Damien Bregiroux
email: damien.bregiroux@upmc.fr

Gilles Wallez

Karin Popa

Structural study of polymorphism and thermal behavior of CaZr(PO 4 ) 2

Keywords: Crystal structure, thermal expansion, calcium zirconium phosphate Highlights: Room temperature structure CaZr

The crystal structure of CaZr(PO 4 ) 2 has been revised by ab initio Rietveld analysis of X-ray powder diffraction data. At room temperature, CaZr(PO 4 ) 2 crystallizes in the orthorhombic space group Pna2 1 (Z = 4). Differential thermal analysis suggests a reversible second order transition at 1000°C confirmed by high temperature XRD analysis that brings out the existence of a high temperature form, very similar to the room temperature one, but more symmetrical (Pnma, Z = 4). Analysis of the crystal parameters evolution during heating reveals that CaZr(PO 4 ) 2 exhibits a quite low thermal expansion coefficient of 6.11 10 -6 K -1 . This value stems from a combination of several mechanisms, including Coulombic repulsion and bridging oxygen rocking motion.

Introduction

M II M' IV (PO 4 ) 2 compounds (M II = Cd, Ca, Sr, Pb, Ba; M' IV = Ge, Ti, Mo, Sn, Hf, Zr, Pu, Np, U, Th) are subject of intensive research since they are proved to be interesting as ionic conductors, dielectrics, catalysts, ion exchangers, luminescent materials and UV-emitting Xray phosphors [1][2][3][4][5][6][7]. They also find applications in the nuclear cycle, either as host matrices for actinide radwastes or, more recently, as products of the reaction of the spent nuclear fuel with tributyl phosphate during the reprocessing [START_REF] Donald | Waste immobilization in glass and ceramic based hosts. Radioactive, toxic and hasardous wastes[END_REF][START_REF] Overstreet | [END_REF][10][11][START_REF] Boatner | Scientific Basis for Nuclear Waste Management[END_REF][START_REF] Boatner | Radioactive waste forms for the future[END_REF][START_REF] Meldrum | [END_REF][15][16][17][18][19][START_REF] Murray | chap. 23: Radioactive Waste Disposal[END_REF][21][22].

M II M' IV (PO 4 ) 2 can be classified according to their crystal structure. One can distinguish two main groups, depending on the cations size:

-

The cheralite-type compounds, analogues of monazite CePO 4 , where trivalent Ce is replaced randomly by M and M'. The archetype, CaTh(PO 4 ) 2 , also named brabantite, was described by Rose et al. in 1980 [23]. Cheralite compounds crystallize in the monoclinic P2 1 /n space group (Z = 4) [24]. This structure consists of chains made up by alternating edges-linked irregular ninefold-coordinated M/M' cations and distorted tetrahedral phosphate groups. This structural form can be found for high radius M' cations (i.e. actinides).

-For smaller M' IV cations, like those of the p-and d-blocks, most of the M II M' IV (PO 4 ) 2 compounds crystallize in the yavapaiite-type structure (isotype of KFe(SO 4 ) 2 ), which consists of layers running parallel to the (001) plane built up of corner-connected MO 6 octahedra and PO 4 tetrahedra. The M II cation takes place into the interlayer, in a ten-fold oxygen environment [25]. Several derivatives of this archetype, or "distorted yavapaiites" have been observed, according the M II and M' IV cation size [26][27][28].

Nevertheless, some compositions exhibit a clearly different crystal structure, like CaZr(PO 4 ) 2 , PbSn(PO 4 ) 2 and SrNp(PO 4 ) 2 [1,29,30]. The structure of CaZr(PO 4 ) 2 was determined for the first time by Fukuda et al. from powder diffraction data [31]. The structure was found to be orthorhombic (space group P2 1 2 1 2 1 , Z = 4). Ca and Zr cations are both sevenfold coordinated but are located in different sites, unlike in the cheralite structure. On the other hand, the structure is not a layered one, as observed for yavapaiite compounds. Within the M II M' IV (PO 4 ) 2 family, CaZr(PO 4 ) 2 is the compound in which the best optical properties were observed [32]. For such applications, a perfect description of the crystal structure, including a very accurate knowledge of cations environment and atomic distances is required, especially for crystal field calculations. As described in the following sections, our XRD observations suggest that the crystal structure proposed by Fukuda et al. is not the most relevant one. In this paper, we propose a revision of the crystal structure of CaZr(PO 4 ) 2 . A low and a high temperature forms are proposed. The mechanisms of the phase transition and the thermal expansion of the low temperature form are also described from the lattice thermal evolution during heating.

Experimental

Synthesis and characterization

CaZr(PO 4 ) to 1200°C for 10h in a platinum crucible [33]. The thermal cycle was performed twice in order to avoid the presence of unreacted phases. the patterns were recorded at high temperature in the same range but over 1h. The Rietveld analyses were carried out with the Fullprof suite [START_REF] Rodriguez-Carvajal | 2k : Rietveld, profile matching and integrated intensity refinement of X-ray and neutron data, V 1.9c[END_REF]. Structures were drawn using the VESTA software [START_REF] Momma | [END_REF].

Structure resolution

Except for minor reflections ascribed to spurious NZP-like Ca 0.5 Zr 2 (PO 4 ) 3 (< 5 %), the powder XRD pattern of the sample appears very similar to that reported by the ICDD file 73-2816 calculated from Fukuda's structural data. Nevertheless, while the P2 1 2 1 2 1 space group proposed by these authors supposes that systematic extinction only affects the h00, 0k0 and 00l reflections with odd Miller indexes, clear hints of the presence of two glide mirrors are observed: a c one perpendicular to Fukuda's cell edge a and a n one perpendicular to the c edge. For instance, the relevant reflections (0kl, k = 2n+1 and hk0, h+k = 2n+1, barring overlapped ones) are extremely weak, respectively less than 0.1 and 0.6 % in intensity in the ICDD file. From our own XRD pattern, those peaks (25 in the 0 < 2θ < 80° range) were all found to be non-observable. Likewise, the Rietveld analysis performed in Le Bail's (profile matching) mode with the symmorphic Pmmm space group resulted in a mean intensity of less than 0.1 % for all of them. In Fukuda's axes setting, these conditions account either for acentric space group Pc2 1 n (Pna2 1 in standard setting) or for centric Pcmn (Pnma). A test of second harmonic generation with an incident YAG:Nd laser beam at 1060 nm was negative, thus no conclusion could be achieved on this basis.

The three most probable space groups (Pna2 1 , Pnma, P2 1 2 1 2 1 ) were considered for the refinement of the crystal structure at room temperature, termed α-CaZr(PO 4 ) 2 . Anisotropic thermal displacements were refined for the heavy Ca and Zr atoms, but all the oxygen atoms of a same PO 4 tetrahedron were given the same isotropic factor. The anisotropic Lorentzian peaks broadening due to crystallites size effects was modeled using the spherical harmonic

M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 6
profile function. Spurious Ca 0.5 Zr 2 (PO 4 ) 3 was treated as a secondary phase in the Rietveld analysis. For all the models, the refinements performed with "free" oxygen coordinates resulted in poorly realistic P-O distances (1.46-1.61 Å), like in Fukuda's reported data (1.46-1.59 Å). Considering the covalency of the P-O bond that makes its length highly predictable in a monophosphate (1.54 Å), soft constraints were applied on these distances.

Results and discussion

3.1 Crystal structure of the room-temperature form α-CaZr(PO 4 ) 2

The following discussion deals mainly with the determination of the space group of the roomtemperature form. This point is pretty delicate, on the one hand because the two hemihedral groups (Pna2 1 and P2 1 2 1 2 1 ) are subgroups of the holohedral one (Pnma), on the other hand, because the three structural models only show minor differences after refinement. As shown by Fukuda, the edge-connected CaO 7 and ZrO 7 polyhedra form linear chains. The P1O 4 tetrahedron shares two opposite edges with CaO 7 polyhedra and the P2O 4 tetrahedra shares an edge with a ZrO 7 . Setting the floating z Zr coordinate in the polar Pna2 1 space group at the same value as in the P2 1 2 1 2 1 model, the atomic positions appear only faintly distant between the two hemihedral models (Zr: 0.02 Å; Ca: 0.03 Å; P1: 0.07 Å; P2: 0.01 Å; distances between oxygen positions are not significant because of the lower weight of these atoms and the application of soft constraints). The reliability factors are not significantly different (R Bragg = 0.0308 for Pna2 1 , 0.0324 for P2 1 2 1 2 1 ), but the systematic absences (see Experimental)

account for the Pna2 1 solution rather than for the P2 1 2 1 2 1 one, defended by Fukuda et al. 1, atomic coordinates in Table 2 and bond lengths in Table 3. The crystal structure of α-CaZr(PO 4 ) 2 is drawn in Fig. 1. The resulting final Rietveld plots are shown in Fig. 2.

The choice between the

Phase transition and high-temperature form β-CaZr(PO 4 ) 2

CaZr(PO 4 ) 2 appears to be stable up to 1200 °C and melts between 1300°C and 1400°C. No peak can be observed by conventional differential thermal analysis between 1000°C and 1200°C, suggesting that the α to β transition could be a reversible second order phase transition. Because no significant variation was observed in the diffraction pattern above this temperature, we refined the structure again in the Pna2 1 space group (Tables 12). This time, the cations positions turned out to be so faintly shifted (< 0.004 Å, lower than the estimated standard deviations) that they could be considered as located right on the m-mirror of the Pnma setting. This high-temperature form will be termed β-CaZr(PO 4 ) 2 in the following. As shown by Table 3, its crystal structure is very similar to that of α-CaZr(PO 4 ) 2 . Therefore, the

M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 8
α-β transition appears as a typical second-order phenomenon in agreement with its thermal signature.

Thermal expansion

The relative variation with temperature of the cell parameters and Ca-P and Zr-P distances of α-CaZr(PO 4 ) 2 is plotted on Fig. 3.

Thermal expansion was calculated according to the following linear equation:

(i)
Values are reported on Table 4. The mean relative linear thermal expansion (l) was determined by dividing the volume expansion by 3.

The resulting relative linear thermal expansion appears to be quite low compared to that of the most common oxides (6.11 vs. 7-8, 8-12, 9-12 10 -6 .K -1 for alumina, zirconia, magnesia, respectively). Results also show that thermal expansion is rather anisotropic (∆α = 6.7 10 -6 .K - 1 ). α-CaZr(PO 4 ) 2 mostly expands along the a-axis. b-and c-axes exhibit similar thermal expansion coefficients. Comparison of thermal behavior of CaZr(PO 4 ) 2 with that of some other phosphates (Table 5) reveals that this compound exhibits a interesting combination between low value and moderate anisotropy of thermal expansion. Associated with a good thermal stability (up to 1200 °C), CaZr(PO 4 ) 2 appears to be an interesting material for applications that require a good dimensional stability with temperature.

