Gwénaël Caravaca

Arnaud Brayard

Emmanuelle Vennin

Michel Guiraud

Laetitia Le Pourhiet

Christophe Thomazo

Anne-Sabine Grosjean

Nicolas Olivier

Emmanuel Fara

Gilles Escarguel

New characterization of the Early Triassic Sonoma Foreland basin (western USA) and its controlling factors using multi-scale integrated approaches

come   L'archive ouverte pluridisciplinaire

Context and localization

In the aftermath of the end-Permian mass extinction (~252 Ma), the Sonoma Foreland Basin (SFB) provides excellent sedimentary and fossil records to describe and understand the Early Triassic biotic recovery. Nevertheless, despite its importance, the basin itself has been poorly constrained until now and most of its controlling factors remain unclear.

The SFB area roughly corresponds to a 600 x 1000 km rectangle encompassing Utah, Idaho, western Wyoming and eastern Nevada (Fig. 1). It displays a ~2Ga-long, complex geodynamical history marked by a succession of tectono-sedimentary events. During the Early Triassic, the SFB was a shallow marine basin, bordered by the Golconda Allochton to the West, and by the remnants of the Ancestral Rockies (ARM) to the East (Fig. 1). Continental borders are still uncertain.

A multi-scale and multi-disciplinary work was conducted on ~50 sections from the literature and field-based data to characterize the paleoenvironmental parameters of the SFB, their 4D evolution as well as their associated controls.

New characterization of the Early Sonoma Foreland basin (western USA) and its controlling factors using multi-scale integrated approaches

Local-scale approaches

Sedimentology (Fig. 2)

•
Fine and detailed study of each individual sections allowed to characterize main lithologies, sedimentary structures and facies to determine local depositional settings and their vertical/lateral evolutions.

Paleontology (Fig. 2)

• Fossils were crucial for high-resolution framework and biostratigraphical correlations, and to decipher the paleoenvironments associated with sedimentary data.

Geochemistry

• Fluctuations of the paired carbon isotopes and trace & major elements concentrations gave info about the composition of the water column and its oxygenic state. Secondary processes (diagenesis) impact was also addressed.

Conclusion

Using this multi-scale integrated method, we were able to better reconstruct the Early Triassic Sonoma Foreland Basin and to decipher previously unknown structures and the controls of this long-lost basin.

Our results highlight a complex interplay of local-to basin-scale controlling factors, responsible for the spatial distribution and migration through time and space of the depositional settings present in both northern and southern parts of the SFB (Fig. 6).

We are therefore able to track the 4D evolution of the paleoenvironments and the multi-scale controlling factors of the Sonoma Foreland Basin.

Data integration and basin-wide interpretations

Integration of these multi-scale data allowed to confirm the foreland nature of this basin.

We also distinguished two parts within the basin: North-SFB and South-SFB (Fig. 4). This previously unrecognized spatial subdivision is highlighted by a central "transitional" part, potentially a topographic high that is yet to be thoroughly detailed (Fig. 4). This subdivision had major consequences through locally-controlled forcing parameters over the sedimentary systems of the entire SFB. 7 facies associations (Fig. 5) were therefore defined to decipher the paleoenvironmental evolution of the entire SFB during the Early Triassic.

Basin-scale approaches

Geodynamical framework (Fig. 3)

• Lithospheric heritage and rheological behavior of the SFB basement were of paramount importance to determine the first order control over subsidence and sedimentary accumulation. 2D numerical modeling of the basement was performed to this end.

Sedimentology (Fig. 3)

• Spatial repartition of the Early Triassic sedimentary thickness was mapped.

Geochemistry

• Geochemical signals and secondary alteration processes were used to highlight locally-or globallydriven (exogenic) forcing on the SFB water column chemistry.

Paleontology

•

The spatio-temporal evolution of marine communities was investigated.

Figure 2 :

 2 Figure 2: Lithostratigraphic columns, associated main general depositional environments and biostratigraphic correlations for 8 selected sections of the SFB. These columns illustrate local succession of environments within each outcrop, but also regional to larger scale similitudes and discrepancies in dominant lithologies and thicknesses (cf. Fig. 3) of the sedimentary record of the SFB. CR: Confusion Range; HS: Hot Springs; LWC: Lower Weber canyon; M: Minersville; PR: Pahvant Range; RC: Rock Canyon; SC: Sheep Creek; T: Torrey.

Figure 1

 1 Figure 1: a) Early Triassic location of the Sonoma Foreland Basin (SFB); b) Simplified paleogeographic map of the SFB and bordering reliefs

Figure 5 (

 5 Figure 5 (top): Simplified synthetic depositional model for the 7 basin-scale facies associations characterized for the Early Triassic SFB. FWWB: Fair weather wave base; SWB: Storm wave base.

Figure 6 :

 6 Figure 6: Illustration of the basin -wide spatial distribution of the main depositional settings in the SFB during the a) Middle Smithian (Owenites beds), and during the b) Upper Smithian (Anasibirites beds). For depositional settings, refer to Fig. 5.

Figure 3 :

 3 Figure 3: Isopach map of the SFB showing the spatial repartition of the sedimentary thicknesses for the Early Triassic up to the Upper Smithian. Difference in tectonic subsidence rates can be observed between northern and southern parts of the SFB. Red lines indicate the limits of the Archean to Mesoproterozoic lithospheric terranes that compose the basement of the SFB; GCB: Archean Grouse Creek Block, WT: Archean Wyoming Terrane; MT: Paleoproterozoic Mojave Terrane; YT: Paleoproterozoic Yavapai Terrane; FT: Mesoproterozoic Farmington Terrane (mobile belt).

  Gwénaël Caravaca* 1 , Arnaud Brayard 1, , Emmanuelle Vennin 1 , Michel Guiraud 1 , Laetitia Le Pourhiet 2 , Christophe Thomazo 1 , Anne-Sabine Grosjean 1 , Nicolas Olivier 3 ,Emmanuel Fara 1 , Gilles Escarguel 4 , Kevin G. Bylund, James F. Jenks, Daniel A. Stephen 5 ,

*Corresponding author; gwenael.caravaca@u-bourgogne.fr 1 UMR 6282 Biogéosciences, Université de Bourgogne; 2 iSTeP, Université Pierre et Marie Curie Paris 6; 3 Laboratoire Magma & Volcans, Université Clermont Auvergne; 4 UMR 5023 LEHNA, Université Claude Bernard Lyon 1, 5 Dept. of Earth Science, Utah Valley University


Gwénaël Caravaca

Christophe Thomazo

Emmanuelle Vennin

Nicolas Olivier

Théophile Cocquerez

Gilles Escarguel

Emmanuel Fara

James F Jenks

Kevin G Bylund

Daniel A Stephen

Influence of the local controling factors over the Early Triassic paired carbon isotopoes fluctuations

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

Context and localization

Important and recurrent perturbations of the carbon isotope signals are recorded in the aftermath of the end-Permian mass extinction (PTB, ~252 Ma) and during the entire Early Triassic. These perturbations are most notably represented by a globally recognized negative-positive isotopic couplet observed at the Smithian/Spathian boundary (SSB) and in a lesser extent by a positive excursion at the Dienerian/Smithian boundary (DSB), within both carbonate and organic matter (OM) reservoirs (Fig. 1). These fluctuations are usually linked to global paleoenvironmental variations related to the Siberian Traps degassing (e.g., [START_REF] Romano | Climatic and biotic upheavals following the end-Permian mass extinction[END_REF].

Here, we propose an original study of the paired carbon isotope record of the Hot Springs (HS) section (southeasternmost Idaho, USA, Fig. 1), which is part of the Early Triassic Northern Sonoma Foreland Basin (SFB).

Influence of the local controlling factors over the Early Triassic paired carbon isotopes fluctuations

Main results

Sedimentology

• HS section spans a continuous interval from the Griesbachian-Dienerian up to the lower Spathian;

• Facies associations represent shallow marine environments;

• A transgressive trend is present, with the maximum flooding occurring during the Upper Smithian (Meekoceras ammonoid biozone).

Carbon isotopic signal (Fig. 2)

•
Both carbonate and OM δ 13 C records show the globally recognized couplet of isotopic excursions at the SSB;

•

The DSB positive excursion is observed but only in the carbonate reservoir;

• Variations in the OM reservoir appears to be dampened compared to their carbonate counterpart.

Trace & Major elements (Fig. 2)

•
Al concentrations do not show any significant variation, excepted for the Upper Smithian interval where a peak in Al concentrations is recorded;

• V shows an unexpected behavior and acts as a proxy for detritism due to its correlation to Al (r = 0.81***), rather than for paleoredox conditions [START_REF] Tribovillard | Trace metals as paleoredox and paleoproductivity proxies: an update[END_REF].

Significance of the paired carbon isotopic signal

Net isotopic effect is represented by Δ 13 C (=δ 13 C carb -δ 13 C org ). Along the HS section, Δ 13 C variations mirror that of both carbonate and OM δ 13 C signals.

These variations may originate from:

• Diagenesis: Secondary modification of the signal may have altered the original signal. However, several tests argue against an important impact of secondary modification (Fig. 3).

• Biological fractionation variations: Evolutions of the biological fractionation may reflect variations of the temperatures, in relation to atmospheric pCO 2 . However, a drop in Δ 13 C is expected when temperatures (and thus [CO 2 ]) increase, which is the opposite of the observed behavior at HS (Fig. 2)

• Contamination by a locally brought secondary source: Local input of terrigenous highly negative OM (-22 to -32 ‰) might modify the positive isotopic excursions by "drawing" the signal towards more negative values (Fig. 4). This hypothesis is supported by regional evidence of such input and sustained detrital input to the basin.

Conclusion

The globally expected and recognized isotopic signal for the Early Triassic, and especially the couplet of negative and positive excursions at the SSB, is observed at HS. However, we argue that influences on the δ 13 C signal that are neither of local diagenetic origin nor representative of the global exogenic carbon cycle, have probably largely contributed to the HS geochemical signature.

We therefore argue that this signal is unfit for accurate long-range correlations and paleoenvironmental interpretations regarding the global carbon cycle of the Early Triassic. In turn, δ 13 C should better be used as a proxy to finely constrain and characterize fluctuating local paleoenvironmental conditions during deposition.

Figure 2 :

 2 Figure 2: Main geochemical signals in the Hot Springs section with δ 13 C org , δ 13 C org , net isotopic effect Δ 13 C, and fluctuations of detrital trace and major elements Al and V/Al ratio. δ 18 O cp and paleotemperatures trends from Romano et al. (2013). Ammonoid biozones: Meek., Meekoceras; "Baj.", ~Bajarunia; Col., Columbites.

Figure 1 :

 1 Figure 1: a) Map of the studied area and location of the Hot Springs section; b) Worldwide Early Triassic variations of the δ 13 C signal for both carbonate and OM reservoirs.

