Jin Ye

Maria Barrio

René Céolin

Navid Qureshi

Philippe Negrier

Ivo B Rietveld Ef

Josep Lluís Tamarit

An order-disorder phase transition in the van der Waals based solvate of C 60 and CClBrH 2 †

The co-crystal of C 60 •2CBrClH 2 possesses a monoclinic (C2/m) structure at room temperature with both molecular entities, C 60 and CBrClH 2 , orientationally ordered. At 322 K, it transforms reversibly into a hexagonal (P6/mmm) setting, revealing a rare example of a heteromolecular stator rotator transition in a fullerene co-crystal, which applies to both the fullerene and the coformer analogous to the paradigmatic C 60 cubane co-crystal. However, in the present case, topological molecular surface matching between the two chemical species is not necessary and the order disorder phase transition reflects simultaneous activation of the orientational disorder of both C 60 and CBrClH 2 .

Introduction

Materials solely consisting of carbon, carbon allotropes, such as fullerenes, carbon nanotubes and graphenes, exhibit extraordinary differences in their properties depending on the synthesis conditions. [1][2][3] Among these materials, fullerenes are of interest due to their large number of potential applications. [4][5][6][7] In particular, co-crystals and solvates formed by intercalation of organic or inorganic molecules or even metals into the fullerene structures have attracted renewed interest during the last decade. 8,9 This is because solvates, or more precisely hexagonal close packed solvates, tend to easily form nanowires not only with high conductivity but also with extraordinary mechanical properties, as has been demon-strated by the discovery of incompressible phases, which are harder than diamond at high pressure. 3,8,10 In these systems, the superior mechanical properties are related to the 3D network of covalently bonded C atoms between rigid C 60 molecules together with dopant molecules acting as a spacer between C 60 units and as a linker between collapsed C 60 units.

The more fundamentally interesting rotator-stator cocrystals of C 60 or C 70 with cubane (C 8 H 8 ) have been discovered recently. 11,12 The cubic shape and the concave surface of cubane create an almost perfect topological fit with the convex surface of the C 60 molecules when static (orientationally ordered) cubane molecules occupy octahedral voids of the face-centered-cubic structures of rotating fullerenes. When cooling such co-crystals, a phase transition (around 140 K for co-crystals with C 60 and 150 K with C 70 ) occurs into an orientationally ordered phase (orthorhombic or tetragonal, respectively). The C 60and C 70 -cubane co-crystals were reported as the first rotator-stator heteromolecular crystals in which stability is provided due to the perfect match of the molecular surfaces of the involved chemical species.

In this work, we report on C 60 -CBrClH 2 co-crystals. It will be demonstrated that a low-temperature monoclinic C 60 •2CBrClH 2 co-crystal in which both molecular species are orientationally ordered undergoes a phase transition around room temperature to a high-temperature hexagonal phase without a change of stoichiometry, in which CBrClH 2 molecules occupy the prismatic voids of the hexagonal lattice and both C 60 and CBrClH 2 are orientationally disordered. Its behavior will be compared with the recently studied monoclinic C 60 •2CBr 2 H 2 co-crystal 13 a C2/m lattice symmetry and despite the overall packing it is quite similar to the hexagonal packing of solvates formed between C 60 and halogen-methane derivatives. [14][15][16][17][18][19][20][21][22] Experimental Fullerene C 60 was purchased from TermUSA (purity higher than 99.98%) whereas bromochloro-methane (CBrClH 2 ) was purchased from Aldrich (purity higher than 99.5%). Cocrystals were prepared at room temperature by mixing C 60 powder with CBrClH 2 liquid. After a few months, the morphology of the fcc C 60 crystals disappeared and new crystals appeared.

The structure and phase transitions of the C 60 •CBrClH 2 cocrystals were studied by means of X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). XRPD was conducted by means of a high-resolution horizontally mounted INEL cylindrical position-sensitive detector (CPS-120) using the Debye-Scherrer geometry (angular step ca. 0.029°-2θ over a 2θ-range from 2 to 115°) equipped with monochromatic Cu Kα 1 (λ = 1.5406 Å) radiation (40 kV and 25 mA). The temperature was controlled with a liquid nitrogen 700 series Cryostream Cooler from Oxford Cryosystems (±0.1 K). Samples were held in a 0.5 mm-diameter Lindemann glass capillary and rotated during data acquisition to minimize the effect of preferential orientation.

Pseudo-Voigt fits of the Bragg peaks were used to determine the peak position and lattice parameters with XCELL. For the disordered structures, Rietveld refinement was carried out using the FullProf Suite [START_REF] Rodriguez-Carvajal | FullProf suite (2005 version)[END_REF] while the C 60 molecule was described with spherical harmonics as a homogeneous distribution of 60 C-atoms positioned on a sphere with a radius of 3.59 Å. For the ordered structures, the Materials Studio [START_REF]Materials Studio) version 5.5[END_REF] package was used. In both cases, the CBrClH 2 molecule was described as a rigid body (C-Cl: 1.76 Å, C-Br: 1.93 Å, C-H: 1.09 Å).

DSC measurements were performed using a Q100 analyzer from TA Instruments (New Castle, DE, USA) with masses from 5 to 20 mg and heating rates typically of 2 K min 1 in hermetically sealed high-pressure stainless steel pans from Perkin-Elmer to resist the vapor pressure of the solvent. TG experiments were conducted under a nitrogen flow using a Q50 thermobalance from TA Instruments (New Castle, DE, USA) at a 2 K min 1 rate with masses ranging between 2 and 10 mg.

Results and discussion

Due to the fast decomposition of the C 60 -CBrClH 2 co-crystals outside of the mother liquor at room temperature, both were introduced into a Lindeman capillary to obtain XRPD patterns at 303 K (Fig. 1).

The XRPD pattern obtained at 303 K was indexed using XCELL. It resulted in a monoclinic unit cell with lattice parameters (after Rietveld refinement) a = 9.9153( 6 Monoclinic co-crystals together with a small quantity of the mother liquor were taken from the beaker for TG analyses. The sample mass was in the first instance recorded at a constant temperature (303 K) leading to the inflection point "a" (in Fig. 2) indicating the complete depletion of the mother liquor. The sample mass continued to decrease, while the temperature remained constant, indicating that the cocrystals are unstable under nitrogen gas. On heating, the sample subsequently lost more mass with a total decrease Fig. 2 Thermogravimetric analysis of a heterogeneous sample consisting of C 60 •2CBrClH 2 co crystals and an excess of mother liquor (vertical axis: sample mass). From t = 0 to t = 60 min under isothermal conditions (303 K) (shaded area) followed by heating with a scanning rate of 5 K min -1 . Evaporation rate: -0.38 mg min -1 in the first part (t = 0 to t = t a ). Inset: Details of the curve following the inflection point "a" (mass loss is expressed in % of the weight of the sample defined by point "a").

from the inflection point "a" of 26%, i.e. close to the 27% calculated for a C 60 : 2CBrClH 2 molar ratio.

With the 1C 60 : 2CBrClH 2 stoichiometry, Rietveld refinement was carried out using Materials Studio and applying the rigid-body constraint for CBrClH 2 (the molecular structure was based on the data of Podsiadło et al.). [START_REF] Podsiadło | [END_REF] The positions and orientations of the molecules were refined with a single overall isotropic displacement parameter and a preferred orientation correction using the March-Dollase formula. 26 The refinement result is presented in Fig. 1, together with the experimental pattern. Surprisingly, both C 60 and CBrClH 2 are orientationally ordered within the co-crystals. The C 60 molecule is located at the 2a Wyckoff position for 2/m symmetry, whereas the solvent molecule is located at the 4h Wyckoff position (0, y = 0.2768(2), 1/2). The two halogen atoms (Cl and Br) are statistically disordered with a 50/50% distribution over their respective sites. For the lowtemperature phase of CBrClH 2 , the halogen atoms, Cl and Br, are also disordered with similar 0.5 occupancies to what was reported for the low-temperature phase of CBrClH 2 . The final Rietveld refinement yielded profile factors of R wp = 5.26% and R p = 3.83%, an overall isotropic temperature factor of 0.064 ± 0.001 and March-Dollase preferred orientation parameters of a* = 0.199IJ19), b* = 0.746IJ24), c* = 0.636 (26), and R o = 0.917 (6).

