France Denoeud

Lorenzo Carretero-Paulet

Alexis Dereeper

Gaëtan Droc

Romain Guyot

Marco Pietrella

Chunfang Zheng

Adriana Alberti

François Anthony

Giuseppe Aprea

Jean-Marc Aury

Pascal Bento

Maria Bernard

Stéphanie Bocs

Claudine Campa

Alberto Cenci

Marie-Christine Combes

Dominique Crouzillat

Corinne Da Silva

Loretta Daddiego

Fabien De Bellis

Stéphane Dussert

Olivier Garsmeur

Thomas Gayraud

Valentin Guignon

Katharina Jahn

Véronique Jamilloux

Thierry Joët

Karine Labadie

Tianying Lan

Julie Leclercq

Maud Lepelley

Thierry Leroy

Lei-Ting Li

Pablo Librado

Loredana Lopez

Adriana Muñoz

Benjamin Noel

Alberto Pallavicini

Gaetano Perrotta

Valérie Poncet

David Pot

Priyono

Michel Rigoreau

Mathieu Rouard

Julio Rozas

Christine Tranchant-Dubreuil

Robert Vanburen

Qiong Zhang

Alan C Andrade

Xavier Argout

Benoît Bertrand

Alexandre De Kochko

Giorgio Graziosi

Robert J Henry

Ray Ming

Chifumi Nagai

Steve Rounsley

David Sankoff

Giovanni Giuliano

Victor A Albert
email: vaalbert@buffalo.edu

Patrick Wincker
email: pwincker@genoscope.cns.fr

Philippe Lashermes
email: philippe.lashermes@ird.fr

The coffee genome provides insight into the convergent evolution of caffeine biosynthesis

Coffee is a valuable beverage crop due to its characteristic flavor, aroma, and the stimulating effects of caffeine. We generated a high-quality draft genome of the species Coffea canephora, which displays a conserved chromosomal gene order among asterid angiosperms. Although it shows no sign of the whole-genome triplication identified in Solanaceae species such as tomato, the genome includes several species-specific gene family expansions, among them N-methyltransferases (NMTs) involved in caffeine production, defense-related genes, and alkaloid and flavonoid enzymes involved in secondary compound synthesis. Comparative analyses of caffeine NMTs demonstrate that these genes expanded through sequential tandem duplications independently of genes from cacao and tea, suggesting that caffeine in eudicots is of polyphyletic origin.

W

ith more than 2.25 billion cups consumed every day, coffee is one of the most important crops on Earth, cultivated across more than 11 million hectares. Coffee belongs to the Rubiaceae family, which is part of the Euasterid I clade and the fourth largest family of angiosperms, consisting of more than 11,000 species in 660 genera (1). We sequenced Coffea canephora (2n = 2x = 22 chromosomes), an outcrossing, highly heterozygous diploid, and one of the parents of C. arabica (2n = 4x = 44 chromosomes), which was derived from hybridization between C. canephora and C. eugenioides (2). A total of 54.4 million Roche 454 single and mate-pair reads and 143,605 Sanger bacterial artificial chromosome-end reads were generated from a doubled haploid accession, representing ~30× coverage of the 710-Mb genome (3). Additional Illumina sequencing data (60×) were used to improve the assembly (table S1) [START_REF]Materials and methods are available as supplementary materials on Science Online[END_REF]. The resulting assembly consists of 25,216 contigs and 13,345 scaffolds with a total length of 568.6 Mb (80% of 710 Mb), including 97 Mb (17%) of intercontig gaps. Eighty percent of the assembly is in 635 scaffolds, and the scaffold N50 (the scaffold size above which 50% of the total length of the sequence assembly can be found) is 1.26 Mb (table S2). A high-density genetic map covering 349 scaffolds and comprising ~64% of the assem-bly (364 Mb) and 86% of the annotated genes was anchored to the 11 C. canephora chromosomes [START_REF]Materials and methods are available as supplementary materials on Science Online[END_REF]. More than 96% of the scaffolds larger than 1 Mb were anchored (Fig. 1A).

We annotated 25,574 protein-coding genes (4) (table S6), 92 microRNA precursors, and 2573 organellar-to-nuclear genome transfers (4). Transposable elements account for ~50% of the genome (4), of which ~85% are long terminal repeat (LTR) retrotransposons. Large-scale comparison between C. canephora LTR retrotransposons and those of reference plant genomes shows outstanding conservation of several Copia groups across distantly related genomes, suggesting that horizontal mobile element transfers may be more frequent than generally recognized [START_REF] Schaack | [END_REF](6)(7)(8).

Structurally, the coffee genome shows no sign of a whole-genome polyploidization in its lineage since the g triplication at the origin of the core eudicots (9) (Fig. 1B). Coffee contains exactly three paralogous regions for each of the seven pre-g ancestral chromosomes (Fig. 1B). Coffee chromosomal regions show unique one-to-one correspondences with grapevine chromosomes (Fig. 1C and fig. S12) and a one-to-three correspondence with the tomato genome, which underwent a second lineage-specific triplication during its evolutionary history (10). Although grapevine, a rosid, is the most conservative core eudicot in terms of integrity of gross chromosomal structure, coffee displays less gene-order divergence to all other rosids, despite being an asterid itself (9). Coffee also shows little syntenic divergence relative to other sequenced asterids (Fig. 1D, table S17, and supplementary text).

To classify gene families in the C. canephora genome, we ran OrthoMCL on inferred protein sequences from coffee, grapevine, tomato, and Arabidopsis (4), generating 16,917 groups of orthologous genes (fig. S5). To examine coffeespecific gene family expansions with potential adaptive value, we fit different branch models implemented in BadiRate (11) to these orthogroups (4). In the coffee lineage, 202 orthogroups SCIENCE sciencemag.org 12 ENEA Trisaia Research Center, 75026 Rotondella, Italy. 13 Center for Biotechnology, Universität Bielefeld, Universitätsstraße 27, D-33615 Bielefeld, Germany. 14 AG Genominformatik, Technische Fakultät, Universität Bielefeld, 33594 Bielefeld, Germany. 15 Institut National de la Recherche Agronomique (INRA), Unité de Recherches en Génomique-Info (UR INRA 1164), Centre de Recherche de Versailles, 78026 Versailles Cedex, France. 16 Department of Biology, Chongqing University of Science and Technology, 4000042 Chongqing, China. 17 Department of Plant Biology, 148 Edward R. Madigan Laboratory, MC-051, 1201 West Gregory Drive, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA. 18 Departament de Genètica and Institut de Recerca de la Biodiversitat (IRBio), Universitat de Barcelona, Diagonal 643, Barcelona 08028, Spain. 19 Department of Mathematics, University of Maryland, Mathematics Building 084, University of Maryland, College Park, MD 20742, USA. 20 School of Electrical Engineering and Computer Science, University of Ottawa, 800 King Edward Avenue, Ottawa, Ontario K1N 6N5, Canada. 21 Department of Life Sciences, University of Trieste, Via Licio Giorgieri 5, 34127 Trieste, Italy. 22 Indonesian Coffee and Cocoa Institute, Jember, East Java, Indonesia. 23 Laboratório de Genética Molecular, Núcleo de Biotecnologia (NTBio), Embrapa Recursos Genéticos e Biotecnologia, Final Av. W/5 Norte, Parque Estação Biológia, Brasília-DF 70770-917, Brazil. 24 CIRAD, UMR RPB (CIRAD, IRD, UM2), BP 64501, 34394 Montpellier Cedex 5, France.

clustering 1270 genes were supported as expanded (Akaike information criterion > 2.7). Among gene ontology (GO) terms annotating these, 98 out of 4300 generic terms were significantly over-or underrepresented (table S14). Most GOs enriched in C. canephora (P < 0.05) belonged to two main functional categories: defense response and metabolic process, the later including different catalytic activities (table S15).

Among defense response functions, there is a clear expansion of nucleotide binding site diseaseresistance genes (12,13) in the C. canephora genome (4). Most genes that grouped together within single orthogroups were tandemly arrayed, suggesting that R genes evolved by tandem duplication and divergence of linked gene families (supplementary text). Several gene functions involved in secondary metabolite biosynthesis are significantly expanded in the C. canephora genome, including enzymes associated with the production of phenylpropanoids such as flavo-noids and isoflavones (naringenin 3-dioxygenase, isoflavone 2′-hydroxylase), alkaloids (strictosidine synthase, tropine dehydrogenase), monoterpenes (e.g., menthol dehydrogenase), and caffeine [N-methyltransferases (NMTs)] (Fig. 2). For example, indole alkaloids such as the monoamine oxidase inhibitor yohimbine and antimalaria drug quinine are prominent secondary compounds of the coffee family and its parent order, Gentianales [START_REF] Gleason | Plant Biochemistry[END_REF], and the GO term indole biosynthetic process was highly enriched (P < 0.001) in coffee relative to tomato, grapevine, and Arabidopsis.

Caffeine is a purine alkaloid synthesized by several eudicot plants, including coffee, cacao (Theobroma cacao), and tea (Camellia sinensis) (Fig. 2). Caffeine is synthesized in both coffee leaves, where it has insecticidal properties [START_REF] Nathanson | [END_REF], and fruits and seeds, where it inhibits seed germination of competing species (16). The late steps in caffeine biosynthesis are mediated by a series of NMTs (Fig. 2A) (17).

Among coffee-expanded genes, NMT activity is one of the more highly enriched GO terms (table S15). A single gene family (ORTHOMCL170) clusters 23 genes in coffee, but none in grapevine, tomato, or Arabidopsis (table S12), and this cluster contains genes encoding known enzymes of the caffeine biosynthetic pathway (18,19). Maximum likelihood (ML) phylogenetic analysis of ORTHOMCL170 with tea and cacao NMTs that have similar activities reveals species-specific gene clades (Fig. 2C). We analyzed these relationships in a broader evolutionary context by including genome-wide samples of NMTs from coffee, cacao, and other eudicot species. ML trees show that the genes encoding the closest Arabidopsis NMT relatives of coffee caffeine biosynthetic enzymes are involved in benzoic, salicylic, and nicotinic functions (4) (supplementary text). Caffeine biosynthetic NMTs from coffee nested within a gene clade distinct from those of cacao or tea, which group together as sister lineages. Thus, a S17) between each of the six species (column labels) and the entire set, showing the gene order conservatism of coffee, especially among asterids, and of peach and cacao among rosids. minimum of two independent origins of caffeine biosynthetic NMT activity can be inferred, as proposed previously (20).

