconfidential elements, such as code, are available to the community (right).

for queries and answers [START_REF] Dwork | On the complexity of differentially private data release: efficient algorithms and hardness results[END_REF]. The curator model [START_REF] Crosas | Automating open science for big data[END_REF], depicted in Figure 8, could be implemented using secured-sharing platforms such as dataverses or datatags. 15 Referees could have access to materials securely and reproduce and check the validity of the results, even with confidential data. A reproducibility certification could be emitted during or even before the submission process to attest to the full reproducibility of the results.

The recent and promising Certification Agency for Scientific Code and Data (CASCAD), supported by the French National Science Foundation (CNRS), proposes the solution of prepublication reproducibility certification [START_REF] Pérignon | Certify reproducibility with confidential data[END_REF]. Authors can ask CASCAD to review their materials, even when confidential data are used, and to certify the reproducibility of their paper's result (Figure 8). The replication process can be performed before publication, which facilitates the journal review process. Alternatively, journals may outsource this task to the certification agency during the referee process. Ex ante contracts between the trusted third party, the data provider and the journal may facilitate the process. The code used and the certification report may then be hosted on an open-access repository, such as Zenodo, and be accessible by the research community.

It is possible to attest that a paper using confidential data has been reproduced so that no doubt remains over the verifiability of the results. However, only a few people, namely, the third-party agency or some reviewers, had access to the research materials, as only the certified code may be finally shared with the community.

The reasons to grant researchers (the community) access to the research materials used to prepare papers dealing

F I G U R E 9
The researcher (left) shares all materials (code-data-workflow), preferably as a package or tale that is securely accessible by the journal's reviewers (middle) within a secured platform. The paper is published with access to a secured platform ("data enclave", such as the ICPSR). The community (right) has access to the secured query platform and can use the materials (e.g., code) without having access to the confidential elements.

with confidential data are numerous. As already stated, independent checks of results are important for science to be trusted, even if those results are based on confidential data. The recent Covid-19 pandemic and the use of individual databases have taught us that "careful data-management practices should govern both data collection and data processing" [START_REF] Ienca | On the responsible use of digital data to tackle the covid-19 pandemic[END_REF]. If papers using confidential data are not trustable, the consequences could be dramatic for policymakers and for researchers. We follow [START_REF] Ienca | On the responsible use of digital data to tackle the covid-19 pandemic[END_REF] and believe that "transparent public communication about (confidential) data processing for the common good should be pursued". Second, reproducing another researcher's paper can lead to new ideas that can be tested using shared materials. Finally, using each other's material is part of science, and sharing should not be an option.

However, working with confidential data does not necessarily mean having access to the dataset. Technical solutions, such as the one illustrated in Figure 9 and based on the idea of "data enclaves", exist. The Inter-university Consortium for Political and Social Research (ICPSR) has developed virtual and physical "data enclaves", allowing online data analysis with strict restrictions on queries, data access and downloads [START_REF] Dunn | Protecting confidentiality in archival data resources[END_REF]. At the time of its creation long ago, physical access to ICPSR resources and all the outputs created were humanly controlled. Currently, an online data analysis tool (survey documentation and analysis (SDA) software, created by the University of California, Berkeley) is used to evaluate output for disclosure risk prior to displaying for the end user. This is again a curator model accepting queries from any researcher and providing only approved analysis output, including the elements (estimations, tables, figures) published in the paper.

To many, the path toward findable, accessible, interoperable, and reproducible research may seem paved with obstacles. We argue here that this is the path to the future, considering the great challenges that we, as a scientific community, should overcome. Erroneous publications, unavailable research materials, and long and sometimes archaic publication processes have generated a research crisis within the research community and within society itself. Some publications [START_REF] Science | Challenges and opportunities[END_REF] advocate for a great change in the individual and collective practices of scientists, journals, funders, institutions, and societies, acknowledging Claerbout's principles that "an article (• • • ) in a scientific publication is not the scholarship itself, (• • • ) the actual scholarship is the complete set of instructions which generated the figures" (de Leeuw, 2001).

We review here some existing publication workflows and identify their weaknesses, observing that many lead to the unavailability of research materials for the research community, even when the researcher has made an effort to prepare the paper to be reproducible. We highlight some promising organizations dedicated to a better transmission of research materials to allow the scientific community to reproduce and verify published results. XXXXX here something on paywalled journals and open access movement. We argue that our community and the public at large will greatly benefit from a change toward greater transparency and better-organized research. This change will only occur if all research actors agree to adhere to FAIR and reproducible research principles.

Most of these principles can be gradually implemented as a growing process toward more reproducible practices.

Researchers should initiate these changes. They now have all the resources needed to improve their individual practices to create more reproducible papers by embedding code and data in a documented and written workflow understandable by others, including researchers' own "future selves" [START_REF] Gentzkow | Nuts and bolts: Computing with large data[END_REF]Orozco et al., Forthcoming 2021). They are probably in the process of changing their habits already under the pressure of certain journals and research institutions such as the ERC and NSF.

Researchers are also reviewers, some of them even journal editors, and thus can promote many valuable actions.

First, journals should reorganize the review process and the way the results of submitted papers are checked, including when some materials are confidential. This is probably one of the most challenging issues, requiring new skills for reviewers, additional resources and a clear internal setup for sharing the submitted paper's materials. Certified trusted third parties (e.g., CASCAD, Odum Institute, CISER R-Squared) already exist, if that process has to be outsourced.

Having an "associate editor for reproducibility", as the JASA does, could also be a good idea to solve many practical questions such as when to check the validity of the submitted materials (before, during, or after the classical review) or to organize the verification and the relations with the author. Second, journals should have a clear data and code availability policy with a proper check of materials by reviewers. Journals should also organize the way research materials are shared. 16 Contracting with public repositories such as Zenodo, Mendeley, or Figshare would reduce the constellation of individual and self-maintained repositories and the fragmentation of arbitrarily different, incompatible standards [START_REF] Sansone | Fairsharing as a community approach to standards, repositories and policies[END_REF]. These platforms also guarantee perennial access to the core materials of science.

Finally, if implemented, this process will provide strong incentives for researchers to only produce RR papers. Some journals (e.g., AJPS, Biostatistics) propose badges tagging reproducible research. Such a practice seems to increase the proportion of papers using open practices and to improve the preservation of research materials [START_REF] Kidwell | Badges to acknowledge open practices: A simple, low-cost, effective method for increasing transparency[END_REF][START_REF] Rowhani-Farid | Badges for sharing data and code at biostatistics: an observational study [version 2; peer review: 2 approved[END_REF].