The stacking of alternating C 60 and CBrClH 2 molecules is presented in Fig. 3. The solvent molecules have their 2-fold axis along the monoclinic b axis and the halogen ligands pointing along the longer diagonal of the a-c plane.

To examine possible phase transitions, mixtures of cocrystals and their mother liquor were placed in stainless steel high-pressure pans for DSC studies and in Lindemann capillaries to identify structural changes. The resulting DSC curve can be seen in Fig. 4. The endothermic peak P1 corresponds to the melting of excess monoclinic (C2/c) CBrClH 2 at virtually the same temperature as the pure solvent. [START_REF] Yaws | Thermophysical Properties of Chemicals and Hydrocarbons[END_REF] It corresponds to a degenerate eutectic equilibrium in the C 60 -CBrClH 2 binary system. Peak P2, at 322 K, corresponds to a reversible solid-solid phase transition (see the inset in Fig. 4a) without a stoichiometric change of the co-crystal. As highlighted in Fig. 4b, the XRPD pattern at 333 K reveals a different structure for the co-crystal in relation to the one at 300 K. Preliminary DICVOL analysis revealed a hexagonal lattice with systematic absences compatible with the P6/mmm space group, isostructural to many other co-crystals of C 60 with halogenated methane derivatives 14,16 and to the hexagonal phase of C 60 . [START_REF] Céolin | [END_REF] The structure was analyzed using the FullProf Suite. [START_REF] Rodriguez-Carvajal | FullProf suite (2005 version)[END_REF] The C 60 molecule was modeled with spherical harmonics describing a homogeneous distribution of 60 C-atoms located on a sphere with an overall radius of 3.59 Å. The center of C 60 was positioned at the 1a Wyckoff position and the carbon of the tetrahedral CBrClH 2 molecule at the (1/3, 2/3, 1/2) position. The CBrClH 2 molecule was again described using a rigid body as for the low-temperature monoclinic structure. The C-atom position and orientation of the molecule were refined, obtaining a position of (0.329(6), 0.711(3), and 0. 544 (5)). The final Rietveld refinement yields profile factors of R wp = 4.02% and R p = 3.09%. Due to the fact that CBrClH 2 has a lower symmetry than the 2d site, the resulting orientation of the molecule is in no special relation to the rotation axis and is therefore orientationally disordered. The refined and experimental patterns are depicted in Fig. 4b.

Finally, the DSC peak P3 at around 390 K in Fig. 4a shows the peritectic invariant (hexagonal C 60 •2CBrClH 2 ↔ liquid L + FCC C 60 ), i.e. the desolvation process of the hexagonal cocrystal. The phase diagram of C 60 :CBrClH 2 is shown in Fig.

S1 (see the ESI †).

The order-disorder phase transition of the C 60 •2CBrClH 2 cocrystal at around 322 K is accompanied by an enthalpy change of 4.85 J g 1 (4.75(20) kJ mol 1 ), as determined from the Tammann diagram of the solvent-rich side of the equilibrium involving the monoclinic and hexagonal forms of the solvate (see Fig. S2,ESI †). This enthalpy change involves an entropy change of 14.7(6) J mol 1 K 1 which is of the same order as that involved in the order-disorder phase transition for the C 60 •cubane co-crystal, in which similarly both C 60 and cubane are orientationally frozen at low temperature. 11,12 For C 60 cocrystals with an order-disorder phase transition involving exclusively the solvent molecule, while C 60 displays orientational disorder in both phases, the entropy change is about twice as small, 6.1 kJ mol 1 K 1 for C 60 •2C(CH 3 )Cl 3 (at 212 K) 22 and 7.8 kJ mol 1 K 1 for C60•2CCl 4 (at 223 K). 29 These thermodynamic values support the structural results reported.

Conclusions

The room temperature co-crystals C 60 •2CBrClH 2 exhibit a monoclinic structure (space group C2/m), as revealed by X-ray powder diffraction, with both C 60 and CBrClH 2 molecules orientationally ordered, the only disorder being that of the halogen atoms, Cl and Br, distributed over two sites with 0.5 occupancies. The structure displays stacking of alternating C 60 and CBrClH 2 molecules with the solvent molecules having their 2-fold axis along the monoclinic b axis and the halogen ligands pointing along the longer diagonal of the a-c plane.

Without a change in stoichiometry, the co-crystal transforms at 322 K into a high-temperature hexagonal structure (space group P6/mmm) with a similar packing to previously reported hexagonal co-crystals with halogen-methane derivatives.

  ) Å, b = 17.412(2) Å, c = 10.0478(6) Å, β = 101.966IJ3)°, and V = 1697.0(5) Å 3 , and the systematic absences are compatible with the space group C2/m (isostructural to the C 60 •2CBr 2 H 2 co-crystals).

Fig. 1

 1 Fig. 1 Experimental (red circles) and calculated (black line) X ray pow der diffraction patterns at 303 K along with the difference profile (blue line) and Bragg reflections (vertical bars) of the monoclinic C2/m space group of the C 60 •2CBrClH 2 co crystal. The inset provides the data be tween 50 and 70°(2θ) at an increased scale.

Fig. 3

 3 Fig. 3 The (001) plane (left panel) and the (010) plane (right panel) of the crystal structure of monoclinic C 60 •2CBrClH 2 at 303 K. The overlap of the red (Br) and green (Cl) colored halogens highlights the occupational disorder.

Fig. 4

 4 Fig. 4 (a) DSC curve of C 60 •2CBrClH 2 in the presence of the mother liquor obtained in a sealed pan. Peak P1 corresponds to the melting of CBrClH 2 , peak P2 to the reversible order disorder phase transition of C 60 •2CBrClH 2 and peak P3 to the peritectic invariant (hexagonal C 60 •2CBrClH 2 ↔ L + FCC C 60 ). (b) XRPD patterns for C 60 •2CBrClH 2 in the presence of the mother liquor in a closed capillary as a function of temperature: 303 K, monoclinic solvate C 60 •2CBrClH 2 ; 333 K, hexagonal solvate C 60 •2CBrClH 2 ; 393 K, FCC C 60 + liquid. The pattern at the top of the figure is that of fcc C 60 and is provided for reference.For the pattern at 333 K, the refinement results have been indicated as well: calculated pattern (black line), difference between calculated and experimental pattern (blue line) and the Bragg reflections (vertical red bars) of the hexagonal P6/mmm space group of the C 60 •2CBrClH 2 co crystal obtained from the low temperature monoclinic co crystal by heating.

  in which both molecular species are orientationally ordered. The co-crystal reported here displays

	a Grup de Caracterització de Materials, Departament de Física, EEBE and
	Barcelona Research Center in Multiscale Science and Engineering, Universitat
	Politècnica de Catalunya, Av. Eduard Maristany, 10 14, 08019 Barcelona,
	Catalonia, Spain. E mail: josep.lluis.tamarit@upc.edu; Tel: +34934016564
	b LETIAM, EA7357, IUT Orsay, Université Paris Sud, Rue Noetzlin, 91405 Orsay
	Cedex, France
	c Institut Laue Langevin, 71 Avenue des Martyrs, CS 20156, 38042 Grenoble Cedex
	9, France
	d LOMA, UMR 5798, CNRS, Université de Bordeaux, F 33400 Talence, France
	e Laboratoire SMS, EA 3233, Normandie Université, Université de Rouen, F76821
	Mont Saint Aignan, France
	f Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de l'Observatoire,
	75006 Paris, France
	† Electronic supplementary information (ESI) available: Crystallographic infor
	mation files for monoclinic C 60 •2CBrClH 2 at 303 K (C 60 2CBrClH 2 C2M.cif) and
	hexagonal C 60 •2CBrClH 2 at 333 K (C 60 2CBrClH 2 P6MMM.cif). See DOI: 10.1039/
	c8ce00271a

Acknowledgements

This work has been supported by the Spanish MEC (FIS2017-82625-P) and by the Catalan government (2017SGR-42).