The thermal expansion behavior of CaZr(PO 4 ) 2 can be explained regarding the polyhedral connections (see Fig. 1). In this structure, different thermal expansion mechanisms can be observed, all described by Sleight on other materials [42]. Along the a axis, strong Coulombic repulsion occurs between edge-sharing Zr 4+ and P 5+ cations since the Zr-P2(a) distance are short and oxygen atoms screening effect is low, resulting in a strong thermal expansion of the

α x = dx x 0 1 dT M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 9
Zr-P2(a) distance (Figs. 1 and 3, Table 4). On the opposite, when polyhedra are cornerconnected, the oxygen shared by the ZrO (Fig. 4). Along b, the structure presents several connections by corners, especially between CaO 7 and PO 4 . This results in a very low thermal expansion along this direction by oxygen rocking effect.

Conclusion

A revised structure of CaZr(PO 4 ) 2 has been proposed. For the first time, the existence of a high temperature form of this compound has been highlighted. These structures are strongly different to that of most of the other compounds of the M II M' IV (PO 4 ) 2 family (yavapaiite and cheralite). Analysis of the crystal parameters evolution during heating reveals that CaZr(PO 4 ) 2 exhibits a quite low thermal expansion coefficient of 6.11 10 -6 K -1 , suggesting that this compounds could find applications when dimensional stability is required. Table 1 Main acquisition, refinement and lattice data for αand β-CaZr(PO 4 ) 2 .

Table 2

Atomic positions and thermal factors for αand β-CaZr(PO 4 ) 2 .

Table 3

Bond lengths in αand β-CaZr(PO 4 ) 2 (in Å).

Table 4

Thermal expansion in α-CaZr(PO 4 ) 2 .

Table 5

Comparison of thermal expansion of CaZr(PO 4 ) 2 with some other phosphates

Figures caption

Fig.

S = Npar=

The following ALERTS were generated. Each ALERT has the format test-name_ALERT_alert-type_alert-level. Click on the hyperlinks for more details of the test. It is advisable to attempt to resolve as many as possible of the alerts in all categories. Often the minor alerts point to easily fixed oversights, errors and omissions in your CIF or refinement strategy, so attention to these fine details can be worthwhile. In order to resolve some of the more serious problems it may be necessary to carry out additional measurements or structure refinements. However, the purpose of your study may justify the reported deviations and the more serious of these should normally be commented upon in the discussion or experimental section of a paper or in the "special_details" fields of the CIF. checkCIF was carefully designed to identify outliers and unusual parameters, but every test has its limitations and alerts that are not important in a particular case may appear. Conversely, the absence of alerts does not guarantee there are no aspects of the results needing attention. It is up to the individual to critically assess their own results and, if necessary, seek expert advice.

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S = Npar=

The following ALERTS were generated. Each ALERT has the format test-name_ALERT_alert-type_alert-level. Click on the hyperlinks for more details of the test. It is advisable to attempt to resolve as many as possible of the alerts in all categories. Often the minor alerts point to easily fixed oversights, errors and omissions in your CIF or refinement strategy, so attention to these fine details can be worthwhile. In order to resolve some of the more serious problems it may be necessary to carry out additional measurements or structure refinements. However, the purpose of your study may justify the reported deviations and the more serious of these should normally be commented upon in the discussion or experimental section of a paper or in the "special_details" fields of the CIF. checkCIF was carefully designed to identify outliers and unusual parameters, but every test has its limitations and alerts that are not important in a particular case may appear. Conversely, the absence of alerts does not guarantee there are no aspects of the results needing attention. It is up to the individual to critically assess their own results and, if necessary, seek expert advice.

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PLATON version of

  Powder purity was checked by X-Ray powder diffraction. Thermal stability and possible phase transition were studied under air using a Setaram DTA-TG instrument. XRPD was performed on a Panalytical X'Pert Pro diffractometer with an incident-beam Ge monochromator, at U = 45 kV and I = 40 mA. The apparatus was equipped with an Anton Paar HTK 1200 N furnace for high temperature diffraction. The patterns for structural analysis were recorded over 8h in the 8 ≤ 2θ ≤ 140° range (130° at high temperature), step 0.013°. For the measurement of the thermal expansion,

Pna2 1 and

 1 Pnma space groups (with b-c axes permutation) can hardly be made on the sole basis of the reliability factors (R Bragg = 0.0308 and 0.0387 respectively) because of the lesser number of intensity-dependent parameters in the latter form (52 and 35 respectively). Indeed, the decision hangs on the existence of the m mirror. In the holohedral the cations and half of the oxygen anions are supposed to occupy this special (1/4 or 3/4) position. Once again, the variations of the cations positions are faint (Zr: 0.00 Å; Ca: 0.01 Å; P1: 0.06 Å; P2: 0.04 Å), but in this case the shifts of the oxygen anions involved in edgesharing between Ca and P1 on the one hand (0.21 and 0.15 Å) and Zr and P2 on the other hand (0.27 and 0.25 Å) are significant enough to be taken into account. Actually, these shared edges, ideally parallel to the b-axis in the Pnma cell, exhibit a clear zig-zag geometry in the Pna2 1 one as a result of the distortion of the PO 4 tetrahedra (Fig.1. lower view). The same distortion is observed in Fukuda's structure. Besides, the O23-P2-O24 (96.5(8)°) angle corresponding to the shared edge between Zr and P2 is low, because of the Coulombic intercations repulsion. As will be shown in the following, these structural features play a role in the peculiar thermal expansion of the compound. Main acquisition and refinement parameters are reported in Table

  7 and P2(b)O 4 polyhedra oscillates within an ellipsoid oriented roughly perpendicular to the Zr-O-P axis. Since the Zr-O and P-O bonds are strong enough to present negligible thermal expansion, the transverse motion of oxygen pulls the cations closer together. This so-called "rocking effect" can explain the quite negligible thermal expansion of the Zr-P2(b) distance. CaO 7 polyhedra are only linked by edge to the two PO 4 tetrahedra. The Coulombic repulsion is weaker than in the case of Zr 4+because of the lower valency and higher ionic radius of Ca 2+ leading to a lower thermal expansion. Note that the shortest Ca-P distance (i.e. Ca-P1(a)) shows the highest thermal expansion coefficient. The combination of these phenomena leads to a moderate thermal expansion along the a axis. The Coulombic repulsion between cations along the a axis has a consequence on the thermal expansion along c. The oxygen atoms involved in the edges perpendicular to the M-P bonds are getting closer, leading to a low thermal expansion along c

13 [

 13 40] L. Perrière, D. Bregiroux, B. Naitali, F. Audubert, E. Champion, D.S. Smith, D. Bernache-Assollant, J.Eur. Ceram. Soc. 27 (2007) 3207.[41] G. Wallez, D. Bregiroux, M. Quarton, J. Solid State Chem. 181 (2008) 1413.[42] A.W. Sleight, Inorg. Chem. 37 (1998) 2854.

1 . 2 Fig. 2 .Fig. 3 .Fig. 4 .

 12234 Fig. 1. Views of the structure of α-CaZr(PO 4 ) 2

χ 2 = 8 . 2 R 3 a 3 Formula

 28233 = 6.3125(2) Å (= a α ) b = 6.7512(2) Å (= c α ) c = 14.5537(4) Å (= b α ) V = 620.23(6) Å

20 Fig. 1 . 21 Fig. 2 . 2 Fig. 3 .Fig. 4 .

 201212234 Fig. 1. Views of the structure of α-CaZr(PO 4 ) 2

  (Pseudo) Centre of Symmetry ..... 100 %Fit Alert level C PLAT163_ALERT_4_C Missing or Zero su (esd) on z-coordinate for ... ZR PLAT213_ALERT_2_C Atom Ca has ADP max/min Ratio ..... 3.9 prolat Alert level G PLAT004_ALERT_5_G Polymeric Structure Found with Dimension ....... 3 Info PLAT112_ALERT_2_G ADDSYM Detects Additional (Pseudo) Symm. Elem... m Check PLAT113_ALERT_2_G ADDSYM Suggests Possible Pseudo/New Space group. Pnma Check PLAT143_ALERT_4_G su on c -Axis Small or Missing ................ 0.00001 Ang. PLAT794_ALERT_5_G Tentative Bond Valency for Zr (IV) ..... 4.33 Note PLAT860_ALERT_3_G Number of Least-Squares Restraints ............. 8 Note PLAT982_ALERT_1_G The Ca-f'= 0.341 Deviates from the IT-value 0.364 Check PLAT982_ALERT_1_G The O-f'= 0.047 Deviates from the IT-value 0.049 Check PLAT982_ALERT_1_G The P-f'= 0.283 Deviates from the IT-value 0.296 Check PLAT982_ALERT_1_G The Zr-f'= -0.314 Deviates from the IT-value -0.186 Check 0 ALERT level A = Most likely a serious problem -resolve or explain 1 ALERT level B = A potentially serious problem, consider carefully 2 ALERT level C = Check. Ensure it is not caused by an omission or oversight 10 ALERT level G = General information/check it is not something unexpected 4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 4 ALERT type 2 Indicator that the structure model may be wrong or deficient 1 ALERT type 3 Indicator that the structure quality may be low 2 ALERT type 4 Improvement, methodology, query or suggestion 2 ALERT type 5 Informative message, check M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT

  Found with Dimension ....... 3 Info PLAT794_ALERT_5_G Tentative Bond Valency for Zr (IV) ..... 4.22 Note PLAT860_ALERT_3_G Number of Least-Squares Restraints ............. 6 Note PLAT982_ALERT_1_G The Ca-f'= 0.341 Deviates from the IT-value 0.364 Check PLAT982_ALERT_1_G The O-f'= 0.047 Deviates from the IT-value 0.049 Check PLAT982_ALERT_1_G The P-f'= 0.283 Deviates from the IT-value 0.296 Check PLAT982_ALERT_1_G The Zr-f'= -0.314 Deviates from the IT-value -0.186 Check 0 ALERT level A = Most likely a serious problem -resolve or explain 0 ALERT level B = A potentially serious problem, consider carefully 0 ALERT level C = Check. Ensure it is not caused by an omission or oversight 7 ALERT level G = General information/check it is not something unexpected 4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 0 ALERT type 2 Indicator that the structure model may be wrong or deficient 1 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 2 ALERT type 5 Informative message, check

Table 1

 1 Main acquisition, refinement and lattice data for αand β-CaZr(PO 4 ) 2 .

	Apparatus	Panalytical X'Pert Pro
	Anode, monochromator	CuKα1 (40 kV, 45 mA), Ge (111)
	Form	α-CaZr(PO 4 ) 2	β-CaZr(PO 4 ) 2
	Temperature	20 °C	1200 °C
	Scan range, step, time	8.00 ≤ 2θ ≤ 140.00°, 0.013°, 8 h	8.00 ≤ 2θ ≤ 130.00°, 0.013°, 8 h
	Measured reflections	626	576
	Intensity / profile parameters	52 / 14	35 / 14
	Reliability factors	R P = 0.012
		R WP = 0.018
		R Bragg = 0.035