Data providers, whether they are private or public, could also facilitate the changes that we call for. Quite often, they are aware of these problems and have implemented some processes for their internal publications that could be inspiring [START_REF] Lagoze | O privacy, where art thou? making confidential data part of reproducible research[END_REF]. In the near future, they may pay increasing attention to the use of the data they provide, checking published results either to publicize their activity or to criticize a misuse. 17 In the case of confidential data, providers and, in particular, NSOs may also find some interest in promoting and organizing the way their data are findable and accessible [START_REF] Pérignon | Certify reproducibility with confidential data[END_REF]. Thus, data providers should encourage researchers, institutions and journals to produce more reproducible and reproduced papers. It is therefore likely that partnerships among journals, data providers and private or public third parties will increase in the future.

Research institutions have already started to impose some conditions on funded projects or grants by requiring researchers to follow a strict RR approach, by promoting the dissemination of the FAIR and RR approaches, and by financing public infrastructures hosting FAIR research materials repositories. 18 If "science is organized knowledge" [START_REF] Spencer | The art of education[END_REF], then we should all work for better organization for better science. We believe that the FAIR and reproducible research movements are there to jointly provide organized resources, tools and practices. Changing the publication workflow and our habits may be a long and probably costly journey. Not changing could be even more costly. 16 Alter and Gonzalez (2018) suggested that to "protect" researchers who want to use their data first (before sharing), journals can propose an "embargo". 17 A recent lawsuit involving the popular training program CrossFit showed that a paper by [START_REF] Smith | Crossfit-based high-intensity power training improves maximal aerobic fitness and body composition[END_REF] erroneously showed an increased risk for injuries for its users. Although the paper was retracted later, the impacts on the researcher's career were severe (for details, see https://retractionwatch.com/). 18 The European Research Council (ERC) recommends "to all its funded researchers that they follow best practice by retaining files of all the research data they have used during the course of their work and that they be prepared to share this data with other researchers" (see https://erc.europa.eu/sites/default/files/ document/file/ERC_Open_Access_Guidelines-revised_2013.pdf).

Overview of statistics and economics journal policies in 2020

We use here a nonexhaustive list of journals. In statistics, we select the most important ones according to the Web of Science index. In economics, we use the journals listed in [START_REF] Mccullough | Open access economics journals and the market for reproducible economic research[END_REF]. We choose to eliminate some specialized journals or journals publishing mainly theoretical work. 19 TA B L E 1 Overview of statistics and economics journal policies in 2020 19 See also Orozco et al. (Forthcoming 2021) for the evolution of economic journal replication policies (2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019).

  in which the researchers are the sole party responsible for the quality F I G U R E 5 The researcher (left) sends all materials to the journal (middle). The journal shares only the code online for the community (right) and signals that the code has been carefully checked, either internally or by a trusted third-party agency. and reproducibility of the files shared and no one checks what is stored are still the most commonly observed.

  AE A indicates that the journal follows the strict AEA Data and Code Availability Policy ( see https://www.aeaweb.org/journals/policies/data-code/).

	Journal	Policy	Platform Used
		(In bold mandatory policies, in plain sharing is encouraged)
	Statistics journals
	Annals of Statistics	-	-
	Annals of Applied Statistics	(data+code) sharing	-(Supplementary materials archive)
	Biometrics	(data+code) sharing	multiple (OSF, Dataverse)
	Biometrika	-	-
	Comput Stat & Data Analysis	(data+code) sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode, ...)
	Electronic Journal of Statistics	code sharing	Statlib
	J of Business & Econ. Stat.	(data+code) sharing	Figshare
	J of Comp. and Graph. Stat.	(data+code) sharing	Figshare
	J of Multivariate Analysis	data citation	-
	JASA	(data+code sharing)	JASA Dataverse, JASA GitHub
	J of the Royal Statistical Society	(data+code) sharing	-
	J of Statistical Software	(data+code) sharing	-(Supplementary materials archive)
	Stat. Methods in Medical Research	(data+code) sharing	-(Supplementary materials online)
	Statistics & Probability Letters	data citation	-
	Statistics and Computing	data sharing	multiple (Figshare, Dryad, openICPSR, Dataverse)
	Stoch. Proc. & their Applications	data citation	-
	CSBIG	data sharing	-
	Economics journals
	Am Econ Review	(data + code) sharing	OpenICPSR (AEA Data and code repository)
	J Finance	code, data sharing	-
	Q J Economics	(data + code) sharing	data repository (Dataverse) linked to the QJE website
	Econometrica	(data + code) sharing	-(Supplementary materials webpage)
	J Financial Econ	data + code sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode)
	J Political Econ	(data + code) sharing	-(JPE website)
	Rev Financial Stud	-	-
	J Econ Theory	(data + code) sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode)
	Rev Econ Studies	(data + code) sharing	Oxford Journals Review Archive
	J Econometrics	(data + code) sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode)
	J Econ Literature	(data + code) sharing AEA	OpenICPSR AEA
	J Monetary Econ	(data + code) sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode)
	J Econ Perspectives	(data + code) sharing AEA	OpenICPSR AEA
	Rev Econ & Stat	(data + code) sharing	-
	Eur Econ Review	(data + code) sharing	-(EER website)
	Int Econ Review	-	-
	J Int Econ	data, code sharing	Mendeley repository
	Economic Journal	-	-
	J Public Econ	(data + code) sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode)
	Game Econ Behav	(data + code) sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode)
	RAND J Economics	-	-
	J Money Credit Bank	(data + code) sharing	web data archives
	Economic Theory	data sharing	multiple repositories
	J Bus & Econ Stat	(data + code) sharing	-(Supplementary online materials)
	Economics Letters	data, code sharing	multiple (Mendeley, DRYAD, ICPSR, RunMyCode, ...)
	J Appl Econometrics	data, code sharing	JAE data archive
	A J Political Science	(data+code) sharing	AJPS Dataverse

Bontemps& Orozco, 2020

We consider here that the research process starts once the data are collected and in possession of the researcher. We do not address here the issue of reproducibility for data collection in experimental economics or field experiments(Bowers et al.,

2017).

We will not discuss here the question of the precise meaning of "same results".

At the European level, one should mention OpenAIRE and in France the "Plan national pour la science ouverte" (https://www.ouvrirlascience.fr/).

Other issues that we do not address directly here include the digital preservation of research data[START_REF] Gutmann | From preserving the past to preserving the future: The data-pass project and the challenges of preserving digital social science data[END_REF][START_REF] Akers | Disciplinary differences in faculty research data management practices and perspectives[END_REF] or the preservation of software[START_REF] Di Cosmo | Software heritage: Why and how to preserve software source code[END_REF].