Conflicts of interest

The authors declare no competing financial interests.


The land rush

Transnational strategies for land grabing

Boris Petric

Over the last decade, a global land market in the agricultural and rural domains has emerged. States, multinational corporations and financial investors are seeking to acquire or control by purchase or lease agricultural areas in different regions around the world. These farms, which can cover several thousand hectares, serve different strategies. States justify these acquisitions by citing the food shortages their societies must come to terms with. Multinational corporations aim to increase their control over global raw material production in order to boost their development. Investors see land and raw materials as safe investments or even speculative opportunities in the context of today's financial crisis. These shifts in controlling production, which also reflect shifts in organising the market and regulations, have an impact on land issues in different societies.

As a result of recent events, this trend has been given considerable media coverage. It is as if we were witnessing a giant Monopoly game on a global scale.

One example is the international firm Benetton 1 , currently facing legal proceedings in Argentina. 2 The Benetton brothers own over 900,000 hectares in Argentina, which they have used to increase production of the merino wool they need to expand internationally their textile production. The Argentinian government's agreement to hand over this land to the Italian brand took the local Mapuche population, which has lived and farmed the region for centuries, by surprise. The Argentinian government took this opportunity to introduce the concept of exclusive private property to a region where natural resources have never been governed in these terms. With support from local and international NGOs, Mapuche leaders have begun legal proceedings against the Italian firm and the Argentinian government. This situation is evidence of a much more widespread process propagating a global norm like private property. It can be seen in the increasing power of bureaucracies, and therefore States, when it comes to giving control of large swathes of land to foreign parties. Some governments or bureaucracies, in collusion with transnational economic actors, tend to generalise the principle of property by giving deeds of ownership or leases to foreigners so that they can farm vast areas of rural land. However, many communities still consider that land cannot be disposed of and man's relationship with nature is based on various local rights of usage specific to each local reality.

A second example, which attracted considerable media attention, shows another trend resulting from the expansion of international agri-business: the development of powerful global economic groups. The Daewoo company, [START_REF][END_REF] almost a law unto itself in South Korea, attempted to take control of thousands of hectares of land in a bid to extend its agricultural activities in Madagascar. Its aim was to grow rice and cereal crops to supply the South Korean market while increasing its ability to take part in global trade in primary food resources. Despite the fact that 6 million Madagascans 4 lacked basic food resources, the Korean giant drew up a historical agreement with the Madagascan President Ravalomanana under which it would rent nearly one million hectares of arable land to produce food for export. When these negotiations were made public, they unleashed a wave of objections that forced Ravalomanana to resign from office. On 18 March 2009, the new Madagascan President, Andry Rajoelina, took the step of purely and simply cancelling the agreement by stating, "Madagascar's land is neither for sale nor for rent." It should be underlined that Ravalomanana's departure and objections to the deal had major international repercussions.

The Madagascar example shows two different trends that deserve our attention. First, there is a developing agri-business linked to the creation of an international market for primary food resources (rice, corn, soya, etc.) over which States have less and less influence, especially in terms of price setting. Secondly, it also shows how political movements are shifting from the local to the global level. Indeed, the political opposition in Madagascar is evidence of the growing number of situations where national political arenas are undergoing major changes in terms of the way they work. These countries are faced with strategies developed by major players in the agri-business industry, but are also experiencing the emergence of new and unprecedented social movements, where international and transnational actors oppose agri-business strategies. These political battles are caught up in global movements that can surpass local issues. In Madagascar, many different actors including NGOs, international organisations and also powerful countries with interests in the island, relayed local discontent and helped put a stop to the Daewoo project. It should be underlined that Madagascar is not a typical political space. A new form of global political conflict based on protecting nature is emerging in the country. The island is considered important from an international biodiversity point of view, and has received unprecedented attention from the different actors seeking to protect this global heritage. While this new form of interaction did cause Daewoo's project to fail, it also creates new challenges for Madagascan society.

New actors emerge and react to these economic powers. Local NGOs, like the International Land Coalition, become opposition forces, battling the strategies of multinational organisations by joining forces with international NGOs to defend small farmers.

However, this phenomenon is not limited to occasional conflicts where transnational institutions are merely opposition powers. International agencies (the UN, the UNDP, the FAO and the World Bank) and large international NGOs are playing an increasingly important role in coproducing norms in these different societies. They are therefore part of these societies' power structures. For instance, they develop programmes that help spread global norms liberalising the land market, generalising private property and

The land rush Transcontinentales, 10/11 | 2011 freedom of contract and protecting investments. One example is the American NGO Chemonics International, 5 which works to privatise land and promote contracts in rural areas in societies concerned by development.

9

The same institutions aim to develop programmes protecting biodiversity and heritage by creating protected areas (zones, national parks, etc.). Despite claiming to protect the environment, these policies can make natural areas into sanctuaries, which is problematic for local populations that depend on these natural resources for their livelihoods.

Consequently, these different groups play a key role in controlling, managing and appropriating shared natural areas (forests, deserts and islands). They have co-produced a new form of sovereignty.

Over and above these highly publicised examples, it is clear that social scientists must reflect on the complexity of this new architecture of influence as it will lead to new forms of tensions affecting land on a global scale. It affects many different players, and is not limited to the issue of land being appropriated for agri-business and cattle farming by transnational companies. These trends are therefore part of a wider process involving the reformulation of sovereignty over vast areas of land within the world's different societies.

As far as the history of humanity is concerned, there is nothing new about foreigners seizing land. Imperialist conquests and colonialist forays often sought to control land in order to develop activities for reasons unrelated to local societies.

The difference is probably that, today, powerful countries are adopting land acquisition strategies that are not located in post-colonial countries. As a result, China, Japan and Saudi Arabia are seeking to control land around the world. Large American companies like Monsanto have well documented strategies, and Indian, Chinese and French agri-food companies are also currently seeking to control land around the world to expand and outsource production.

In addition, financial players (including banks and investment funds) now offer financial products based on acquiring land in particular countries. Two French companies are especially active in this field. Charles Beigbeder's Agrogeneration Group has invested heavily by purchasing land in Ukraine. Olivier Combastet's Pergam Finance, which is based in South America, gives international clients the opportunity to buy land in Argentina, Chile and Uruguay. These companies cannot only be considered as "national", because they develop by building up "transnational" capital. The unprecedented development of this kind of actor shows the complexity of interdependencies affecting the globalisation of trade.

One of the risks we run is adopting the denunciatory attitude used by some media to describe the threat of agrarian neocolonialism 6 by reducing this process to actions by predatory Western companies. This kind of analysis overlooks the responsibilities of elite groups and national bureaucracies in implementing these social processes. We must therefore examine how transnational ties linking elite groups on different scales develop on local and global levels.

Moreover, there is a reason why many transactions are currently taking place in the postsocialist area, where bureaucracies have considerable leeway to transfer large areas of land that were previously collectively owned. The privatisation of land is developing as a result of new economic, social and political ties between local elite bureaucratic groups and global players. The liberalisation currently taking place in Ethiopia is particularly revealing in this respect. In a remarkable documentary film, [START_REF] Cf | Planète à vendre (Planet for Sale), documentary[END_REF] Alexis Marant illustrated this phenomena by the story of an Indian company setting up in Addis Ababa. Karuturi Global Limited managed to obtain a 50-year lease from the Ethiopian government to exploit land in the country. As the country's largest horticultural company, Karuturi Global Limited exports tulips to the Netherlands and thus increases its expansion in the global cut flower market. The Indian company also plans to grow wheat and corn to produce agrofuels. In the long run, it anticipates it will employ over 15,000 workers. Because the company exports almost all of its production, its setting up in Ethiopia has many consequences for Ethiopian society. These consequences should be studied further to understand the new situations affecting employment, conflicts over land and water use, different forms of exclusion, the strategic position of elite national groups, etc.