Table 2

 2 Atomic positions and thermal factors for αand β-CaZr(PO 4 ) 2 .

		α-CaZr(PO 4 ) 2			β-CaZr(PO 4 ) 2
	Atom	x	y	z	B* (Å 2 )	x	y	z	B* (Å 2 )
	Ca	0.5492(2) 0.3518(1) 0.256(2)	1.74(4)	0.5466(5) 1/4	0.3534(3) 3.82(9)
	Zr	0.8239(1) 0.3907(1) 0.75	1.61(1)	0.8340(2) 3/4	0.3896(1) 2.07(3)
	P1	0.5459(2) 0.1151(1) 0.2435(4) 2.05(6)	0.5385(5) 1/4	0.1146(3) 2.26(8)
	O11	0.6996(6) 0.0306(2) 0.244(4)	1.24(6)	0.687(1)	1/4	0.0292(5) 3.4(1)
	O12	0.6784(7) 0.2051(2) 0.238(3)	"	0.681(1)	1/4	0.2001(5) "
	O13** 0.396(2)	0.1194(7) 0.425(2)	"	0.3901(8) 0.4308(7) 0.1119(5) "
	O14** 0.389(2)	0.1043(6) 0.067(2)	"
	P2	0.1313(2) 0.8533(1) 0.2480(4) 2.16(6)	0.1281(5) 1/4	0.8520(2) 2.5(1)
	O21	0.1728(7) 0.7493(2) 0.268(2)	1.43(7)	0.169(1)	1/4	0.7482(4) 3.5(1)
	O22	0.3425(5) 0.9078(3) 0.259(3)	"	0.339(1)	1/4	0.9037(6) "
	O23** -0.014(2)	0.8730(6) 0.428(1)	"	-0.146(8)	0.4196(8) 0.8815(5) "
	O24** -0.016(2)	0.8970(5) 0.091(1)	"
	see supplementary material
	** atoms O13 and O14 of α-CaZr(PO 4 ) 2 merge into a single atom in the β-form, idem for
	O23 and O24

* given values are B iso for oxygen and phosphorus; B eq for calcium and zirconium. For B aniso ,

Table 3

 3 Bond lengths in αand β-CaZr(PO 4 ) 2 (in Å).

	Bond	α-CaZr(PO 4 ) 2	β-CaZr(PO 4 ) 2	Bond	α-CaZr(PO 4 ) 2	β-CaZr(PO 4 ) 2
	Ca-O11	2.766(4)	2.842(9)	Zr-O22	2.095(3)	2.073(7)
	Ca-O12	2.275(4)	2.387(9)	Zr-O23	2.287(9)	2.322(6)
	Ca-O12	2.457(5)	2.435(9)	Zr-O24	2.20(1)	"
	Ca-O13	2.48(1)	2.539(6)	P1-O11	1.553(4)	1.556(9)
	Ca-O14	2.55(1)	"	P1-O12	1.545(4)	1.536(9)
	Ca-O23	2.23(1)	2.276(6)	P1-O13	1.54(1)	1.539(5)
	Ca-O24	2.35(1)	"	P1-O14	1.54(1)	"
	Zr-O11	2.033(3)	2.035(7)	P2-O21	1.533(3)	1.532(7)
	Zr-O13	2.23(1)	2.184(5)	P2-O22	1.536(4)	1.530(8)
	Zr-O14	2.17(1)	"	P2-O23	1.537(9)	1.519(6)
	Zr-O21	2.032(3)	2.006(6)	P2-O24	1.538(9)	"
	Bond valence sums (v.u.) from [36]: Ca : 2.12 (α), 1.99 (β); Zr: 4.06 (α), 4.06 (β); for O-P-O
	angles, see supplementary material

  You have not supplied any structure factors. As a result the full set of tests cannot be run.THIS REPORT IS FOR GUIDANCE ONLY. IF USED AS PART OF A REVIEW PROCEDURE FOR PUBLICATION, IT SHOULD NOT REPLACE THE EXPERTISE OF AN EXPERIENCED CRYSTALLOGRAPHIC REFEREE.

	No syntax errors found.	CIF dictionary	Interpreting this report
	Datablock: I
	Bond precision: P-O = 0.0074 A	Wavelength=1.54180
		a=6.2330(1)	b=14.4852(4)	c=6.72130(1)
		alpha=90	beta=90	gamma=90
	Temperature:	293 K
		Calculated	Reported
	Volume	606.841(19)	606.841(19)
	Space group	P n a 21	P n a 21
	Hall group	P 2c -2n	P 2c -2n
	Moiety formula O8 P2 Zr, Ca	O8 P2 Zr, Ca
	Sum formula	Ca O8 P2 Zr	Ca1 O8 P2 Zr
	Mr	321.24	321.24
	Dx,g cm-3	3.516	3.516
	Z	4	4
	Mu (mm-1)	27.547	27.547
	F000	616.0	616.0
	F000'	620.78
	h,k,lmax	7,17,8	7,17,8
	Nref	1147[ 626]	626
	Tmin,Tmax
	Tmin'
	Correction method= Not given
	Data completeness= 1.00/0.55	Theta(max)= 69.998
	R(reflections)=		wR2(reflections)=

  You have not supplied any structure factors. As a result the full set of tests cannot be run.THIS REPORT IS FOR GUIDANCE ONLY. IF USED AS PART OF A REVIEW PROCEDURE FOR PUBLICATION, IT SHOULD NOT REPLACE THE EXPERTISE OF AN EXPERIENCED CRYSTALLOGRAPHIC REFEREE.

	No syntax errors found.	CIF dictionary	Interpreting this report
	Datablock: I
	Bond precision: P-O = 0.0070 A	Wavelength=1.54180
	Cell:	a=6.3125(2)	b=6.7512(2)	c=14.5537(4)
		alpha=90	beta=90	gamma=90
	Temperature:	?
		Calculated	Reported
	Volume	620.23(3)	620.23(3)
	Space group	P n m a	P n m a
	Hall group	-P 2ac 2n	-P 2ac 2n
	Moiety formula O8 P2 Zr, Ca	O8 P2 Zr, Ca
	Sum formula	Ca O8 P2 Zr	Ca1 O8 P2 Zr
	Mr	321.24	321.24
	Dx,g cm-3	3.440	3.440
	Z	4	4
	Mu (mm-1)	26.953	26.953
	F000	616.0	616.0
	F000'	620.78
	h,k,lmax	7,7,17	7,7,17
	Nref	576	576
	Tmin,Tmax
	Tmin'
	Correction method= Not given
	Data completeness= 1.000	Theta(max)= 64.996
	R(reflections)=		wR2(reflections)=

Datablock I -ellipsoid plot

Acknowledgements

The authors are grateful to Guillaume Le for his enthusiastic participation in the synthesis experimentations. K.P. acknowledges La Mairie de Paris for the ''Research in Paris'' 2010-2011 fellowship.

Appendix A. Supplementary data

Supplementary data related to this article:

-CIF and CheckCIF files of α-CaZr(PO 4 ) 2 -CIF and CheckCIF files of β-CaZr(PO 4 ) 2 -CSD number of α-CaZr(PO 4 ) 2 : 428800 -CSD number of β-CaZr(PO 4 ) 2 : 428801 -Peak list file of α-CaZr(PO 4 ) 2

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

The following list summarizes all the diffraction peaks of CaZr(PO 4 ) 2 up to 80 °, measured by Fullprof assuming Fukuda's P2 1 2 1 2 1 space group. Maximum intensity is 26204 counts (002). Reflections in red, all below detection threshold, account for 0kl, k+l=2n+1 or h0l, h=2n+1 extinctions. Strongly overlapped peaks, yellow highlighted, should not be taken into account.


Mukesh Barange

Pierre De Loor

Vincent Louis

Ronan Querrec

Julien Soler

Thanh-Hai Trinh

Eric Maisel

Pierre Chevaillier

Éric Maisel

Get Involved in an Interactive Virtual Tour of Brest Harbour: Follow the Guide and Participate

Keywords: Semantic Modelling, Dialogue Management, Cultural Heritage

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

Introduction

This study takes place in a general perspective to make the development of richcontent virtual reality (VR) applications more rational, and we address more specifically issues related to the design of conversational agents. As proposed by many authors [START_REF] Bogdanovych | Virtual agents and 3D virtual worlds for preserving and simulating cultures[END_REF][START_REF] Latoschik | Knowledge in the loop: Semantics representation for multimodal simulative environments[END_REF], one promising approach is to center the architecture on an abstract semantic layer. The main motivations are as follows: [START_REF] Bogdanovych | Virtual agents and 3D virtual worlds for preserving and simulating cultures[END_REF] The design of the VE and that of agents, should be independent. That means that the communicative capabilities of an agent, such as a guide in an interactive virtual tour (or an educational agent), should be independent to the environment it is supposed to act in. [START_REF] Chevaillier | Semantic modelling of virtual environments using Mascaret[END_REF] The semantic model of the environment, both physical and social, can be used as a source of knowledge for agents to make decisions and to support dialogues [START_REF] Ijaz | Enhancing the believability of embodied conversational agents through environment-, self-and interaction-awareness[END_REF].

This article presents how these principles have been successfully used to develop Brest'Coz, an interactive virtual tour dedicated to the learning of techniques used for shipbuilding in France in early 18 th century. The learning is based on a gaming approach. Users receive directions from a virtual guide and have to communicate with non-playing characters to get information and participate to some collaborative activities.

Providing NL dialogue capabilities to conversational agents using semantic modelling, rises many scientific issues. One of the issues is what the agent can say? In Brest'Coz, agents should be able to describe the structure of the environment, i.e., properties of objects, their behaviors and their spatial relationships. Moreover, the visitor may ask agents to describe their own activities or the activities of other agents. Also, agents can be involved in some collaborative activities. Thus, while communicating with other agents and visitors, agents should take into account the social norms, including their roles and organisational rules.

Another issue is how does the agent generate the NL dialogue structure? In many applications [START_REF] Kopp | A conversational agent as museum guide design and evaluation of a real-world application[END_REF][START_REF] Traum | Talking to virtual humans: Dialogue models and methodologies for embodied conversational agents[END_REF], the dialogue management is based on dialogue acts. However, this approach is highly dependent on contents of the application, and requires extra efforts for the annotation of dialogue acts [START_REF] Gandhe | Creating spoken dialogue characters from corpora without annotations[END_REF]. In contrast, the rule-based dialogue management approach, like in [START_REF] Wallace | Be Your Own Botmaster[END_REF] operates on a hard-coded set of rules, using pattern matching and substitution, to generate the response. The fundamental bottleneck of this approach is that the knowledge is explicitly presented in the form of hard-coded values in dialogue rules. All these approaches do not take into account the semantics of the VE and therefore, are not suitable for the modelling of dialogue behaviors, independent from the application.