Microsynteny analyses of ORTHOMCL170, which includes three tandem arrays, show that some known and putative coffee caffeine synthase genes-CcXMT (encoding xanthosine N-methyltransferase), CcMTL, and CcNMT3-form a tight assemblage of coexpressed tandem duplicates (Fig. 2D) reminiscent of a metabolic gene cluster (21,22). Given that some plant metabolic gene clusters are of relatively recent origin [START_REF] Field | Proc. Natl. Acad. Sci. U.S.A[END_REF], we sought to further unravel the role of gene duplication in the expansion of the coffee NMT gene family (Fig. 2D) (supplementary text). The three main coffee NMT clades in ORTHOMCL170 are distributed among a minimum of three genomic blocks; however, some phylogenetically recent tandem duplicates have moved away from their original positions via block rearrangements (Fig. 2D). One such movement involving the putative metabolic cluster appears to have left the CcDXMT gene (encoding 3,7-dimethylxanthine methyltransferase) behind, physically separated from its ancestral tandem array. In cacao, the functionally characterized TcBCS1 gene has a tandem duplicate, but this pair of genes evolved independently from the NMT tandem arrays found in C. canephora (fig. S29). We also examined the role of positive selection (PS) in the evolution of caffeine biosynthesis among coffee, tea, and cacao (4) (supplementary text). We found significant evidence for PS [likelihood ratio test for PAML (Phylogenetic Analysis by Maximum Likelihood) branch-site test, P = 5.78 × 10 -3 (24)] only for the coffee NMT lineage, indicating that the independent evolution of caffeine biosynthesis in coffee was adaptive and probably involved specific amino acid changes fixed by PS. These results highlight the distinct acquisition of caffeine biosynthesis in the coffee plant, providing an example of convergent evolution of secondary metabolic pathways encoded by tandemly duplicated genes.

Genomic functional diversification via tandem duplication may have helped shape other aspects of coffee bean chemical composition. Linoleic acid, which is produced by the oleate desaturase FAD2, is the major polyunsaturated fatty acid in the coffee bean (25,26), where it contributes to aroma composition and flavor retention after roasting (4). Coffee has six FAD2 genes compared with one in Arabidopsis, and most of these have arisen from tandem duplications on chromosome 1 (fig. S33). RNA sequencing data suggest transcriptional specialization for two of the six FAD2 copies, with CcFAD2. transcribed in developing endosperm (supplementary text). Peak transcript abundance coincides with the dramatic increase in linoleic acid content that occurs during seed development at the perisperm-endosperm transition (27).

Our analysis of the adaptive genomic landscape of C. canephora identifies the convergent evolution of caffeine biosynthesis among plant lineages and establishes coffee as a reference species for understanding the evolution of genome structure in asterid angiosperms.

1182 5 Fig. 1 .

 51 Fig. 1. Structure of the C. canephora genome. (A) Alignment of the pseudochromosome 1 sequence with the genetic map of C. canephora and genomic overview. Correspondences between the genetic linkage map and the DNA pseudomolecule are shown at left (oriented and nonoriented scaffolds are indicated in blue and green, respectively; gray lines denote consistent data; orange lines indicate markers with an approximate genetic location). The relative proportions (percentage of nucleotides) in sliding windows (1-Mb size, 500-kb step) of transposable elements (Copia in red, Gypsy in green) and genes (exons in blue, introns in dark blue) are shown at right. (B) Coffee chromosomal blocks descending from the seven ancestral core eudicot chromosomes.The three paralogous descendants of the seven ancestral chromosomes are shown in shared colors but different textures. (C) Comparison of three grapevine chromosomes (descendants of the prehexaploidization core eudicot chromosome) mapped to a single coffee chromosome and three regions in the tomato genome. (D) Phylogeny and genome duplication history of core eudicots. Arrowheads indicate tetraploidization (blue) or hexaploidization (green) events. Red lines trace lineages of six species that have not undergone further polyploidization. Bar graphs and colors reflect gene-order differences (tableS17) between each of the six species (column labels) and the entire set, showing the gene order conservatism of coffee, especially among asterids, and of peach and cacao among rosids.

Fig. 2 .

 2 Fig. 2. Evolution of caffeine biosynthesis. (A) The principal caffeine biosynthetic pathway. Three methylation steps are necessary to produce caffeine from xanthosine, involving the successive action of three NMTs: xanthosine methyltransferase (XMT), theobromine synthase [7-methylxanthine methyltransferase (MXMT)], and caffeine synthase [3,7-dimethylxanthine methyltransferase (DXMT)]. SAM, S-adenosylmethionine; SAH, Sadenosylhomocysteine. (B) Evolutionary position of caffeine-producing plants with respect to other eudicots (phylogeny adapted from www.mobot. org/MOBOT/research/APweb/). (C) ML phylogeny of coffee, tea, and cacao NMTs. Bootstrap support values (percentages) from 1000 replicates are shown next to relevant clades. Branch lengths are proportional to expected numbers of nucleotide substitutions per site. Colors identify genes assignable to the genomic blocks denoted in (D).(D) (Left) A model summarizing the duplication history of coffee NMT genes, following the phylogeny in (C). Three distinct tandem gene arrays evolved in situ on chromosome 1 from nearby gene duplicates (bold squares). The red and green blocks, colored as in (C), translocated (to chromosome 9) or rearranged (to elsewhere on chromosome 1) from their ancestral locus (blue region), respectively. (Right) Gene orders on modern chromosomes. Translocation of the red block, containing the putative caffeine NMTmetabolic cluster, left the phylogenetically derived CcDXMTgene behind. Similarly, CcNMT19 is a derived gene within its own NMT clade that remained in place following movement of the green block. Numbers at branches indicate relative times since major duplication events or diversification times of the tandem arrays, calculated from approximately neutral synonymous substitution rates. (E) Expression profiles (reads per kilobase per million reads mapped) of known Coffea canephora NMTs. The genes in the putative metabolic cluster (along with CcDXMTand CcMXMT) exhibit similar expression patterns, higher in perisperm than endosperm. Data are plotted as log2 values. DAP, days after pollination.

  Energie Atomique, Genoscope, Institut de Génomique, BP5706, 91057 Evry, France.2 CNRS, UMR 8030, CP5706, Evry, France. 3 Université d'Evry, UMR 8030, CP5706, Evry, France. 4 Department of Biological Sciences, 109 Cooke Hall, University at Buffalo (State University of New York), Buffalo, NY 14260, USA. 5 Institut de Recherche pour le Développement (IRD), UMR Résistance des Plantes aux Bioagresseurs (RPB) [Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD), IRD, UM2)], BP 64501, 34394 Montpellier Cedex 5, France. Italian National Agency for New Technologies, Energy and Sustainable Development (ENEA) Casaccia Research Center, Via Anguillarese 301, 00123 Roma, Italy. 9 Department of Mathematics and Statistics, University of Ottawa, 585 King Edward Avenue, Ottawa, Ontario K1N 6N5, Canada. Parc Scientifique Agropolis II, 34397 Montpellier Cedex 5, France. 11 Nestlé Research and Development Centre, 101 Avenue Gustave Eiffel, Notre-Dame-d'Oé, BP 49716, 37097 Tours Cedex 2, France.

	1 Commissariat à l'
	5 SEPTEMBER 2014 • VOL 345 ISSUE 6201	1181

6 CIRAD, UMR Amélioration Génétique et Adaptation des Plantes Méditerranéennes et Tropicales (AGAP), F-34398 Montpellier, France. 7 IRD, UMR Diversité Adaptation et Développement des Plantes (CIRAD, IRD, UM2), BP 64501, 34394 Montpellier Cedex 5, France.

8 10 Bioversity International,

Corrected 8 October, 2014; see full text. on January 22, 2015 www.sciencemag.org Downloaded from on January 22, 2015 www.sciencemag.org Downloaded from on January 22, 2015 www.sciencemag.org Downloaded from on January 22, 2015 www.sciencemag.org Downloaded from

SEPTEMBER 2014 • VOL 345 ISSUE

Department of Molecular Biology and Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.

Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.

ACKNOWLEDGMENTS

We acknowledge the following sources for funding: ANR-08-GENM-022-001 (to P.L.); ANR-09-GENM-014-002 (to P.W.); Australian Research Council (to R.J.H.); Natural Sciences and Engineering Research Council of Canada (to D.S.); CNR-ENEA Agrifood Project A2 C44 L191 (to G.Gi.); FINEP-Qualicafé, INCT-CAFÉ (to A.C.A.); NSF grants 0922742 (to V.A.A.) and 0922545 (to R.M.); and the College of Arts and Sciences, University at Buffalo (to V.A.A.). We thank P. Facella (ENEA) for Roche 454 sequencing and Instituto Agronômico do Paraná (Paraná, Brazil) for fruit RNA. This work was supported by the high-performance cluster of the SouthGreen Bioinformatics platform (UMR AGAP) CIRAD (www.southgreen.fr). The C. canephora genome assembly and gene models are available on the Coffee Genome Hub (http://coffee-genome.org) and the CoGe platform (www.genomevolution.org). Sequencing data are deposited in the European Nucleotide Archive under the accession numbers CBUE020000001 to CBUE020025216 (contigs), HG739085 to HG752429 (scaffolds), and HG974428 to HG974439 (chromosomes). Gene family alignments and phylogenetic trees for BAHD acyltransferases and NMTs are available in the GreenPhylDB (www.greenphyl.org/cgi-bin/index.cgi) under the gene family IDs CF158535 and CF158539 to CF158545, respectively. We declare no competing financial interests.