While this phenomenon is particularly visible in countries concerned by post-socialist transitions, it also affects other regions.

Generally, these situations are met with indifference from local populations; however, it is obvious that they can lead to new forms of conflict. New social movements appear criticising the importance of "foreigners" in the local economy and the government's role in economic regulation. One example is the Estragneros movement in Uruguay, where foreigners control one third of the country's land.

We are also currently witnessing occasional violent conflicts, such as those that affected Kyrgyzstan in 2004. People in this former Soviet republic, located at the Western border of China, rioted after learning that President Akayev had signed a secret agreement with China giving the Chinese control over a mountainous border zone where they hoped to find new water resources and new lands for pastoral activities for Chinese farmers. This phenomenon is also affecting the European continent. The changing status of land has played an essential role in the construction of Europe. The liberalisation of the land market changed considerably when Eastern European countries joined the European Union. Poland, Romania and Hungary all attracted many foreign investors. Some Western European companies set up in these countries by purchasing land or signing emphyteutic leases.

This situation led to the development of national populist political movements in Poland and Hungary. It also affects societies in Western Europe, where land acquisitions by foreigners are growing in importance. In France, for example, the Chinese company CofCo recently bought a vineyard in the Bordeaux region. The American company, Mondavi has also tried to buy a huge vineyard in Aniane, a village in the South of France and was obliged to resign taking into account the local opposition of his project. This current thematic issue of the Review focuses on case studies with both local and global dimensions by attempting to encourage discussion on several crucial questions concerning the reformulation of sovereignty and the complex ties between local, national and global players.

The new land rush is an extremely interesting field of study for social sciences. This issue outlines several areas of research that deserve further attention. The questions raised concern both social upheavals in different societies and future changes to the current world order.

bpetric@msh-paris.fr

The land rush Transcontinentales, 10/11 | 2011




  Study of non-premixed turbulent flames stabilized by a swirler  Improve performances of combustion plants  Reduction of pollutant emissions / emissions standards  Investigations on flame characteristics  Effects of oxygen enrichment  Effects of steam and CO 2 dilution  Effects of swirl intensity  Measurement and analysis of flue gases  Concentrations of NO X , CO, CO 2 , O 2 and SO 2 in the flue gases are measured.  ABB 220 and HORIBA PG250 multi-gas analyzers. NOx and CO emissions are reported for ɸ=0.8, Ω = 25%O 2 , Sn = 1.4 in the case of diluting with CO 2 and H 2 O separately (Fig.a) and for Sn=0.8 in the case of EGR (H 2 O+CO 2 ) (Fig.b). • Better stabilization is obtained with O 2 enrichment. The dilution with EGR destabilizes slightly the flame without blowout (up to 20%). • Dilution with CO 2 , H 2 O and EGR decreases highly NOx emissions and increases CO emissions. • Swirling part of the flow and the central recirculation zone are clearly identified by Stereo-PIV measurements. 1 *, T. Boushaki 1, * , JC. Sautet 2 , C. Chauveau 1 1 ICARE CNRS, 1C Avenue de la recherche scientifique, 45071 Orléans Cedex 2, France 2 Normandie University, CORIA UMR 6614, 76801 Saint Etienne du Rouvray, France * hajar.zaidaoui@cnrs-orleans.fr / toufik.boushaki@cnrs-orleans.fr  EGR dilution promotes flamme fluctuations and increases the lift-off heights about 60% compared to the case without EGR (Fig. g).  CO 2 dilution disrupts more the flame compared to water vapor dilution (Fig. e). In both cases, liftoff heights increase when increasing dilution ratios. g) In the case of H 2 O dilution (Fig. f), the flame becomes leaner, appears more lifted and remains compact. Lift-off height = f(%CO 2 ), Sn= 0.8, ɸ =0.8, 21%O 2 Lift-off height = f(%H 2 O), Sn= 0.8, ɸ =0.8, 21%O 2 Lift-off height = f(%O 2 ), Sn= 0.8, ɸ =0.8, EGR (10CO 2 -10H 2 double-pulsed Nd:YAG laser (25 mJ/pulse) at 532 nm, 10 Hz. 2 cameras TSI Powerview Plus 4MP CCDs, 12-bit output and 2048 x 2048 px 2 . Scheimpflug adapters. Seeding : Al 2 O 3 0.5-1 μm. Velocity mean fields of non reacting and reacting flows  Recirculation zone at the flow center, and the swirling jet in the peripheral flow.  Reacting flow: -greater radial expansion + larger recirculation zone. Apparatus : ICCD camera, a 105 mm UV lens, a 306 nm filter, an acquisition card with a computer.  OH* : Spontaneous emission on the band (0-0) at 306.4 nm  Visualization of flame front : stability, liftoff heights, flame lengths.  Two concentric tubes with a swirler in the annular part  Combustion chamber : 25 kW, dimensions 0.5x0.5x1 m 3  2 Planes of velocity measurements  3 Positions in the transverse plane

Acknowledgments

The authors are grateful for the financial support of this work provided by the French Government's Investissement d'Avenir program: LABEX CAPRYSSES, under GrantANR-11-LABX-0006-01.


est destinée au dépôt

Experimental and numerical studies of the influence of diluent on characteristic micro-scale combustion flame behaviour

Hugo Chouraqui, Christian Chauveau, Philippe Dagaut, Guillaume Dayma,

Fabien Halter

To cite this version: • Growing need to improve knowledge in the field of small-scale combustion and take advantage of high energy density of fuel [START_REF] Fernandez-Pello | Micropower generation using combustion: Issues and approaches[END_REF] in different applications such as portable power device [START_REF] Lee | Studies on a heat-recirculating microemitter for a micro thermophotovoltaic system[END_REF], micro-satellite thrusters [START_REF] Galie | Kinetic Enhancement of Mesoscale Combustion by Using a Novel Nested Doll Combustor[END_REF], heat sources [START_REF] Wierzbicki | Rh assisted catalytic oxidation of jet fuel surrogates in a meso-scale combustor[END_REF]. • Previous studies have been done with fuel/air mixtures. Combustion of a CH 4 /O 2 mixture with different diluents can improve the understanding of flame behaviour in micro-scale reactor by changing physical properties of the environment. Hence, be able to point out physico-chemical properties that play an important role in micro-scale combustion.

• Cylindrical quartz tube heated by 3 hydrogen/oxygen blowtorches.

• The temperature profile on the outer side is measured by a infrared camera A655sc.

Conclusions

1 . Goal of the study 2 .

 12 Chouraqui, Christian Chauveau, Philippe Dagaut, Guillaume Dayma, Fabien Halter. Experimental and numerical studies of the influence of diluent on characteristic micro-scale combustion flame behaviour. 37th International Symposium on Combustion, Jul 2018, Dublin, Ireland. 10.13140/RG.2.2.25682.81608. hal-01848556 Experimental set-up H. CHOURAQUI a , C. CHAUVEAU b , P. DAGAUT b , G. DAYMA a , F. HALTER a Experimental and numerical studies of the influence of diluent on characteristic micro-scale combustion flame behaviour

3 .••

 3 • A spectroscopy EMCCD camera ProEM 1600 with a CH* band-pass filter (20BPF1_430) is used to detect the flame positions. • CH 4 /diluent mixture is supplied in a 1.85 mm internal diameter reactor. (Quenching distance of CH 4 /air is 2.50 mm) Different flame behaviour a) FREI (Flame with Repetitive Extinction and Ignition): the ignition occurs downstream in high temperature region and extinction occurs upstream in low temperature region. b) Stable flame: flames with no relative motion with the reactor wall. CH 4 /Air stoichiometric mixture with a flow velocity of a) 0.4 m/s, 0.415 m/s, b) 0.7 to 1.0 m/s [6] For a given fuel/oxydant mixture: when the flow velocity increases  frequency increases. • For a given flow velocity: when the flame propagation speed of a mixture A is bigger than a mixture B  τ ie in A is smaller than in B. Image from FLIR camera of the external temperature for a stoichiometric mixture of CH 4 /air, a flow velocity of 0.7 m/s, in a 1.85 mm internal diameter tube Schematic of the data acquisition system and microreactor For a given fuel/oxydant mixture: flow velocity increases  the flame front goes toward colder wall reactor region • For a given flow velocity: when the adiabatic flame temperature of a mixture A is bigger than a mixture B  the front flame is located to colder wall reactor region.