To develop Brest'Coz, we used Mascaret framework in which we embedded NabuTalk, a commercial rule-based dialogue engine. We defined the generic queries agents can perform on the semantic model in order to interpret, and to generate utterances. Because these NLU/NLG rules are defined at an abstract level (meta-model) they are independent of the content of the application and have clear semantics.

In Sect. 2, we present the Brest'Coz application. Sect. 3 gives main elements of the semantic layer used as linguistic resources for conversational agents. Sect. 4 illustrates how these semantic information are used in NLU/NLG rules.

The Brest'Coz Application

Brest'Coz is an application for interactively visiting the harbour of Brest, France. In early 18 th century, it was an important site for the French navy where various specific shipbuilding techniques were used. It is a task-oriented tour. At the beginning, a virtual guide gives some directions about the goal assigned to the user, which is represented by a human-like avatar. The user has to take part to the transshipment of a boat, and can learn how middle-age wheeled cranes were operated for that. To get involved in this collaborative activity (supported by autonomous agents), the user has to communicate with different characters and to interact with the environment using VR peripherals.

The 3D modelling encompassed the docks, some noticeable buildings and various shipbuilding sites (Fig. 1). We simulated different shipbuilding activities (e.g., shipwrighting, transshipment), performed by different categories of workers (autonomous virtual agents).

Semantic Modelling Using Mascaret

Mascaret, which stands for MultiAgent System for Collaborative, Adaptive & Realistic Environments for Training, is a generic framework that provides necessary abstractions for both content-and system-oriented semantic modelling of VR applications [START_REF] Chevaillier | Semantic modelling of virtual environments using Mascaret[END_REF]. It provides a modelling language expressive enough for subject matter experts to formulate their knowledge about a specific domain (content-oriented approach). The language has clear operational semantics for models to be interpreted by the execution platform (system-oriented approach). Mascaret is based on two complementary metamodels, Veha and Have. These metamodels have been defined as extensions of those of Uml, the Unified Modelling Language. Uml is used here as a content description language and not as an abstraction for object-oriented programming.

Modelling the VE Using Veha. This metamodel is dedicated to the modelling of entities compounding the VE, their categories, internal structures, relationships, and behaviors. Fig. 2 illustrates how cranes have been modelled in Brest'Coz (based on Worldnet3 ). A crane structurally contains one hook that can be logically linked to one container. Fig. 2 shows the partial model of the behavior of the crane, which is supported in Mascaret by state machines. Here, the crane can grasp an object if it is stopped and when the condition canBeLoaded is satisfied. Such logical constraints are expressed using vrX-Ocl [START_REF] Trinh | Ensuring semantic spatial constraints in virtual environments using UML/OCL[END_REF].

Modelling Human Activities into the VE using Have. This metamodel supports the modelling of collaborative activities of agents in the environment, which is supposed to be described using Veha. Agents are here the autonomous characters for whom the activity is simulated and the users. As for existing multiagent models, the organisational metamodel is based on the concept of agent, role and organisational entity. It allows to define social rules that govern agents' behavior within an organisation.

Fig. 3 (left) illustrates how the organisational structure used for the boat transshipment can be instantiated: agents have been associated to roles (e.g., crane operator) and the available resources been defined. Have supports the modelling of the collaborative activity (i.e., actions to be performed by an organisational entity) using activity charts similar to those of Uml. Each action is defined by its feasibility conditions (precondition), rational effect (post-condition), and action to be done (do: statement). Fig. 3 (right) shows how the user (visitor) can collaborate with other agents to manipulating the crane.

The way the description of the activity is interpreted by agents is defined using behave, which is a generic model of an agent architecture, independent to any domain specific application. The dependency between agents and the environment takes place at the meta level, i.e., the actual model of the environment and of the activities that agents are supposed to perform, are viewed as data available for agents to make decisions and to execute their behaviors.

Inform Ask Permission

Fig. 3. Modelling of the transshipment activity using Have (partial).

Conceptualisation of Dialogues using Semantic Modelling

In this section, we show how semantic modelling presented previously has been used to process NL utterances using generic parameterized rules, that preserve the independence of the communicative behavior of agents from the VE. We also illustrate how it has been implemented using Mascaret and NabuTalk. NabuTalk is a NL dialogue engine that relies on the concepts of Artimis [START_REF] Sadek | Artimis rational dialogue agent technology: An overview[END_REF] and the JADE Semantics Add-on [START_REF] Louis | Jade semantics framework[END_REF]. It is based on a high-level agent programming language, named Nabu, that includes appropriate mechanisms to handle NLU/NLG concepts, such as utterance templates, dialogue interpretation and generation rules. It provides a rule-based mechanism to deal with users' utterances. The pattern-matching algorithm relies not only on the matching of usual regular expressions but also on the unification of feature structures, based on the theory of functional unification grammars [START_REF] Kay | Functional unification grammar: A formalism for machine translation[END_REF].

Both users and agents can initiate the dialogue. In Mascaret, each agent is associated with a thread of the NabuTalk engine. For each communicative function, NabuTalk selects the best appropriate pattern for the NLU rule. The patterns may contain parameters, which can be substituted with semantic information retrieved from Mascaret models. The properties of model elements depend on their type, which are defined at the meta level. Because the NLU/NLG rules rely only on meta level concepts, they are independent from specific contents of the application.

All the agents share a common set of dialogue rules. The individuality of agent's dialogues comes from the role associated to the agent. Furthermore, agents may use additional NLU/NLG rules to support application-specific dialogues.

In the transshipment scenario (Fig. 3), when the user (playing the role of worker) accesses the crane, the operator agent, named Pierre, initiates the following dialogues with the user: When the user accesses the crane, the operator executes the communicative action inform(require(Ask Permission)). The precondition of this action is to verify the physical constraint Crane.state=Available. This vrX-Ocl constraint is evaluated according to the state machine of the Crane provided by Veha (Fig. 2). If it fails, the operator generates the utterance 1.1.

The natural language rule (nlu-rule) in NabuTalk can use predicates implemented as Mascaret connectors to access meta level information. To go further in details, utterance 3.1 is interpreted as a Query-ref on the capabilities of a class (Crane is a class name). The agent looks in the Veha model and retrieves the names of all the operations of the class. The Nabu code to handle this looks like: The result of this method is converted into a NabuTalk object that can be post-processed by the NabuTalk engine to generate the utterance 3.2.

Mascaret agents are able to talk about spatial relationships (topological and directional relationships) between entities using vrX-Ocl. Dialogues may also refer to the activity of agents, based on the information from activity charts. Thus, the agent can reply to user's questions like What can I do now? (the name of the next action belonging to the role of the locutor), Why should I do it? (the description associated to the post-condition of the referred action) or How can I do it? (the description of the do:statement associated to the action), etc.

Thus, using meta level information, agents can talk about the entities of the VE, their behaviors, their social organizations, and collaborative activities. This approach is particularly suitable for complex VEs where many human activities have to be simulated. In such a context, using specific NLU/NLG rules would make the drawing of the scenario far too complex. Our approach does not cover all types of dialogues. It is more suitable to handle inquiry, requestresponse or question-answering dialogues. A trade-off has to be reached between the genericity of dialogue rules and the ability to deal with specific application conversational styles, like in [START_REF] Jan | A virtual tour guide for virtual worlds[END_REF] which uses learning mechanisms and is based on annotated corpus.

Conclusion

In this article, we have presented the benefits of semantic modelling for dialogue modelling. Because our approach is anchored to a meta-modelling framework, it ensures the consistency between the model of the VE and behaviors of autonomous agents. It also makes NLU/NLG rules independent from contents of the application and provides a high expressiveness. Our solution has been used to develop an interactive cultural heritage application, Brest'Coz, using Mascaret and the NabuTalk engine. Although, we have not yet performed its formal evaluation, the application has been successfully presented during a video game exhibition at Brest, and feedbacks from users were very positive. Our long term goal is to enrich agents' behaviors, so that they can engage themselves into dialogical interactions to coordinate their collaborative activities. One can expect to significantly lower the complexity of the description of the activity.

Fig. 1 .

 1 Fig. 1. Brest'Coz: overview of shipbuilding activities on the harbour (left) -example of dialogue with a worker (right)

Fig. 2 .

 2 Fig. 2. Partial modelling of the Crane entity class using Veha. Left: properties and structure; right: behavior

- 1 . 1

 11 Pierre: Hey! You do not have the permission to use the Crane. -2.1 user: Who can give the permission to use the Crane? -2.2 Pierre: The supervisor can do it. His name is Ronan. -3.1 user: What can I do with the Crane? -3.2 Pierre: You can pull-up, pull-down, rotate, take and release with the Crane.

(

  nlu-rule {[what-can-do-with] [class($class)]} { let (eval $list listClassOperations($class)) {if (empty $list) { talk($other {"You can do nothing with a" $class}) } else { talk($other {"You can" list($list "," "and") "with a" $class}) } } })NabuTalk performs pattern matching with resources like [what-can-do-with].The NabuTalk resource is a regular expression that can support different ways to express a phrase. Thus, it provides some flexibility for the user to communicate with agents. [class($class)] is a resource implemented with NabuTalk predicates and Mascaret connectors. It represents any class found in the semantic model. If such a pattern matches, the condition (eval $list listClassOperations($class)) is evaluated and if true, the $list variable will contain names of all operations of the class. The listClassOperations predicate is implemented as a Mascaret connector. The code just walks through Mascaret model to get operations of the class:Class c=MascaretApplication::getModel()->getClassByName(className); vector <Operation> op=c->getOperations(); // returns operation names

http://wordnetweb.princeton.edu/perl/webwn

Acknowledgments. This work was supported in part by a grant from Région Bretagne and in part by the Anr (Corvette project Anr-10-Cord-012).


A Jarnac

M Durand

A Houard

Y Liu

B Prade

M Richardson

A Mysyrowicz
email: andre.mysyrowicz@ensta-paristech.fr

Spatio-temporal cleaning of a femtosecond laser pulse through interaction with counter-propagating filaments in air

We demonstrate spatio-temporal cleaning of a femtosecond laser pulse impinging on two counter propagating filaments in air. The retro-reflected signal has essentially a perfect beam profile. Pre-pulses present in the incident pulse are also efficiently removed. The performance of the 'filament mirror' is explained by a plasma-mediated wave mixing process that can be viewed as a transient 3d hologram.