Figure 3 (

 3 Figure 3 (top): Cross-plots for isotopic and elemental geochemical parameters; a) δ 13 C carb vs CaCO 3 content; b) δ 13 C carb vs Mn/Sr. δ 13 C carb does not follow any diagenetic trend and does not show any correlation.

Figure 4 (

 4 Figure 4 (left): Schematic representation of the modification of the δ 13 C org signal due to contamination by terrigenous input. This highly negative OM (~-22 to -32 ‰) would therefore modify the positive excursion signal by "drawing" it toward more negative values..

  Gwénaël Caravaca* 1 , Christophe Thomazo 1 , Emmanuelle Vennin 1 , Nicolas Olivier 2 , Théophile Cocquerez 1 , Gilles Escarguel 3 , Emmanuel Fara 1 , James F. Jenks, Kevin G. Bylund, Daniel A. Stephen 4 , Arnaud Brayard 1

*Corresponding author; gwenael.caravaca@u-bourgogne.fr 1 UMR 6282 Biogéosciences, Université de Bourgogne; 2 Laboratoire Magma & Volcans, Université Clermont Auvergne; 3 UMR 5023 LEHNA, Université Claude Bernard Lyon 1, 4 Dept. of Earth Science, Utah Valley University


Lin Zheng

Stéphane Holé

Study of contact conditions at conductor/insulator interfaces used in space charge distribution measurements

Keywords: space charge, interface dipole, contact potential, interface voltage, conductor/insulator interface, polymer, pressure-wave-propagation (PWP) method Social

ouverte pluridisciplinaire HAL, est destinée au dépôt

Study of contact conditions at conductor/insulator

interfaces used in space charge distribution measurements

Introduction

Charges that accumulate in insulating materials under high voltage, originate either from the insulator itself by molecular dissociation and migration, or from charge injection through the interfaces with adjacent materials, electrodes holding the voltage most of the time [START_REF] Coelho | Physics of Dielectrics for the Engineer[END_REF][START_REF] Fothergill | Space Charge in Solid Dielectrics[END_REF]. As injection adds charges to the material, the charge content and buildup may reach levels well above the material withstanding. This can lead to dramatic effects such as voltage breakdown and even to the failure of the system in which the material is used. The study of charge effects in insulating materials, specially the interface effects, is therefore of particular interest.

In the conventional view of the situation [START_REF] Kittel | Introduction to Solid State Physics[END_REF], a charge exchange between two materials is triggered when they are brought into contact in order to reach energy equilibrium on both sides. As a consequence, a voltage appears across the interface, known as the contact potential, often associated with the difference of the energy levels (work functions) of both materials divided by the electronic charge [START_REF] Kittel | Introduction to Solid State Physics[END_REF][START_REF] Sze | Semiconductor devices: physics and technology[END_REF]. However, the interface is a break-up of the material bulk structure introducing modifications in the energy levels known as interface states that impact the contact potential [START_REF] Sze | Semiconductor devices: physics and technology[END_REF]. This is something well studied in the case of metal/semi-conductor interfaces thanks to measurement methods relying on current-voltage characterization [START_REF] Sze | Semiconductor devices: physics and technology[END_REF][START_REF] Nicollian | MOS (Metal Oxide Semiconductor) physics and technology[END_REF]. Unfortunately, these methods cannot be used in the case of metal/insulator interfaces because there is no mobile carrier in the insulator for acting as a virtual electrode and therefore only charge barycenter could be obtained [START_REF] Zhang | Charge transport in silicon nitride/silicon oxide double layers[END_REF]. In the case of polymers, the situation is even more complex since the material structure is not totally crystalline. For instance, charge distributions in low density polyethylene (LDPE) with different electrode materials show that other processes should be considered in addition to work function and interface states . These other processes, such as polarization or the presence of residues or impurities, indeed disturb the local electric field [START_REF] Taleb | Modeling of charge injection and extraction in a metal/polymer interface through an exponential distribution of surface states[END_REF][START_REF] Wu | Interface charges between insulating materials[END_REF].

Various well known models are used to describe charge injection which depends on the actual energy barrier at the interface, and thus on the contact potential [START_REF] Neumann | Self-consistent analytical solution of a problem of charge-carrier injection at a conductor/insulator interface[END_REF]. There is the Schottky effect where charges pass over the energy barrier [START_REF] Simmons | Richardson-Schottky effect in solids[END_REF], the Fowler-Nordheim effect where charges tunnel through the barrier [START_REF] Fowler | Electron emission in intense electric fields[END_REF], or the trap-assisted-tunneling effect where charges tunnel through the barrier to or from a trap in the insulator [START_REF] Gaillard | Etude des Propriétés Morphologiques[END_REF][START_REF] Papaioannou | On the modeling of dielectric charging in RF-MEMS capacitive switches[END_REF]. In all cases, the energy barrier, which depends on the contact potential, is altered by the applied voltage; either lowered and/or made thinner. Therefore, current-voltage measurements can be informative though sensitive to all the interfaces encountered in the current loop during the measurements.

Until now, the effects at conductor/insulator interfaces were studied indirectly, by fitting current-voltage measurements on models [START_REF] Fothergill | Space Charge in Solid Dielectrics[END_REF] or by simulations [START_REF] Boufayed | Simulation of bipolar charge transport in polyethylene featuring trapping and hopping conduction through an exponential distribution of traps[END_REF][START_REF] Guffond | Polymer electrical property simulation using genetic model[END_REF]. Extracting parameters from a model implies controlling perfectly all testing conditions, which is far from being the case when couplings or additional electrodes are necessary to perform the measurements. Indeed, all these additional layers modify the local electric field at the interface, thus deform energy levels between the electrode and the insulator, and therefore may interact with the rate charges can cross the interface [START_REF] Taleb | Modeling of charge injection and extraction in a metal/polymer interface through an exponential distribution of surface states[END_REF][START_REF] Wu | Interface charges between insulating materials[END_REF]. It is therefore of great interest to directly detect and quantify the effect of contact conditions in order to take them into account in the analysis. There were attempts to study interface effects by using space charge distribution measurements [START_REF] Morin | Correlation between space charge distributions and external current measurements during the discharge of low density polyethylene samples[END_REF][START_REF] Fothergill | Advanced pulsed electro-acoustic system for space charge measurement[END_REF] with the advantage of spatially separating the effects taking place at the different interfaces of the sample under test. However, the sensibility was too small to directly observe the voltage across the interface between materials. Recently, the pressure-wave-propagation (PWP) method [START_REF] Holé | Non-destructive methods for space charge distribution measurements: what are the differences?[END_REF][START_REF] Lewiner | Pressure wave propagation methods: a rich history and a bright future[END_REF] has greatly improved its sensibility making it possible to observe directly the contact potential at interfaces under ultra low or zero electric field application [START_REF] Holé | Contact potential measurement at metal/insulator interface[END_REF][START_REF] Ndour | Direct observation of electric charges at solid/liquid interfaces with the pressure-wave-propagation method[END_REF][START_REF] Zheng | Space charge measurement under very low voltage for assessing interface effects due to measurement conditions[END_REF]. The gain in sensibility of the PWP setup was made possible by an optimization of the pressure wave generator presented in Reference [START_REF] Holé | Design and optimization of unipolar pressure pulse generators with a single transducer[END_REF] and by using averaging. Electric fields as small as 1 V/mm on a 1-mm thick sample can be detected, which is about 100 times better than conventional setups.

In this paper, space charge distribution measurements at very low voltage were carried out to study the influence of different sample mountings. For that purpose, low density polyethylene (LDPE) with antioxidant was tested with various ways of mounting. It includes carbon-loaded-polymer electrodes (semicon) either hot-pressed or directly coupled by silicone oil or gel, or through vacuum deposited electrodes (aluminum or gold). In the following section, samples, measurement setup and measurement protocol are presented. The calibration technique and how the information is obtained are also described. In the last section before conclusion, measurements are shown, analyzed and discussed.

Samples, set-up and protocol

Samples

Samples were taken from the same high voltage low-density-polyethylene specimen (see Figure 1). The high voltage specimen contains antioxidant and is 20-cm diameter and 1-mm thick and has two 5-cmdiameter 0.5-mm thick carbon-loaded polyethylene hot-pressed on both sides. Because the study is under low voltage, the high voltage specimen was cut into various 3-cm-diameter samples. This ensures that the insulating polymer samples studied in this paper have very similar chemical composition since they have been extracted from the same specimen and thus have been made at the same time in the same conditions. Nine samples were cut out from the high voltage specimen, one in the center having then two hot-pressed carbon-loaded polyethylene electrodes on both sides, and height in the periphery being then free of electrodes. From these 8 latter samples, two have been coated under vacuum with aluminum electrodes on both sides, two have been coated under vacuum with gold electrodes on both sides, and the last four remained uncoated, thus without electrodes. In addition, carbon-loaded Ethylene Vinyl Acetate (EVA) electrodes, 1 mm in thickness, were coupled either with silicone oil or gel (Sofranel gel D) to all samples except the one having hot pressed electrodes. It was then possible to test 7 sample mountings with two different couplings.

Measurement set-up

The pressure-wave-propagation (PWP) method [START_REF] Laurenceau | Une méthode nouvelle de détermination de la distribution spatiale des potentiels dans les diélectriques[END_REF] is a well suited space charge distribution measurement method for studying interfaces. Compared to the other measurement methods [START_REF] Holé | Non-destructive methods for space charge distribution measurements: what are the differences?[END_REF], it does not induce intrinsic signals at the interfaces that mask the effect of interest such as in the case of the pulsed electro-acoustic (PEA) method. Moreover, it allows the various interfaces of the sample to be well distinguished thanks to elastic wave propagation instead of heat diffusion as in thermal methods. The principle of the PWP method is illustrated in Figure 2. A pressure pulse is transmitted to the sample to test. During the propagation, the charges encountered are displaced resulting in an electric current in the circuit connecting the electrodes of the sample. Because the pressure pulse propagates at the velocity of sound, the current generated at a given time corresponds to the charge displaced at the position of the pressure pulse at that time. As a consequence, the current profile is an image of the charge distribution inside the sample and the charge position can be deduced by the time at which the signal appeared multiplied by the velocity of sound.