In these figures, for clarity reasons, we do not illustrate the fact that researchers may share their materials themselves.

In 2003, Hashem Pesaran announced the creation of a new section of the Journal of Applied Econometrics dedicated to the replication of previously published empirical papers[START_REF] Pesaran | Introducing a replication section[END_REF]. Since then, some journals have followed this idea leading to an increase in the number of replication papers in economics[START_REF] Mueller-Langer | Replication studies in economics-how many and which papers are chosen for replication, and why?[END_REF].

Some data providers, in particular national statistical offices (NSOs), already perform RR on their confidential data, controlling output files and code, to check if they satisfy confidentiality restrictions before publication[START_REF] Lagoze | O privacy, where art thou? making confidential data part of reproducible research[END_REF].

Acknowledgments

The authors wish to thank the participants of the Banco de Portugal Reproducible Research Workshop in Porto ( 2019) for the stimulating discussions, which are at the origin of this paper. We are grateful to Virginie Piguet as well as the two anonymous referees for their careful reading and inspiring comments and suggestions.


Sébastien Grech-Angelini

Frédéric Stachurski

Renaud Lancelot

Jérôme Boissier

Jean-François Allienne

Mohamed Gharbi

Gerrit Uilenberg

First report of the tick Hyalomma scupense (natural vector of bovine tropical theileriosis) on the French Mediterranean island of Corsica

Keywords: Hyalomma scupense, Cattle, Molecular identification, Theileria annulata, Corsica

Hyalomma scupense (Acari, Ixodidae) is a common tick species found in several areas in North Africa, Asia and South Europe and an efficient natural vector of bovine tropical theileriosis (Theileria annulata), a livestock disease with an important economic impact. For one year, 1938 ticks were collected on cattle in several Corsican slaughterhouses; 168 of them were morphologically identified as H. scupense. This result was confirmed by genetic identification using sequences of mitochondrial cytochrome c oxidase subunit I (COI) and ribosomal internal transcribed spacer 2 (ITS2) genes. The presence of 2 different stages (adults and nymphs), collected in various areas of the island, indicates that a population of H. scupense is established in Corsica. However, bovine tropical theileriosis has not been diagnosed on the island so far.

-INTRODUCTION

Hyalomma scupense occurs in a wide area ranging from northernAfrica, Sudan, Turkey, the Middle East, southern Russia and centralAsia, to China; it has also been reported from some southern Euro-pean countries [START_REF] Apanaskevich | The genus Hyalomma Koch,1844. X. Redescription of all parasitic stages of H. (Euhyalomma) scupense Schulze, (= H. detritum Schulze) (Acari: Ixodidae) and notes on its biology[END_REF]. Taxonomic uncertaintyas to the identity of Hyalomma (Euhyalomma) scupense Schulze,1919 and Hyalomma detritum Schulze, 1919 has existed for a longtime, but it is now established that the two names correspond tothe same species; H. scupense is the valid name and H. detritum is asynonym [START_REF] Apanaskevich | The genus Hyalomma Koch,1844. X. Redescription of all parasitic stages of H. (Euhyalomma) scupense Schulze, (= H. detritum Schulze) (Acari: Ixodidae) and notes on its biology[END_REF]. It is the most abundant ixo-did tick infesting cattle in Morocco and Tunisia [START_REF] Estrada-Pena | Ticks of Domestic Animals in the Mediterranean Region: A Guide to Identification of Species[END_REF][START_REF] Gharbi | A review of Hyalomma scupense (Acari, Ixodidae) in the Maghreb region: from biology to control[END_REF]. This tick species is monotropicand has become endophilic in many regions. H. scupense is a one-or two-host tick; domestic cattle are the most common hostsfor adults and immature stages, but almost all ungulates may beinfested. Single records are also known from other hosts (domes-tic dogs, hares (Lepus sp.), foxes (Vulpes sp.)) and humans areoften attacked by the adults [START_REF] Hoogstraal | African Ixodoidea. Volume I. Ticks of the Sudan[END_REF][START_REF] Apanaskevich | The genus Hyalomma Koch,1844. X. Redescription of all parasitic stages of H. (Euhyalomma) scupense Schulze, (= H. detritum Schulze) (Acari: Ixodidae) and notes on its biology[END_REF]. It is one of the most important vectors of bovine tropical theileriosis (Theileria annulata). This protozoan is a major pathogenin the Maghreb region, causing high economic losses in cattle (milkyield decrease, weight loss, abortions, high treatment costs anddeaths; [START_REF] Gharbi | Ranking control options for tropical theileriosis in at-risk dairy cattle inTunisia: using benefit-cost analysis[END_REF]. H. scupense is also a vector of otherdiseases, including Q-fever (Coxiella burnetii) and equine piroplas-mosis (Theileria equi) [START_REF] Hoogstraal | African Ixodoidea. Volume I. Ticks of the Sudan[END_REF]. Although H. scupense canprobably transmit the virus of Crimean-Congo hemorrhagic fever(CCHF), it does not appear to be a major vector. [START_REF] Hoogstraal | The epidemiology of tick-borne Crimean-Congo hemorrhagic fever in Asia, Europe and Africa[END_REF]quoted a study by [START_REF] Chumakov | Proofs of ecological identity of Crimean hemorrhagic fever and Central Asian hemorrhagic fever[END_REF] in which CCHF virusinfection was demonstrated by the fluorescent antibody test inthe salivary glands of H. scupense in Kzyl-Orda Oblast, Kazakhstan.According to [START_REF] Estrada-Pena | Unraveling the ecological complexities of tick-associated Crimean-CongoHemorrhagic Fever virus transmission: a gap analysis for the Western Palearctic[END_REF], H. scupense is one of themain Hyalomma species implicated in the transmission of the virusin Eurasia, but no other evidence of this is given.

Corsica is a French Mediterranean island situated 15 km northof Sardinia and 90 km west of Tuscany in Italy (Fig. 1). The island is183 km long and 83 km wide; it is the most mountainous island inthe Mediterranean area (with Monte Cinto peaking at 2706 m). Itsclimate is classified as hot summer Mediterranean. About 300,000people live in Corsica and livestock farming is an important eco-nomic activity with approximately 150,000 sheep, 48,000 goats,40,000 pigs and 70,000 cattle. Cattle farming is of a very extensivetype, the animals (mainly local Bos taurus cattle) live outside allyear and usually without any barn.