The propagation of an intense sub-picosecond laser pulse in air, even with an energy of a few mJ, is highly nonlinear. Two effects play a major role to induce these strong optical nonlinearities during propagation. The first is the optical Kerr effect. By inducing a change of the air refractive index, it leads to beam selffocusing. Although weak at first, self-focusing is cumulative on propagation and becomes precipitous after some distance if the pulse initial peak power exceeds a critical value P cr = which varies between 2.8 GW and 12 GW at 800 nm in normal atmosphere, depending upon pulse duration [1]. Here, n 0 is the linear refractive index, n 2 the non linear index coefficient, and 0 is the laser wavelength. The second effect is high field ionization. Total beam collapse is prevented by the onset of ionization, a process requiring the simultaneous absorption of a large number of photons in air. The ensuing plasma is responsible for beam defocusing, an effect which clamps the pulse peak intensity to a value ~ [2,3]. The dynamic competition between optical Kerr induced self-focusing and plasma defocusing thus leads to the emergence of an intense contracted pulse propagating over distances exceeding its Rayleigh length. Due to its high intensity, the contracted pulse leaves in its wake a narrow string of under-dense plasma. This highly nonlinear propagation regime is called filamentation [4]. In this letter, we examine experimentally the situation of three femtosecond laser pulses 1, 2, 3 crossing in air, two of which (1 and 2) are intense and consist of counter-propagating filamentary pulses. The pulse 3 is weaker and is non collinear. In traditional non-linear optics, a configuration of lower intensity counterpropagating beams forms a phase conjugate mirror that retro-reflects a non collinear wave and inverts its spatial phase [START_REF] Fisher | Optical Phase Conjugation[END_REF][START_REF] Boyd | Nonlinear Optics[END_REF]. In a similar way, we detect a signal in direction opposite to beam 3. The counterpropagating filaments thus can be viewed as a transient mirror that retro-reflects part of the incoming beam 3. However in contrast to the usual case of phase conjugation, the retro-reflected beam (4) in the present case has a distortion-free profile, irrespective of the initial spatial phase of beam 3. We also show that precursor light present in beam 3 is efficiently removed in the retro-reflected pulse. To explain our results we consider the interaction of the three beams in the high intensity limit. This experiment illustrates the difference between traditional and femtosecond nonlinear optics. The high peak intensity of femtosecond laser pulses leads to specific effects such as non-linear propagation and plasma formation [4]. In addition, this experiment shows that two counter-propagating filaments provide a simple scheme to clean femtosecond laser pulses. Such pulses could find applications in ultrafast physics where femtosecond laser pulses with a high quality beam profile, good stability and a high contrast are needed [7][8][9].

The principle of the experiment is shown in Fig. 1(a). Two ultra-short laser pulses 1, 2 of equal peak power > 12 GW undergo filamentation in air and then meet from opposite directions along z. The formation of a plasma bubble in the interaction zone is verified by the appearance of a bright spot superimposed on the blue filament luminescence tracks from ionized N 2 molecules [10], as shown in Fig. 1(b). A weaker pulse 3 (beam diameter: 2 mm, P max = 2 GW) is focused with an f = 150 mm lens onto the bubble and is time coincident with the filament pulses. Due to the highly nonlinear ionization rate with laser intensity, the size of the plasma shrinks to a small volume. Through luminescence imaging, we measured the shape of this bubble in the presence of the three pulses. It is an ellipsoid of revolution with axis 11 µm along z and 30 µm along x, y. It induces two signal beams 4, 4', one counter-propagating with beam 3, the other copropagating and amplifying it. All laser pulses 1, 2, 3 with a central wavelength at 800 nm and duration of 85 fs are derived from the same Ti: Sapphire laser. They are contained in the horizontal plane (y, z) and are polarized along x. Figure 2 shows an example of a beam profile before and after reflection on the filament mirror recorded with a CCD camera. Here, the incident beam 3 propagates perpendicular to the filament paths ( = 90°) and is intentionally of poor quality, with a pronounced diffraction pattern and two holes in its fluence profile. By contrast, the retro-reflected pulse 4 has essentially a single spatial mode profile (Fig 2(b)). We have verified that other strong initial beam distortions, such as those introduced by masking part of the beam, are also removed. As shown in Fig. 3(a), the filament mirror reflectivity R = W 4 /W 3 increases with decreasing angle  between beams 1 and 3, where W i is the energy of pulse i. Fig. 3(b) shows R as a function of the incident filament pulse energy for a  = 90° geometry. One notices a fast increase of the reflected signal 4 above 100 µJ when the pulses 1, 2 start ionizing air until a plateau is reached with a reflectivity of 10 20%. We have also measured an amplification of the transmitted energy of pulse 3 in the presence of the filament pulses. The amplified part 4' is equal to the retro-reflected signal 4. It shows that laser energy is transferred from the filament pulses 1, 2 to the signal pulses 4, 4'. To discuss these results, we examine the effect of a change of refractive index of air in the presence of the three waves. The superposition of the three waves 1, 2, 3 leads to a transient 3-d plasma hologram that encodes the spatial phase profile of the three beams. The phase profile is dominated by the index variation from the plasma. It is of the form: ,

,.

(2) N is the number of effective photons simultaneously absorbed to create the plasma and E i the complex electric field of wave i. For example E 1 has the standard form:

(3). The holographic volume is simultaneously read by the three waves. We are concerned with the signal diffracted in the direction opposite to wave 3. It takes the general form:

,. (4) where F is a slowly varying amplitude that includes a number of terms that increases rapidly with N. It amounts to 40 terms in the case N = 5, which applies to a laser pulse at 800 nm [START_REF] Chin | From Multiphoton to Tunnel Ionization[END_REF]. Note that wave 4 carries the phase of the filament waves and the inverted phase of wave 3. Pursuing the analogy with optical phase conjugation by degenerate four-wave mixing, we identify the main mechanism responsible for the generation of wave 4. In conventional degenerate four-wave mixing, a pure index grating diffracts part of the counter-propagating beams in direction . In our model, all incident beams contribute to wave 4. However the major contribution is due to beams 1 and 2: the plasma grating formed by filament pulse 1(2) and converging pulse 3 scatters part of the second filament pulse 2(1) at Bragg angle into the direction opposite to the incident beam 3 (dashed-dotted lines in Fig. 1(c,d)). Therefore pulse 4 carries the properties of the intense pulses. Now a remarkable property of filamentation is spatial self-cleaning of the contracted beam profile [START_REF] Prade | [END_REF][13][14][15] which acquires a Townes mode profile [16].We have verified that pulse 4 fits indeed a Townes mode profile (see Fig. 2(d)). An additional effect plays a role in removing phase distortions of beam 3, namely the small size of the grating that acts as a filtering pinhole. To confirm this interpretation, we have measured the signal 4 as a function of delay of pulse 2 with respect to pulses 1 and 3 (see Fig. 4(a)). The signal decays within 30 ps [17], because the plasma grating of long lifetime in air can still diffract a delayed pulse 2 [18]. On the other hand, the signal vanishes within 100 fs if pulse 3 is delayed with respect to the filament pulses (see Fig. 4(b)). This is expected since the formation of the plasma grating requires chronological coincidence of the pulse 3 with at least one of the filamentary pulses. The filament based mirror also displays interesting temporal pulse cleaning properties. The steep initial increase of the reflectivity shown in Fig. 3(b) is responsible for the removal of laser pulse precursors. Indeed the field interference between precursors present in the three pulses does not form a diffracting plasma grating due to their weaker intensities. On the other hand, the saturated reflectivity region above 1 mJ energy reduces shot-to-shot intensity fluctuations of pulse 4. We have verified experimentally the temporal cleaning property of the filament mirror, starting with a laser pulse with a marked temporal precursor, obtained by misaligning the compression stage of the laser. Figure 5 gives the time profile of the pulse, (a) before and (b) after reflection by the filament mirror. The time profile and the temporal phase of the incident pulse 3 and reflected pulse 4 were obtained with a commercial Frequency-Resolved Optical Gating system apparatus (FROG). Figure 5(b) shows that the front pedestal is totally removed after reflection on the filament mirror. The cleaning properties have also been measured over a larger time scale with a third-order cross correlator [19]. As can be seen in Fig. 5(c), pulse precursors are completely removed over the 10 6 dynamic range of the cross correlator in the trace of the reflected pulse 4. Laser pulses with high contrast are desirable for studies of their interaction with intact samples. A prepulse, even of modest energy content, can pre-ionize a sample and thereby modify the conditions of interaction at the peak of the pulse [20]. Usual cleaning techniques are (i) the use of pinholes which require strict alignment and are subject to damage [21], (ii) the XPW method which is fragile and expensive [22] or (iii) the plasma mirror which requires a fresh sample after each shot [23]. A filament mirror is cheap since it uses air or another gas as a non-linear material, it is not subject to damage and is relatively easy to align.

In conclusion, we have shown that it is possible to convert a short pulse of arbitrary spatial profile into a single spatial mode pulse by reflecting it on a mirror formed by counter-propagating filaments. The mirror enhances the temporal contrast of the pulse by at least three orders of magnitude. Its action has been described in terms of a transient 3-d plasma hologram. This hologram diffracts part of the filaments light in the direction opposite to that of a third incoming femtosecond laser pulse.

FIG. 1 .

 1 FIG. 1. (a) Schematic set-up. D: diaphragm; BS: beam splitter; L: lens; CCD: charge coupled device camera; FM: filament mirror. (b) Photograph of the blue plasma luminescence emitted by the three overlapping beams; (c) and (d) Schematic diagram of the main diffraction process giving rise to the signal beam 4.

FIG. 2 .

 2 FIG. 2. Fluence profile of a femtosecond pulse before (a) and after (b) reflection on the filament mirror, as recorded in a single shot with a CCD camera. Scan of the fluence profile along x at z = 0, before (c) and after (d) reflection. The red open circles represent a fit of the reflected beam 4 by a Townes mode profile function.

FIG. 4 .

 4 FIG. 4. (a) Signal of pulse 4 as a function of delay of filament pulse 2. Pulse 3 is incident at an angle of 90°. Pulses 1 and 3 are coincident in time. (b) The same, but delaying the pulse 3 with respect to pulses 1 and 2.

FIG. 5 .

 5 FIG. 5. Temporal profile of incident pulse 3 (a) and reflected pulse 4 (b) measured with a FROG apparatus. (c) Contrast measurement performed with a 3ω cross-correlator of laser pulse 3 before (black line) and after (red line) reflection by the filament mirror. The black arrow indicates an artifact of the correlator.

Acknowledgments

The authors thank G. Hamoniaux and P. Rousseau for technical help. This work was partially supported by DGA through a Ph. D. grant.