RNA-guided, nuclease-mediated genome editing, based on type II CRISPR (clustered regularly interspaced short palindromic repeat)/Cas (CRISPR-associated) systems, offers a new approach to alter the genome (4-6). In brief, Cas9, a nuclease guided by single-guide RNA (sgRNA), binds to a targeted genomic locus next to the protospacer adjacent motif (PAM) and generates a double-strand break (DSB). The DSB is then repaired either by nonhomologous end-joining (NHEJ), which leads to insertion/deletion (indel) mutations, or by homology-directed repair (HDR), which requires an exogenous template and can generate a precise modification at a target locus (7). Unlike other gene therapy methods, which add a functional, or partially functional, copy of a gene to a patient's cells but retain the original dysfunctional copy of the gene, this system can remove the defect. Genetic correction using engineered nucleases (8-12) has been demonstrated in immortalized myoblasts derived from DMD patients in vitro (9), and rodent models of rare diseases (13), but not yet in animal models of relatively common and currently incurable diseases, such as DMD.

The objective of this study was to correct the genetic defect in the Dmd gene of mdx mice by CRISPR/Cas9-mediated genome editing in vivo. The mdx mouse (C57BL/10ScSn-Dmd mdx /J) contains a nonsense mutation in exon 23 of the Dmd gene (14, 15) (Fig. 1A). We injected Cas9, sgRNA, and HDR template into mouse zygotes to correct the disease-causing gene mutation in the germ line (16,17), a strategy that has the potential to correct the mutation in all cells of the body, including myogenic progenitors. Safety and efficacy of CRISPR/ Cas9-based gene therapy was also evaluated.


Sandrine S Auger

Cecile Morin

Cindy Bokobza

D Guenoun

F Faure

I Sautet

S Diao

V Faivre

J Hua

C Demene

M Tanter

L Schwendimann

P Young-Ten

T Bourgeois

N Ramanantsoa

B Matrot

J Gallego

P Gressens

J Van Steenwinckel

Additive deleterious

come

Introduction

Most cases are associated with materno-fetal infection/inflammation, leading to white matter injuries (WMI). Preterm infants delivered by Csection are at higher risk of neurodevelopmental disorders (NDD) compared with vaginally delivered infants.

Are there additive effects of (i) induced vaginal preterm birth or (ii) cesarean surgical preterm birth with perinatal inflammation?

A

Events count

Fluorescence intensity

RU-486

Fluorescence intensity

  mouse model for brain injuries associated with preterm birth and differential delivery route Preterm birth by cesarean delivery worsens WMI Mifepristone (RU-486) administration induced vaginal preterm delivery without affecting WMI Morin et al. (2022)Mifepristone (RU-486) is a glucocorticoid receptor (GR) antagonist. As an anti-progesterone drug, RU-486 is used in pharmacological abortion, and to induce delivery rarely for living fetuses and mostly in case of in utero fetal death.

  Global cesarean section (C-sections) rates have increased in recent decades. Numerous studies have revealed the existence of a "gut-brain axis" and the impact of an alteration of gut microbiota composition in brain diseases. Many factors in early life such as the mode of delivery or preterm birth could lead to disturbances in the assembly and maturation of gut microbiota. worsens hypomyelination induced by perinatal inflammation, leading to brain connectivity defects


Mikhail G Katz

St Éphane Sabourau
email: stephane.sabourau@u-pec.fr

A PU-BONNESEN INEQUALITY

Keywords: 2020 Mathematics Subject Classification. Primary 53C45; Secondary 52A38, 53A05, 52A15, 53C20 Convex surfaces, Pu's inequality, Bonnesen's inequality, circumscribed and inscribed radii

We prove an inequality of Bonnesen type for the real projective plane, generalizing Pu's systolic inequality for positivelycurved metrics. The remainder term in the inequality, analogous to that in Bonnesen's inequality, is a function of R -r (suitably normalized), where R and r are respectively the circumradius and the inradius of the Weyl-Lewy Euclidean embedding of the orientable double cover. We exploit John ellipsoids of a convex body and Pogorelov's ridigity theorem.

Pu, Bonnesen, and Weyl-Lewy

Pu's inequality asserts that area(g) -2 π sys 2 (g) ≥ 0 for every Riemannian metric g on RP 2 where equality is satisfied if and only if g has constant Gaussian curvature ( [START_REF] Pu | Some inequalities in certain nonorientable Riemannian manifolds[END_REF], 1952). The inequality has recently been strengthened [START_REF] Katz | A systolic inequality with remainder in the real projective plane[END_REF] to area(g) -2 π sys 2 (g) ≥ 2π Var µ (f ) (1.1) where the variance Var µ is with respect to the probability measure µ induced by the constant curvature unit area metric g 0 in the conformal class of g, so that g = f 2 g 0 . A similar strengthened version exists for Loewner's torus inequality; see [START_REF] Horowitz | Loewner's torus inequality with isosystolic defect[END_REF]. However, the remainder term Var µ (f ) in these inequalities does not exhibit any explicit relation to the geometry of the metric. In this paper we seek a strengthening of Pu's inequality where the relation to the metric is more explicit. Bonnesen's inequality and its analogs involve a strengthening of the isoperimetric inequality of the following type:

L 2 -4πA ≥ f (R, r), (1.2)
where L is the length of a Jordan curve in R 2 , A is the area of the region bounded by the curve, R is the circumradius and r is the inradius [4, p. 3]. In Bonnesen's inequality, one has f (R, r) = π 2 (R -r) 2 . Additional inequalities exist with f dependent on parameters A or L,

namely f (R, r) = A 2 1 r -1 R 2 and f (R, r) = L 2 R-r R+r 2 (ibid.).
Now suppose (RP 2 , g) has positive curvature. Then by the generalisation of the Weyl-Lewy theorem [START_REF] Weyl | Über die Bestimmung einer geschlossenen konvexen Fläche durch ihr Linienelement[END_REF], [START_REF] Lewy | On the existence of a closed convex surface realizing a given Riemannian metric[END_REF], the orientable double cover S g admits a unique (up to congruence) isometric embedding as a convex surface S g ⊆ R 3 (Nirenberg [START_REF] Nirenberg | The Weyl and Minkowski problems in differential geometry in the large[END_REF], Lu [START_REF] Lu | On Weyl's embedding problem in Riemannian manifolds[END_REF]). Here, we seek an analog of the inequality (1.1) with a remainder term exhibiting a more explicit relation to the geometry of S g . The relation is expressed in terms of the difference R -r between the circumscribed and inscribed radii of S g , analogous to (1.2). Let R and r be the circumradius and inradius of S g ⊆ R 3 , respectively. Theorem 1.1. There exists a monotone continuous function λ(t) > 0 for t > 0 such that if (RP 2 , g) has positive Gaussian curvature, then area(g) sys 2 (g)

- 2 π ≥ λ R -r sys , (1.3)
where λ(t) is asymptotically linear as t → ∞, and R and r are the circumscribed and inscribed radii of the Euclidean embedding of the orientable double cover S g ⊆ R 3 .

Our argument produces asymptotically linear bounds for the remainer term for large R -r (when the systole is normalized) that can easily be made effective. It would be interesting to develop effective lower bounds for the remainder term for small R -r as in Volkov [START_REF] Volkov | An estimate of the deformation of a convex surface as a function of the change in its intrinsic metric[END_REF].

Generalisations of Pu's inequality are studied in [START_REF] Babenko | Systolic freedom of orientable manifolds[END_REF], [START_REF] Guth | Systolic inequalities and minimal hypersurfaces[END_REF], [START_REF] Ivanov | Generalized degree and optimal Loewner-type inequalities[END_REF], [START_REF] Katz | Lusternik-Schnirelmann category and systolic category of low-dimensional manifolds[END_REF], [START_REF] Katz | Hyperelliptic surfaces are Loewner[END_REF], and elsewhere.

Rigidity in Pu's inequality for singular metrics

In this section, we review some aspects of Reshetnyak's work on Alexandrov surfaces (i.e., singular surfaces with bounded integral curvature) focusing on nonnegatively curved metrics.

We refer to [START_REF] Reshetnyak | Two-dimensional manifolds of bounded curvature[END_REF], [START_REF] Reshetnyak | On the conformal representation of Alexandrov surfaces[END_REF], [START_REF] Troyanov | Les surfaces à courbure intégrale bornée au sens d'Alexandrov[END_REF], [START_REF] Debin | A compactness theorem for surfaces with bounded integral curvature[END_REF] and [START_REF] Fillastre | An introduction to Reshetnyak's theory of subharmonic distances[END_REF] for a more detailed exposition. Let (S 2 , g n ) be a sequence of nonnegatively curved Riemannian metrics on S 2 such that the curvature measures ω n = K gn dg n weakly converge to ω. The measure difference µ = ω -dg 0 is a Radon measure of zero total mass on S 2 . Suppose that µ({x}) < 2π for every x ∈ S 2 . Then d gn → d for the uniform topology; see [START_REF] Troyanov | Les surfaces à courbure intégrale bornée au sens d'Alexandrov[END_REF]Theorem 6.2] or [START_REF] Reshetnyak | Isothermal coordinates on manifolds of bounded curvature I, II. Sibirsk[END_REF]. Here d is the intrinsic distance induced by g = e u g 0 , where u is the potential of µ with respect to the canonical metric g 0 on S 2 (i.e., µ = ∆ g 0 u in the distribution sense). Note that u is expressed via the Green function G :

S 2 × S 2 → R ∪ {+∞} through the formula u(x) = ˆS2 G(x, y) dµ(y). (2.1)
For general Alexandrov surfaces, the potential u is the difference of two subharmonic functions, and one has u ∈ ∩ p<2 W 1,p (S 2 ); see [START_REF] Troyanov | Les surfaces à courbure intégrale bornée au sens d'Alexandrov[END_REF] and references therein (this won't be needed though). Furthermore, area(g n ) → area(g) and area(g) =

ˆS2

e u dg 0 .