In the case of the present work, the pressure pulses were generated by a piezoelectric generator [START_REF] Ndour | Direct observation of electric charges at solid/liquid interfaces with the pressure-wave-propagation method[END_REF] made of a 15-mm-diameter 0.2-mm-thick Pz24 piezoelectric ceramic from Meggitt stuck by epoxy resin with a 3-cm-long brass backing on one side and a 2-cm-long aluminum wave-guide on the other side. As this structure has a derivative response [START_REF] Holé | Design and optimization of unipolar pressure pulse generators with a single transducer[END_REF], 380-V voltage steps were applied every 20 ms, generating one pressure pulse every 20 ms. The sample, acoustically coupled to the wave-guide on one side and pressed by 0.5 bar with a brass counter electrode on the other side, could be stressed by a voltage through a 5-kΩ resistor. The generated signal was decoupled from the stress voltage by a 880 nF capacitor and then amplified by a 66-dB HCA-10M-100K FEMTO amplifier. The signal was finally acquired and averaged by a MSO44 Tektronix scope. A picture of the setup is shown in Figure 3.

Although less efficient, a stainless steel wave-guide was also used to evaluate the possible interactions between the aluminum wave-guide and the couplings and their influence in the signal. With 7 sample mountings, 2 different couplings and 2 different wave-guides, there were finally 28 different situations evaluated.

Measurement protocol

Prior to any measurements, the samples were cured at 80°C under short-circuit for 7 days in order to relax the residual charges that could have been present or injected for instance by triboelectricity during the cutting, the cleaning or the coating. When the samples were mounted in the measurement setup, a first measurement was carried out under short-circuit, then under positive voltages up to +30 V, under short-circuit again, under negative voltage down to -30 V, and finally under short-circuit. All measurements were averaged 1024 times. The flowchart in Figure 4 illustrates the sample preparation (in blue) and measurement protocol (in green).

Calibration and analysis technique

The expression of the signal i(t) in short-circuit measurement conditions for a planar sample is [START_REF] Holé | Influence of divergent fields on space charge distribution measurements using elastic methods[END_REF]

i(t) = -C 0 (1 -a/ǫ) E(x) ∂S(x, t) ∂t dx, (1)
where C 0 is the capacitance at rest of the sample, a its electrostrictive coefficient and ǫ its permittivity.

In this expression, x is the position in depth, t is time, E(x) is the electric field distribution and S(x, t) is the strain wave. As the insulating polymer can be considered uniform in the scope of this study, a and ǫ can get out of the integral. In addition, the strain being the derivative over space of the local material displacement, one has ∂S/∂t = ∂V/∂x, where V(x, t) is the particle velocity, in other words the speed at which matter is locally displaced due to the pressure wave. It is worth noting that pressure and particle velocity are proportional together and the coefficient of proportionality is the acoustic impedance [START_REF] Morse | Theoretical acoustics[END_REF].

Therefore, the shape of the particle velocity is the same as the one of the pressure pulse.Using Gauss-Maxwell equation to make charge density ρ(x) appear and after an integration by parts, it comes

i(t) = κ ρ(x) V(x, t) dx, (2)
where κ = A (1a/ǫ)/d, A is the sample area and d its thickness. Expression (2) explicitly shows that the measured current i(t) originates from the charges that are displaced at particle velocity V. Providing a sample free of internal charges and since charges are not expected to buildup in the sample under very low electric field, at most 30 V/mm in the present study, it can be assumed that charges are present only at the interfaces on very small extent compared to the pressure pulse extent. As a consequence, for a charge density ρ(x) = σ δ(xx 0 ) confined at the interface x = x 0 , with δ(x) the Dirac function, one obtains from (2) the signal

i σ (t) = κ σ V(x = x 0 , t) (3)
which is proportional to the surface charge density σ at x = x 0 and to the particle velocity V(x = x 0 , t) at that interface. This situation is illustrated in Figure 5a. Induced charges due to the voltage application generate such signal peaks. For an applied voltage V app , one would obtain the calibration signal i cal (t)

at the first interface (x 0 = 0 which is ground electrode)

i cal (t) = -κ ǫ V app d V(x = 0, t) (4)
with d the sample thickness.

In presence of a surface dipole density π = σδ ℓ at x = x 0 , the signal is the superposition of a signal generated first by the negative charge -σ of the dipole and second by the positive charge +σ of the dipole. The delay between these two signals is δℓ/v s , where v s is the speed of sound, hence the overall current is

i π (t) = -i σ (t + δℓ 2v s ) + i σ (t - δℓ 2v s ) ≈ - ∂i σ (t) ∂t δℓ v s ≈ -κ σ ∂V(x = x 0 , t) ∂t δℓ v s = - κ π v s ∂V(x = x 0 , t) ∂t . ( 5
)
This signal has a bipolar shape and is proportional to the surface dipole density π. This is illustrated in Figure 5b.

The integral over time of i π (t) is proportional to the particle velocity at the interface and can be directly compared to the calibration signal i cal (t). As a consequence

i π (t) dt = - κ π v s V(x = x 0 , t) = d v s V app π ǫ i cal (t) (6)
so the (algebraic) peak amplitude of the integral over time of i π (t) divided by the (algebraic) peak amplitude of i cal (t) gives a constant from which the dipole surface density π and thus the interface voltage or contact potential π/ǫ can be determined by:

π ǫ = v s V app d peak ( i π (t) dt) peak (i cal (t)) , (7)
where peak(s(t)) denotes the algebraic peak amplitude of the signal s(t). It is worth noting that v s V app /d corresponds to the ratio of the applied voltage during calibration with transit time of the pressure pulse through the sample. The transit time can be directly obtained from the calibration measurement since it exhibits two peaks, a first one due to the charges on the electrode at the first interface and a second one due to the charges on the electrode at the second interface. The delay between these two peaks is therefore the time for the pressure pulse to travel through the sample, thus the transit time by definition.

This factor is therefore easy to extract from measurements without introducing other source of errors. It is also worth noting that peak amplitudes can be confidently used as long as attenuation and dispersion are negligible or if peaks are taken at the same position. Otherwise, the peak surface should be taken instead in order to get rid of this uncertainty. and the last with back electrode held to -30 V (blue curve). The acquired raw signals appear in millivolts which correspond to the measured current i(t) multiplied by the gain of the amplifier and its 50-Ω-input impedance (see Figure 2). As the ratio in (7) cancels these coefficients, the acquired signals are shown in their raw units, thus millivolts. The front electrode is always connected to ground through the waveguide. All signals show a bipolar peak when the pressure arrives at the interface between the aluminum wave-guide and the front electrode. This corresponds to the dipole induced by the coupling gel that may have reacted with the aluminum of the wave-guide [START_REF] Vargel | Corrosion of aluminium[END_REF]. This bipolar peak, which begins at 3.13 µs since the wave-guide is 20-mm thick, can be modeled by [START_REF] Nicollian | MOS (Metal Oxide Semiconductor) physics and technology[END_REF]. Then an unipolar peak, negative under +30 V and positive under -30 V, is generated at 3.37 µs when the pressure arrives at the interface between the front electrode and the insulating polymer. This corresponds to the charges, negative under +30 V and positive under -30 V, induced by the applied voltage on the ground electrode and can be modeled by [START_REF] Kittel | Introduction to Solid State Physics[END_REF]. Finally an unipolar peak, positive under +30 V and negative under -30 V, is generated at 3.80 µs when the pressure reaches the interface between the insulating polymer and the back electrode. This corresponds to the charges, positive under +30 V and negative under -30 V, induced by the applied voltage on the back electrode and can also be modeled by [START_REF] Kittel | Introduction to Solid State Physics[END_REF].

Results and discussion

Detailed analysis of a typical signal

A combined signal depending only on the applied voltage can be easily calculated for instance from half the difference of the signal under +30 V and the one under -30 V. This signal combination is used thereafter as the calibration signal which is necessary to obtain the required information for the interface voltage estimation (see signal processing part in red in Figure 4). In a similar way, a combined signal independent of the applied voltage can be calculated for instance from half the sum of the signal under +30 V and the one under -30 V. This latter combination should correspond to the signal under shortcircuit which is useful for a double check of experimental results. These combined signals are shown in Figure 7a and their integration over time in Figure 7b. Because noise is present in the measurements, calculated interface voltage are given thereafter within an interval of confidence (± sign) corresponding to the standard deviation of the estimation. From [START_REF] Taleb | Modeling of charge injection and extraction in a metal/polymer interface through an exponential distribution of surface states[END_REF], one obtains a voltage at the wave-guide interface of -879 ± 104 mV and -825 ± 98 mV when taking peak surface instead of peak amplitude. A negative voltage means that wave-guide is positively charged compared to carbon loaded electrode. These results are similar considering their interval of confidence, which means that attenuation and dispersion through the carbon loaded electrode have little influence in this example. Peak surface is used thereafter to get rid of slight differences in peak shape. As there is no detectable signal at the interfaces of the insulating polymer under short-circuit, the voltage at these interfaces can be estimated lower than 100 mV which corresponds more or less to the limit of detection.

Notice that integration over time of the voltage dependent combined signal does not go back to zero at the back side, i.e. A 2 = 0 (see blue curve in Figure 7b). In fact, hot-pressed electrodes do not perfectly mechanically match the insulating polymer. The pressure wave reflection at the back side of the insulator then lowers the peak. If the sample is assumed symmetrical, this brings information on the matching at the interface between the front electrode and the insulator. Figure 8 describes the effects of partial reflections at each interface. The ratio of the levels of the integrated signal after (A 2 ) and before (A 1 ) the back electrode peak gives directly the refection coefficient Γ 2 of the pressure at the back interface, here

Γ 2 = A 2 /A 1 = 0.
12. The signal at the back interface is therefore 1 -Γ 2 = 0.88 folds the one at the front interface of the insulator. Hence, due to the assumed sample symmetry which leads to Γ 1 = -Γ 2 , the signal at front interface is itself 1 + Γ 2 = 1.12 folds the one at the interface between the wave-guide and the front electrode. As a consequence, the former results for the voltage at the wave-guide interface should be divided by 1.12 leading to -738 ± 88 mV.

Other results

Compared to aqueous gel, silicone oil increases the intrinsic voltage at the wave-guide interface up to -3010 ± 117 mV and an induced dipole of -17 ± 1 mV/V superimposes. The induced dipole and the applied electric field are in the same direction (from back electrode to front electrode). This is conventional for oil polarization in electric field and is certainly due to a non-perfect electrical contact between carbon loaded polyethylene and aluminum wave-guide. When a stainless steel wave-guide is used, the voltage at the wave-guide interface drastically reduces to -458 ± 307 mV and -487 ± 157 mV respectively for gel and oil and there is no longer induced dipole detected. It can thus be assumed that aluminum of the wave-guide has a great influence on the interface voltage, probably due to chemical reactions [START_REF] Vargel | Corrosion of aluminium[END_REF] with the coupling media with a much larger impact of oil than gel. On the contrary, a wave-guide made of a more inert material produces lower effects, relatively similar for oil and gel, which may be attributed to the coupling.