Aurélie Goutte
email: aurelie.goutte@ephe.sorbonne.fr

Christophe Barbraud

Dorte Herzke

Paco Bustamante

Frédéric Angelier

Sabrina Tartu

Céline Clément-Chastel

Børge Moe

Claus Bech

Geir W Gabrielsen

Jan Ove Bustnes

Olivier Chastel

Survival rate and breeding outputs in a high Arctic seabird exposed to legacy persistent organic pollutants and mercury

Keywords: heavy metals, kittiwake, population, pesticides, PCBs

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Contaminants, such as mercury (Hg) and persistent organic pollutants (hereafter POPs) may represent a threat for wildlife, because of their detrimental effects on developmental, neurological, physiological, endocrine and immune functions [START_REF] Barron | Comparative reproductive and developmental toxicology of PCB in birds[END_REF]Bustnes et al., 2003a;Tan et al., 2009;[START_REF] Letcher | Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish[END_REF]. Despite a growing environmental concern during the last decades, the demographic consequences of pollution remain poorly evaluated in free-living vertebrates. Only a few long-term monitoring studies have addressed the consequences of environmental pollutants on survival rate and long-term reproductive outputs. Hg or POP levels were negatively related to long-term breeding probability and success in the wandering albatross Diomedea exulans and in two Catharacta skua species (Goutte et al., 2014a,b). Apparent survival rate was lower in glaucous gulls Larus hyperboreus, bearing the highest levels of oxychlordane, a metabolite of the chlordane mixture, which is regarded as one of the most toxic POPs [START_REF] Erikstad | Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival[END_REF]. However, adult survival rate was not related to POPs or Hg in tree swallows (Tachycineta bicolor), king eiders (Somateria spectabilis), white-winged scoters (Melanitta fusca), wandering albatrosses and two Catharacta skua species [START_REF] Wayland | Survival rates and blood metal concentrations in two species of free-ranging North American sea ducks[END_REF][START_REF] Hallinger | Mercury exposure and survival in free-living tree swallows (Tachycineta bicolor)[END_REF]Goutte et al. 2014a,b). Some seabird species appear as ideal models for assessing the demographic consequences of environmental pollution. Firstly, individual detection probabilities of seabirds at breeding colonies are generally high because of high overall site fidelity (e.g. [START_REF] Gauthier | Estimating dispersal, recruitment and survival in a biennially-breeding species, the wandering albatross[END_REF]. Secondly, large sample sizes and accurate measures of breeding outputs are relatively easy to obtain in seabird's colonies. Thirdly, these long-lived top predators are particularly exposed to contaminants, because of bioaccumulation process and biomagnification along the trophic web [START_REF] Rowe | The calamity of so long life:" life histories, contaminants, and potential emerging threats to long -lived vertebrates[END_REF][START_REF] Letcher | Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish[END_REF].

The present study focusses on black-legged kittiwakes Rissa tridactyla breeding in Svalbard, a Norwegian archipelago in the north-western part of the Barents Sea. The Norwegian Arctic is recognized as a final sink for organic and metallic pollutants, which are transported by atmospheric and oceanic currents and by large rivers [START_REF] Gabrielsen | Persistent organic pollutants in Arctic animals in the Barents Sea area and at Svalbard: levels and effects[END_REF]. Previous studies in this population of Svalbard kittiwakes have reported deleterious effects of Hg and POPs on endocrine mechanisms [START_REF] Nordstad | Relationships between POPs and baseline corticosterone levels in black-legged kittiwakes (Rissa tridactyla) across their breeding cycle[END_REF][START_REF] Tartu | To breed or not to breed: endocrine response to mercury contamination by an arctic seabird[END_REF]Tartu et al., , 2014)). The estimated number of breeding pairs in the Svalbard archipelago is 270 000 in 215 colonies [START_REF] Strøm | The endocrine effects of mercury in humans and wildlife[END_REF]. The status of black-legged kittiwakes is near threatened, with a pronounced population decline from 1995 to 2002 and a slight increase from 2002 to 2012 [START_REF] Barrett | Key-site monitoring in Norway[END_REF]. This study aims at detecting whether breeding probability the year of sampling and demographic traits the following year (apparent adult survival rate, breeding probability, probability of successfully raising at least one chick and probability of successfully raising two chicks) were correlated with individual blood levels of Hg or POPs. According to the few available long-term studies on polar seabird species [START_REF] Erikstad | Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival[END_REF]Goutte et al., 2014a,b), we predicted deleterious effects of Hg or POPs on breeding probability and breeding success during the year of sampling and during the following year and deleterious effects of the chlordane mixture and metabolites on survival rate in black legged kittiwakes.

Materials and methods

Study area and birds

Our study was conducted in a colony of black legged kittiwakes at Kongsfjorden, Svalbard (78°54′N, 12°13′E), seven kilometers southeast of Ny-Ålesund, Norway. Kittiwakes are colonial seabirds that breed on cliffs throughout the northern parts of the Pacific and Atlantic, including the Barents Sea region up to the Svalbard Archipelago [START_REF] Anker-Nilssen | The status of marine birds breeding in the Barents sea region[END_REF]. Kittiwakes were studied in one plot of around 150 pairs breeding on cliff ledges at heights of 5-10 m. Male and female kittiwakes were sampled once, between 2007 to 2010 years, during the pre-laying stage (arrival, nest building, courtship and mating period) from 23 rd of April to 16 th of June. Table 1 summarizes sampling information: a total of 105 kittiwakes were sampled for measurement of Hg and 138 kittiwakes for POPs. We chose to focus our study on the pre-laying period, because sampling kittiwakes during the incubating or chick-rearing period would have biased our demographic study towards good-quality birds (breeders) and would have missed possible effects in non-breeders.

Capture and blood sampling

Male and female kittiwakes were caught on the nests with a noose at the end of a 5 m fishing rod. Blood samples were collected from the alar vein with a 2 ml heparinized syringe and a 23-gauge needle. Kittiwakes were individually marked with metal rings and PVC plastic bands engraved with a three-digit code and fixed to the bird's tarsus for identification from a distance without perturbation.

Laboratory analyses

Blood samples were centrifuged. Plasma and red blood cells were separated and stored at -20°C. Molecular sexing was performed on red blood cells as detailed in Weimerskirch et al. (2005).Total Hg was measured at the laboratory Littoral Environnement et Sociétés (LIENSs) from lyophilized red blood cells with an Advanced Mercury Analyzer spectrophotometer (Altec AMA 254). At least two aliquots ranging from 5 to 10 mg dry weight were analyzed for each individual until having a relative standard deviation <5 %. As described by [START_REF] Bustamante | Total and organic Hg concentrations in cephalopods from the North East Atlantic waters: influence of geographical origin and feeding ecology[END_REF], accuracy was checked using a certified reference material (CRM, Tort-2 Lobster Hepatopancreas, NRC, Canada; certified Hg concentration: 0.27 ± 0.06 μg g-1 dry mass; with recoveries of 98 to 102%). Mass of CRM was adjusted to represent the same amount of Hg introduced in the AMA compared to that in blood samples.

Blanks were analysed at the beginning of each set of samples and the detection limit of the method was 0.005 μg g-1 dry mass. Mean values of replicates were used in statistical analyses.

POPs were analysed from whole blood samples at the Norwegian Institute for Air Research (NILU) in Tromsø. The following compounds were analysed: polychlorinated biphenyl (CB, hereafter referred as ∑ PCBs, p,p′-DDE (p,p'-dichlorodiphenyldichloroethylene, HCB (hexachlorobenzene), and the chlordane mixture (trans-chlordane, trans-, cis-nonachlor) and metabolites (oxychlordane), hereafter referred as CHL. To a blood sample of 0.5 to 1.5 ml, an internal standard solution was added (13C-labelled compounds from Cambridge Isotope Laboratories: Woburn, MA, USA). The sample was extracted twice with 6 ml of n-hexane, after denaturation with ethanol and a saturated solution of ammonium sulphate in water. Matrix removal on florisil columns, separation on an Agilent Technology 7890 GC and detection on an Agilent Technology 5975C MSD were performed as described by [START_REF] Herzke | Perfluorinated and other persistent halogenated organic compounds in European shag (Phalacrocorax aristotelis) and common eider (Somateria mollissima) from Norway: a suburban to remote pollutant gradient[END_REF]. The limit for detection was threefold the signal-to-noise ratio, and for the compounds investigated the limit ranged from 0.4 to 122 pg.g -1 wet weights (ww). For quality assurance, blanks (clean and empty glass tubes treated like a sample) were run for every 10 samples similar to standard reference material (1589 a human serum from NIST). The accuracy of the method was within the 70 and 108% range.

Life history traits

From 2007 to 2012, individuals were individually identified, through PVC plastic bands reading. Using a mirror at the end of an 8 m fishing rod, we checked the whole plot (about 120 nests) every two days to monitor breeding status (at least one egg is laid or no egg laid). Then, we checked the nest content every 2 or 3 days to monitor the number of chicks that reached at least 12 days of age per nest.

Statistical analyses

We used R software (R Development Core Team 2012) and generalized linear models (GLMs) with normal distribution and a link function to test whether log-transformed Hg, ∑ PCBs, DDE, HCB or CHL levels were linked to sex, year and the interaction sex × year.

GLMs with binomial error distribution and a logit link function were then used to test whether breeding probability (will breed or will skip) the year of sampling was linked to pre-laying Hg, ∑ PCBs, DDE, HCB or CHL levels.

Estimating the effect of Hg and POPs on demographic parameters

The effects of Hg and POPs concentrations on the demographic parameters were evaluated through the capture-recapture data of sampled kittiwakes. A MSMR (Multi-State Mark Recapture, [START_REF] Lebreton | Multistate recapture models: modelling incomplete individual histories[END_REF] model was constructed by distinguishing five states: non-breeder (NB, defined as an individual that was not observed with an egg), failed breeder (FB, defined as an individual that was observed with one or two eggs, or one or two chicks but that failed to raise a chick), successful breeder with one chick (SB1, defined as an individual that raised one chick), successful breeder with two chicks (SB2, defined as an individual that raised two chicks), and dead. The state dead ( †) was an absorbing state representing death or permanent emigration from the study area. Kittiwakes that were ringed and observed the years before sampling for Hg or POPs were considered as non-observed, in order to test the effect of contaminants (at year t) on future (year t+1) survival and breeding performances. Models were parameterized in terms of the probability of survival (S), the probability of breeding (β), the probability of breeding successfully (γ), the probability of successfully raising two chicks (δ), and the detection probability (p). Transition probabilities between states were thus modeled with a four-step procedure where S, β, γ and δ were considered as four successive steps in transition matrices. Figure 1 presents a multinomial tree diagram describing the probability structure for multistate observations, and parameters of the model are defined in Table 2. We chose a MSMR approach since this allows taking into account the probability of detecting individuals given their return to the study sites. It also allows taking into account the previous breeding state of individuals which might be important to obtain unbiased estimates of demographic parameters [START_REF] Lebreton | Multistate recapture models: modelling incomplete individual histories[END_REF].

Several constraints were made to ensure that the parameters of the model were estimable. The state "dead" being explicitly included in the model but being never encountered, transition probabilities from the state dead were fixed to 0 and capture probability was fixed to 0 [START_REF] Pradel | Multievent: an extension of multistate capture-recapture models to uncertain states[END_REF], Choquet et al. 2009a). Because our capture-recapture analyses relied on a limited number of individual capture histories, parameters S, β, γ, δ and p were constrained to be constant over time but state and sex dependent. With this constraint the initial model was full-rank. Note that we ran a model where all demographic parameters were time, sex and state dependent but this model was highly rank deficient.