Neither the tick fauna of Corsica nor the transmitted pathogenshave been fully investigated. However, a few ad hoc studies showedthe existence of three species of the genus Hyalomma on theisland. (i) Hyalomma marginatum is well-established, widespread,and found on many hosts [START_REF] Morel | Les Hyalomma (Acariens: Ixodidae) de France[END_REF][START_REF] Pérez-Eid | Les tiques. Identification, biologie, importance médicale et vétérinaire[END_REF]personal observations). It is one of the main vectors of the zoonotic CCHF virus and an experimental vector of Theileria annulata butunlikely to play a significant role in the field [START_REF] Estrada-Pena | Ticks of Domestic Animals in the Mediterranean Region: A Guide to Identification of Species[END_REF]. It is also a vector of Rickettsia spp., including Rickettsia aeschlimanni in Corsica [START_REF] Matsumoto | Rickettsia aeschlimanni in Hyalomma ticks from Corsica[END_REF], and of Babesia caballi, the agent of equine babesiosis [START_REF] Estrada-Pena | Ticks of Domestic Animals in the Mediterranean Region: A Guide to Identification of Species[END_REF]. According to [START_REF] Hoogstraal | African Ixodoidea. Volume I. Ticks of the Sudan[END_REF] it is also a natural reservoir of theagent of Q-fever (C. burnetii); (ii) Hyalomma aegyptium is mainlyfound on tortoises although it occasionally infests other hosts, small mammals (hedgehogs, hares, rodents, etc.), lizards and evenbirds (partridges). It has been identified only once in Corsica (onemale) on a tortoise Testudo hermanni [START_REF] Matsumoto | Rickettsia aeschlimanni in Hyalomma ticks from Corsica[END_REF]

1;(iii)
Hyalomma rufipes, a tropical sub-Saharan species, has beencollected on migrating birds and may play a role in the dissemination of R. aeschlimanni, with which it has been found infected in Corsica [START_REF] Matsumoto | Rickettsia aeschlimanni in Hyalomma ticks from Corsica[END_REF]. This species is known to bethe most important vector of CCHF virus in southern Africa and italso transmits Anaplasma marginale and Babesia occultans to cattle [START_REF] Estrada-Pena | Ticks of Domestic Animals in the Mediterranean Region: A Guide to Identification of Species[END_REF]. Nymphs of this species are commonly found on birds migrating from Africa to Europe [START_REF] Hoogstraal | Ticks (Ixodoidea) on birds migrating from Africa to Europe and Asia 1959-61[END_REF] and isolated adults have even been reported in Northern Europe.

A better knowledge of the Corsican tick fauna is needed to deter-mine present and potential dangers to human and animal healthrelated to tick-borne pathogens. This was the aim of a systematictick survey carried out in 2014-2015. The finding of the species H. scupense during this study is presented here in advance because ofits great potential importance as an efficient vector of T. annulataon cattle.

-MATERIALS AND METHODS

From May 2014 to May 2015, ticks were collected in the 3 Corsican cattle slaughterhouses (Ponte-Leccia, Cuttoli and Porto-Vecchio, Fig. 1), from cattle living in different areas of the island. The national cattle identification system (eartags) allowed to traceback the origin of the cattle. The slaughterhouses of Ponte-Lecciaand Cuttoli were visited monthly, whereas samples were collectedonly three times in Porto-Vecchio. During each visit, the whole skinsof 15-25 cows were examined, just after flaying, and the ticks were manually collected. They were stored in 70% ethanol at -20•C until their identification according to their morphological characteristics using a stereomicroscope, with the keys and descriptions by [START_REF] Hoogstraal | African Ixodoidea. Volume I. Ticks of the Sudan[END_REF], [START_REF] Walker | Ticks of Domestic Animals in Africa. A Guide to Identification of Species[END_REF], [START_REF] Estrada-Pena | Ticks of Domestic Animals in the Mediterranean Region: A Guide to Identification of Species[END_REF] and [START_REF] Apanaskevich | The genus Hyalomma Koch,1844. X. Redescription of all parasitic stages of H. (Euhyalomma) scupense Schulze, (= H. detritum Schulze) (Acari: Ixodidae) and notes on its biology[END_REF].

To confirm the morphological identification of H. scupense,genomic DNA (gDNA) was extracted and purified from either one ortwo legs, using the QIAamp DNA microkit following manufacturer protocol (Qiagen). The use of only one or two legs allowed both morphological and molecular identification and the remainder of the specimen was kept for examining the presence of pathogenic organisms. Target genomic regions included the mitochondrial cytochrome c oxidase subunit I (COI) genes, as well as the whole sequences of the ribosomal internal transcribed spacer-2 (ITS2) region. The primers used for COI amplification were LCO1490(5_-GGTCAACAAATCATAAAGATATTGG-3_) and HCO2198 (5_-TAAACTTCAGGGTGACCAAAAAATCA-3_) [START_REF] Folmer | DNA primers for amplification of mitochondrial cytochrome c oxidase subunit I from diverse metazoan invertebrates[END_REF]. The primers used for ITS2 were H1 (5_-TGGCTTCGTCTGTCTGAGGGTC-3_) and H2 (5_-TGCTTAAATTCAGCGGGTTGTC-3_). Conventional polymerase chain reaction (PCR) was performed in a total reaction volume of 25 _L consisting of 2 _L of gDNA, 1X Colourless GoTaqflexi buffer (Promega, Madison, WI, USA), 1.5 mM MgCl2 (Promega, Madison, WI, USA), 0.2 mM of each dNTP (Promega, Madison, WI,USA, reference U1420), 0.4 _M forward primer, 0.4 _M reverseprimer and 1U GoTaq G2 hotstart Polymerase (Promega, Madison,WI, USA, reference M7405). DNA amplification consisted in anactivation step of 95•C for 4 min, followed by 35 cycles of 95•C for40 s, 52•C for 40 s, and 72•C for 1 min (COI) or 1 min 40 (ITS2), anda final extension at 72•C for 5 min. PCR products were visualizedon Labchip GX1 (PerkinElmer). Positive products were sent to Genoscreen (France) for sequencing in both directions using dilutions of the original PCR primers. The sequences were then assembled and manually edited using Sequencher (GeneCodesCorp) to remove any ambiguities between strands and sequences.Genetic distance between sequences obtained and reference sequences from GenBank were calculated using Mega V6.0

-RESULTS

A total of 1,938 ticks were collected from cattle, among which168 were identified as H. scupense (70 females, 74 males and 24nymphs), representing 8.7% of the collected ticks (Fig. 2). Ticks were obtained from 72 "communes" (smallest administrative unitin France, Fig. 1) and H. scupense were collected from cattle raisedin 21 of them. It represented more than 50% of the collected ticksin 10 communes. Individuals from this species were collected from December to May, with a peak in January-March, during which H. scupense constituted 40-53% of the ticks infesting the slaughtered cattle. The 24 nymphs were collected from December to March Eleven specimens morphologically identified as H. scupense (4 males, 4 females and 3 nymphs) were submitted to molecular identification. Ten COI and 8 ITS2 sequences were obtained. Sequence divergence was found within the COI sequences (4 haplotypes; GenBank accession numbers, AN: KT598361, KT598360, KT598362,KT598363). The genetic distance within Corsican specimens was 0.002 (standard deviation of 0.001). No sequence variation was found within ITS sequences (AN: KT598364). All sequences confirm the morphological identification of H. scupense. Table 1 showsmean pairwise distance of all the sequences obtained for COI, forITS2 and reference sequences. The genetic distance between the Corsican specimens and H. scupense was 0.7% for both genes while the minimum genetic distance between the Corsican specimens and the other species was 7.7%.