In the figures presented now on, all measurements have been corrected from calibration and amplitudes are expressed in Volt per square microseconds. Assuming the shape of the bipolar peak as the convolution of a decreasing exponential with the derivative of a Gaussian pulse, the interface voltage can be roughly estimated by

0.846A 1 τ 2 1 1 - A 1 A 2 - A 1 A 2 -0.6 0.1 , (8)
where τ 1 is the width at mid amplitude of the first part of the bipolar peak and A 1 and A 2 are the algebraic amplitudes of the first and second parts of the bipolar peak; A 1 and A 2 are obviously of opposite polarity. Estimations given in the text are however directly calculated from the measurements and are thus more accurate and intervals of confidence can be evaluated. It is worth noting that curves are similar to charge profiles except that amplitudes are opposite. Thus positive charges appear as a negative signal and negative charges appear as a positive signal. This is due to the minus in E = -grad(V).

Though cable manufacturers co-extrude insulation with carbon loaded electrodes in order to obtain a well defined contact [START_REF] Kegerise | Manufacturing and performance criteria for medium voltage power cable semiconducting shields[END_REF], many tests are carried out without such a close contact only made possible by co-extrusion or hot-pressing. Instead, carbon loaded polymer layers, for instance EVA, are coupled to the insulting polymer under test. In Figure 9, the combined signals independent to applied voltage are shown, corrected from setup efficiency thanks to the calibration signal. A 1-mm-thick EVA electrode is inserted on both sides of the insulating polymer and gel or oil is used as acoustic coupling. The insulating polymer is either aluminum coated, gold coated or left uncoated. In all cases, aluminumcoated sample presents the larger dipole at the insulating interface, i.e. 1474 ± 262 mV with gel and 2347 ± 188 mV with oil. The lower dipole at the insulator interface is obtained by the gold-coated sample when using gel (+521 ± 256 mV) whereas it is obtained without coating when using oil (almost undetectable).

Although all signals at the wave-guide interface should be similar for gel or for oil, it is clear that charge exchange exists across EVA electrode. When aluminum is present on both sides of the EVA layer, the dipole is large on both sides with gel or oil. However, with gold-coated or uncoated samples, the dipole at the wave-guide interface is quite similar and the dipole at the insulator interface is much smaller with oil. This points to the great impact of aluminum and, to a smaller extent, of gel for uncoated sample.

The use of a stainless steel wave-guide (see Figure 10) gives similar results except that dipoles at the wave-guide interface are mush smaller than with an aluminum wave-guide.

A direct contact of the sample with the wave-guide exposes the signal to more perturbation since it is no longer possible to dissociate the coupling impact on the wave-guide and on the insulating polymer.

In Figure 11a, the contact is made through gel. Whatever the coating of the insulating polymer, a quite large dipole appears at the interface with the wave-guide. It corresponds to a voltage at the interface of +282 ± 87 mV for the aluminum-coated insulator, -121 ± 28 mV for the gold-coated insulator and +350 ± 59 mV for the uncoated insulator. Notice that voltage at the interface is opposite (wave-guide charges negatively compared to insulator) for aluminum-coated and uncoated insulator compared to previous situations. Notice also the asymmetry of the bipolar peak of the gold-coated insulator indicating a possible competition between two dipoles, one between gel and the aluminum of the wave-guide, and one between gel and the gold-coated insulating polymer. As a consequence the estimated dipole may in fact be not well calculated.

When using oil instead of gel, the voltage at the interface changes drastically only for uncoated sample since one obtains -5023 ± 252 mV, therefore a large increase in amplitude and a polarity reversal. When stainless steel is used for the wave-guide instead of aluminum, similar behavior is observed with gel (see Figure 12a) in terms of shape and amplitude considering the lower sensitivity of the stainless steel setup. The counter dipole due to the aluminum of the wave-guide in case of gold-coated sample is however more visible since one peak is visible and delayed at the interface. This can be explained by a compensation of the bipolar signals as sketched in the inset of Figure 12a. This indicate actually an intrinsic effect of gold with the insulating polymer. Using oil, (see Figure 12b) the effects are similar than with the aluminum wave-guide for aluminum or gold coated insulating polymer showing more the impact of the coating than the one of the wave-guide. As to the uncoated polymer, the voltage at the interface is still reversed but the amplitude is reduced by a factor 3.

Discussion

From all results, a clear voltage appears at the interfaces in all cases except when carbon loaded polymer electrodes are hot-pressed on the insulating polymer, and, to a lower extent, when carbon-loaded EVA is directly coupled through silicone oil to the uncoated insulating polymer. Aluminum has a great impact on the voltage at the interfaces, larger for silicone oil than for aqueous gel. This is visible at the aluminum wave-guide interface or at aluminum coated electrodes. The use of a stainless steel wave-guide reduces the effect compared to an aluminum wave-guide but not cancels them.

Gold coating has a different behavior than aluminum. Indeed, though the dipole appearing at the interface with the insulating polymer is clearly almost symmetrical in terms of shape for any other contacts, the contact with gold present a sharp peak on gold side and a much broader peak inside the insulator.

Both peaks have more or less the same surface which is compatible with a dipole, but this points out that charges clearly spread inside the polymer with gold-coating contrarily to aluminum-coated or uncoated polymer. Figure 13 shows it clearly and, though the amplitude slightly changes depending on the material the gold-coated polymer is coupled to, the shape is rather similar. As the broader peak in the polymer is much larger than spatial resolution, this is significant. This could be explained by the diffusion of charges inside the insulator according to a kind of Debye length. Hence it can be assumed that charges are blocked at the interface for aluminum and uncoated polymer, whereas they can much more easily drift in the polymer with gold coating. Furthermore, as gold is positively polarized compared to the insulating polymer when using oil whereas it is negatively polarized when using gel, both positive and negative charges could drift. This show the impact of the coupling on the interface prop-erties. It is worth noting that 5-nm thick chromium is deposited on the surface of the polymer before gold to improve adhesion. In addition, by thoroughly analyzing measurements with gold electrodes, one observes that it starts slightly after the others, as if a preceding (in the course of the measurement) counter dipole would have existed. A sketch of these dipoles is shown in dashed lines superimposed to the signals in Figure 13. The assumed dipole due to the sample is positive with gel and negative and twice as much with oil. The assumed dipole due to the coupling seems to be always negative with a much larger amplitude in case of direct contact with the aluminum wave-guide. Stainless steel greatly reduces the influence of aluminum without completely canceling the influence of the wave-guide.

Conclusion

It is clearly demonstrated that interface effects may drastically vary from one measurement condition to another. Measurements show the appearance of intrinsic dipoles at the interface that generate interface voltages. The potential distribution at the interface, and thus the energy levels, is then modified which may interact directly with different charge injection processes or threshold when the structure will be subjected to high voltage. Hot-pressed carbon loaded electrode presents negligible interface voltage.

As it is known that coupling material can polarize under voltage, one would have expected that metallized polymers should be better than uncoated polymers. However, it is shown in the results that a carbon-loaded EVA electrodes coupled through silicone oil to an uncoated polymer generate a smaller interface voltage than when the polymer is aluminum coated or gold coated. On the contrary, a coupling directly on aluminum generates a very large interface voltage and in that case, gel may be better. It has been emphasis that aluminum generates in all cases a large interface voltage. The uses of stainless steel reduces the impact without canceling it. Last but not least, gold-coating seems to ease charge spreading in the polymer.

This study points to the great impact of interface conditions that must be well defined and well controlled in the study of space charges in materials. Indeed, they can result to different behaviors as those expected and thus to dramatic situation if test conditions are not representative to operating conditions.

The use of a high sensitive pressure-wave-propagation (PWP) setup makes it possible to study interface phenomena. Though physical effects were mainly considered at interface in the case of dielectric insulation, chemical reactions should also be considered. In case of a single surface charge +σ located at x 0 , the signal starts at x 0 /v s and is proportional to σ and to the pressure pulse. (b) In case of a surface dipole σℓ which negative charge -σ is located at x 0 and positive charge +σ at x 0 + ℓ, the signal also starts at x 0 /v s and is proportional to σℓ and to the pressure pulse derivative over time. In dotted lines, the signals that would have been produced if only one of the dipole surface charge were present.

+30 V 0 V -30 V

In waveguide

In front electrode

In insulating polymer

In back electrode Wave-guide Electrode Electrode Polymer In waveguide

Z 0 Z 1 Z 1 Z 2 1 Γ 0 T 0 Γ 1 T 0 T 1 T 0 Γ 2 T 1 T 0 T 2 T 1 T 0

In insulating polymer

In insulating polymer

In insulating polymer

In insulating polymer

Figure 6

 6 Figure 6 presents three typical raw signals for the hot-pressed sample coupled with gel to the aluminum wave-guide, one under short-circuit (green curve), one with back electrode held to +30 V (red curve)

Figure 1 :

 1 Figure1: Original high voltage specimen from which 3-cm-diameter samples were cut out. The high voltage specimen is made of a 1-mm-thick 20-cm-diameter polyethylene disk including antioxidant on which 5-cm-diameter 0.5-mm-thick carbon loaded polyethylene electrode were hot-pressed stuck on both sides in the middle of the disk. The sample taken from the middle has got hot-pressed electrodes. Samples taken from the periphery were coated with aluminum electrodes, gold electrodes, or left without electrodes (uncoated).

Figure 2 :

 2 Figure 2: Pressure-wave-propagation principle. (a) A pressure pulse is transmitted to the sample under test. It displaces the charges one after another at the velocity of sound v s generating a current i(t) at (b) the image of the charge distribution.

Figure 3 :

 3 Figure 3: Picture of a PWP setup used for low voltage measurements.

Figure 5 :

 5 Figure5: Illustration of the signal produced by a pressure pulse. (a) In case of a single surface charge +σ located at x 0 , the signal starts at x 0 /v s and is proportional to σ and to the pressure pulse. (b) In case of a surface dipole σℓ which negative charge -σ is located at x 0 and positive charge +σ at x 0 + ℓ, the signal also starts at x 0 /v s and is proportional to σℓ and to the pressure pulse derivative over time. In dotted lines, the signals that would have been produced if only one of the dipole surface charge were present.

Figure 6 :

 6 Figure 6: Typical signals for the hot-pressed sample under different voltages. A voltage independent bipolar peak is detected at the interface between wave-guide and front electrode and voltage dependent unipolar peaks are detected at the interfaces between the insulator and its electrodes. Dotted lines indicate when the pressure begins to cross an interface.

2 Figure 7 :

 27 Figure 7: (a) Typical combined signals for the hot-pressed sample. This allows to evidence what depends or not on the applied voltage. (b) integration over time of the combined signals. Dotted lines indicate when the pressure begins to cross an interface.

Figure 8 :

 8 Figure8: Pressure wave amplitude at the various interfaces. Material displacement and pressure are continuous at an interface but the pressure wave is modified from one interface to another due impedance mismatches. Here Z stands for the acoustic impedance, Γ for the pressure-wave reflection coefficient and T for the pressure-wave transmission coefficient.