This result readily applies to a sequence of smooth convex spheres S n ⊆ R 3 converging to a convex sphere S (bounding a convex body) for the Hausdorff topology in R 3 . Equivalently, it applies to a sequence of nonnegatively curved metrics g n on S 2 Gromov-Hausdorff converging (without collapse) to a metric on S 2 with nonnegative curvature in Alexandrov's sense. Indeed, in this case, the distance on S n uniformly converges to the distance on S; see [1, §III.1] or [3, Lemma 10.2.7]. Furthermore, the condition µ S ({x}) < 2π, where x ∈ S, is always satisfied on the boundary S of a convex body in R 3 ; see [1, §V.3]. Thus, the metric on S can be written as g = e u g 0 for some weakly regular function u on S as above.

For such singular metrics, the characterization of the equality case in Pu's inequality still holds. More generally, we have Theorem 2.1. Let RP n be the projective n-space with a singular Riemannian metric g = f 2 g 0 with nonzero systole, where g 0 is the standard round metric and f ∈ L n is a nonnegative function. Then vol(RP n , g)

sys(RP n , g) n ≥ vol(RP n , g 0 ) sys(RP n , g 0 ) n .
Furthermore, when n = 2 and f = e u , where u is the potential of a Radon measure µ of zero total mass given by (2.1), equality holds if and only if g is a metric of constant Gaussian curvature.

Proof. Denote by f the lift of f to the double orientable cover S n of RP n . Let us recall a simple version of Santaló's formula on the standard sphere S n ; see [START_REF] Santaló | Integral geometry and geometric probability[END_REF]IV.19.4]. The space Γ of closed oriented geodesics on S n is a (2n -2)-dimensional manifold admitting a natural symplectic structure whose corresponding natural volume measure is denoted by ν. Every integrable function F :

S n → R satisfies ˆSn F dg S n = 1 vol(S n-1 , g 0 ) ˆγ∈Γ ˆS1 F (γ(t)) dt dν(γ). (2.2)
Taking F ≡ 1, we observe that ν(Γ) = 1 2π vol(S n-1 , g 0 ) vol(S n , g 0 ). Applied to F = f n , Santaló's formula yields

vol(S n , g) = ˆSn f n dg 0 = 1 vol(S n-1 , g 0 ) ˆγ∈Γ ˆS1 f (γ(t)) n dt dν(γ).
By Hölder's inequality

(2π) n-1 n ˆS1 f (γ(t)) n dt 1 n ≥ ˆS1 f (γ(t)) dt = length g (γ), we deduce vol(S n , g) ≥ 1 (2π) n-1 vol(S n-1 , g 0 ) ˆγ∈Γ length g (γ) dν(γ) n ≥ 2 n ν(Γ) (2π) n-1 vol(S n-1 , g 0 ) sys(RP n , g) n
since length g (γ) ≥ 2 sys(RP n , g) for every γ ∈ Γ. Combined with the value of ν(Γ), we derive vol(RP n , g) ≥ 1 2 vol(S n , g 0 ) π n sys(RP n , g) n as desired. Furthermore, equality holds if and only if equality holds in Hölder's inequality, that is, if f is constant almost everywhere. Suppose that n = 2 and f = e u , where u is given by (2.1). Since f , and so u, are constant almost everywhere, we have µ = ∆ g 0 u = 0. By (2.1), this implies that u, and so f , are constant everywhere. Hence the extremal metric has constant curvature. Specifically, we have Corollary 2.2. Let RP 2 be the projective plane with a singular Riemannian metric g = e u g 0 , where u is the potential of a Radon measure µ of zero total mass given by (2.1). Then

area(RP 2 , g) ≥ 2 π sys(RP 2 , g) 2
with equality if and only if g is a metric of constant Gaussian curvature.

Pu's inequality with an R -r remainder

In this section, we present two proofs of Theorem 1.1. The first one follows an extrinsic geometry approach, while the second relies on intrinsic geometry arguments.

First proof of Theorem 1.1. We will exploit John ellipsoids as well as Pogorelov's rigidity theorem.

Step 1. Consider a pair of John ellipsoids E ⊆ S g ⊆ √ 3 E as in [START_REF] John | Extremum problems with inequalities as subsidiary conditions. Studies and Essays Presented to R[END_REF]. Let a ≤ b ≤ c be the principal axes of E ⊆ R 3 . Then up to a uniform multiplicative constant, each nonnegative curved metric g on RP 2 has the following properties:

(1) sys(g) ∼ b;

(2) the inradius r of S g satisfies r ∼ a;

(3) the circumradius R of S g satisfies R ∼ c;

(4) area(g) ∼ bc. Here, we write α ∼ β if there exist two positive constants C and C (which do not depend on g) such that Cα ≤ β ≤ C α.

This follows from the existence of distance-decreasing nearest-point projections from √ 3 E to S g and from S g to E, due to the convexity of S g .

Since the relation (1.3) is scale-invariant, we can introduce a normalisation b = 1. Then the systole is uniformly bounded above and below by item [START_REF] Alexandrov | Part II. Intrinsic geometry of convex surfaces[END_REF]. For a sequence of metrics with c → ∞, we have area(g) ∼ c and therefore the inequality (1.3) follows from items ( 3) and ( 4), including the linear asymptotic behavior of the remainder term as t → ∞.

Step 2. By the characterization of the equality case in Pu's inequality (see Corollary 2.2), it remains to show that if for a sequence of metrics (with b = 1) the difference area -2 π sys 2 tends to 0 then S g converges to a round metric. For such a sequence, the major axis c is uniformly bounded in view of estimates (1) and (4). We need to show that the minor axis a stays away from zero in such a sequence of metrics. Suppose a → 0. Then sys(g) tends to the width W of the Jordan curve obtained as the boundary of the orthogonal projection of S g to the plane spanned by the principal axes b and c. Similarly, area(g) tends to the area A of the planar region D ⊆ R 2 bounded by the curve. Since D is a centrally symmetric convex planar domain, we have W 2 ≤ 4 π A. Therefore, in the limit, we obtain area -

2 π sys 2 = A - 2 π W 2 ≥ A 1 - 8 π 2
> 0 which contradicts the assumption that area -2 π sys 2 tends to 0. Hence, the minor axis a stays uniformly away from 0.

Thus, for a family of metrics with the difference area -2 π sys 2 tending to 0, the corresponding John ellipsoids have uniformly bounded eccentricity.

Step 3. Convex sets of uniformly bounded eccentricity form a compact family by the Blaschke selection theorem. Let λ(t) be the minimum of area sys 2 -2 π among nonnegatively curved metrics with R-r sys ≥ t. Every metric which is not internally isometric to the metric of constant curvature, satisfies R -r > 0.

Step 4. Now suppose the metric of the convex surface is internally isometric to the metric of constant curvature. It follows that the surface is congruent to the standard one by Pogorelov's rigidity theorem [17, p. 167] (see Prosanov [START_REF] Prosanov | Rigidity of compact Fuchsian manifolds with convex boundary[END_REF] for a discussion of the status of the various proofs of this ridigity result), and therefore R -r = 0. Thus λ(t) > 0 for t > 0.

Our second proof of Theorem 1.1 relies on a more intrinsic argument.

Second proof of Theorem 1.1. Since the relation (1.3) is scale-invariant, we can assume that sys(g) = 1.

Consider the lift γ on S g ⊆ R 3 of a systolic loop of (RP 2 , g). Note that γ is a simple closed geodesic of S g of length L = 2 sys(g). Furthermore, 2πr ≤ L. Thus, r ≤ 1 π . Let p be a point of S g at maximal intrinsic distance from γ. There exist at least two arcs of length D = d Sg (p, γ) starting at p and ending perpendicularly at γ. These two arcs along with γ decompose the hemisphere of S g bounded by γ into two isosceles triangles ∆ i . Now, consider the comparison triangles T i with the same side lengths in the Euclidean plane. By Toponogov's theorem, the area of ∆ i is greater or equal to the area of T i . Also, one of the edges of one of the triangles ∆ i (and so of T i ) is of length at least L 2 , and its other two edges are of length D. If D goes to infinity (while the systole of g is fixed), the area of T i goes to infinity and so does the area of ∆ i (and RP 2 ). More precisely, the area of g grows roughly as D. Note that 2R ≤ diam(g) ≤ 2D + L 2 . This implies that the remainder term λ is asymptotically linear in (1.3).

Let λ(t) be the infimum of the difference area -2 π sys 2 among nonnegatively curved metric with R-r sys ≥ t. From the previous discussion, we can assume that the diameter of g is bounded when considering λ(t). Since the space M(n, D, v) of n-dimensional compact Alexandrov spaces of diameter at most D and of volume at least v > 0 is compact for the Gromov-Hausdorff topology (see Theorem 10.7.2 and Corollary 10.10.11 of [START_REF] Burago | A course in metric geometry[END_REF]), it follows from Perelman's Stability Theorem (see [START_REF] Burago | A course in metric geometry[END_REF]Theorem 10.10.5]) that this infimum is attained by an extremal metric with nonnegative curvature in Alexandrov's sense. Such a (singular) metric can be written as g = e u g 0 , where g 0 is the canonical metric on RP 2 and u is the difference of two subharmonic functions; see Section 2. Suppose that λ(t) = 0. By the characterization of the equality case in Pu's inequality (see Corollary 2.2), the extremal metric g is internally isometric to a metric of constant Gaussian curvature. By Pogorelov's rigidity theorem, such a convex surface is congruent to the standard round sphere, so that R -r = 0. Therefore, λ(t) > 0 for t > 0.

Partially supported by the ANR project Min-Max (ANR-19-CE40-0014).


Anjela Mayer
email: anjela.mayer@kit.edu

Kevin Kastner
email: k.kastner@hs-mannheim.de

Julian Reichwald
email: j.reichwald@hs-mannheim.de

Jean-Rémy Chardonnet
email: jean-remy.chardonnet@ensam.eu

Jivka Ovtcharova
email: jivka.ovtcharova@kit.edu

Comparing Avatar and Face-to-Face Collaboration in VR Education: Concept and Preliminary Insights

Keywords: collaboration, digital twins, education, virtual reality

Virtual education is gaining prominence, providing opportunities for dynamic interactive content, such as Digital Twins, and novel collaboration modalities, including options for remote classrooms. In this work, we present a concept that leverages Digital Twins for interactive group work in engineering education through the use of Virtual Reality technology. We propose an experimental investigation to compare diverse collaboration alternatives facilitated by Virtual Reality, specifically face-to-face and avatar-based interaction. Preliminary findings are discussed, along with their implications for the design and implementation of future experiments in this emerging field.