• 2

 2 A laminar viscous model • The effect of enthalpy transport due to species diffusion in the energy equation • Ideal gas • Chemical, transport and thermodynamics properties are computed with the GRI-Mech 3.0 scheme Geometry/ Meshing: • A 2D-axisymmetric geometry • Total length of 10 cm, inner diameter of 0.925 mm, external diameter of 3.0 mm • Quadrilateral elements • 25 elements to mesh the inner radius, 20 elements for the wall. A constant size mesh of 33 µm where the temperature is the highest, and a progressively bigger size toward the coldest region  22500 elements for all the domain Boundary conditions: • Experimental external wall temperature is averaged and used as boundary condition • A velocity inlet boundary condition is applied on the left part of the geometry, and a pressure outlet boundary condition (1 atm) on the right part Flame position defined at the wall temperature as a function of the mixture flow velocity Wall temperature and flame front visualisation (CH* molar fraction) of the simulation of a CH 4 /air mixture with an inlet velocity of 0.6 m/s Flow a. FREI velocity domains increases b. Extinction is located to colder wall region c. Stable flame is located to colder wall region

τ ei air τ ei He/O 2 τ ei He/N 2 /O 2

  Flame position defined as the external wall temperature as a function of flow velocity

	FREI air
	FREI He/O 2
	FREI He/N 2 /O 2

• All characteristic flame behaviours are conserved with different diluents studied • The increase in He molar fraction in diluent 

• Flame/wall thermal interaction clearly identified experimentally with stable flames but not numerically Time between Extinction and Ignition

τ ie air τ ie He/O 2 τ ie He/N 2 /O 2

	Solution methods and solvers
	• Steady state simulation
	• The Stiff Chemistry Solver of ANSYS Fluent is
	used to solve the reactive flow
	• PISO method for velocity-pressure coupling is
	used to solve the discretized form of the
	Navier-Stokes system
	• A second order upwind spatial discretization
	is used and a least squares cell-based method
	for the evaluation of gradients
	4

. Experimental and numerical results

  Stable flame position defined at the external wall temperature as a function of the mixture flow velocity

						air
						He/O 2
						He/N 2 /O 2
	Diluent Air He/N 2 /O 2 21.18% O 2 20% He/O 2 21.68%	He 0% 39.20% 78.32%	N 2 80% 39.62% 0%	Diluent Air He/N 2 /O 2 He/O 2	Laminar burning velocity (cm/s) 30 61 119	Adiabatic flame temperature (K) 2221 2367 2519
	Compositions of diluents used in this study	Laminar burning velocity and adiabatic
	in molar fraction		flame temperature of a stoichiometric
					mixture CH 4 /diluent

Stable air Stable He/O 2 Stable He/N 2 /O 2 Simulation stable air Simulation stable He/O 2 /N 2

	Frequency of FREI variation as a function
	of inlet velocity

Acknowledgements

Time between Ignition and Extinction HC thanks the Ministry of Research en Higher Education (MESRI) for a PhD grant. Support from the CAPRYSSES project (ANR-11-LABX-006-01) funded by ANR through the PIA (Programme d'Investissement d'Avenir) is gratefully acknowledged.


Guilaine Boursier

Marion Alméras

Delphine Buthiau

Sébastien Jugant

Delphine Daubin

Nils Kuster

Anne-Marie Dupuy

Jean Ribstein

Kada Klouche

Jean-Paul Cristol
email: jp-cristol@chu-montpellier.fr

CT-pro-AVP as a tool for assessment of intravascular volume depletion in severe hyponatremia

Keywords: CT-pro-AVP Hyponatremia Intravascular volume Hypovolemia AVP, arginine vasopressin, CT-pro-AVP, C-terminal pro-arginine vasopressin, ECV, extracellular volume, FENa, fractional sodium excretion, IVV, intravascular volume, Ur/Cr, urea-to-creatinine ratio

Background: Assessment of volume status is essential to best manage hyponatremic patients but is not always accurate in clinical practice. The aim of this study was to evaluate the reliability of C-terminal portion of pro-arginine-vasopressin (CT-pro-AVP), a surrogate biomarker of vasopressin release, in assessing intravascu-lar volume (IVV) depletion in hypoosmolar hyponatremic patients.

Methods: Plasma CT-pro-AVP and urea-to-creatinine ratio (Ur/Cr) were performed in 131 hospitalized patients presenting chronic severe hypoosmolar hyponatremia. At hospital discharge, their IVV was evaluated regardless of CT-pro-AVP concentrations. All patients were then classified as decreased or as normal/expanded IVV group.

Results: Plasma CT-pro-AVP levels were higher in patients with decreased IVV (34.6 vs. 11.3 pmol/L, p b 0.001) and exhibited a reliable performance for assessment of decreased IVV (ROC AUC at 0.717 [95% CI 0.629-0.805]). The combination of CT-pro-AVP and Ur/Cr resulted in an improved ROC AUC up to 0.787 (95%CI 0.709-0.866).

Conclusions: Our findings support the hypothesis that CT-pro-AVP plasma level may reflect IVV and would be a tool for its assessment. This performance has been magnified by its combination with Ur/Cr. A dual-marker strategy may help clinicians to optimize the management of severe hyponatremia especially in case of confusing clinical presentations.

Introduction

Hyponatremia, defined as a plasma sodium concentration of less than 135 mmol/L, occurs frequently in hospitalized patients and has prognostic implications. A recent study of [START_REF] Schrock | Elevated blood urea nitrogen/creatinine ratio is associated with poor outcome in patients with ischemic stroke[END_REF]276 Intensive Care Unit patients reported the prevalence of hyponatremia at 12.9% and of severe hyponatremia (sodium level ≤125 mmol/L) at 5.9%. Hospital mortality reached more than 40% among these severe patients [START_REF] Vandergheynst | Incidence and prognosis of dysnatraemia in critically ill patients: analysis of a large prevalence study[END_REF]. This mortality was not only due to the associated cause of hyponatremia but also to its therapeutic management. Indeed, the evaluation of hyponatremia is not always accurate because of the lack of constant and specific signs. In the study of Hula et al., significant management errors were reported in 33% of hyponatremia and conferred a higher mortality [START_REF] Huda | Investigation and management of severe hyponatraemia in a hospital setting[END_REF]. Hypotonic hyponatremia is an imbalance of water and sodium homeostasis induced by a proportional excess of total body water relative to the total body sodium [START_REF] Schrier | Water and sodium retention in edematous disorders: role of vasopressin and aldosterone[END_REF][START_REF] Verbalis | Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations[END_REF][START_REF] Spasovski | Clinical practice guideline on diagnosis and treatment of hyponatraemia[END_REF]. The assessment of effective intravascular volume (IVV) is a main condition to decide appropriate treatment as rehydration [START_REF] Spasovski | Clinical practice guideline on diagnosis and treatment of hyponatraemia[END_REF]. The routine approach consists of patient's history and physical examination but the assessment of volume status is not always reliable and the distinction between total extracellular volume (ECV) and effective IVV status is difficult in clinical practice [START_REF] Verbalis | Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations[END_REF][START_REF] Spasovski | Clinical practice guideline on diagnosis and treatment of hyponatraemia[END_REF][START_REF] Schrier | Hyponatraemia: more than just a marker of disease severity?[END_REF]. In fact, as seen in Fig. 1, an expanded ECV could be associated with a decreased IVV, such as congestive heart failure, hepatic cirrhosis, and nephrotic syndrome, or with an expanded IVV such as renal failure.