-DISCUSSION

In spite of the large geographic distribution of H. scupense inthe world, its presence in Corsica and its relative abundance (8.7% of the collected ticks) were not expected since the species was rarely found in the areas neighboring the island where significant tick studies have been carried out. Two specimens were recorded in Sardinia, on deer [START_REF] Garippa | Endo ed ectoparassiti di Cervus elaphus corsicanus della Sardegna[END_REF] and on man (Montarsiet al., 2011); and 7 questing adults (designated as H. detritum) were collected on the vegetation on the Tuscan island of Pianosa [START_REF] Tomassone | Lyme borreliosis spirochetes and spotted fever group rickettsiae in ixodid ticks from Pianosa Island, Tuscany Archipelago, Italy. Vector-Borne Zoonotic[END_REF]. It is not frequent in continental Spain [START_REF] Oteo | Prevalence of spotted fever group Rickettsia species detected in ticks in La Rioja, Spain[END_REF] and has not been found on Minorca Island [START_REF] García-Pérez | Monitoring piroplasms infection in three cattle farms in Minorca (Balearic Islands, Spain) with previous history of clinical piroplasmosis[END_REF]. In continental France, the tick was reported inthe South-West where it seems to be established [START_REF] Macaigne | Hyalomma scupense Schulze 1919 (Acarina, Ixodoidea) tique autochtone du sud-ouest de la France[END_REF] though the collected numbers were low. But in Northern Africa where tropical theileriosis is a major cattle disease, H. scupense is often the most widespread tick species on cattle, representing between 84.3 and 99.1% of the ticks population in Tunisia (in farms affected by tropical theileriosis), 30.8% in Morocco (Gharbiand Darghouth, 2014) and13.6% in Algeria (Benchikh Elfegounet al., 2013). In Corsica, H. scupense was reported in almost 30%of the investigated areas (Fig. 1) and two different stages (adults and nymphs) were found several times on the same animals. These observations provide strong arguments for the existence of an endemic and well-established population of H. scupense ticks inCorsica, which is rather surprising for an area of south-western Europe.

The way H. scupense arrived in Corsica remains unexplained. The role played in the dispersion of ticks by migratory birds has to beconsidered, although this species was so far not found on migrating birds (e.g., [START_REF] Hoogstraal | Ticks (Ixodoidea) on birds migrating from Africa to Europe and Asia 1959-61[END_REF][START_REF] Wallménius | Spotted fever Rickettsia species in Hyalomma and Ixodes ticks infesting migratory birds in the European Mediterranean area[END_REF]. Cattle are the main hosts of H. scupense and although there is currently no introduction of animals from countries where the tick is established to Corsica, this could have happened earlier. As the Corsican tick fauna had never been fully investigated before this study, it cannot be excluded that H. scupense may be a long-time established species. A phylogenetic analysis of several H. scupense populations, from Corsica but also from Maghreb countries, could perhaps give clues regarding the origin of Corsican ticks.

Although its seasonal dynamics have not been systematically studied as yet, it appears that the habitat and life cycle of H. scupense are different in Corsica and in the Maghreb countries, for two reasons. H. scupense is usually described, in the latter regions, as an endophilic tick [START_REF] Estrada-Pena | Ticks of Domestic Animals in the Mediterranean Region: A Guide to Identification of Species[END_REF]Gharbi and Darghouth,2014) with infestations often associated with barns, stables, shedsand pens; because cattle are kept outside in Corsica, the tick can not be endophilic. Secondly, maximum activity of the species was observed from January to March in this study, which is quite different from what [START_REF] Gharbi | A review of Hyalomma scupense (Acari, Ixodidae) in the Maghreb region: from biology to control[END_REF] described in North Africa with a peak adult activity from May to August.

Theileria buffeli/orientalis, the causative agent of benign theile-riosis, has been reported in Corsica [START_REF] Uilenberg | Tick-borne infections of cattle on Corsica[END_REF] but bovine tropical theileriosis (T. annulata) has not been diagnosed so far. T.annulata is only transstadially transmitted, so the immature H. scupense stages cannot be infected before feeding on an infested host.If indeed the Corsican population of H. scupense is presently notinfected, migrating birds coming from enzootic areas would notconstitute a risk of introducing T. annulata. Such birds have so farnot been found infested by immature H. scupense, and moreover,as larvae (and therefore the resulting nymphs) are never infected,the greatest potential danger of T. annulata introduction would bethe importation of live carrier cattle from an infected country The occurrence of H. scupense in Corsica highlights however therisk of transmission of T. annulata to the local cattle population. Bovine tropical theileriosis occurs in many neighboring Mediter-ranean countries, but has not been reported in continental Italy and Sardinia. It is present in Sicily [START_REF] Loria | Clinical and laboratory studies on theileriosis outbreaks in Sicily, Italy[END_REF], the Spanish Island of Minorca [START_REF] García-Pérez | Monitoring piroplasms infection in three cattle farms in Minorca (Balearic Islands, Spain) with previous history of clinical piroplasmosis[END_REF] and continental Spain [START_REF] García-Sanmartín | Molecular diagnosis of Theileria and Babesia species infecting cattle in Northern Spain using reverse line blot macroarrays[END_REF]. In Sicily and continental Spain the main vector of T. annulata is Hyalomma lusitanicum while the vec-tor species is uncertain in Minorca. In the other countries of the Mediterranean area, the main vector appears to be H. scupense. Using partial amplification and sequencing of the 18s rRNA gene, [START_REF] Criado-Fornelio | Molecular studies on Babesia, Theileria and Hepatozoon in southern Europe. Part I. Epizootiological aspects[END_REF] reported the identification of T. annulata in the blood of a bovine animal reared in France. Also [START_REF] Bonnet | Prevalence of tick-borne pathogens in adult Dermacentor ticks from nine collection sites in France[END_REF] detected T. annulata DNA in a single Dermacentor marginatus collected in the field by flagging in southern France (Aveyron). This tick species is not known as a vector of T. annulata and finding the pathogen in the tick does not necessarily mean that the tick can transmit it. These two reports certainly need further confirmations and if tropical theileriosis occurred in south-ern France, it would probably have been detected. Because of the extensive livestock management and the rustic local cattle breed, the infection might however remain undetected in Corsica. Bovine tropical theileriosis is one of the most economically important diseases and for the future of eventual improvements on the animal husbandry in Corsica, it is of the utmost importance to determine whether it is present or not on the island