I. INTRODUCTION

The key fields Industry 4.0 and Internet of Things (IoT) have been significantly growing in recent years, with the Digital Twin (DT) playing an increasingly important role [START_REF] Grieves | Intelligent digital twins and the development and management of complex systems[END_REF]. This not only affects the industrial environment, but also how people can interact and communicate with each other using these technologies [2]. In consequence, the importance of immersive technologies such as Virtual Reality (VR) are becoming increasingly popular. Emerged from the the gaming sector, gamification and its symbiosis with VR technologies receives growing interest and adoption in the engineering and education domains [START_REF] Koca | Augmented reality application for preschool children with unity 3d platform[END_REF], [2], [START_REF] Yin | A state-of-the-art survey on augmented reality-assisted digital twin for futuristic humancentric industry transformation[END_REF]. Within these domains, one key advantage of immersive technologies is the possibility to experience and get in touch with complex topics in a virtual space. For instance, students can get a real impression of industrial plants or explore scientific phenomena like magnetic fields. In some cases, physical access for larger student groups is not possible or restricted at all for facilities located in inaccessible or dangerous areas. Here, immersive technologies offer possibilities to make education more accessible by providing digital representations of physical assets -Digital Twins -with which students can interact naturally and make realtime experiences within a virtual environment. At last, since the COVID-19 pandemic and the associated social distancing rules, it has become clear that educational content should also be virtually available for students. Therefore, the two technologies, VR and DTs, complement each other perfectly: visualization and interaction can be realized in virtual space through VR and mirrored on physical content through the DT system. In this work, we want to outline a coalescence between DT and VR technologies and demonstrate how they can be applied in the educational context. The challenge here is to consider and realize the most various aspects: from the technical obstacles of VR technology through the avatar and interaction design and finally a user-friendly introduction of this technology to students and educators.

In the last years, a significant increase in the popularity of Collaborative Virtual Environments (CVEs) such as the Metaverse or Omniverse can be observed [START_REF] Mohamed | Metaverse![END_REF], [START_REF] Tlili | Metaverse for climbing the ladder toward 'industry 5.0' and 'society 5.0'?[END_REF], [START_REF] Xu | A trustless architecture of blockchain-enabled metaverse[END_REF]. In CVEs, avatars represent the human collaborators and help to address the loss of the physical body, allowing them to interact with the virtual environment and with each other's avatars [START_REF] Ens | Revisiting collaboration through mixed reality: The evolution of groupware[END_REF].

To approximate a natural interaction between the collaborators, as in face-to-face meetings, it is necessary to research avatarto-avatar interaction in CVEs. In this context, we strive to address the following research questions in our experiments: How well does avatar-to-avatar group work perform compared to face-to-face group work in Collaborative Virtual Environments? Which factors can improve the performance of avatarto-avatar collaboration in remote or asynchronous education?

This paper introduces our concept for studying VR-assisted education, specifically group work with Digital Twins (DTs), comparing face-to-face and avatar-to-avatar collaboration. Our goal is to provide insights for the design of VR education. The related work is summarized in section II, followed by section III presenting our concept and prototype implementation. For validation, the prototype was used in a pre-study as described in section IV. The preliminary results are summarized in section V and discussed in VI further presenting the limitations. Finally, the conclusion is drawn in section VII.

II. RELATED WORK

Various alternative solutions to traditional teaching methods are offered due to the technological revolution supported by Digital Twins and the possibility of entering a true-to-scale world through VR technology, in which the user can navigate as a virtual model in a (nearly) humanoid or abstract form [START_REF] Suk | Influence of avatar facial appearance on users' perceived embodiment and presence in immersive virtual reality[END_REF]. In 2002, Michael Grieves coined the concept of DTs and laid the foundation for one of the most important technologies for obtaining the optimum processes for production companies. This involves a dual data communication between the physical and digital space. As [START_REF] Van Der | A taxonomy of digital twins[END_REF] has shown, there are different definitions and concepts of DTs, in this case the DT is an exact virtual dynamic image of exactly one physical representation [START_REF] Grieves | Intelligent digital twins and the development and management of complex systems[END_REF], [START_REF] Kastner | Leveraging transdisciplinary engineering through the coalescence of digital twins and xr-technologies[END_REF]. Oda et al. utilizes a DT to remotely guide an on-site worker through maintenance steps of a physical machine [12]. However, the application of DT systems is not limited to the industrial environment. Lehmann et al. [START_REF] Lehmann | Establishing reliable research data management by integrating measurement devices utilizing intelligent digital twins[END_REF] demonstrated that such cyber-physical systems can also be used in a scientific context to organize research data. Furthermore, these technological approaches can also be used for knowledge transfer for students and teachers to their advantage. When combined with a virtual learning environment, DTs can be interacted with in realtime via the bidirectional communication interface between the physical and digital space and, with the help of VR technology, create intelligent interactive classrooms [START_REF] Liljaniemi | Using digital twin technology in engineering education -course concept to explore benefits and barriers[END_REF], [2], [START_REF] Tlili | Metaverse for climbing the ladder toward 'industry 5.0' and 'society 5.0'?[END_REF], [START_REF] Guc | Digital twins enabled remote laboratory learning experience for mechatronics education[END_REF]. Due to the architectural structure of the DTs, they offer different interfaces for joint collaboration between humans and machines, for which VR systems such as Cave Automatic Virtual Environment (CAVE), Powerwall, or Head-Mounted-Displays (HMDs) are required. Virtual Reality means trying to completely integrate a human in a computerized interactive world and to stimulate several senses (e.g. visual, auditive, haptic, and so on) with suitable actuators in order to create a highly immersive experience [START_REF] Stacchio | Empowering digital twins with eXtended reality collaborations[END_REF], [START_REF]Virtual und Augmented Reality (VR/AR)[END_REF].

In terms of collaboration, VR systems such as CAVE or Powerwall are different from HMDs. While CAVEs and Powerwalls offer an in-person VR group experience with the possibility for face-to-face collaboration, HMDs isolate the users from their real environment. As a consequence, HMD users do not see other collaborators, even if being in the same room. Thus, for group experiences, HMD users have to be visualized by avatars within the virtual environment, replacing face-toface collaboration with avatar-to-avatar interaction. Avatarbased collaboration can lead to a shift of emotional awareness and affect the collaboration [START_REF] Greiner | Is avatar-to-avatar communication as effective as face-to-face communication? an ultimatum game experiment in first and second life[END_REF]. Thus, there are efforts to improve the expressiveness of avatars and support high fidelity non-verbal expressions by tracking body movements of the users, hand gestures and facial expressions [START_REF] Wu | Using a fully expressive avatar to collaborate in virtual reality: Evaluation of task performance, presence, and attraction[END_REF]. Kruzic et al. investigate how avatars affect the conversational outcome in VR and show that facial expressions have a greater impact on virtual conversations than body movements [START_REF] Kruzic | Facial expressions contribute more than body movements to conversational outcomes in avatar-mediated virtual environments[END_REF]. How avatars can affect group performance in CVEs has been researched by Greiner et al. [START_REF] Greiner | Is avatar-to-avatar communication as effective as face-to-face communication? an ultimatum game experiment in first and second life[END_REF]. VR collaboration seem to benefit from visualizing avatars and achieve similar results as face-to-face collaboration in terms of completion time of the tasks. Furthermore, between avatars a higher cooperativeness was observed, as well as a lower need for additional communication [START_REF] Greiner | Is avatar-to-avatar communication as effective as face-to-face communication? an ultimatum game experiment in first and second life[END_REF].

The current research is limited to small group sizes, with experiments showing collaboration between two participants. In our education use cases, a collaboration of larger student groups is required, with at least three but preferably more participants. Furthermore, we want to focus on effective group work with the DT in co-local and remote class scenarios.

III. CONCEPT AND IMPLEMENTATION

As a measure to improve our engineering lectures, participants get the opportunity to experience and work with Digital Twins in interactive group work sessions. According to Guc et al. [START_REF] Guc | Digital twins enabled remote laboratory learning experience for mechatronics education[END_REF] and Sala et al. [START_REF] Sala | On the development of the digital shadow of the fischertechnik training factory industry 4.0: an educational perspective[END_REF] the students should get a better understanding of DTs and improve their skills utilizing it. To enable interaction with the DT while keeping the human-to-human interaction as natural as possible, a CVE is to be created using VR technology. Within the CVE students can interact with the virtual scene, including the DT, while still being able to communicate and interact with each other to solve group tasks. There are several design options for collaborative work to be considered, in the time, space [START_REF] Johansen | Groupware: Computer support for business teams[END_REF] and Extended Reality dimension [START_REF] Mayer | Collaborative work enabled by immersive environments[END_REF]. With a focus on synchronous collaboration with VR, we aim to research the differences between face-to-face (f2f ) collaboration, limited to co-located group work, and avatar-to-avatar (a2a) collaboration, which allows remote group work. Therefore, a VR environment will be implemented to compare the f2f and a2a modalities as depicted in Figure 1.

In the f2f modality, large immersive screen setups will be used to run the CVE. There, the students can meet in person within a shared space and interact with the DT through the VR system. Although, only one person is able to interact with the virtual environment at the same time.

In the a2a modality, the students wear VR HMDs, isolating them from the real environment. Since the students can not see and hear each other, we use this modality to study remote collaboration setups, where other participants are visualized by 3D avatars. In this work, we present our concept to address the research questions stated in section I and the results of a pre-study to validate our VR prototype and test the experiment design. The results of the pre-study will be used to improve our future experiments. For simplicity, the f2f condition is implemented with a stereoscopic VR wall system (Powerwall) instead of a CAVE in the pre-study. To evaluate, the group work modalities, the CAVE system will be used in future experiments since it is more immersive.