Arginine vasopressin (AVP) is one of the key hormones of water homeostasis. Urine sodium concentration and osmolality are usually measured to assess its activity. The suppression of AVP activity by increased IVV generally results in urine osmolality b100 mOsm/kg [START_REF] Spasovski | Clinical practice guideline on diagnosis and treatment of hyponatraemia[END_REF], while its stimulation by hypovolemia increases urine osmolality above serum osmolality. Consequently, urine osmolalities between 100 mOsm/kg and the level of plasma osmolality represent a gray area in which it is difficult to precisely assess fluid status [START_REF] Spasovski | Clinical practice guideline on diagnosis and treatment of hyponatraemia[END_REF][START_REF] Hoorn | Development of severe hyponatraemia in hospitalized patients: treatment-related risk factors and inadequate management[END_REF]. However, urine analysis is influenced by diuretics and urine samples are often difficult to be taken, especially in emergency units. Direct measurement of endogenous AVP in plasma could be therefore useful to assess IVV [START_REF] Schrier | Hormones and hemodynamics in heart failure[END_REF][START_REF] Robertson | The use of vasopressin assays in physiology and pathophysiology[END_REF], but it is not suitable for use in clinical practice due to the binding of AVP to platelets and its unstability in isolated plasma [START_REF] Szinnai | Changes in plasma copeptin, the C-terminal portion of arginine vasopressin during water deprivation and excess in healthy subjects[END_REF][START_REF] Bolignano | Copeptin (CTproAVP), a new tool for understanding the role of vasopressin in pathophysiology[END_REF]. In contrast, the C-terminal portion of provasopressin (CT-pro-AVP), which is co-secreted with AVP, is much easier to quantify. CT-pro-AVP is a 39-amino acid glycopeptide that may have a role during the intracellular processing of provasopressin. It is produced together with AVP in an equimolar ratio and has similar kinetics as described for AVP. CT-pro-AVP is now frequently used as a surrogate marker for AVP secretion in clinical studies [START_REF] Schrier | Hormones and hemodynamics in heart failure[END_REF][START_REF] Robertson | The use of vasopressin assays in physiology and pathophysiology[END_REF][START_REF] Szinnai | Changes in plasma copeptin, the C-terminal portion of arginine vasopressin during water deprivation and excess in healthy subjects[END_REF][START_REF] Bolignano | Copeptin (CTproAVP), a new tool for understanding the role of vasopressin in pathophysiology[END_REF][START_REF] Morgenthaler | Assay for the measurement of copeptin, a stable peptide derived from the precursor of vasopressin[END_REF].

The aim of this study was therefore to evaluate the reliability of the plasma CT-pro-AVP concentration in assessing IVV status in hypoosmolar hyponatremic patients. Our hypothesis was that CT-pro-AVP may reflect IVV and should help for the management of severe hyponatremia. If IVV is decreased, AVP levels, and so CT-pro-AVP levels, should dramatically increase much more than in the case of syndrome of inappropriate secretion of antidiuretic hormone or in the case of expanded IVV (in which CT-pro-AVP concentrations should decrease). We sought also to compare it to routine biological parameters used to diagnosis hyponatremia in clinical settings including the ratio of plasma urea to plasma creatinine [START_REF] Schrock | Elevated blood urea nitrogen/creatinine ratio is associated with poor outcome in patients with ischemic stroke[END_REF][START_REF] Leibovitz | Dehydration among long-term care elderly patients with oropharyngeal dysphagia[END_REF][START_REF] Miura | Prognostic impact of blood urea nitrogen changes during hospitalization in patients with acute heart failure syndrome[END_REF].

Patients and methods

Study design and population

All hospitalized patients presenting hyponatremia at the University Hospital of Montpellier between July 2012 and January 2013 were screened for the study. Inclusion criteria included an age older than 18 years and a chronic (≥ 48 h) severe hypoosmolar hyponatremia defined as a plasma sodium concentration less than 125 mmol/L and a plasma osmolality less than 275 mOsm/kg. Patients with renal failure with an estimated glomerular filtration rate b15 mL/min/1.73 m 2 were not eligible. The study was performed according to the principles of the Declaration of Helsinki and was approved by the local ethics committee. Demographic, clinical and laboratory data were collected during hospitalization. All laboratory values (plasma glucose, creatinine, urea, urine sodium excretion and urine osmolality) were collected upon the occurrence of hypoosmolar hyponatremia within first sodium measurement.

Diagnostic criteria and classification

The assessment of the ECV, IVV and body sodium compartments was reinterpreted after the discharge of patients by three trained investigators (KK, JPC, SJ) using weight (at admission and at discharge), clinical picture (orthostatic hypotension, clinical signs of dehydration, history), therapeutic management (including saline loads), response to treatment, biology (urinary sodium concentration), and final diagnosis according to consensus-based clinical recommendations [START_REF] Verbalis | Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations[END_REF][START_REF] Spasovski | Clinical practice guideline on diagnosis and treatment of hyponatraemia[END_REF]. All patients were classified into one of the two categories depending on IVV status as shown in Fig. 1: 1) Decreased IVV and 2) Normal or expanded IVV. The investigators were blinded to results of plasma CT-pro-AVP measurements.

Laboratory assessment

Blood samples were collected into lithium heparin tubes and were processed at the clinical chemistry laboratory. A plasma aliquot was stored at -20 °C for later analysis. Routine laboratory parameters were measured by automated Cobas 8000 analyzer (Roche Diagnostics, Meylan, France). Urine and plasma samples were analyzed using ionselective electrodes for sodium. The glutamate dehydrogenase and hexokinase method were used for the determination of plasma urea and glucose levels and IDMS-traceable creatinine enzymatic assays was used for plasma creatinine measurement. Osmolality was measured with an osmometer by means of freezing point depression (ThermoFisher Scientific, Clichy, France). The effective osmolality was obtained as serum osmolality less serum urea level in millimoles per liters [START_REF] Milionis | The hyponatremic patient: a systematic approach to laboratory diagnosis[END_REF][START_REF] Oster | Hyponatremia, hyposmolality, and hypotonicity: tables and fables[END_REF]. Plasma urea-to-creatinine ratio was calculated by the formula: (urea (mmol/L) / creatinine (μmol/L)) × 10 3 [START_REF] Schrock | Elevated blood urea nitrogen/creatinine ratio is associated with poor outcome in patients with ischemic stroke[END_REF][START_REF] Leibovitz | Dehydration among long-term care elderly patients with oropharyngeal dysphagia[END_REF][START_REF] Miura | Prognostic impact of blood urea nitrogen changes during hospitalization in patients with acute heart failure syndrome[END_REF]. The fractional sodium excretion (FENa) was calculated by the formula: 100 × [urinary sodium (mmol/L) × (plasma creatinine (μmol/L) / 1000)] / [plasma sodium (mmol/L) × urinary creatinine (mmol/L)].

The CT-pro-AVP was performed from frozen lithium heparin plasma samples using the CT-pro-AVP assay on the Kryptor Compact Plus systems (Thermofisher Scientific, Clichy, France) which allows a time to result of 18 min as previously described [START_REF] Sebbane | Early rule out of acute myocardial infarction in ED patients: value of combined high-sensitivity cardiac troponin T and ultrasensitive copeptin assays at admission[END_REF]. For values between 3 and 16 pmol/L, within-and between-assay imprecision ranged from 2.4% to 11.3% and from 3.9% to 10.2%, respectively. The LoD was 1.90 pmol/L in our conditions.

Appropriate AVP stimulation

History Physical examination Blood & Urine analysis

Low ECV

High ECV

Low IVV Normal or Expanded IVV

Extra renal losses

Vomiting, diarrhea, pancreatitis, peritonitis, malnutrition.