This MSMR model was parameterized by the survival-transition probabilities matrix:

⎣ ⎢ ⎢ ⎢ ⎡ S(1 -β) Sβ(1 -γ) Sβγ(1 -δ) Sβγδ * S(1 -β) Sβ(1 -γ) Sβγ(1 -δ) Sβγδ * S(1 -β) Sβ(1 -γ) Sβγ(1 -δ) Sβγδ * S(1 -β) Sβ(1 -γ) Sβγ(1 -δ) Sβγδ * - - - - * ⎦ ⎥ ⎥ ⎥ ⎤ NB FB SB1 SB2 † NB FB SB1 SB2 †
Because we were interested to test for sex-specific effects of Hg and POPs on demographic parameters we started from an initial model including an effect of sex (g) on each parameter. Model selection was first performed on detection probability by testing statedependency (difference between all states, between breeders and non-breeders, or no difference). We then tested for sex difference and state-dependency (difference between all states, difference between breeders and non-breeders or no difference) for S, β, γ and δ. We tested for an effect of Hg, ∑ PCBs, DDE, HCB, or CHL on demographic parameters the following year to test the hypothesis that contamination levels in one breeding season may influence the survival and breeding success of an individual in the following season. We built MSMR models where each demographic parameter θ was modeled as a function of contaminant C using a logit link function:

i C b a × + = ) ( logit θ
, where a is an intercept, b is a slope and Ci is Hg or POPs concentration for individual i. The 95% confidence interval (CI) of the slope parameters b was used, as well as Akaike's Information Criterion corrected for small sample size (AICc, [START_REF] Burnham | Model selection and multimodel inference: a practical information-theoretic approach[END_REF] for inference. We considered an effect of contaminant as statistically supported when 0 was outside the 95% CI of the mean of the slope of the relationship [START_REF] Grosbois | Assessing the impact of climate variation on survival in vertebrate populations[END_REF]. When b < 0, or b > 0, the covariate C has a negative or positive effect on the demographic parameter, respectively. We tested the goodness-of-fit (GOF) of the time dependent MSMR model using U-CARE (Choquet et al. 2009b). All models were run under program E-SU RGE 1.8.5 allowing splitting transition probabilities between states (Choquet et al. 2009a).

Results

Associations between Hg or POPs and breeding probability in year of blood sampling

Table 1 summarizes the values of Hg, ∑ PCBs, DDE, HCB and CHL in males and females. Appendix 1 gives the concentrations of each POP congener and appendix 2 presents the relationships between levels of Hg, ∑ PCBs, DDE, HCB and CHL.

Hg levels were significantly higher in males than in females (F 1,103 = 3.993, p = 0.048), but did not differ between the two sampling years (year: F 1,102 = 3.339, p = 0.071; sex × year: F 1,101 = 1.102, p = 0.296). Breeding probability during the sampling year was influenced by Hg levels (df = 103, χ² = 12.983, p < 0.001): kittiwakes that would skip (mean ± SD: 2.284 ± 0.417 µg.g -1 ) had higher pre-laying Hg levels than kittiwakes that would breed (1.962 ± 0.470 µg.g -1 ).

Levels of ∑ PCBs, DDE, HCB, or CHL did not differ between males and females (sex: p > 0.07 for all tests: sex × year: p > 0.09 for all tests). Levels of ∑ PCBs (F 3,134 = 4.935, p = 0.003), HCB (F 3,134 = 37.035, p < 0.001), ∑ CHL (F 3,134 = 12.818, p < 0.001), but not DDE (F 3,134 = 2.519, p = 0.061) differed among years. Breeding probability was not influenced by levels of ∑ PCBs, DDE, HCB, or CHL during the sampling year (p > 0.61 for all tests).

Associations between Hg and demographic parameters in year after blood sampling

The GOF of the MSMR model was overall not significant (males: χ² = 48.913, df = 69, p = 0.968 and females: χ² = 47.435, df = 71, p = 0.986). The best model according to AICc (model 16, Appendix 3) indicated that breeders in the previous year had higher breeding probabilities and detection probabilities than non-breeders in the previous year. However birds captured as breeders or non-breeders did not differ in survival rate, probabilities of successfully raising one or two chicks (Appendix 3 and Table 3). Demographic parameters did not differ between males and females (Appendix 3 and Table 3).

Model selection and slope estimates suggested no effect of Hg on demographic parameters. Model Hg3 had a ΔAICc lower than 2 compared to the null model, but the effect of Hg on breeding probability the following year was not supported, since the 95% CI of the slope parameter included 0 (Table 4).

Associations between POPs and demographic parameters in year after blood sampling

Model selection was based on ΔAICc higher than 2 compared to the intercept model and the 95% CI of the slope of the relationship that did not include zero. Hence, in spite of good AICc, several models suggesting an effect of Ʃ PCBs, DDE, HCB or CHL on demographic parameters were not retained. Only six models met these requirements (Table 5). Models HCB5 and HCB6 suggested a negative effect of HCB on breeding probability the following year for individuals and especially males observed as breeders (Fig. 2A,2B).

Model CHL6 suggested a negative effect of CHL on breeding probability the following year for males observed as breeders (Fig. 2C). Model HCB1 suggested a positive effect of HCB on the probability of successfully raising two chicks the following year (Fig. 3). Model HCB8 suggested a negative effect of HCB on survival rate of females (Fig. 4A). Model CHL7 suggested a negative effect of CHL on survival rate (Fig. 4B). We could also notice a tendency towards a negative effect between survival rates and levels of ∑ PCBs (model PCB7, ∆AICc = 1.24, mean slope and 95% CI = -0.44 [-0.82 ; -0.03]), DDE (Model: DDE7, ∆AICc = 0.88, slope = -0.42 [-0.82 ; -0.01]), HCB for males and females (Model HCB7, ∆AICc = 1.73, slope = -0.47 [-0.88 ; -0.06]), or CHL for females only (Model CHL8, ∆AICc = 1.50, slope = -0.73 [-1.29 ; -0.17]).

Discussion

Using a long-term data set and MSMR models, this study explores the demographic effects of Hg or families of legacy POPs (7 PCB congeners, p-p' DDE, HCB, and the chlordane mixture and metabolites (trans-chlordane, trans-, cis-nonachlor, oxychlordane)) in a free-living Arctic seabird species. It should be noticed that differences in toxicity among POP congeners were not taken into account in these analyses, because toxic equivalent factors (TEFs) were only available for PCB-105 and PCB-118. Moreover interactions among families of pollutants may occur within an organism to induce synergistic effects, but they are difficult to demonstrate within a field study.

Survival and contaminants

Estimated demographic parameters were similar to those previously estimated in other populations of black legged kittiwakes [START_REF] Frederiksen | Inter-population variation in demographic parameters: a neglected subject?[END_REF]. Adult survival rate in this study (85% [82 -88%]) was within the range of estimated survival rates in north Atlantic populations (80-92%, [START_REF] Danchin | Population dynamics modelling of two neighbouring kittiwake Rissa tridactyla colonies[END_REF][START_REF] Erikstad | Adult survival and chick production in longlived seabirds: a 5-year study of the kittiwake Rissa tridactyla[END_REF][START_REF] Oro | Influences of food availability and predation on survival of kittiwakes[END_REF][START_REF] Frederiksen | Inter-population variation in demographic parameters: a neglected subject?[END_REF].

The adult survival rate of kittiwakes was not jeopardized by Hg, which corroborates most of the previous studies in free-living birds [START_REF] Wayland | Survival rates and blood metal concentrations in two species of free-ranging North American sea ducks[END_REF][START_REF] Hallinger | Mercury exposure and survival in free-living tree swallows (Tachycineta bicolor)[END_REF]Goutte et al., 2014a,b). Apparent survival rate was negatively linked to HCB levels in females, to mixture of chlordane and oxychlordane, and tended to be negatively correlated with ∑ PCBs or DDE levels. Only one study [START_REF] Erikstad | Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival[END_REF]) highlighted a negative effect of oxychlordane on adult survival rate in the glaucous gull breeding in the Bjørnøya Island (blood levels of oxychlordane: 1.3 to 128.8 ng.g -1 wet weight, median: 13.2 ng.g -1 ww) and this effect was the most pronounced among the most contaminated females. Even if kittiwakes were more than 10-time less contaminated than glaucous gull (blood levels of oxychlordane: 0.007 to 6.0 ng.g -1 wet weight), this study reveals that high levels of the chlordane mixture and metabolites or HCB could negatively affect adult survival rate, and especially in female kittiwakes.

The correlation between POP levels and survival rate could be a by-product of agedependent mechanisms, with older kittiwakes having the highest POP burden and the lowest survival probability. Age of kittiwakes was unknown in this study and we could not control for age. However, blood levels of PCB-153, p,p'-DDE, HCB, and oxychlordane were unrelated to age in glaucous gulls (Bustnes et al., 2003b). Similarly, blood levels of PCBs or organochlorine pesticides (HCB, lindane, chlordane mixture, mirex, DDT and metabolites) were unrelated to age in wandering albatrosses [START_REF] Carravieri | Wandering albatrosses document latitudinal variations in the transfer of persistent organic pollutants and mercury to Southern Ocean predators[END_REF]. Therefore, it seems unlikely that age was a confounding factor in the correlation between POP levels and survival rate. In addition, as we did not monitor long-distance dispersal, our findings on apparent survival rate could also include the effects of POPs on long-term emigration of the most polluted birds.

This study suggests that HCB or the chlordane mixture and metabolites may weaken the general health of kittiwakes and may increase their vulnerability to harsh environmental pressures in the Arctic [START_REF] Letcher | Exposure and effects assessment of persistent organohalogen contaminants in arctic wildlife and fish[END_REF]. In that context, it is conceivable that the effect of POPs on survival rate is only detected during harsh environmental events. Because our sample size did not allow taking into account an effect of years, we could not have tested whether harsh environmental conditions during a specific year would exacerbate the effects of pollutants on demographic parameters the following year.