The pre-study is based on ViewR, a state-of-the-art Virtual Reality software for the industry from CMC Engineers GmbH, which supports multi-display VR systems operated on a single node, but also different HMDs such as Oculus Quest or Varjo XR-3. The software supports the Unity game engine which was used to create the 3D environment, as visualized in Figure 2, and to integrate the DT infrastructure. The VR setup for ViewR consists of a 6x2m passive stereo powerwall and a VRenabled computer. Within the VR scene, users are represented by avatars, visualized by 3D geometry for head and hands. For interaction and navigation within the VR scene, HTC Vive 2.0 controllers were used in Powerwall and HMD setups.

IV. VALIDATION

The primary objective of the experimental study is to evaluate the effectiveness of the VR collaboration in education, specifically comparing f2f and a2a modalities. This comparison is essential for advancing our understanding of the dynamics inherent to collaboration within immersive environments. To substantiate this claim, a preliminary study was designed and executed, which serves as a prelude to more extensive studies in this domain. The methodology and findings of these experiments are described in the subsequent sections.

All participants are studying the Master's programme Engineering and Management and take part in Digital Business Technologies at Mannheim University of Applied Sciences. It is a heterogeneous group with different backgrounds in electrical engineering, computer science, information technology and economics. Prior to the experiments, an introduction to digital transformation and how it can be realized as a business idea took place as part of the lecture, where definitions and terms were explained related to DTs. During the experiment, the participants were free to split into two groups and informed that the following three different tasks would not be evaluated. One group worked with HTC Vive HMDs to evaluate the a2a condition, while the other group worked with a Powerwall to assess the f2f condition.

During the experiments, participants had to work on three tasks, which were addressing the topic of DT differently and helped to evaluate how well the students could comprehend the topic. Therefore, a physical measuring station (PM) unit was used, which can measure time, temperature, CO 2 and Fig. 2. Different views on the VR environment where the study participants had to interactively complete the group tasks. The first two tasks took place in VR, while the last task provided creative freedom in which the students could freely decide to utilize VR and the DT or not. The first task aimed to teach the students the interplay between DT and VR. Therefore, they had to interact with the PM as well as with the DTM to solve the tasks. One interaction was to turn on and off the display light of the PM, which was only possible by interacting with the DTM. For comprehension assessment, the students were asked to identify and write down the differences between the PM and its DT and to argument whether the DTM is an ideal DT. In the next exercise, the participants were asked to develop a cost-efficient concept of monitoring the temperature and CO 2 using VR. Eight additional virtual twin models were available on demand, which could be distributed. In the final task, the groups had to design a rough business model for the DT as a Service use case.

V. PRELIMINARY RESULTS

This pre-study collected qualitative feedback from 17 students (5 females, ages 21-34), 50% of whom were casual computer gamers and 52.9% VR novices. Feedback, collected via post-experiment questionnaires (including the System Usability Scale (SUS), NASA Task Load Index (TLX), and a custom questionnaire), will guide the refinement of our implementation. Both modalities demonstrated marginal usability, with SUS scores below 70. The cognitive workload was reported higher for the a2a group, although it was perceived as offering better performance and lower frustration as depicted in Figure 3. In the custom questionnaire 28 criteria were defined to assess the six categories (Engagement, Verbal Communication, Satisfaction, Ray-Tool, Sketch-Tool, and Digital Twin) using a 5-point Likert-scale. Statistical analysis was performed using t-tests, employing Welch's test for significant variance differences and the independent samples t-test otherwise. The results are summarized in Tables I and II.

VI. DISCUSSION AND LIMITATIONS

Overall, the a2a modality performed slightly better in all categories of the custom questionnaire, except for the Ray-Tool. Especially the Engagement and Verbal Communication were perceived well by the participants in both modalities. Meanwhile, the Sketch-Tool received the worst rating from the participants in both modalities.

Engagement was assessed by four criteria and was perceived especially positive compared to other categories. The participants rated their participation highly and also perceived their group members as highly engaged. Furthermore, they did not have the feeling of not being perceived or ignored by the others, but rather felt as an active part of the group. Overall, both collaborative VR setups and the tasks, seem to be very engaging to the participants. The a2a modality may be even more engaging compared to f2f, that may be because Powerwall and CAVE (f2f ) setups characteristically have one controller for the whole group, while in HMDs setups (a2a) everyone has their own controllers and can interact with the CVE and other users simultaneously.

Verbal Communication, rated by three criteria, was, as well, perceived significantly positive in front of other categories. According to the participants, they could easily communicate with other group members, discuss a lot about ideas and solutions within the groups, and quickly find a solution. Although f2f verbal communication was assumed to be perceived more positive compared to a2a, the preliminary results indicate the opposite. A statistically significant difference was identified in maintaining focus on the solution. The HMD (a2a) modality seems to have a greater positive effect on maintaining focus during verbal communication.

Satisfaction was assessed by nine items, according to participants were satisfied with the interaction between each other with their individual performance as well as the team performance, and their solution. With the provided VR technology and scenario, the tasks were perceived as easy to solve. The given time was not perceived as positively as other criteria, especially in the a2a condition. Nevertheless, the participants were content with the provided information for the tasks. Statistically significant differences were observed in overall satisfaction, with the a2a condition being slightly more satisfying. When examining individual criteria, only Team Performance, Solution Quality, and VR Technology utilization displayed significant variations, all favoring the a2a condition. Despite these positive findings, our intention is to explore VR collaboration under more challenging scenarios. In the present study, the participants were encouraged to solve the tasks collaboratively, although they did not explicitly necessitate teamwork. Recognizing this, we aim to design more complex tasks for follow-up experiments which require cooperation. Ray-Tool, Sketch-Tool and the DT categories were evaluated based on four criteria. The Ray-Tool was frequently used both individually and collectively, and was perceived useful for group work. However, it was reported to be significantly easier to use in the f2f condition than in the a2a condition. The Sketch-Tool saw less frequent use and was perceived as significantly less useful in the f2f condition, as in the a2a group. Despite disagreements about its utility, it was deemed easy to use. The DT was frequently used by participants and their groups, but it was seen as relatively complicated to use despite its utility in group discussions. In summary, the tools provided were useful but not necessarily user-friendly. Notably, the Sketch-Tool's usability needs significant improvement for future use. Given that participants had limited time to acclimate to the VR environment and tools, a training scenario should be provided in future experiments.

This pre-study has several limitations. As previously mentioned, the tasks in our study were not sufficiently collaborative and may have been too simple. Additionally, we did not provide a VR training scenario before the experiment, a step that might have aided participants in adapting to VR usage. Given that over 52% of participants were experiencing VR for the first time, their unfamiliarity could have significantly impacted the results. Moreover, in this pre-study, a Powerwall was used for the f2f condition, offering a lower degree of immersion compared to a CAVE system. In light of this, our forthcoming study will incorporate a CAVE system, which might lead to different outcomes. Lastly, it's essential to emphasize that our subject pool was relatively small, posing challenges in drawing statistically robust conclusions. These limitations underscore the need for further, larger-scale studies to validate and build upon our initial findings.

VII. CONCLUSION AND FUTURE WORK

This study introduced a concept for using Digital Twins in engineering education via VR technology. We examined two interaction modalities for collaborative work in VR: faceto-face and avatar-to-avatar, which we will further evaluate in future studies. This preliminary work validated the VR setups and experiment procedures for both modalities, and we presented implications based on participant feedback. These early insights led to the formation of hypotheses for subsequent studies: (H1) Avatar-to-avatar collaboration in VR is more engaging and satisfying than face-to-face group work; (H2) Avatar design (fidelity, realism, humanoid vs nonhuman) significantly impacts group work and can enhance task performance and learning outcome; (H3) Difference in non-verbal communication are more significant than in verbal communication when comparing avatar-based and face-to-face collaboration in VR.

Fig. 1 .

 1 Fig. 1. VR collaboration with a Digital Twin: a) Face-to-face collaboration in a CAVE system between in-person participants. b) Avatar-to-avatar collaboration in a VR environment between distant participants wearing HMDs.

Fig. 3 .

 3 Fig. 3. NASA TLX results and total SUS Score by modalities.

TABLE I NASA

 I TLX AND SUS RESULTS FOR THE a2a AND f2f CONDITIONS (*STATISTICALLY SIGNIFICANT DIFFERENCE)

	Category/Item	f2f Mean ± SD	a2a Mean ± SD	p-value
		NASA TLX Scores
	Mental Demand	5.15 ± 1.52	6.25 ± 1.71	0.12
	Physical Demand	3.0 ± 1.96	4.5 ± 1.91	0.1
	Temporal Demand	4.23 ± 2.8	5.75 ± 3.4	0.19
	Performance	6.0 ± 2.0	8.0 ± 1.41	0.04 *
	Effort	4.92 ± 1.5	5.5 ± 1.29	0.25
	Frustration	3.92 ± 2.1	2.25 ± 0.96	0.07
		SUS Scores
	SUS Score	55.31 ± 18.67	66.5 ± 14.25	0.06
	humidity was provided, as well as a DT of the measuring
	station (DTM) which could be interacted with in VR.