Renal losses

Diuretic

Data analysis

Characteristics of study patients are presented as frequencies (percent) for categorical variables and median (interquartile range, IQR) for continuous variables. Patient groups were compared using Wilcoxon test for continuous variables and Fisher's exact test for categorical variables. Age and sex adjusted linear regression was used to compare CT-pro-AVP, urea to creatinine ratio (Ur/Cr), fractional sodium excretion (FENa) and urinary osmolality values according to IVV status. Regression coefficients with 95% confidence intervals (CI) were determined. Overall diagnostic values were quantified by calculating the area under the receiver operating characteristic (ROC) curve (AUC) using the trapezoidal method, with 95% CI computed by using the Delong method. Comparison between AUCs was performed through the Delong test for correlated ROC curves. Sensitivity, specificity, and predictive values were calculated along with 95% CI based on binomial distribution. Optimal CT-pro-AVP thresholds were determined using the Youden index. The significance level was set at 5% for all tests. Statistical analysis was performed using R 2.15 (R Foundation for Statistical Computing, Vienna, Austria).

Results

Characteristics of population study

A total of 131 hypoosmolar hyponatremic patients were included into the study. Their median age was at 71 years with a slight predominance of females (58%). Plasma sodium concentrations ranged between 102 and 125 mmol/L. Median (IQR) measured and effective osmolality were at 260 (249-269) and 252 (244-259) mOsm/kg respectively, whereas median urinary osmolality was at 295 (233-487) mOsm/kg and median FENa was 0.6 (0.2-1.3) %. All other characteristics of study population are displayed in Table 1. Hyponatremia was induced by sodium depletion due to renal or non-renal losses in 29%, water and sodium expansion with third spacing or oliguria in 34%, syndrome of inappropriate secretion of antidiuretic hormone in 23% and high water with low solute intake in 14% of the patients.

Comparison of the two groups depending on IVV status

Table 1 provides the characteristics of the hyponatremic patients divided into groups depending on IVV status. Within the 73 patients who had a hyponatremia associated with a decreased IVV, 36 (49.3%) had a high ECV. The comparison between groups with decreased IVV and with normal or expanded IVV showed no differences regarding to age, sex, natremia and natriuresis, FENa and urinary osmolality (Table 1 and Fig. 2A,B). In addition, percentage of patients with a FENa ≤ 1% was not significantly different between the two groups (23.8% in patients with decreased IVV and 37.5% in patients with normal or expanded IVV). By contrast, plasma urea, plasma creatinine and Ur/Cr ratio were significantly higher in the decreased IVV group (Fig. 2C). Indeed, Ur/Cr ratios were 1.3 fold higher in patients with decreased IVV than patients with normal or expanded IVV; independently of age and sex according to linear regression analysis. In all our hyponatremic population, median plasma CT-pro-AVP level was 22.1 pmol/L and ranged from 1.9 to 1073 pmol/L. The values differed significantly between groups according to IVV status as shown in Fig. 2D. A doubling of plasma CT-pro-AVP levels (34.6 vs. 11.3 pmol/L) was observed in patients in whom IVV was judged decreased, than others. By linear regression analysis, the association of CT-pro-AVP with decreased IVV status was independent of age and sex.

Diagnostic performance of CT-pro-AVP, FENa and Ur/Cr for assessment of IVV

Sensitivity and specificity for assessment of decreased IVV are reported in Table 2. Decision thresholds were determined using the 99th percentile of a general population (CT-pro-AVP N 18.9 pmol/L) or empiric values (Ur/Cr N 100, FENa ≤ 1%). The diagnostic performance of FENa was poorer than Ur/Cr ratio, thus we used Ur/Cr levels as a validated determinant of IVV extracellular body volume status. In addition, CT-pro-AVP plasma concentrations and Ur/Cr levels were independent of each other. Since both plasma Ur/Cr ratio and CT-pro-AVP levels significantly distinguished between the two groups, we tested their performance in isolated manner or in combination for the assessment of IVV depletion in all hyponatremic patients. The ROC AUC was 0.717 (95% CI. 0.629-0.805) for CT-pro-AVP concentrations and 0.698 (95% CI, 0.608-0.788) for Ur/Cr and it was not significantly different. Combining CT-pro-AVP with Ur/Cr resulted in improved ROC AUC up to 0.787 (95% CI. 0.709-0.866) with a significant difference compared with that of Ur/Cr (p = 0.011) and CT-pro-AVP (Fig. 3). Using the Youden index, the thresholds to distinguish decreased IVV from others were 16.3 pmol/L and 91.9 for CT-pro-AVP and Ur/Cr respectively. As seen in Table 2, adding CT-pro-AVP to Ur/Cr, set at a cut-off value of 18.9 pmol/L and 100 respectively, increased specificity for decreased IVV assessment from 83.9% to 94.6%.

Discussion

Investigating 131 patients with severe hyponatremia, we found that CT-pro-AVP plasma concentrations, as well as plasma Ur/Cr ratio, were significantly elevated in those with decreased IVV. Our results indicate also that plasma CT-pro-AVP levels are a better discriminant than Ur/Cr ratio for the assessment of IVV status and that the combination of both levels improved significantly their specificity. Hyponatremia is the most common electrolyte disorder in clinical medicine and is associated with substantial morbidity and mortality. A precise diagnostic evaluation for initiation of the adequate treatment is the sole condition to guarantee the best outcome. The diagnosis based on clinical signs and routine laboratory parameters has a limited sensitivity and specificity [START_REF] Musch | Combined fractional excretion of sodium and urea better predicts response to saline in hyponatremia than do usual clinical and biochemical parameters[END_REF]. Readily available and reliable parameters for the differential diagnosis of hyponatremia are therefore needed to facilitate a timely therapeutic strategy.

Hyponatremia often develops as a consequence of water intake associated with water retention due to elevated levels of AVP [START_REF] Robertson | Antidiuretic hormone. Normal and disordered function[END_REF][START_REF] Robertson | Regulation of arginine vasopressin in the syndrome of inappropriate antidiuresis[END_REF]. The amount of plasma AVP is regulated by osmotic and non-osmotic stimuli namely the blood volume contraction. When decreased osmolality and IVV (more than 10%) occurs simultaneously, AVP release is not suppressed in order to maintain primarily blood volume. Thus, in hyponatremia, AVP levels are either appropriately (in case of decreased IVV) or inappropriately (in syndrome of inappropriate secretion of antidiuretic hormone) elevated in relation to osmolar status (Fig. 1). The persistence of AVP release due to non-osmotic hemodynamic stimuli is predominantly responsible for water retention and hyponatremia with decreased IVV, as well as in edema-forming disorders such as heart failure, liver cirrhosis and nephrotic syndrome [START_REF] Schrier | Water and sodium retention in edematous disorders: role of vasopressin and aldosterone[END_REF]. It is then questionable whether there is a cut off differentiating appropriate and inappropriate AVP increases and whether AVP measurement is helpful in the differential diagnosis of hyponatremia. The measurement of AVP is however cumbersome. CT-pro-AVP is produced in equimolar amounts to AVP and its levels mirror AVP levels. CT-pro-AVP also shows parallel changes during disordered water states as shown for AVP [START_REF] Szinnai | Changes in plasma copeptin, the C-terminal portion of arginine vasopressin during water deprivation and excess in healthy subjects[END_REF][START_REF] Bolignano | Copeptin (CTproAVP), a new tool for understanding the role of vasopressin in pathophysiology[END_REF]. As compared to AVP, CT-pro-AVP is very stable in plasma and serum and can be easily determined including with a fully automatized assay such as Kryptor Compact Plus [START_REF] Sebbane | Early rule out of acute myocardial infarction in ED patients: value of combined high-sensitivity cardiac troponin T and ultrasensitive copeptin assays at admission[END_REF], which have performances closed to those of the reference method initially developed [START_REF] Morgenthaler | Assay for the measurement of copeptin, a stable peptide derived from the precursor of vasopressin[END_REF]. Consequently, CT-pro-AVP appears as a new promising diagnostic tool in the differential diagnosis of patients with hypoosmolar hyponatremia.