FIGURE 1

 1 FIGURE 1Localization of Hyalomma scupense and proportion of this species among the ticks collected on cattle in Corsica

TABLE 1

 1 Pair-wise genetic distances between COI and ITS2 of reference sequences and Corsican specimens (accesssion numbers are between parentheses)

ACKNOWLEDGMENTS

We are grateful to the staff of the slaughterhouse of Ponte-Leccia (especially Dr. Sidonie Lefevbre), Cuttoli (especially Magalie Mon-taggioni) and Porto-Vecchio for their help in collecting ticks

CONFLICT OF INTEREST

The authors declare no conflicts of interest.


Joachim Richter
email: joachim.richter@med.uni-duesseldorf.de

Martha Holtfreter

Gabriel Mouahid

Hélène Mone

Acute anuria after a family vacation to Corsica/France

Keywords: Schistosoma haematobium, Schistosoma bovis, Urinary schistosomiasis, Hematuria, Acute anuria, Blood clot, Corsica, France, 2013

A 12-year-old male patient suffered hematuria. Histopathology of a biopsy showed granulomata suspicious for schistosomiasis. The patient had never travelled outside Europe duringhisentirelifetime.Hehadtakenfrequentbathesinvarious rivers during his last family holidays 5 months earlier in Corsica. Microfiltration of urine revealed viable ova of Schistosoma haematobium with alterated size and shape. Ultrasonography showed a large focal echopoor mass attached to the bladder roof. Four days after antihelminthic therapy, the patient suffered inferior abdominal pain and acute anuria. Ultrasound revealed an approximately 5-cm mass in the bladder lumen suspicious for a large blood clot. After taking non-invasive measures such as drinking high amounts of fluid and treating the lower abdomen with a warm water bag and massage, the clot was excreted with urine and symptoms subsided. The further course was uneventful until 11 months later when hematuria recurred. This time, parasitological urine examination confirmed non-viable schistosome ova. Hematuria was likely due to erosion of the bladder mucosa by calcified non-viable ova.

Case report

A 12-year-old male patient noticed bloody urine. Therefore, he was referred to a urology department. Since no infectious agent could be detected, cystoscopy was performed where a severe cystitis was detected. Histology of a bladder wall biopsy showed a granulomatous inflammation and schistosomiasis was suspected. Because of the suspected tropical origin of the disease the adolescent was referred to our Tropical Medicine Unit. Detailed history was again taken which confirmed that he had never travelled outside Europe during his entire lifetime. The travels which had headed most south were to Spain, where no exposure to freshwater had taken place and Southern France including South Eastern Corsica, where the patient had spent his last summer holidays 5 months earlier together with his family and taken frequent bathes in various rivers.

At presentation in our unit, the patient had a normal leukocyte count with a relative blood eosinophilia of 10.6 % (normal [n] 1-5 %) and an absolute eosinophilia of 700 eosinophiles/μl (n 100-400/μl). All other hematology and biochemistry results including IgE were normal. Urin dipstick revealed erythrocyturia (250 erythrocytes/μl) and leukocyturia (25/μl) with a normal pH (5) and negative nitrite.

Microfiltration of urine collected from 11.00 am until 1.00 pm of the following day revealed viable ova of Schistosoma haematobium with a slightly decreased size and alterated shape. In parasitological stool examinations, no ova were detected. Serology revealed antibodies against schistosomal cercariae and adult schistosomes.

Ultrasonography showed generalized thickening of the bladder wall in a bladder insufficiently filled because the boy had difficulties to withhold the urine with a large focal echopoor mass attached to the bladder roof (Fig. 1). Besides, a moderate splenomegaly with an increased acoustic radiation force impulse (ARFI) of 2.62 m/s no other sonographic abnormality was detected. The boy was treated with praziquantel at a single standard dose of 40 mg/kg body weight (AWMF 2013). Four days later, the patient suffered acute lower abdominal pain and anuria. Ultrasound revealed an approximately 5-cm mass in the bladder lumen suggesting a large blood clot (Fig. 2). Upper urinary tract obstruction was excluded sonographically. Since the boy was afraid of another bladder catheterism, non-invasive measures were attempted by advising the patient to drink high amounts of fluid and to treat the lower abdomen with a hot water bag and massage.

Thereby, he succeeded in mobilizing the clot and excreting it with urine (Fig. 3). Ultrasound performed on the following day confirmed that the blood clot had been successfully excreted; the bladder lumen was free. To reduce the risk of sequelae, the patient was retreated 3 months later. The further course was uneventful until 11 months later when hematuria recurred after soccer training. This time, parasitological urine examination confirmed schistosome ova which by morphology were no more viable. Hematuria in this circumstance was most likely due to erosion of the bladder mucosa by calcified non-viable ova and did not indicate a persistent infection a finding supported by a normalized eosinophil count, decreasing titers in anti-schistosome-antibodies and normal ultrasound findings of the urinary tract.

Discussion

Schistosomiasis is a helminthic infection involving 240 to 400 million people worldwide. It is endemic in Africa, the Arabian peninsula, South America, and East and South-East Asia (WHO 2012; [START_REF] Colley | Human schistosomiasis[END_REF]. Intestinal schistosomiasis is caused by Schistosoma (S.) mansoni, S. japonicum, S. intercalatum, S. guineensis, and S. mekongi. However, the most prevalent species is S. haematobium, causing urinary and genital schistosomiasis. Human and zoonotic schistosomiasis had been endemic until 55 years ago in the extreme South of Europe including Portugal and Greece (Davies 2009).