TABLE II CUSTOM

 II QUESTIONNAIRE RESULTS FOR THE a2a AND f2f CONDITIONS (*STATISTICALLY SIGNIFICANT DIFFERENCE)

	Criteria	f2f M ± SD	a2a M ± SD	p-value
	Engagement	4.21 ± 0.56	4.69 ± 0.38	0.07
	Group Participation	4.08 ± 0.95	4.5 ± 1.0	0.23
	Individual Participation	4.15 ± 0.8	4.75 ± 0.5	0.09
	Inclusion in Group	4.23 ± 1.3	4.75 ± 0.5	0.23
	Recognition by Group	4.38 ± 1.12	4.75 ± 0.5	0.27
	Verbal Communication	3.82 ± 0.46	4.25 ± 0.17	0.05
	Ease of Communication	4.54 ± 0.52	4.75 ± 0.52	0.25
	Discussion Dynamics	3.69 ± 0.95	4.0 ± 0	0.27
	Focus on Solution	3.23 ± 0.44	4.0 ± 0	0.002 *
	Satisfaction	3.48 ± 0.47	3.89 ± 0.09	0.005 *
	Group Interaction	4.15 ± 0.38	4.25 ± 0.5	0.34
	Individual Performance	3.69 ± 0.75	4.25 ± 0.5	0.09
	Team Performance	3.85 ± 0.55	4.75 ± 0.5	0.005 *
	Solution Quality	3.69 ± 0.48	4.25 ± 0.5	0.03 *
	VR Technology	3.15 ± 1.07	4.0 ± 0	0.007 *
	VR Environment	3.15 ± 1.28	4.0 ± 0	0.17
	Task Difficulty	3.0 ± 1.15	3.75 ± 0.5	0.12
	Given Time	3.13 ± 0.95	2.75 ± 0.96	0.16
	Provided Information	3.31 ± 0.85	3.0 ± 0.82	0.27
	Ray-Tool	3.58 ± 0.47	3.13 ± 0.32	0.05
	Group Usage	4.15 ± 0.69	3.5 ± 0.58	0.05
	Individual Usage	3.23 ± 0.93	3.5 ± 0.58	0.3
	Utility	3.23 ± 1.09	3.5 ± 0.58	0.32
	Usage Difficulty	3.69 ± 0.75	2.0 ± 0.82	<0.001 *
	Sketch-Tool	2.21 ± 0.38	2.69 ± 0.9	0.09
	Group Usage	2.62 ± 1.19	2.25 ± 1.26	0.3
	Individual Usage	1.77 ± 1.01	2.25 ± 1.26	0.22
	Utility	1.92 ± 0.86	3.0 ± 0.82	0.02 *
	Usage Difficulty	2.54 ± 0.88	3.25 ± 0.5	0.07
	Digital Twin	3.29 ± 0.68	3.56 ± 0.55	0.24
	Group Usage	3.54 ± 0.66	4.0 ± 0.82	0.13
	Individual Usage	3.46 ± 0.97	4.0 ± 0.82	0.17
	Utility	3.38 ± 0.65	3.5 ± 0.58	0.38

Authorized licensed use limited to: KIT Library. Downloaded on November 04,2023 at 09:18:33 UTC from IEEE Xplore. Restrictions apply.

ACKNOWLEDGMENT

The paper was supported by a grant of Stiftung Innovation in der Hochschullehre (SHELLS 4.0) and the German research project "RemoteCave" supported from the Central Innovation program for SMEs. The authors would also like to thank the Ministry of Science, Research and Arts of the Federal State of Baden-Württemberg for supporting the KoLabBW III project.


Morelle Marie
email: mmorelle@ensc.fr

Cegarra Julien
email: julien.cegarra@univ-jfc.fr

Marion Damien
email: damien.marion@thalesgroup.com

André Jean-Marc
email: jean-marc.andre@ensc.fr

Towards a Definition of Cognitive Warfare

Keywords: cognitive warfare, influence strategies, destabilization actions, intelligence

Cognitive warfare is an emerging concept in the literature, linked to the development of new technologies and of knowledge on cognition, as well as the involvement of public opinion in conflicts. It is currently the subject of debate within NATO. Used to destabilize adversaries or make them "destroy themselves from the inside", it is becoming a major concern, and we need to learn how to detect it and protect ourselves against it. This paper aims to define cognitive warfare, other close concepts and its players, and to outline the issues at stake.

I. INTRODUCTION

This paper will provide some insights into cognitive warfare, its definition and related concepts. Bernal et al. [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF] suggest that modern cognitive warfare emerged during the Cold War: to avoid another destructive open war between superpowers, they set up proxy conflicts, supporting and opposing small countries or armed groups against each other. In this context, numerous actions have been carried out discreetly, notably by the CIA, the FBI and the KGB. Since the 2000s, there has been an increase in destabilization actions [231], particularly by Russia in its attempts to influence elections, propaganda and cyberattacks, notably against the Baltic states, France and the United States, as described by Backes and Swab [START_REF] Backes | Cognitive Warfare-The Russian Threat to Election Integrity in the Baltic States[END_REF]. Du Cluzel explains that some countries, like Russia and China, are conducting research into neuroscience and technology for medical, social and military purposes, which could also serve as a means of action for cognitive warfare [START_REF] Cluzel | Cognitive Warfare[END_REF]. But it is in the field of economics that the term "cognitive warfare" was first used, to describe the influences and destabilizing actions implemented by companies, towards consumers, legislators (lobbying) or even competing companies [START_REF] Harbulot | De la légitimité de la guerre cognitive[END_REF].

Cognitive warfare thus represents a new mode of conflict blurring the boundaries between war and peace [START_REF] Orinx | La guerre cognitive -Pourquoi l'Occident pourrait perdre face à la Chine ?[END_REF], not open warfare on a battlefield, but undeclared warfare aimed at influencing the cognitive mechanisms, notably the decisionmaking processes, of an adversary or competitor. It's a recent term, and not yet universally accepted. We propose a definition, and discuss the challenges of this new type of confrontation.

II. COGNITIVE WARFARE

Cognitive warfare is an emerging concept aiming to weaken the enemy in order to gain a tactical or strategic advantage [START_REF] Montocchio | Avant-propos par le directeur adjoint du Collaboration Support Office (CSO) STO[END_REF], in the military, economics, gaming, sports and other fields. It encompasses various operations carried out against the human mind, targeting both individual and collective cognition and decision-making. It can be carried out and suffered at different scales, and remotely: populations, soldiers, experts, engineers, technicians, groups or minorities of opinion, ethnic or religious, companies, communities, decision-makers, political, economic, religious, academic or military leaders [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF][START_REF] Claverie | Cognitive Warfare : La guerre cognitique[END_REF]… It relies on NBIC (Nanotechnologies, Biotechnologies, Information technologies and Cognitive sciences) tools, such as digital tools and social networks, chemical substances, illusions, attention saturation [START_REF] Claverie | Cognitive Warfare : La guerre cognitique[END_REF], or exploitable cognitive biases of targets [START_REF] Legry | Neurosciences et sciences cognitives : Comment se préparer à la guerre des cerveaux ?[END_REF]. The objectives of cognitive warfare can be to conquer a territory, disrupt public services, bring about a change of government, influence elections, undermine confidence, inhibit critical thinking [START_REF] Cluzel | Cognitive Warfare[END_REF], or destabilize and influence a target population [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF] by radicalizing opinion, discrediting governing bodies, triggering or inhibiting actions, etc. These actions are difficult to detect, as both targets and relays are unaware that they are victims.

Here are different examples of actions that could be considered as cognitive warfare.

1. Cognitive warfare launched via cyber tools: On the 23 rd of February, 2022, just before the Russian offensive against Ukraine, almost 500 cyber-attacks were detected on Ukrainian networks. They targeted essentially the government, critical networks and energy suppliers. According to Malin [START_REF] Malin | Cyberattaques : comment l'Ukraine a failli perdre la guerre avant même l'invasion russe[END_REF], the goal was seemingly to prevent the Ukrainian government from communicating and providing vital resources to its population, so that they lose confidence in the government. Even though this action is widely considered as cyberwarfare, it can be studied in the perspective of cognitive warfare because it is part of a strategy using different tools with a broader goal of destabilization.

2. Cognitive warfare launched contacting directly key individuals: On the 6 th of February 2023 in France, several women deputies from the Rassemblement National received a vocal message telling them one of their children was hospitalized, so that they would leave the National Assembly before a critical vote [START_REF]Réforme des retraites : Des députées RN cibles de messages d'intimidation[END_REF]. This was an intimidation attack trying to prevent the targeted people from voting and thus taking their role in a decision.

3. Cognitive warfare launched on social media: Our last example takes place in Mali, in April 2022. The Wagner mercenary group staged a human mass grave and edited a video to make it look like the French military created it [START_REF] Jousset | Wagner, l'armée de l'ombre de Poutine[END_REF]. The French military managed to film them preparing this staged scene, allowing them to create a video refuting these accusations.

According to Jousset and Bolchakova [START_REF] Jousset | Wagner, l'armée de l'ombre de Poutine[END_REF], the Wagner group would have used this opportunity to create an influence campaign on social networks to delegitimize the French army in Mali and be welcomed as liberators against French oppression.

4. Another example often used to describe cognitive warfare is the Havana Syndrome [START_REF]Wikipedia contributors[END_REF], which could potentially be a cognitive warfare attack launched using targeted nano or biological tools to induce fear for the key individuals who were targeted and cloud their judgment, but there is no definite cause officially identified, so this example is not supported by evidence to present day.

These examples show how cognitive warfare strategies can be led using different means and channels of action. We propose 3 criteria to help determine whether an action falls within the scope of cognitive warfare:

1. Its purpose is broader than what is immediately apparent: for example, a cyberattack launched in order to steal credit cards and use them to gain a monetary advantage would not be cognitive warfare; but if the aim is to instill doubt in customers' minds about the bank's ability to be secure, and the perpetrator communicates about this to discredit it, this could be an example of cognitive warfare.

2. Its nature is diffuse: it is often part of a strategy encompassing different actions and different means with a goal of chain reactions which can be difficult to measure in time and space. For example, an action could aim at changing behaviors in a population, so another group of people would have a different point of view on this population and then it would have an impact on some votes or decision-makers, and we can imagine a whole chain of resulting consequences and actions; it would thus prove difficult to find the origin of the attack and determine how long-term its effects can be.

3. Its target is cognition: cognitive warfare targets the human mind, representations and cognition, it aims at sowing doubt, preventing or influencing decisions, undermining the opponent's will [START_REF] Orinx | La guerre cognitive -Pourquoi l'Occident pourrait perdre face à la Chine ?[END_REF], manipulating the way people see and interpret specific parts of the world around them [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF]… In short, how people think and react [START_REF] Weldon | Bytes not bombs : Student team works with NATO to define, track cognitive warfare attacks[END_REF].