In our study, median CT-pro-AVP values were significantly higher in patients with decreased IVV compared with other groups. In case of decreased IVV, CT-pro-AVP levels were indeed above the 99th percentile of a general population (18.9 pmol/L according to the most recent study) [START_REF] Keller | Copeptin improves early diagnosis of acute myocardial infarction[END_REF]. These data extend the previous observations by Fenske et al. [START_REF] Fenske | Copeptin in the differential diagnosis of hyponatremia[END_REF] suggesting that CT-pro-AVP levels are higher in hyponatremic patients with sodium depletion when compared to syndrome of inappropriate secretion of antidiuretic hormone patients or control patients. Nevertheless, we observed a large overlap in CTpro-AVP values and CT-pro-AVP sensitivity and specificity do not allow to reliably differentiate between all hyponatremia causes. Few of our hyponatremic patients showed a normal level of their basal CTpro-AVP, as described in healthy population (b 7.1 pmol/L in women and b 9.4 pmol/L in men) [START_REF] Morgenthaler | Assay for the measurement of copeptin, a stable peptide derived from the precursor of vasopressin[END_REF], stressing the fact that several causes may be involved in the same patient inducing a multifactorial AVP stimulation.

In routine evaluation of hyponatremic patients, plasma Ur/Cr ratio has been used as a marker of IVV in several studies [START_REF] Schrock | Elevated blood urea nitrogen/creatinine ratio is associated with poor outcome in patients with ischemic stroke[END_REF][START_REF] Leibovitz | Dehydration among long-term care elderly patients with oropharyngeal dysphagia[END_REF][START_REF] Miura | Prognostic impact of blood urea nitrogen changes during hospitalization in patients with acute heart failure syndrome[END_REF]. We confirmed herein that Ur/Cr ratio is significantly higher in patients with a decreased IVV compared to others with, however, a relatively weak AUC and sensitivity. Urea levels depend on dehydration but are also linked to protein degradation while creatinine generation is related to muscle metabolism. In addition, the relationship between dehydration and Ur/Cr ratio would vary according to gender, race, or occurrence of atrial fibrillation [START_REF] Schrock | Elevated blood urea nitrogen/creatinine ratio is associated with poor outcome in patients with ischemic stroke[END_REF]. These observations may explain, at least for a part, the poor sensitivity of Ur/Cr ratio alone for IVV assessment. It has been suggested that Ur/Cr ratio should be used in combination with other indexes such as urinary/serum osmolality [START_REF] Leibovitz | Dehydration among long-term care elderly patients with oropharyngeal dysphagia[END_REF]. In our study, we investigated an original diagnostic approach with a dual-marker (plasma CT-pro-AVP with a cut-off value at the 99th percentile and Ur/Cr) to identify decreased IVV in hypoosmolar hyponatremic patients. We found that markers are both effective but their combination is more effective. This combined index improves both AUC and specificity compared with Ur/Cr or CT-pro-AVP alone.

This work is a pilot study and limitations should be underlined. First of all, the IVV is only assessed by clinical parameters and not by reference methods such as isotopic one which cannot be used in clinical practice. Imaging methods were not available to assess IVV status. Second, our study is a monocentric observational study with a relatively small number of patients.

In clinical practice, the precise evaluation of IVV is of paramount importance to avoid errors in hyponatremia management including diuretic abuse and erroneous fluid restriction or intravenous fluid infusion. Since IVV status is often difficult to evaluate at the bedside, a simple plasma biomarker would be helpful to determine appropriate therapeutic option in such a circumstance. Our findings support the hypothesis that CT-pro-AVP, as a surrogate for AVP release, may reflect IVV and the combination of CT-pro-AVP with Ur/Cr ratio would be even better. A strategy considering CT-pro-AVP and Ur/Cr measures could be relevant in some difficult clinical presentations of hyponatremia but further studies are needed to confirm the reliability of CT-pro-AVP and Ur/Cr levels in management of hypoosmolar hyponatremia. Decision thresholds were determined using the 99th percentile of a general population (CT-pro-AVP N 18.9 pmol/L) or empiric values (Ur/Cr N 100, FENa ≤ 1%). Abbreviations: CT-pro-AVP, C-terminal pro-arginine vasopressin; Ur/Cr, urea to creatinine ratio; FENa, fractional sodium excretion; PPV, positive predictive value; NPV, negative predictive value; and CI, confidence interval.

Fig. 2 .

 2 Fig. 2. Fractional sodium excretion, urinary osmolality, urea-to-creatinine ratio and plasma CT-pro-AVP levels according to intravascular volume status. A. Fractional sodium excretion calculated by the formula: 100 × [urinary sodium (mmol/L) × (plasma creatinine (μmol/L) / 1000)] / [plasma sodium (mmol/L) × urinary creatinine (mmol/L)]; B. Measured urinary osmolality; C. Urea-creatinine ratio calculated by the formula: (urea / creatinine) * 103; and D. Log plasma CT-pro-AVP concentrations (pmol/L). Scatter plots with red solid median line and box plots depicting interquartile ranges. CTpro-AVP values are reported using a logarithmic scale. Patient groups were compared using Wilcoxon test with a significance level of 5%. Further age and sex adjusted linear regression did not change the significance. Abbreviations: CT-pro-AVP, C-terminal pro-arginine vasopressin; FENa, fractional sodium excretion; and IVV, intracellular fluid volume.

Fig. 3 .

 3 Fig. 3. Receiver operating curve analysis of individual or combined CT-pro-AVP and Ur/Cr ratio for assessment of intravascular volume depletion. Abbreviations: CT-pro-AVP, C-terminal pro-arginine vasopressin; and Ur/Cr, Urea to creatinine ratio.

Table 1

 1 Baseline characteristics of the study population.

	Patient's characteristics	Total	Decreased IVV	Normal or expanded IVV	p value
	Diagnosis	131 (100)	73 (55.7)	58 (44.3)
	Sex				0.724
	Male	58 (44.3)	31 (42.5%)	27 (46.6%)
	Female	73 (55.7)	42 (57.5%)	31 (53.4%)
	Age, years	71 (58-84)	76 (58-86)	66 (58-81)	0.145
	Plasma sodium, mmol/L	121 (117-124)	121 (118-123)	122 (116-124)	0.893
	Measured plasma osmolality, mOsm/kg	260 (249-269)	264 (252-275)	255.5 (243-263)	0.001
	Effective plasma osmolality, mOsm/kg	252 (244-259)	255 (247-261)	250 (239-256)	0.009
	Glycemia, mmol/L	6.3 (5.2-7.8)	6.4 (5.6-8.6)	6.1 (5.0-7.4)	0.087
	Plasma urea, mmol/L	5.7 (3.7-10.4)	7.2 (5.4-13.5)	4.4 (3.02-5.9)	b0.001
	Creatininemia, μmol/L	69.0 (49.0-100.0)	84.0 (61.0-111.0)	60.5 (44.3-72.0)	b0.001
	Urinary sodium, mmol/L	43 (17-68)	30 (16-66)	44 (21-68)	0.334

Data are shown as n (%) or median (Q25-Q75). Patient with decreased IVV and others were compared using Wilcoxon test for continuous variables and Fisher's exact test for categorical variables with a significance level of 5%. Abbreviation: IVV, intracellular fluid volume.

Table 2

 2 Diagnostic performance of CT-pro-AVP and Ur/Cr and their combination for assessment of IVV depletion. AVP N 18,9 pmol/l AND Ur/Cr N 100 94.6% 29.3% 88.0% 50.0% CT-pro-AVP N 18,9 pmol/l OR Ur/Cr N 100 51.8% 84.0% 70.0% 70.7% N = 131 hospitalized patients. Performance values are shown along with 95% CI.

	Decision rule	Specificity Sensitivity PPV	NPV
	CT-pro-AVP N 18,9 pmol/L	62.5%	66.7%	70.4% 58.3%
	Ur/Cr N 100	83.9%	46.7%	79.5% 54.0%
	Fractional sodium excretion ≤ 1%	62.8%	23.8%	28.0% 55.5%
	CT-pro-

Acknowledgment

The authors would like to thank the nursing, technical, and medical staff at the critical care unit, internal medicine department and biochemistry laboratory for their assistance throughout the study. The CT-pro-AVP reagents used in this study were kindly provided by B.R.A.H.M.S., France.

Conflict of interest

The authors declare no financial or competing interests.