Figure 9 :

 9 Figure 9: Calibrated combined signals independent to applied voltage with samples coupled to 1-mm thick EVA electrode either (a) with gel or (b) with silicone oil. Samples are aluminum coated, gold coated of left uncoated and tested in the aluminum-wave-guide setup. A double integration over time of each bipolar peak gives the voltage at the corresponding interface. Dotted lines indicate when the pressure begins to cross an interface.

Figure 10 :

 10 Figure 10: Calibrated combined signals independent to applied voltage with samples coupled to 1-mm thick EVA electrode either (a) with gel or (b) with silicone oil. Samples are aluminum coated, gold coated of left uncoated and tested in the stainless steel wave-guide setup. A double integration over time of each bipolar peak gives the voltage at the corresponding interface. Dotted lines indicate when the pressure begins to cross an interface.

Figure 11 :

 11 Figure 11: Calibrated combined signals independent to applied voltage with samples directly coupled either (a) with gel or (b) with silicone oil to the aluminum wave-guide of the setup. Samples are aluminum coated, gold coated of left uncoated. A double integration over time of each bipolar peak gives the voltage at the corresponding interface. Dotted lines indicate when the pressure begins to cross an interface.

Figure 12 :

 12 Figure12: Calibrated combined signals independent to applied voltage with samples directly coupled either (a) with gel or (b) with silicone oil to the stainless steel wave-guide of the setup. Samples are aluminum coated, gold coated of left uncoated. A double integration over time of each bipolar peak gives the voltage at the corresponding interface. Dotted lines indicate when the pressure begins to cross an interface. In the inset, a possible explanation of the delay for gold signal with gel using the superposition of two dipoles.

Figure 13 :

 13 Figure 13: Calibrated combined signals independent to applied voltage with gold-coated sample in aluminum setup (left) or stainless-steel setup (right). (a) Sample coupled through gel to carbon-loaded EVA. (b) Sample coupled through oil to carbon-loaded EVA. (c) Sample coupled through gel to the wave-guide. (d) Sample coupled through oil to the wave-guide. Dotted lines indicate when the pressure begins to cross an interface.

Sample preparation

Measurements under voltages

Signal processing

Sample cutting, coating and curing

Sample placement with coupling in the holder

Transit time estimation

Capacitive peak estimation

Dipole peak estmation Interface voltage calculation

Figure 4: Flowchart of the measurement protocol from the sample preparation to the interface voltage determination. Half the difference of measurements under positive and negative voltages of the same amplitude is referred to as 1 2 (Pos -Neg) and half the sum of measurements under positive and negative voltages of the same amplitude is referred to as 1 2 (Pos + Neg).


Dalila Benzid

Laetitia De Jong

Christophe Lejeusne

Pierre Chevaldonné

Xavier Moreau
email: xavier.moreau@up.univ-mrs.fr

Serotonin expression in the optic lobes of cavernicolous crustaceans during the light-dark transition phases: role of the lamina ganglionaris

Keywords: Lamina ganglionaris, Light-dark transitions, Mysidacea, Serotonin, Zooplankton

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

1 1. Introduction
Mysid crustaceans are important elements of the marine food webs. They live in various habitats and have been recorded from shallow to deep waters in the world oceans and at all latitudes and longitudes; moreover, some live in marine caves where they can account for a significant part of the community biomass. In the open sea, many planktonic species accomplish vertical and circadian migrations that are homologous with the nycthemeral migrations of some cave mysids [START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. The distribution and the circadian migrations of cavernicolous Hemimysis species have been previously studied [START_REF] Chevaldonné | Regional warming-induced species shift in north-west Mediterranean marine caves[END_REF][START_REF] Coma | Horizontal transfer of matter by a cave-dwelling mysid[END_REF][START_REF] Macquart-Moulin | Mouvements nycthéméraux d'Hemimysis speluncola Ledoyer, espèce cavernicole, et de Leptomysis lingvura G.O. Sars, espèce non cavernicole (Crustacea, Mysidacea)[END_REF][START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. However, the physiological mechanisms involved in the control of these migrations are unknown.

Crustaceans display a variety of circadian rhythms that are controlled by periodic functions of the nervous system [START_REF] Fanjul-Moles | The circadian system of crayfish, a developmental approach[END_REF]. In the Decapoda crustaceans, although some of these rhythms are well documented, the regulation processes are not completely understood. It has been suggested that some tissues of the optic lobe, such as the lamina ganglionaris [START_REF] Aréchiga | Circadian clock function in isolated eyestalk tissue of crayfish[END_REF], the retina [START_REF] Aréchiga | Coupling of environmental and endogenous factors in the control of the rhythmic behaviour in decapod crustaceans[END_REF][START_REF] Escamilla-Chimal | The retina of crayfish Procambarus clarkii during development shows serotonin and tryptophan hydroxylase-like immunoreactivity daily changes[END_REF], and the X-organ-sinus gland complex [START_REF] Sáenz | Modulation of electrical activity by 5-hydroxytryptamine in crayfish neurosecretory cells[END_REF] may play a role in this regulation.

In decapods, serotonin (5-hydroxytryptamine, 5-HT) is involved in the regulation of several behaviours and biological functions by acting either as a classical neurotransmitter, a neuromodulator or a neurohormone [START_REF] Beltz | Distribution and functional anatomy of aminecontaining neurons in decapod crustaceans[END_REF]. Indeed, 5-HT plays a key role in feeding and reproductive behaviours and also aggressive, postural and social behaviours [START_REF] Edwards | Fifty years of a command neuron: the neurobiology of escape behavior in the crayfish[END_REF][START_REF] Harris-Warrick | Cellular mechanism for modulation of posture by octopamine and serotonin in the lobster[END_REF][START_REF] Kravitz | Hormonal control of behavior: amines and the biasing of behavioral output in lobsters[END_REF][START_REF] Livingstone | Serotonin and octopamine produce opposite postures in lobsters[END_REF][START_REF] Weiger | Serotonergic modulation of behaviour: a phylogenetic overview[END_REF][START_REF] Yeh | Neuronal adaptations to changes in the social dominance status of crayfish[END_REF]. In the decapod optic lobes, 5-HT has been located in all neuropiles. Although 5-HT has been proposed to modulate the release of some hormones from neurosecretory cells [START_REF] Sáenz | Modulation of electrical activity by 5-hydroxytryptamine in crayfish neurosecretory cells[END_REF] such as the crustacean hyperglycaemic hormone (CHH), the red pigment dispersing hormone (RPDH) and the neurodepressing hormone (NDH) [START_REF] Crow | Serotonin modulates photoresponses in Hermissenda type-B photoreceptors[END_REF][START_REF] García | Regulation of crustacean neurosecretory cell activity[END_REF][START_REF] Kravitz | Hormonal control of behavior: amines and the biasing of behavioral output in lobsters[END_REF], 5-HT plays a major role in the response to light or obscurity. Indeed, the 5-HT content in the entire eyestalk is higher at night [START_REF] Fingerman | Circadian variation in the levels of red pigment dispersing hormone and 5-hydroxytryptamine in the eyestalk of fiddler crab Uca pugilator[END_REF] and 5-HT has been shown to enhance the sensitivity to light in crayfish retinal photoreceptors [START_REF] Aréchiga | Modulation of crayfish retinal sensitivity by 5hydroxytryptamine[END_REF]. However, little is known about the role of this biogenic amine in Crustacea other than Decapoda. In Mysidacea, 5-HT neurons have been evidenced and mapped in the brain and optic lobes only recently [START_REF] Moreau | Evidence for the presence of serotonin in Mysidacea (Crustacea, Peracarida) as revealed by fluorescence immunohistochemistry[END_REF].

As light intensity is thought to be the major factor influencing the migrations of crustaceans, the purpose of this study was to investigate the effects of various conditions of illumination, especially during the light-dark and dark-light transition phases, on the expression pattern of 5-HT in the optic lobes of two mysid species easily kept alive in laboratory conditions. These investigations were conducted on a Mediterranean endemic marine cave species that exhibit nycthemeral migrations, Hemimysis margalefi Alcaraz, Riera and Gili, 1986, and on Leptomysis lingvura G.O. Sars, 1866, a shallow lagoonal species living at comparable depth and not subject to circadian migrations.

Materials and methods

Experimental designs

During winter 2003-2004, biological material was collected off the French Mediterranean coast: the specimens of H. margalefi were obtained from the Figuier cave (15 m depth) near Marseille and L. lingvura from the Brusc lagoon near Toulon. Experiments were carried out under artificial lighting (cool-white fluorescent light at 150 μmol m -2 s -1 ). Adult specimens of H. margalefi were randomly sampled under low red light intensity.

For both species, eight groups of 10 randomly chosen specimens were maintained one night (12 h) in the dark at 21 °C in natural seawater. For each species, one group was fixed in the dark after the 12 h in darkness. Four groups were illuminated with coolwhite fluorescent light and respectively fixed after 30 min, 1 h, 2 h or 3 h of illumination. Three groups were illuminated with cool-white fluorescent light for 3 h and then, placed back in the dark and, respectively, fixed in darkness after 30 min, 1 h or 2 h. The period of light exposure was not longer than 3 h in order to preserve the functional integrity of the visual system of the cave mysids.

For each condition, the specimens were fixed in saline phosphate buffer (PBS, 0.1 M pH 7.2) containing 4% paraformaldehyde (PFA) and used for immunoassays. Fixed samples were stored at 4 °C until immunohistochemical assay.

Immunohistochemistry

The detailed protocol was previously described by [START_REF] Moreau | Evidence for the presence of serotonin in Mysidacea (Crustacea, Peracarida) as revealed by fluorescence immunohistochemistry[END_REF]. Briefly, specimens were fixed in PBS-PFA and then rinsed in PBS containing 0.6% Triton X-100 for 2 days. Entire animals were embedded in Cryomount® (Histolab, Göteborg, Sweden) and frozen in liquid nitrogen. To saturate non-specific sites, the frontal sections of the optic lobes (18 μm) were pre-incubated 20 min at room temperature in 0.1 M PBS (pH 7.2) containing 0.6% Triton X-100, 10% goat serum, 2% bovine serum albumin (PBS-T buffer) and 10 μM pargyline (Sigma, Saint Quentin-Fallavier, France). Slides were incubated overnight at 4 °C in a dilution (1:200) of an anti-5-HT antibody, raised in rabbit (Sigma, Saint Quentin-Fallavier, France), in PBS-T containing 10 μM pargyline. Sections were rinsed 30 min three times in PBS-T then incubated 1 h at room temperature with a goat anti-rabbit IgG secondary antibody (1:200) labelled with AlexaFluor 488 (Interchim, Montluçon, France). Sections were then mounted and observed under an epifluorescence microscope (Leica M1560). Some sections were also observed under a confocal laser microscope (Olympus IX70, Fluoview Program). We have estimated the number of 5-HT immunoreactive elements (cell bodies and fibres) at each experimental condition and in each structure, then we have assigned the sign "++" when we have detected the presence of numerous 5-HT immunoreactive elements, the sign "+" when 5-HT immunoreactive elements were less numerous than previously, the sign "+/-" at the detection limit and, finally, the sign "-" in absence of 5-HT immunoreactivity.