III. CLOSE CONCEPTS

There are other concepts closely related to cognitive warfare. We propose a clarification of terminology to better organize and define related terms. Most of them are intertwined with cognitive warfare and/or can be used as tools to lead a cognitive warfare strategy, under the circumstances explained earlier. A. Information Warfare, or Information Operations NATO 1 describes information warfare as "an operation conducted to gain an informational advantage over the opponent". It focuses on information, its manipulation, its flow, the way it is protected or stolen, and the way it is used. Du Cluzel [START_REF] Norton | Behind NATO's 'cognitive warfare': « Battle for your brain » waged by Western militaries[END_REF] reminds us that cognitive warfare, on the contrary, is "an action against the way we think, the way we process information and turn it into knowledge". Bernal et al. [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF] argue that cognitive warfare is the "fight to control or alter the way people react to information". Intelligence, on the other hand, is a process of knowledge construction [START_REF] Bulinge | Renseignement militaire : une approche épistémologique[END_REF]. Unlike information warfare, cognitive warfare does not focus on tactical battlefield information, but also acts on information for the general public [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF].

B. Psychological Operations (PsyOps)

According to Bernal et al. [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF], U.S.-led PsyOps involve informational products that are either identifiable as officially U.S.-produced (white products), ambiguously sourced (gray products), or created to "seem as if they originate from a hostile source" (black products). They often have a military purpose. Bernal et al. point out that cognitive warfare works mostly with gray products, which can be denied, and that it "tends to target civilian social infrastructure and governments".

C. Propaganda

Propaganda is the transmission of communications, information, and messages for the purpose of causing changes in the consciousness or subconsciousness of the target population, in order to change attitudes and behaviors [START_REF] Bobric | The Overton Window : A Tool for Information Warfare[END_REF]. Its author assumes authorship, so it is directly attributable. Cognitive warfare is subtler than propaganda. It allows one to influence targets without them being aware of it, and to use these same targets as weapons to reach others. According to du Cluzel [START_REF] Cluzel | Cognitive Warfare[END_REF], with cognitive warfare, "everyone participates, mostly inadvertently, to information processing and knowledge formation in an unprecedented way". The author states that cognitive warfare "feeds on the techniques of disinformation and propaganda aimed at psychologically exhausting the receptors of information": they can therefore be cognitive warfare tools.

D. Cyber Warfare

Bernal et al. [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF] define cyber warfare as "the use of cyberattacks with the intention of causing harm to a nation's assets". In our connected societies, especially with the Internet of Things, many functions are digitally controlled: "from construction equipment, to financial institutions, to civilian infrastructure, and even to military installations". Thus, cyberattacks can cause "massive damages not just in terms of time and data loss but in physical damage that can be measured in dollars and lives". Computer warfare falls under the technical domain, and the cognitive effect is a consequence, whereas for cognitive warfare, it is the goal of the action [START_REF] Claverie | Cognitive Warfare : La guerre cognitique[END_REF].

E. Cyberpsychology

According to Claverie and Kowalczuk [START_REF] Claverie | Chapitre 9 -Cyberpsychologie[END_REF], cyberpsychology is the study of mental phenomena in relation to cyber systems and cyber contexts. It is therefore a field of research that could produce knowledge that could be exploited as weapons for cognitive warfare, or, on the contrary, conceive ways of protecting against it.

F. Military Brain Science

According to Jin, Hou, and Wang [START_REF] Jin | Military Brain Science -How to influence future wars[END_REF], "Military Brain Science (MBS) is a cutting-edge innovative science […] based on the theories and technologies of medicine […], biology, physics, computer science, military science, and multiple other disciplines". It aims to monitor, protect, fight, repair, improve the brain. These are applications and tools that can be used for cognitive warfare, but remain focused on the military domain.

IV. TARGETS AND ACTORS

One of the characteristics of Cognitive Warfare is that it can be conducted by anyone, against anyone, and at a distance.

A. Targets

We propose that three kinds of targets can be considered:

1) Large groups of people sharing a common characteristic (populations, opinion, ethnic or religious groups or minorities, etc.);

2) Small groups of people sharing a common goal (companies, teams, armed forces, etc.);

3) Critical individuals (decision-makers, politicians, military leaders or leaders of the various groups mentioned above, experts…); People who have influence (critical individuals), either on a decision or on a group of people, can be particularly targeted, either directly or indirectly by attacking the large or small group they belong to, which will have repercussions on them (for example, a shift in public opinion can lead to a change of policy or a resignation). Bernal et al. [START_REF] Bernal | Cognitive Warfare: An Attack on Truth and Thought[END_REF] remind us as well that we should not forget "connectors, mavens, and salespeople", who "can be instrumental in the application of cognitive warfare". As du Cluzel emphasizes, "any user of modern information technologies is a potential target. It targets the whole of a nation's human capital" [START_REF] Cluzel | Cognitive Warfare[END_REF].

B. Actors

Like targets, actors conducting Cognitive Warfare can be varied. Du Cluzel [START_REF] Cluzel | Cognitive Warfare[END_REF] points out that cognitive warfare and the advances in human sciences could potentially confer significant power to anyone who takes the trouble to study them, so that even isolated individuals or small groups can represent a major threat to democracies or military operations.

V. COGNITIVE WARFARE AND AI

Artificial Intelligence (AI) is bringing new tools facilitating cognitive warfare, that can amplify it and make it even more accessible and low cost, especially when it comes to fake news and disinformation diffusion.

Du Cluzel reminds us that fake news campaigns combine real and distorted information (misinformation), exaggerated facts and fabricated news (disinformation) [START_REF] Cluzel | Cognitive Warfare[END_REF]. Among these facilitating tools, Mad Scientist Laboratory [START_REF]The Death of Authenticity : New Era Information Warfare[END_REF] cites deepfakes, videos generated by artificial intelligence that can show a person reciting a speech he or she never actually gave: their danger is obvious, given that any influential personality can be made to say anything. They can be rendered even more realistic by technologies that imitate the tone of a person's voice and their accent [START_REF] Chenouard | L'intelligence artificielle peut-elle piéger votre mère en imitant votre voix ?[END_REF]. The risk associated with AI-generated bodies and faces is less obvious, but just as real: it enables the creation of numerous fake accounts on social networks with people who do not exist, and makes it possible to humanize bots to give them more credibility. Generating the face of a person who does not exist is instantaneous, as can be seen at https://thispersondoesnotexist.com/. The last tool cited by Mad Scientist Laboratory is AI text generation, and this tool is brought up to date by the deployment of Chat-GPT in November 2022. This type of tool helps spread false information since it can write articles, posts and comments on social networks much faster and on a larger scale than a team of humans could. Thus, a single group could generate thousands or even millions of comments and posts on social networks, oriented to support or undermine a cause; and these actions would have "the potential to erode the relationship between governments and their citizens, provoking severe reactions throughout the world and leading people to question the very reality they believe" [START_REF]The Death of Authenticity : New Era Information Warfare[END_REF]. For example, the Twitter social media is host to many bots, which can "pursue malicious goals such as election interference and extreme propaganda" [START_REF] Feng | TwiBot-20: A Comprehensive Twitter Bot Detection Benchmark[END_REF].

An example of the possible application of destabilization campaigns via fake news on social networks is the influence of elections. Russia is particularly active in this field, and "the Kremlin considers disinformation and information operations to be the most effective means of affecting political outcomes in other countries", seizing on "existing domestic political, social, or ethnic divisions and instrumentalizes them to change how voters thinkand through that how they vote" [START_REF] Backes | Cognitive Warfare-The Russian Threat to Election Integrity in the Baltic States[END_REF].

VI. A FEW APPROACHES TO PROTECT OURSELVES

Some examples of individual solutions exist against specific cognitive warfare actions. For example, some countermeasures against public influence and fake news on social media were listed: public education, communication about fake news, automatic and human moderation, debunks, legal regulations [START_REF] Backes | Cognitive Warfare-The Russian Threat to Election Integrity in the Baltic States[END_REF][START_REF]Sensibilisation et résilience, les meilleures armes contre la guerre cognitive[END_REF][START_REF] Wunder | Chapitre 7 -Les narrations submergent le monde[END_REF], etc.

Another way for protection and prevention is to use cognitive warfare defensively. Cognitive warfare tools can be used to educate the populations through media and social media [START_REF] Battrawi | The Use of Social Networks as a Tool to Increase Interest in Science and Science Literacy : A Case Study of « Creative Minds[END_REF], enhance cognitive readiness [START_REF] Morrison | Cognitive Readiness[END_REF] or even augment soldiers' cognition [START_REF] Jin | Military Brain Science -How to influence future wars[END_REF]. We could also imagine decisionmaking tools taking into account cognitive biases and potential cognitive warfare aggressions.

The first step to organize an overall solution is to analyze the opponent and understand how they lead cognitive warfare strategies [START_REF] Orinx | La guerre cognitive -Pourquoi l'Occident pourrait perdre face à la Chine ?[END_REF]. This would enable those under attack to be able to detect cognitive warfare offensives early and lift the fog of war [START_REF] Weldon | Bytes not bombs : Student team works with NATO to define, track cognitive warfare attacks[END_REF]. Further research on this topic is necessary in order to build systematic solutions.

VII. LIMITATIONS AND CRITICISMS OF COGNITIVE WARFARE

Certain destabilizing or influencing actions can be detected and countered: for example, a company implementing a cognitive warfare strategy towards its competitors or customers could be denounced by a data leak or a whistleblower, and this strategy would then backfire by damaging its public image.

Cognitive warfare may also face ethical challenges: it involves influencing the thinking and decision-making of a person or group of people without their knowledge. In this respect, it can be compared to nudges, which encourage the user of a system or tool to behave optimally [START_REF] Loewenstein | Putting Nudges in Perspective[END_REF]: it is also a tool of influence, but it is its use that determines its ethical characteristics. Indeed, if the nudge consists in pushing a consumer to buy more or at a higher price, it will be judged more negatively; but if it pushes him or her to behave more respectfully (according to the applicable societal and cultural norms), as with the example of the fly-shaped sticker in the toilet to encourage "better aim", it will be judged more positively. The same applies to cognitive warfare, which must be used in a reasonable and justifiable way.

  1 https://www.nato.int/nato_static_fl2014/assets/pdf/2020/5/p df/2005-deepportal4-information-warfare.pdf

ACKNOWLEDGMENT

This research is financially supported by the French Ministry of Defence -Defense Innovation Agency (AID).