This was the first autochthonous case of schistosomiasis acquired in Europe published since its eradication in the 1960s of the last century and the first human case ever reported from Corsica [START_REF] Holtfreter | Schistosoma haematobium infections acquired in Corsica, France, August 2013[END_REF]. The alert via the surveillance networks soon was followed by reports of other cases occurring in European travelers [START_REF] Berry | Schistosomiasis haematobium, Corsica, France[END_REF][START_REF] Patard | Urinary schistosomiasis contracted in a child in Corsica[END_REF][START_REF] Brunet | An unusual case of hematuria in a French family returning from Corsica[END_REF] Our patient's father also excreted schistosome ova whereas his siblings, who had been exposed in the same rivers had a positive schistosomiasis serology only, but did not excrete ova. Schistosomiasis had never been described to be endemic in Corsica before. However, at least one of the vector snails of S. haematobium, i.e., Bulinus (B.) truncatus, was known to be endemic in some areas of South Europe including Corsica, a notion which was confirmed recently [START_REF] Berry | Schistosomiasis haematobium, Corsica, France[END_REF]. Most likely, local B. truncatus snails have been infected by miracidia from urines excreted by African immigrants or travelers originating from endemic areas to Corsica and a transmission cycle has been established during the hot summer months also involving local zoonotic S. bovis strains [START_REF] Moné | Introgressive hybridizations of Schistosoma haematobium by Schistosoma bovis at the origin of the first case report of schistosomiasis in Corsica (France, Europe)[END_REF]. In such a circumstance, schistosomiasis may affect individuals who have never travelled to known endemic areas.

Usually, even severe abnormalities of the bladder wall due to schistosomiasis are astonishingly well reversible after therapy [START_REF] Richter | Evolution of schistosomiasis-induced pathology after therapy and interruption of exposure to schistosomes: a review of ultrasonographic studies[END_REF][START_REF] Akpata | Arbeitsgemeinschaft Wissenschaftlicher Medizinischer Fachgesellschaften (AWMF) guideline diagnostics and therapy of schistosomiasis (Leitlinie: Diagnostik und Therapie der Schistosomiasis [Bilharziose[END_REF]. In the present case, a bladder mass was formed by coagulated blood which once detached from the bladder roof fell into the lumen and obstructed the urethra causing acute anuria. After excretion of the blood clot the bladder mass initially seen had also disappeared. To our knowledge in schistosomiasis, acute anuria due to an obstructing blot clot in the urinary bladder has so far not been described in the literature. The hematuria recurrency illustrates that sequelae of schistosomiasis may occur months to years after successful treatment and cause confusion. This shows that even without any reexposure a year after successful treatment, hematuria may recur which does not necessarily indicate the evolution of praziquantel resistant parasites. This has also importance in the context of schistosomiasis control in endemic areas [START_REF] Cioli | Schistosomiasis control: praziquantel forever?[END_REF].

The acute anuria due to the obstruction of the urethra adds to other unusual presentations of schistosomiasis including vesicovaginal fistulae, hydrocele, or placental involvement (Richter et al. 2002a(Richter et al. , b, 2008;;[START_REF] Schleenvoigt | Placental Schistosoma haematobium infection in a German returnee from Malawi[END_REF]. The case also illustrates the possible expansion of autochthonous transmission to formerly non-endemic areas. It confirms the potential transmission of "exotic" infections among these malaria, leishmaniasis, dengue fever, chikungunya, amoebiasis, rickettsial infections, cutaneous larva migrans, or cystic echinococcosis to people who have never left Europe or have acquired their infection in Germany [START_REF] Krüger | Two cases of autochthonous P. falciparum malaria in Germany with evidence for local transmission by indegenous Anopheles plumbeus[END_REF][START_REF] Schönian | Visceral leishmaniasis in a German child who had never entered a known endemic area: a case report and review of the literature[END_REF]Richter et al. 2002b[START_REF] Richter | An unsuspected cause of chronic colitis[END_REF][START_REF] Richter | Autochthonous cystic echinococcosis in patients who grew up in Germany[END_REF] Compliance with ethical standards

Figure 1 Figure 2

 12 Figure 1Ultrasound mass attached to the urinary bladder roof and generally thickened bladder wall (during examination, the patient had difficulties to hold his urine)

Conflict of interest

The authors declare that they have no conflicts of interest.


K Ram

Mohan Rao

Kalimi Trinadh

Corinne Nouveau

Elevated temperature plasma nitriding and effects on electrochemical properties of steel

Keywords:

published or not. The documents may come

Elevated temperature plasma nitriding and effects on electrochemical properties of steel

Introduction

Surface microstructural and the crystal lattice modifications had been proved to be the main reasons for the improvement of surface hardness, resistance to fatigue, wear and corrosion. The improvement of these properties has recently been realized in tool industries where the premature failure caused by the wear and corrosion in the service conditions demands the early replacement of the tools. Though the other processes like physical/chemical vapour deposition has been practiced to overcome these for a long time but the poor adhesion and delamination of the deposited layer had been the subject of concern [1][2][3][START_REF] Michler | Influence of plasma nitriding on hydrogen environment embrittlement of austenitic stainless steel[END_REF]. Among the various surface modification methods plasma mediated nitriding has already been recognized as an environmental friendly and efficient process which has circumvented these limitations.

Formation of desirable nitride phases and the modification of surface microstructure, generation of stresses in the crystal lattice are well controlled and hence the process is successful and widely accepted for mechanical properties, corrosion and biocompatibility [START_REF] Wang | Plasma nitriding of low alloy steels at floating and cathodic potentials[END_REF][START_REF] Maniee | The study of tribological and corrosion behavior of plasma nitrided 34CrNiMo6 steel under hot and cold wall conditions[END_REF][START_REF] O'brien | Plasma (Ion) Nitriding, Metals Handbook[END_REF][START_REF] Wen | Microstructure and corrosion resistance of the layers formed on the surface of precipitation hardenable plastic mold steel by plasma nitriding[END_REF][START_REF] Nouveau | Plasma nitriding of 90CrMoV8 tool steel for the enhancement of hardness and corrosion resistance[END_REF][START_REF] Muñoz Riofano | Improved wear resistance of P/M tool steel alloy with different vanadium contents after ion nitriding[END_REF][START_REF] Arslan | Mechanical properties and biocompatibility of plasma-nitrided laser-cut 316L cardiovascular stents[END_REF][START_REF] Janine | Plasma nitriding under low temperature improves the endothelial cell biocompatibility of 316L stainless steel[END_REF][START_REF] Zhao | Tribocorrosion studies of metallic biomaterials: the effect of plasma nitriding and DLC surface modifications[END_REF][START_REF] Forati Rad | Wear assessment of plasma nitrided AISI H11 steel[END_REF][START_REF] Mashreghi | The investigation of wear and corrosion behavior of plasma nitrided DIN 1.2210 cold work tool steel[END_REF]. In the plasma nitriding process, the samples to be nitrided are polished to mirror finish and cleaned ultrasonically to remove the dirt on the surface. Samples are placed on the sample holder inside the nitriding chamber then evacuated to around 10 À6 mbar. A mixture of nitrogen and hydrogen at certain ratio is then fed into the chamber then triggered the plasma. Samples are biased negatively to attract the positively charged ions from the plasma towards itself. Sample temperature is raised to the desired level by auxiliary heater.