The specificity of the 5-HT antiserum was determined by preincubating the diluted antiserum with 1.5 mM 5-HT (Sigma, Saint Quentin-Fallavier, France) overnight at 4 °C before normal treatment of the nervous system. Other controls were done by incubating the slides without the primary antibody. Immunostaining was almost totally abolished by preincubation with 5-HT and totally abolished in absence of the primary antibody.

Results

The nomenclature of the histological structures of the optic lobes is that previously detailed in [START_REF] Moreau | Evidence for the presence of serotonin in Mysidacea (Crustacea, Peracarida) as revealed by fluorescence immunohistochemistry[END_REF].

H. margalefi

All the results are summarized in Table 1. First of all, whatever the experimental conditions, i.e. during light or dark periods, a 5-HT-like immunolabelling in the medulla terminalis and in the X-organ is observed (Fig. 1A-C).

The rhabdom of the retinular cells, the distal pigment cells, the internal medulla, the external medulla, and the sinus gland (Fig. 1D) are immunoreactive during light exposure. In these structures, 5-HT-like-immunoreactivity is quickly detected after illumination (30 min). Back to darkness, it takes longer to disappear: 1 h for rh and dpc, and more for the others. Some 5-HT somata and fibres are observed after 1 h in the external and internal medullae (Fig. 1E) and in the sinus gland. The 5-HT-like-immunoreactivity persists up to 2 h in the external medulla and the sinus gland (Fig. 1D).

After one night in darkness, no immunoreactive elements are detected in the lamina ganglionaris (Fig. 2A). The 5-HT-like immunoreactivity appears quickly, i.e. after 30 min of exposure to light (Fig. 2B) and many 5-HT elements are present at 1 h of light exposure (Fig. 2C). Then, their number decreases progressively to reach the detection limit at 3 h of exposure to light (Fig. 2D). Back to darkness, it needs 1 h to observe a 5-HTlike-immunolabelling represented only by portions of 5-HT fibres (Fig. 2E). After 2 h of darkness, the number of 5-HT-like-immunoreactive elements increases since more 5-HT somata and axons are detected (Fig. 2F,G).

The rhabdom of the retinular cells and the distal pigment cells are always immunoreactive when exposed to light. When the mysids are placed back to darkness, after an illumination period of 3 h, the number of 5-HTlike-immunolabelled structures decreases progressively: -dpc: distal pigment cells; lg: lamina ganglionaris; em: external medulla; im: internal medulla; mt: medulla terminalis; rh: rhabdom of the retinular cells; sg: sinus gland; XO: X-organ; ++: presence of numerous serotonin-like immunoreactive elements; +: presence of some serotonin-like immunoreactive elements; +/-: detection limit; -: absence of serotonin-like immunoreactivity. 5-HT is still expressed after 30 min of darkness (Fig. 2H) but not any longer after 1 h.

L. lingvura

To go further, the 5-HT expression pattern in the lamina ganglionaris of L. lingvura was investigated. The results are summarized in Table 2. An absence of 5-HTlike immunolabelling after one night of darkness is followed by a response of the lamina ganglionaris: many 5-HT neurons are observed after 30 min (Fig. 3A) and 1 h of light exposure (Fig. 3B). Then, after 2 h of light exposure, their number decreases considerably (Fig. 3C). No 5-HT-like immunoreactivity is detected in the lamina ganglionaris when L. lingvura are exposed 3 h to light. When L. lingvura are placed in the dark, i.e. after the light-dark transition, 5-HT-like immunolabelling is observed in the lamina ganglionaris as soon as 30 min (Fig. 3D). When darkness is longer, the 5-HT-like immunoreactivity is no more detected.

Discussion

The first evidence for the presence of 5-HT in mysids (Crustacea, Mysidacea) has been reported by [START_REF] Moreau | Evidence for the presence of serotonin in Mysidacea (Crustacea, Peracarida) as revealed by fluorescence immunohistochemistry[END_REF]. In the present study, the X-organ and the medulla terminalis are always 5-HT immunoreactive during light or dark periods. The rhabdom of the retinular cells, the distal pigment cells, the internal medulla, the external medulla, and the sinus gland are 5-HT immunoreactive during light exposure. In these latter structures, immunoreactivity is quickly detected after illumination (30 min) while, back to darkness, it takes longer to disappear. The 5-HT expression pattern in the lamina ganglionaris is very different and is discussed regarding to its possible implication during the light-dark transition phases.

In H. margalefi and L. lingvura, at least six 5-HT immunoreactive cell bodies are found in the lamina ganglionaris with many 5-HT-like fibres that project towards the retinular cells [START_REF] Moreau | Evidence for the presence of serotonin in Mysidacea (Crustacea, Peracarida) as revealed by fluorescence immunohistochemistry[END_REF]. Similar organization has been found in decapod species [START_REF] Beltz | Distribution and functional anatomy of aminecontaining neurons in decapod crustaceans[END_REF][START_REF] Sandeman | Atlas of serotonin-containing neurons in the optic lobes and brain of the crayfish, Cherax destructor[END_REF]. Although the structure of the lamina ganglionaris and some of its expressed neurotransmitters are well known in various arthropods, the functional implication of this first neuropile involved in the treatment of light information arising from retinular cells is still poorly understood. In crayfish, Aréchiga and Rodríguez-Sosa (1998) have suggested an implication of the lamina ganglionaris in the generation of circadian rhythmicity. However, despite the numerous works conducted on the circadian 1998) have reported daily changes in 5-HT-like immunoreactivity in the retina, and a circadian rhythm in the retinal electrical activity has been described in isolated retinas [START_REF] Aréchiga | Coupling of environmental and endogenous factors in the control of the rhythmic behaviour in decapod crustaceans[END_REF]. Morphological evidence of changes in the rhabdom shape suggests a possible sequence of events involving production, utilization and degradation of the photoreceptor membranes during changes from light to dark and dark to light [START_REF] Itaya | Rhabdom changes in the shrimp, Palaemonetes[END_REF]. During light adaptation, the eye of the nocturnal crayfish Cherax destructor reduces the ommatidial acceptance angle by pigment migrations [START_REF] Bryceson | Image quality and acceptance angle in reflecting superposition eye[END_REF]. [START_REF] Balzer | Daily variations of immunoreactive melatonin in the visual system of crayfish[END_REF] have proposed that, in crayfish, melatonin, which is synthesized from 5-HT, acts on the gain of photoreceptors and on the movements of accessory pigments toward the "dark-adaptation position" and that melatonin is involved in the expression of circadian rhythms. In insects, it has also been proposed that 5-HT neurons located in the medullae are involved in circadian rhythms [START_REF] Leitinger | Serotonin-immunoreactive neurons in the visual system of the praying mantis: an immunohistochemical, confocal laser scanning and electron microscopic study[END_REF].

The present study underlines a fundamental role of 5-HT neurons of the lamina ganglionaris during the light-dark transition phase in mysid crustaceans, and especially in H. margalefi. From the present results, it can be ascertained that the expression pattern of 5-HT in the lamina ganglionaris is linked to the daily migrations of this cave species. Indeed, H. margalefi swarms have been noticed to have different positions in the cave according to the outside light intensity (Chevaldonné P and Lejeusne C, personal observations). By the past, nycthemeral movements of Hemimysis swarms have been well documented [START_REF] Macquart-Moulin | Ecophysiologie comparée des mysidacés Hemimysis speluncola Ledoyer (cavernicole) et Leptomysis lingvura G.O. Sars (non-cavernicole). L'orientation à la lumière: tests ponctuels[END_REF][START_REF] Macquart-Moulin | Mouvements nycthéméraux d'Hemimysis speluncola Ledoyer, espèce cavernicole, et de Leptomysis lingvura G.O. Sars, espèce non cavernicole (Crustacea, Mysidacea)[END_REF][START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. It is established that the swarms display circadian migrations in and out of the caves: during daytime, the cave shelters an important population of Hemimysis mysids; each night, these mysids undergo horizontal migrations, leaving the cave at sunset and turning back into the cave at daybreak. These migrations are homologous to vertical circadian migrations of the plankton and have been related to fluctuations in solar and lunar light intensities [START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. The cave mysid species for which the nycthemeral migra-tion pattern has been well established is H. speluncola Ledoyer, 1963. Since June 1999, due to a regional warming of the NW Mediterranean, H. speluncola, which was the unique cave mysid species of the Figuier cave, has totally disappeared from this marine cave and has been replaced by the more thermotolerant H. margalefi [START_REF] Chevaldonné | Regional warming-induced species shift in north-west Mediterranean marine caves[END_REF][START_REF] Lejeusne | Population structure and life history of Hemimysis margalefi (Crustacea: Mysidacea), a "thermophilic" cave-dwelling species benefiting from the warming of the NW Mediterranean[END_REF]. As both Hemimysis species share very similar biology and ecology (Chevaldonné and [START_REF] Chevaldonné | Regional warming-induced species shift in north-west Mediterranean marine caves[END_REF][START_REF] Lejeusne | Population structure and life history of Hemimysis margalefi (Crustacea: Mysidacea), a "thermophilic" cave-dwelling species benefiting from the warming of the NW Mediterranean[END_REF], it is interesting to confront data obtained for the migration pattern of H. speluncola and data of expression of 5-HT obtained for H. margalefi in present study. During daytime, Hemimysis mysids are confined to the darkest parts of the caves. A progressive migration of these animals from those parts of the cave has been evidenced showing that the swarm progresses slowly towards the outside [START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. As long as the solar illumination is higher than the lunar one, the swarm stays at the entrance of the cave. When the solar illumination becomes lower than the lunar one, the number of mysids at the entrance decreases slowly and the exit is general only after moonset. At the end of the night, mysids go back into the cave half an hour before daybreak. The rapidity of the return migration contrasts with the progressive movement toward the exit. Therefore, it seems that the sensitivity to light of these animals is lower at the beginning of the night than at the end [START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. In the same way, the present study shows that the 5-HT-like immunoreactivity in the lamina ganglionaris appears quickly, i.e. at 30 min, after the beginning of the light exposure, while when animals are brought back to darkness immunolabelling is detected only after 1 h. When H. margalefi is exposed to artificial light, a strong 5-HT-like immunolabelling occurs in the lamina ganglionaris after 1 h. In their natural habitat, the return migration of the whole population of H. speluncola back into the cave, takes only 1 h [START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. The 5-HT-like immunoreactivity increases when mysids are placed in obscurity for 2 h. The exit of the cave is progressive and requires up to 5 h for the entire population. For both H. margalefi and L. lingvura, the 5-HT-like immunoreactivity of the lamina ganglionaris is transient: it disappears after 3 h of illumination and after one night in darkness. However, the comparison between the 5-HT-like immunoreactivity in the lamina ganglionaris of H. margalefi and L. lingvura reveals a different pattern of 5-HT expression. In contrast to H. margalefi, 5-HT-like immunoreactivity is rapidly detected in L. lingvura, i.e. as soon as 30 min, and this, whether the transition is from light to dark or dark to light. It is noteworthy that specimens of L. lingvura form swarms in shallow water in places where they are submitted to light variations. Moreover, L. lingvura does not undergo nycthemeral migrations. Therefore, in H. margalefi, it seems that the 5-HT expression in the lamina ganglionaris acts as the departure signal for the migration during the dark-tolight and light-to-dark transitional phases.