Long-term fecundity and contaminants

A previous study on this population of kittiwakes has highlighted that total blood Hg load during the pre-laying period predicted the likelihood of breeding, with non-breeders having higher Hg levels than breeders, but not the timing of breeding, clutch size, and breeding success [START_REF] Tartu | To breed or not to breed: endocrine response to mercury contamination by an arctic seabird[END_REF]. Moreover experimentally elevated Hg levels (total Hg in blood, mean ± SD: from 0.73 ± 0.09 to 3.95 ± 0.68 mg.kg -1 fresh weight) led to an altered pairing behaviour in white ibises Eudocimus albus (Frederick and Jayasena, 2011). In the present study, Hg levels were higher in kittiwakes that would skip breeding than in birds that would breed, as previously shown [START_REF] Tartu | To breed or not to breed: endocrine response to mercury contamination by an arctic seabird[END_REF]. Hg levels did not affect breeding probability and breeding success the following year, which differed from previous studies in the south polar skua Catharacta maccormicki (Hg levels in blood: mean ± SE: 2.15 ± 0.17 µg.g -1 dry mass), in the brown skua C. lonnbergi (8.22 ± 0.24 µg.g -1 dry mass) and in the wandering albatross (7.7 ± 3.6 µg.g -1 dry mass) (Goutte et al., 2014 a,b). However, Hg levels in these species were measured during the incubation and the chick-rearing period, while Hg levels in the present study were measured in pre-laying kittiwakes. Furthermore, breeding success was monitored on chicks that reached at least 12 days of age and did not allow testing an effect of contaminants on late developmental stage.

POPs burden did not influence the breeding probability the year of sampling, which was consistent with a previous study on the same population of kittiwakes [START_REF] Tartu | The stress of being contaminated? Adrenocortical function and reproduction in relation to persistant organic pollutants in female Black-legged kittiwakes[END_REF].

Breeding probability the following years was reduced by high HCB levels in breeders and especially in males, or by high levels of the chlordane mixture and metabolites in male breeders. A negative correlation between POP levels and breeding probabilities the following year has been highlighted in the wandering albatross (Goutte et al., 2014b). Male breeders seemed to be the most sensitive to POPs. Energetic and time-dependent costs of reproduction have been shown to induce downstream consequences on reproductive investment during the following breeding season (carry over effect, [START_REF] Catry | Carry-over effects from breeding modulate the annual cycle of a long-distance migrant: an experimental demonstration[END_REF]. One may suggest that POPs burden may intensify these carry over effects, but studies are needed to either rebut or confirm this hypothesis.

Levels of ∑ PCB, DDE, HCB, and the chlordane mixture and metabolites did not influence the probability of successfully raising one chick the following year, which was consistent with a previous study on the same population of kittiwakes and during the year of sampling [START_REF] Tartu | The stress of being contaminated? Adrenocortical function and reproduction in relation to persistant organic pollutants in female Black-legged kittiwakes[END_REF]. We detected a positive relationship between the probability of successfully raising two chicks the following year and HCB levels, but not PCBs, DDE or the chlordane mixture. This positive relationship between HCB and breeding performance appears surprising, as contaminants are believed to induce deleterious effects on reproductive traits. Previous studies have pointed out that female kittiwakes and gulls with higher levels of organochlorine pesticides laid their eggs earlier in the season [START_REF] Bustnes | The potential impact of environmental variation on the concentrations and ecological effects of pollutants in a marine avian top predator[END_REF]Tartu et al., 2014). As laying early is related to high breeding success [START_REF] Lack | Ecological adaptations for breeding in birds[END_REF], this could explain the positive relationship between HCB and the probability of successfully raising two chicks.

In another hand, this relationship may not be causal and may be enhanced by confounding factors: for instance, kittiwakes succeeding in raising two chicks may be of higher quality, rely on higher trophic level organisms and hence be more exposed to pollutant.

It appears that some families of POPs may be more prone to trigger damaging effects the following year. Specifically, high levels of HCB or the chlordane mixture and metabolites were correlated to lower survival rate and lower probability to breed the following year. These findings corroborate a previous study: despite their lower concentrations, HCB and oxychlordane tended to be more often related to adverse effects than PCB and DDE in glaucous gull [START_REF] Bustnes | Pinpointing potential causative agents in mixtures of persistent organic pollutants in observational field studies: a review of glaucous gull studies[END_REF]. Although levels of these "legacy" POPs are expected to decline, as shown in Canadian Arctic seabirds from the 1970s to the late 1990s [START_REF] Braune | Persistent organic pollutants and mercury in marine biota of the Canadian Arctic: an overview of spatial and temporal trends[END_REF], they appear to represent a potential threat for adult survival rate and thus for population dynamics.

Figure 1 :

 1 Figure 1: A multinomial tree diagram describing the probability structure for multistate

Figure 2 :

 2 Figure 2: Relationship between breeding probability at year t+1 in black-legged kittiwakes

  levels of the chlordane mixture and metabolite at year t

Table 2

 2 Definition of parameters used in the multistate mark-recapture model Probability that an individual in state s at time t raises successfully two chicks at time t + 1 given that it survives to and breeds successfully at time t + 1 p t

	515
	Parameter	Definition
	S t	s	Probability that an individual in state s at time t survives to time t + 1 and does not
				permanently emigrate from the study area
	β t	s	Probability that an individual in state s at time t breeds at time t + 1 given that it
	γ t	s	survives to t + 1 Probability that an individual in state s at time t breeds successfully at time t + 1 given
	δ t	s	that it survives to and breeds at time t + 1

s

  Probability that an individual in state s at time t is encountered at time t + 1

and γ are constant; β differs between NB and B

		Model8	18	3636,86	0
	Sex difference on S, β and δ Sex difference on S, γ and δ Sex difference on β, γ and δ Sex difference on S, β and γ Sex difference on S, β, γ and δ	Model5 Model6 Model7 Model4 Model2	27 27 27 30 31	3632,09 3632,90 3633,21 3630,77 3630,77	14,08 14,88 15,19 19,11 21,24
	C. Hypothesis	# Model Rank Deviance ΔAICc
	S and γ are constant; β is state-dependent	Model15	12	3640,14	0
	S Model16	10	3644,82	0,59
	S, β and γ are constant γ is constant; S and β are state-dependent S is constant; β and γ are state-dependent S differs between NB and B; β and γ are state-dependent S, β and γ are state-dependent β differs between NB and B; S and γ are state-dependent γ differs between NB and B; S and β are state-dependent β is constant; S and γ are state-dependent	Model17 Model10 Model14 Model13 Model8 Model11 Model9 Model12	11 15 15 16 18 16 16 15	3644,79 3638,35 3638,68 3637,55 3636,86 3641,59 3678,02 3725,68	2,61 4,38 4,72 5,64 9,10 9,69 46,12 91,71

S, β, γ and δ

Acknowledgments

The study was funded by the Institut Paul-Émile Victor (IPEV Programme 330, O Chastel), Agence Nationale de la Recherche (ANR PolarTop, O. Chastel), COPOL (G.W. Gabrielsen & J.O. Bustnes) and AVITOX (J. O. Bustnes). This study was approved by the French and Norwegian Ethic committees and by the Governor of Svalbard. The authors thank the numerous fieldworkers who helped with blood sampling and ring-reading: A. Lendvai, E. Noreen, T. Nordstad, K. Sagerup, S.A. Hanssen, C. Trouvé, and J. Welcker. At the LIENSs, the authors thank M. Brault-Favrou from the Plateforme Analyses Elementaires for her excellent technical assistance in laboratory analyses. AMA was funded by the CPER (Contrat de Projet Etat Région).

Appendix 3) for breeders and non-breeders. # This effect is not supported because the 95% confidence intervals of the mean of the slope of the relationship included zero. included zero and the model has a ΔAICc < 2 compared to the intercept model.

Figure 3: Relationship between probability of successfully raising two chicks at year t+1 in black-legged kittiwakes and standardized HCB levels at year t.

Standardized HCB levels at year t standardized HCB levels in females at year t, (B) standardized levels of the chlordane mixture and metabolites at year t.

Standardized levels of the chlordane mixture and metabolite at year t


Mg2al Mg2cr

S Bourgerie

M Motelica-Heino

B Sajaloli

E Yengué

D Morabito

Functional profiles of soil microbial populations under various climatic conditions and agricultural practices in Burkina-Faso

Introduction Results

BIOSOL is a multidisciplinary scientific program (soil science, agronomy, geography) which aims at understanding and promoting agro-ecological practices among peasant communities in Burkina-Faso. In this work, the pedological, geochemical and microbiological characteristics of agricultural soils were investigated in order to make an inventory of soil fertility. Two sites (villages of Sampiéri and Bandougou) with contrasted pedo-climatic conditions were selected.

Results indicate that the microbial biomass for all samples are low. Metabolic quotients (qCO 2 ) are very different and compared to samples from Sampiéri, statistically higher for samples from Bandougou, reflecting disturbed soils for these latter. Catabolic evenness were quite similar for all the samples. The soil ecosystem from Bandougou has significantly influenced the functions of soil microbial community and hence probably its composition. More generally, catabolic diversity of soil microbial community is variable under contrasted climatic and the influence of various cultural practices. This may indicate that the efficiency of soil quality restoration is under the control of many factors which could be further investigated such as the position on the slope along the topo-sequence, the composition of soils and particularly the availability of nutrients and the various cultural practices.

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Burkina Faso

The microbial biomass and community level physiological profiles were determined by using the MicroResp TM system in topsoils. Surface soil samples (0-15 cm) were also evaluated for physico-chemical characteristics such as the organic carbon and nitrogen concentrations, exchangeable cations and pH together with their structure and texture and other soil physical parameters.

Bandougou

  water extracts (1:2.5 w/v) (NF ISO 10390) Total organic carbon and total nitrogen: Flash pyroliser Exchangeable cations: LaMotte universal extraction solution (S/L 1/10) and ionic chromatography (Dionex ICS-2000, Sunnyvale, CA) Sampling with a edelman auger 2 mm mesh sieving LaMotte textural soil kit (code 1067)

g dry soil Metabolic quotient (qCO 2 )

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		pH C mg/g soil N mg/g soil C/N Mg++ exch. (cmol/kg) K+ exch. (cmol/kg) Ca++ exch. (cmol/kg)	KO 7,3 11,7 3,3 3,5 6,67 4,38 41,19	KC zippelé 6,6 5,36 2,8 1,9 7,94 3,60 23,91	KC zai 6,6 12,2 3,4 3,6 10,71 5,51 42,22	DO 6,7 10 3 3,3 7,54 7,00 25,79	PO zai 6,7 6,5 3,5 1,9 4,75 4,03 20,99	KjC 7,5 7,1 3,1 2,3 4,18 20,17 22,23	East	Sampieri KC "zippelé" µg C/Sites 0 10 20 30 KO PO zaï DO KC zaï	KjC	Bandougou field 1 field 5 Samples Metabolic quotient (qCO2)	Catabolic evenness	Field 1
												KO	0.09	SITES	Samples	Catabolic evenness (E)
												KC « zippelé »	0.07	KO KC	0.88
	West									Sampiéri	KC zaï DO	0.32 0.18	Sampiéri	DO « zippelé » KC zaï	0.84 0.88 0.87
												PO zaï	0.13	PO zaï KjC	0.84 0.95
										KjC Field 5 Bandougou Field 1	0.12 0.53 0.22	Bandougou Field 1 Field 5	0.83 0.91
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