Nitrogen and hydrogen ions accelerate towards the surface, adsorb on the surface, diffuse towards the bulk of the sample and form the nitrides.

Though several works have been reported so far in the literature on nitriding of steel, however very less is known about the nitriding and corrosion of wood machining CrMoV martensitic steel. Previously, Corinne et al. shown an improvement of hardness similar steel and shown a significantly higher hardness of around 1150 H v than steel without nitriding which had $655 H v [START_REF] Nouveau | Plasma nitriding of 90CrMoV8 tool steel for the enhancement of hardness and corrosion resistance[END_REF]. So far there is no sufficient literature on the electrochemical characterization of this steel after nitriding. Hence, an attempt has been made in the present work to understand the electrochemical corrosion this steel after nitriding in an environment of 3.5% NaCl. From the previous studies [START_REF] Nouveau | Plasma nitriding of 90CrMoV8 tool steel for the enhancement of hardness and corrosion resistance[END_REF] it is understood that the hardness improvement is significant after nitriding at 500 °C but reduced when nitrided at 520 °C. Hence in the present studies the nitriding temperature was kept at 500 °C.

Experimental details

Austenitized steel was quenched in a bath of oil followed by tempering. Samples of dimension of 8 Â 8 Â 4 mm 3 were cut from this steel then polished to mirror finish and cleaned with ultrasonic ⇑ Corresponding author. E-mail address: rammohanrao.k@gmail.com (K. Ram Mohan Rao).

bath. The composition of the steel is given as: Carbon (0.5%), Silicon (1%), Manganese (0.5%), Chromium (8.0%), Molybdenum (1.5%), Vanadium (0.5%) and balance iron.

Method

Then samples was kept on the sample holder inside the nitriding chamber. By using rotary and diffusion pump vacuum to a pressure of 0.05 Pa was created in the chamber. Sample was negatively biased and with Ar+ sputtering nitriding cycle initiated.

Nitrogen and hydrogen at a ratio of 80:20 fed into the chamber. Nitriding was followed at 500 Pa when the temperature reached to 500 °C. After nitriding the samples with bare sample were exposed to detailed X-ray diffraction studies.

Bare and nitrided steel samples then subjected to corrosion tests by following potentiodynamic polarization and subsequently impedance spectroscopic tests (EIS) in an environment of 3.5% NaCl. The electrochemical testing was followed by using the system Model SI 1287-Solatron Analytical, U.K. The cell was consisting of nitrided sample, a saturated calomel (SCE) and Pt electrodes in 3.5% NaCl already purged with nitrogen. The tests were conducted when once the equilibrium attained. The sample was scanned through ±1 V at free atmosphere at the rate 1 mV/s.

To further understand the corrosion behaviour of the nitrided and bare steel, electrochemical impedance spectroscopic analyses in 3.5% NaCl was followed by using A.C. signals.

Results

Phase evolution

The nitrided and bare samples were exposed to detailed XRD analyses. Fig. 1 reveals the phases of bare and nitrided steel samples. From these XRD patterns it is found that the bare sample has only the Fe (1 1 0), Fe (2 0 0) and Fe (2 1 1) phase (Fig. 1a). The samples nitrided at 500 °C for 8 h (b) modified to the surface containing Fe-nitrides Fe x N (x = 2-3, 4). These peaks are c 0 (Fe 4 N) along with e N.

e N shows a good corrosion resistance. c 0 (Fe 4 N) contributes to the hardness of the surface but the not so beneficial to corrosion resistances. Similarly, sample nitrided for 10 h shows both these nitrides.

Electrochemical characterization

For the samples before and after plasma nitriding corrosion tests were conducted in an electrolyte NaCl at room temperature. The electrochemical system Model SI 1287 ELECTROCHEMICAL INTERFACE-Solatron Analytical, U.K. was used for the tests.

1Stability of potential (O.C,P.)

The bare and the nitrided steel samples were exposed to the electrolyte 3.5% NaCl for a duration until a stable equilibrium state was attained. The steel nitrided at 500 °C had shown the decreased susceptibility towards corrosion. Initially a variation in corrosion potential was noted which ultimately reached to a stable state.

Potentiodynamic polarization

Potentiodynamic polarization tests were performed after equilibrium attained in 3.5% NaCl electrolyte (Fig. 2).

From the polarization diagrams as shown in Fig. 3 the asreceived sample (a) has faster dissolution kinetics as compared to the nitrided steel (b). It has also been found that the other steel nitrided for longer time 10 h at the same temperature has similar dissolution kinetics. The rate of corrosion of as-received sample was found to be 3.6597 MPY much higher than the nitrided steel 1.8071 MPY.

Corrosion tests by electrochemical impedance spectroscopy (EIS)

Bare and nitrided samples were exposed to further tests by electrochemical impedance spectroscopic method in the electrolyte 3.5% NaCl .by using the system Model SI 1287 ELECTRO-CHEMICAL INTERFACE-Solatron Analytical, U.K.

In the above Nyquist plots the Z 0 represents impdance real and Z 00 represents imaginary values. The Z real represents the resistance to corrosion. Higher the Z real value more will be the corrosion resistance i.e., the larger the diameter of the semicircle the greater will be the corrosion resistance. From the above Fig. 3 the plasma nitrided steel shows corrosion resistance more than the bare steel. From the XRD studies it is understood that after plasma nitriding the microstructure contains Fe x N (x = 2-3, 4). The modified microstructures of the nitrided steel containing mainly the e N and Fe 4 N nitrides are responsible for the corrosion resistance properties.

Conclusions

Martensitic tool steel after elevated temperature plasma nitriding shows the enhancement of resistance to corrosion significantly. Fe x N (x = 2-3, 4) phases were found on the surface microstructure after nitriding. e N phase in the modified microstructure is responsible for the resistance to corrosion. Both the nitrided sample treated for 8 and 10 h show better corrosion resistance when compared to bare steel. However, the improvement of corrosion resistance of both these steels was found to be almost similar. The tool life in the harsh corrosive atmosphere can be prolonged after nitriding. This would be beneficial for machining and tool industries.

Fig. 2 .

 2 Fig. 2. Potentiodynamic polarization curves of (a) bare steel and (b) the nitrided steel at 500 °C for 8 h.

Fig. 1 .

 1 Fig. 1. X-ray diffractograms of (a) bare steel (S0) and nitrided samples at 500 °C for 8 h (b).

Acknowledgements

The encouragements and support by GITAM (Deemed to be University) is thankfully acknowledged. Valuable discussions and support from ENSAM, France is gratefully acknowledged.