In the present work, the observed transient 5-HTlike immunoreactivity in the lamina ganglionaris may underline a possible function of the lamina ganglionaris as a photoreception signal integrator and, especially, for species showing circadian migrations. In the decapods, a circadian rhythmic function has been suggested for the lamina ganglionaris [START_REF] Aréchiga | Coupling of environmental and endogenous factors in the control of the rhythmic behaviour in decapod crustaceans[END_REF]. In these animals, environmental factors such as light intensities are known to modulate tonic patterns of behaviour. In crayfish, the product of the Drosophila per-gene (period gene), involved in the genesis of rhythms in insects and vertebrates, has been detected in cell bodies of the lamina ganglionaris [START_REF] Aréchiga | Circadian clock function in isolated eyestalk tissue of crayfish[END_REF]. It would be interesting to investigate the relationships between 5-HT and per-gene in the genesis of these rhythms.

In the decapods, the biological mechanisms that regulate circadian rhythms have been investigated for several decades. In fact, more than one circadian pacemaker may operate in the control of some circadian rhythms [START_REF] Aréchiga | The circadian system of crustaceans[END_REF]. Two main organs have been identified as essential for the maintenance of circadian rhythms in decapod crustaceans: the optic neuropile in the eyestalk and the supraoesophageal ganglion [START_REF] Aréchiga | The circadian system of crustaceans[END_REF][START_REF] Escamilla-Chimal | Daily variations in crustacean hyperglycaemic hormone and serotonin (5-HT) immunoreactivity during the development of crayfish[END_REF][START_REF] Fanjul-Moles | The circadian system of crayfish, a developmental approach[END_REF]. In the eyestalk, it is likely that at least two sources of circadian rhythmicity exist, one at the level of the retina and the lamina ganglionaris, generating the photoreceptor rhythmicity, and one near or in the medulla terminalis, responsible for neurosecretory rhythms [START_REF] Aréchiga | Coupling of environmental and endogenous factors in the control of the rhythmic behaviour in decapod crustaceans[END_REF]. Pacemaker neurons undergo circadian rhythms of electrical and of secretory activity. Besides their endogenous rhythmicity, they are also influenced by neurotransmitters and modulators mediating the effects of light and darkness [START_REF] Aréchiga | The neural substrate of biological rhythms[END_REF]. Furthermore, 5-HT has been proposed as a local modulator of the retinal activity [START_REF] Aréchiga | Modulation of crayfish retinal sensitivity by 5hydroxytryptamine[END_REF]. Horizontal migrations of Hemimysis species, which consist in leaving and turning back into the cave, are under control of an endogenous circadian rhythm that depends on light and darkness. To our knowledge, the present study is the first report suggesting that a neurobiological phenomenon is synchronized with horizontal migration, an important crustacean behaviour. It is likely that 5-HT expression in the lamina ganglionaris is one of the key elements to explain this complex behaviour. Therefore, the circadian behaviour of the Hemimysis cave mysids may correspond to a complex physiological mechanism involving neurotransmitters, neurohormones and several pacemakers.

With regard to light intensity, it has been suggested that the horizontal migrations of cavernicolous Hemimysis species are similar to the vertical migrations of many zooplankton organisms. Indeed, it has been demonstrated that the illumination in the blind end of the caves, i.e. the diurnal habitat of these mysids, corresponds to that prevailing at depths about 400 to 500 m in the open sea [START_REF] Passelaigue | Distribution and circadian migrations of the cavernicolous mysid Hemimysis speluncola Ledoyer[END_REF]. Therefore, for further investigations, we agree with these authors to consider cavernicolous mysids as a very good model for the study of the mechanisms determining and regulating the circadian migrations of zooplankton.

Fig. 1 .

 1 Fig. 1. Serotonin-like immunoreactivity in the optic lobe of the cave-dwelling mysid Hemimysis margalefi under artificial conditions of illumination. (A, B) Medulla terminalis. Terminal network after 2 h of illumination (A) and cell bodies after 1 h of darkness (B) of 5-HT neurons. (C) X-organ after 3 h of illumination. (D) Long 5-HT axon that ends in the sinus gland (sg) after 2 h of illumination. (E) External and internal medulla after 1 h of darkness. Arrowhead, 5-HT cell body; double arrowhead, 5-HT terminals; arrow, 5-HT fibres; em, external medulla; im, internal medulla; mt, medulla terminalis.

Fig. 2 .

 2 Fig. 2. Serotonin-like immunoreactivity in the optic lobe of the cave-dwelling mysid Hemimysis margalefi under various periods of illumination. (A) Absence of 5-HT-like labelling in the lamina ganglionaris after one night in darkness. (B, C, D) 5-HT-like immunoreactivity after 30 min, 1 h and 3 h of exposure to light, respectively. (E) 5-HT-like-immunoreactivity of the lamina ganglionaris 1 h after darkness. (F, G) 5-HT-like-immunoreactivity of the lamina ganglionaris 2 h after darkness: comparison between observation with an epifluorescence (F) or a confocal (G) microscope. (H) 5-HT-likeimmunolabelling in the rhabdom of retinular cells after 30 min of darkness. b, brain; lg, lamina ganglionaris; rh, rhabdom; XO, X-organ. For other abbreviations see legends to Fig. 1.

Fig. 3 .

 3 Fig. 3. (A-D) Serotonin-like immunoreactivity in the lamina ganglionaris (lg) of the shallow lagoonal mysid Leptomysis lingvura after 30 min (A), 1 h (B), 2 h (C) of light exposure and 30 min of darkness (D). For other abbreviations see legends to Fig. 1.

Table 1

 1 Serotonin-like immunoreactive areas in the optic lobes of the cave dwelling mysid Hemimysis margalefi kept in the dark for one night and then exposed to light and placed back in darkness

	Duration of	XO Medullae		sg lg	rh	dpc
	light or dark periods		mt im em
	1 night darkness +	+	--	--	--
	30 min light	+	+	+	+	+	++	+	++
	1 h light	+	+	+	+	+	++	++ +
	2 h light	+	+	+	+	+	+	++ +
	3 h light	+	+	++ +	+	+/-++ +
	30 min darkness +	+	+	+/-+	-	++
	1 h darkness	+	+	+	+	+	+	--
	2 h darkness	+	+	-	++	+ +

Acknowledgements

We thank J. Durand (P3M-CNRS 31, Marseille) and N. Jaafari (ER "Biodiversité and Environnement", Université de Provence, Marseille) for their technical assistance in confocal microscopy. [SS]


Dwinanto Sukamto
email: dwinanto.sukamto@insa-strasbourg.fr

Franç Ois Gloriant

Monica Siroux

Thermal performance evaluation of a bioclimatic ventilated wall using a Hot Box

Nowadays, external isolation is highly recommended for both building renovation and new building construction. This isolation requires the installation of structure protecting the insulating materials from the humidity and weather variations. One of the current techniques is the installation of ventilated facades. The recovered energy by this process could be used in winter for the preheating of ventilated air or could be evacuated in summer to protect the building from potential overheating. This study describes the design and application of Hot Box developed specifically to test the thermal performance of a ventilated bioclimatic wall. Based on experiments test, this paper discusses the experimental set-up and the thermal metrology. Data collected from testing a ventilated wall were used to estimate the convection heat transfer coefficients of the ventilated wall.

Introduction

Climate change is the major challenge facing the world in the future. In this context, France is placing the construction sector at the heart of its strategy to meet this challenge [START_REF]Bâ timents à é nergie positive et ré duction carbone[END_REF]. Saving energy is a priority in developed countries. The building sector is responsible for 40% of energy consumption in Europe [START_REF] Commission | Evaluation of the Energy Performance of Building Directive[END_REF]. The building envelope is the construction element that has the greatest impact on the overall energy consumption of the building [START_REF] Manioğlu | Economic evaluation of the building envelope and operation period of heating system in terms of thermal comfort[END_REF] [START_REF] Pacheco | Energy efficient design of building: A review[END_REF]. It must be taken into account that the facade represents the interface between external environmental factors and the interior requirements of the occupants. In recent years, architecture has shown a particular interest in ventilated walls. It cannot be denied that there are a considerable number of studies and publications on "ventilated envelopes" [5][6] [START_REF] Lai | Solar faç ades: A review[END_REF], especially on double skin facades [START_REF] Barbosa | Perspectives of double skin faç ades for naturally ventilated buildings: A review[END_REF][9] [START_REF] Shameri | Perspectives of double skin faç ade systems in buildings and energy saving[END_REF], building-integrated photovoltaics [START_REF] Quesada | A comprehensive review of solar facades. Opaque solar facades[END_REF][12] [START_REF] Zogou | Experimental validation of an improved concept of building integrated photovoltaic panels[END_REF], solar chimneys, solar walls and Trombe walls [START_REF] Harris | Solar chimney and building ventilation[END_REF][15] [START_REF] Saadatian | Trombe walls: A review of opportunities and challenges in research and development[END_REF], or faç ade solar collectors [START_REF] Gunnewiek | Flow distribution in unglazed transpired plate solar air heaters of large area[END_REF] [START_REF] Leon | Mathematical modeling and thermal performance analysis of unglazed transpired solar collectors[END_REF]. The ventilated facade is chosen by architects and contractors as an envelope solution in a wide variety of building types, climates and design configurations. The system offers a wide variety of exterior claddings and the ability to select a wide variety of materials, colors and panel sizes. In addition to the aesthetic aspect, the primary purpose of this type of faç ade is to protect the insulation materials by dissipating moisture. The objective of a bioclimatic design of a building is to achieve indoor comfort in the most "natural" way possible. For a given site, it is no longer just a question of protecting against the vagaries of the climate but also of enhancing its benefits. In this approach, we therefore seek to adapt the building to its environment as well as possible. The ventilated wall is a response to this approach. The objective of this study is to characterize the thermal performance of a bioclimatic ventilated wall. An original system has been set up for the experimental study of a bioclimatic ventilated wall. It is the relevance of this device that we discuss in this paper.

Description of the experimental set up

Bioclimatic ventilated wall and Hot Box

The ventilated wall is a wall with a non-hermetically insulated channel that participates in the supply of fresh air to the building; a convective exchange takes place in the cavity along the axis of the wall, which disturbs the radial heat flow between the interior and exterior environments (Figure 1). The air flowing inside the cavity is then preheated and introduced into the building. This system reduces the heating requirements of the building. The sample studied is composed of two grey walls 1m high and 1m wide. The first one is fixed while the second one is mobile, allowing the thickness of the ventilated cavity to be varied. These two walls are made of an aluminum alloy and polyethylene of 3 mm thickness and have a thermal resistance of 0.008 m² .K.W -1 . Their surfaces are smooth (low roughness) with an emissivity of 0.9. The ventilated air gap is introduced inside the Hot Box (Figure 1). The Hot Box is a device composed of two climatic chambers capable of reproducing selected the temperature and relative humidity conditions. The range of temperature and humidity is from -30°C to +60°C and from 10% to 98%. Each chamber has its own refrigeration unit guaranteeing the production of cold with a temperature accuracy of ± 2°C. Each one also has 3 electric resistors of 2.5 kW, guaranteeing the production of heat with a temperature accuracy of ± 3 °C [START_REF] Entreprise | Manual Usuario[END_REF]. The Hot Box is connected to a computer to control the temperature and humidity parameters of each chamber.

Thermal metrology

To characterize the thermal behaviour of the sample under study, the ventilated wall is equipped with type K thermocouples and flowmeters of the Captec Entreprise® brand, allowing the joint measurement of surface temperatures, the air inside and outside the cavity, as well as the estimation of heat flux on both sides of the ventilated cavity (Figure 2). In each of the climate cells, 3 thermocouples are used to determine the ambient temperatures. On each of the walls of the ventilated cavity, 12 thermocouples and 4 flux meters have been installed on 4 levels of different heights and are equally distributed over the width. For the measurement of the air temperature, 3 thermocouples have been placed at the entrance and 3 others at the exit of the cavity. Inside and in the middle of the cavity there are also 4 thermocouples. The airflow within the cavity is generated by means of a fan controlled by a voltage variator and the measurement of the flow rate is estimated by means of a CTV 210 hot wire anemometer from the manufacturer KIMO. All the sensors are connected to a Keithley 2700® multimeter allowing a voltage measurement in the order of one-tenth of a microVolt. The multimeter itself is connected to a computer via the RS-232 serial communication channel. Data acquisition and processing are then carried out via the LabVIEW software. An infrared camera is also used to estimate the temperature of the hot wall of the device.

Results

Several tests have been undertaken to ensure that the device works properly. For all these control tests, the ambient conditions were set at 20°C and 55% relative humidity for the fixed cell, and 0°C and 75% relative humidity for the mobile cell. The measurement readings are taken in a steady state, the airflow rate is 20 m 3 .h -1 and flows from the mobile cell (cold environment) to the fixed cell (hot environment) in a cavity 0.01 m thick.

Hot Box Temperatures

The measurement of the ambient temperature in each of the cells of the Hot Box was carried out. A temperature difference of at least 20°C between the 2 cells was aimed at obtaining heat fluxes high enough to be correctly measured by the flux meters. [START_REF] Gloriant | Study Of The Performances Of A Supply-Air Window For Air Renewal Pre-Heating[END_REF]. With the setpoints considered (20°C in the fixed cell and 0°C in the mobile cell), we observe for each of the cells, a significant difference on the measurement of the ambient temperature between the integrated sensor of the Hot Box and the thermocouple measurements (Figure 3). One cannot trust the temperature sensor integrated in the Hot Box because it overestimates the ambient temperature by 2.6°C for the mobile cell and by 4.3°C for the fixed cell. This inaccuracy can partly be explained by the fact that the cells are not airtight since an artificial airflow has been created between them. However, for standard use of the Hot Box, there should be no air exchange between the cells; the regulation system of the device is then disturbed. Moreover, it can be seen that the air circulation is sufficient to obtain a homogeneous temperature distribution in time and space. On average, the maximum measuring difference between the thermocouples is 0.04°C in the mobile cell and 0.7°C in the fixed cell.

Surface temperatures

Measurement of surface temperatures is done by thermocouples. Thermocouple's measurements are compared to that obtained using an infrared camera. The area covered by the infrared camera has a surface area of 10 cm 2 . The T8 and T5 thermocouples are located on the upper and lower part of this surface (Figure 4). It can be observed that the temperature measurements of each of the sensors are stable over time and are quite close together. The averages over the period considered for the thermocouples T5, T8 and the infrared camera are 12.14°C, 12.11°C and 12.18°C respectively. It is an expected result to obtain a slightly higher temperature at the T5 thermocouple level than at the T8 thermocouple level [START_REF] Gloriant | Study Of The Performances Of A Supply-Air Window For Air Renewal Pre-Heating[END_REF]. Indeed, the air circulating in the wall heats up little by recovering part of the thermal flow coming from the hot cell. Thus, the wall adjacent to the cold cell, which is in contact with this increasingly hot air, also heats up along the cavity. By averaging the temperature with thermocouples T5 and T8, we obtain an average temperature over the surface covered by the infrared camera. We can then see that the measurement difference between these 2 types of probes is 0.05°C. The measurements of surface temperatures by the thermocouples are in adequacy with the measurements made by the infrared camera and confirm the reliability of the instrumentation of the walls. Figure 5 presents the air temperature in the ventilated chamber as a function of vertical position H for an air space thickness of 50 mm and for different airflow rate (10 m 3 .h -1 , 20 m 3 .h -1 and 30 m 3 .h -1 ). It can be seen that in the top of the air chamber, the air temperature decreases with the airflow rate. This indicates that the efficiency of the ventilated wall decreases with the airflow rate.

The convection heat transfer coefficient

The objective is to quantify the convection heat transfer coefficient between the ventilated bioclimatic wall and the atmospheres of each of the cells. We considered 2 distinct air gap thicknesses (0.005 m and 0.01 m) and 3 airflows (10 m 3 .h -1 , 20 m 3 .h -1 and 30 m 3 .h -1 ). The joint use of thermocouples and fluxmeters allows an experimental estimation of these exchange coefficients without using existing correlations. To estimate these parameters, we use Newton's law: h=q/(Ts-Ta) [START_REF]Bâ timents à é nergie positive et ré duction carbone[END_REF] According to this relation, the estimation of the convection heat transfer coefficient h, requires the knowledge of the heat flux q, the ambient air temperature in the cell Ta and of the wall surface temperature Ts.

Since each wall of the sample is equipped, at different heights, with 4 flux meters and 4 thermocouples, it is possible to obtain 4 local estimates of the heat transfer coefficient per cell. For the ambient temperature in each of the cells, a single air temperature is considered, corresponding to the average of the measurements of the 3 thermocouples installed in each cell.

Figure 5 shows the estimates of the heat transfer coefficient at the wall surface in each of the cells and for different cavity thicknesses and flow rates. The coefficient h varies between 15 W.m -2 .K -1 and 24 W.m - 2 .K -1 over the set of tests with a mean of 20.42.7 W.m - 2 .K -1 for the mobile cell and 18.41.5 W.m -2 .K -1 for the fixed cell. This order of magnitude is consistent with the correlations that can be found in the literature [START_REF] Padet | Convection thermique et massique Principes gé né raux[END_REF]. It can be noted that neither the thickness of the cavity nor the flow of air in the wall has any real influence on the estimates of the coefficient h. This means that these 2 parameters have no influence on the ambiances of the 2 climate cells. On the other hand, the coefficient h depends on the position at which it has been calculated and it can be seen that, for a given height, the estimates of the coefficient h are relatively homogeneous [START_REF] Sukamto | Hot Box Investigations of a Ventilated Bioclimatic Wall for NZEB Building Faç ade[END_REF]. The results concerning the uncertainties for the convection heat transfer coefficient h (Table 1) are globally satisfactory. An uncertainty of 5% was considered for flux meters and uncertainty of 0.02°C for thermocouples. It can be seen that the uncertainties are smaller in the hot cell as the fluxes and temperature differences involved are larger. It is in the cold cell, at the lower part of the wall, that the uncertainties are the greatest; at this point, the temperatures between the wall and the environment of the cold cell are very close and often of the order of a tenth of a degree.

Conclusion

The purpose of this study was to investigate the thermal performance of a ventilated bioclimatic wall. For this reason, the Hot Box thermal metrology was developed specifically. Based on experiments test, this study discusses the experimental set-up and the thermal metrology. Data collected from the Hot Box were used to estimate the convection heat transfer coefficients of the ventilated wall. This study was completed by an analysis of the measurement uncertainties, which proved satisfactory.

Fig. 1 .

 1 Fig. 1. Presentation of the ventilated wall (left) integrated to the sample holder of the Hot Box (right).

Fig. 2 .

 2 Fig. 2. Hot Box instrumentation.

Fig. 3 .

 3 Fig. 3. Ambient temperature measurements in the cold cell (left) and in the hot cell (right).

Fig. 4 .

 4 Fig. 4. Surface temperatures.

  for temperature mesurement on the wall surface (26 pcs) type K thermocouple for temperature mesurement of the air (10 pcs) high sensibility of flux meter (8pcs)

Fig. 5 .

 5 Fig. 5. Air temperature in the ventilated chamber.

Fig. 6 .

 6 Fig. 6. The convection heat transfer coefficient in the cold cell (left) and in the hot cell (right).

Fig. 7 .

 7 Fig. 7. Nusselt number in the ventilated chamber.

Figure 7

 7 Figure 7 presents the local and global Nusselt number in the ventilated chamber as a function of Reynolds number for an air space thickness of 50 mm and for different airflow rates (10 m 3 .h -1 , 20 m 3 .h -1 and 30 m 3 .h -1 ). Experimental results shows that the local and global Nusselt number increases with the airflow rate.

  for a flow rate (in m 3 .h -1 ) of cavity of 10 mm for a flow rate (in m 3 .h - 1 ) of cavity of 5 mm for a flow rate (in m 3 .h -1 ) of cavity of 10 mm for a flow rate (in m 3 .h -

Table 1 .

 1 Uncertainties for the convection heat transfer coefficient.

E3S Web of Conferences 294, 04003 (2021) https://doi.org/10.1051/e3sconf/202129404003 ICSREE 2021