domain: spi chim phys sde

text:
H Q Do

L D Ngo

Y Carpentier

Xavier Mercier

Eric Therssen

Absolute soot volume fraction measurement by laser induced incandescence calibration in sooting turbulent diffusion flame

Keywords: Soot volume fraction, laser induce incandescence, diesel, bio-fuel, sooting turbulent diffusion flame

teaching and research institutions in France or abroad, or from public or private research centers.

Absolute soot volume fraction measurement by laser induced incandescence calibration in sooting turbulent diffusion flame

Introduction

The formation and emission of soot particles from fuel combustion have a harmful effect on the climate, environment and human health [START_REF] Hansen | Soot climate forcing via snow and ice albedos[END_REF]. Soot volume fraction (fv) measurement is a critical need to validate kinetic soot model in different combustion systems and for different fuels [START_REF] Koo | Large-Eddy Simulation of Soot Formation in a Model Gas Turbine Combustor[END_REF][START_REF] Betrancourt | Experimental and numerical investigation of the transition from non sooting to sooting premixed n-butane flames, encompassing the nucleation flame conditions[END_REF]. A large panel of in situ and ex situ techniques have been used to quantify soot particles in flames. In that context, the scanning mobility particle sizing (SMPS) appears as a method of choice for the measurement of size distribution and number of soot particles and therefore soot volume fraction [START_REF] Camacho | Mobility size and mass of nascent soot particles in a benchmark premixed ethylene flame[END_REF]. However, the SMPS is an intrusive method, hardly usable for turbulent flames which moreover requires the dilution of the species along a sampling line that can lead to alteration of the sampled particles (notably of the smallest particles by condensation or coagulation). By comparison, optical method as extinction or LII enable soot volume fraction measurements in flames without intrusive sampling probes or sensors. Moreover, laser diagnostic techniques possess highly spatial and temporal resolution better adapted to turbulent flame studies. LII is a conventional technique which has been widely used to measure soot particles in flames [START_REF] Mouton | Laser-induced incandescence technique to identify soot nucleation and very small particles in low-pressure methane flames[END_REF]. Nevertheless, the absolute value of soot volume fraction cannot be determined only through the LII technique which needs other measurement approaches to calibrate the LII signals, as by the complementary use of the laser extinction method [START_REF] Simonsson | Wavelength dependence of extinction in sooting flat premixed flames in the visible and near-infrared regimes[END_REF][START_REF] Wang | Soot formation in laminar counterflow flames[END_REF]. To simplify the fv measurement by LII, we propose here a new autocalibrated laser based method we developed for  Corresponding author: eric.therssen@univ-lille.fr Proceedings of the European Combustion Meeting 2023 quantitative measurements of soot volume in the context of turbulent flames, based on the recording of the LII spectrum in the near IR region and the calibration of the detection system by using a black body radiation source of measured luminescence. As an application of the method we first determined the fv in a turbulent diesel flame which generates soot particles from inception to mature soot. Then we applied the method in very slight sooting flame of commercial biofuel (E85) highlighting both the sensitivity of the technique and the very amount of soot produced in this last flame.

Experimental set-up

Burner and flame conditions

The spray jet flames in this study are generated in a home-made burner at atmospheric pressure as presented in Fig. 1. The burner is equipped with a direct liquid injection high efficient nebulizer (DIHEN-170-AA). This nebulizer allows us to transform the liquid fuel into very small droplets (7 -18 µm) which are able to vaporize quickly. This type of injector required a gas flow supply with high speed as the driving force for liquid atomization. In our work, the nitrogen is used as nebulization gas. The liquid fuel was introduced in the nebulizer capillary and was regulated by a liquid mass flow controller from Bronkhorst, model M13V14I with mass flow accuracy of ± 0.2%. The oxidation air flows enter the burner from two symmetrized sides and are homogenized with the help of a honeycomb. The gas flow rates of N2 and air were measured by using regulated mass flow controllers (Bronkhorst) with mass flow accuracy of ± 0.5%. The burner was mounted on a vertical translation stage allowing to modify the burner position on the vertical axis with 1µm precision.

Fig.1. Sketch of the burner generating the jet spray flames

The conditions of the two studied flames are summarized in table 1. The LHV of diesel around 43 MJ.kg -1 [START_REF] Leermakers | Experimental Study of Fuel Composition Impact on PCCI Combustion in a Heavy-Duty Diesel Engine[END_REF] is higher than that of gasoline E85 around 29.1 MJ.kg -1 . The LHV of E85 was calculated from the LHV of ethanol around 26.8 MJ.kg -1 [START_REF] Tran | Progress in detailed kinetic modeling of the combustion of oxygenated components of biofuels[END_REF] and gasoline SP95 around 43.2 MJ.kg -1 [START_REF] Fenkl | N-butanol and isobutanol as alternatives to gasoline: Comparison of port fuel injector characteristics[END_REF] for the mixture (15% SP95 / 85% ethanol) in volume. Thus, the mass flow rate of E85 flame was adjusted to produce the same LHV than the diesel flame.

Temperature measurement

The vertical center line temperature profiles of the two flames were measured with a type S thermocouple (TC S.A., Pt-Pt/10%Rh) having 0.35 mm wire diameter and 1.01 mm bead diameter measured with a 5 µm sensitivity micrometer. The thermocouple was inserted radially into the centerline of the turbulent flames at different HABs by using a motorized remote-controlled system. The soot particle movement in turbulent flames is very fast, allowing to minimize the soot deposit on the thermocouple. The thermocouple was cleaned by using a lean flame after each three measurements in the sooting zone. The thermocouple temperature measurements were corrected from the radiation losses according to procedure described in Elias et al [START_REF] Elias | Thermocouple-based thermometry for laminar sooting flames: Implementation of a fast and simple methodology[END_REF]. Temperature uncertainties were estimated this way to be ± 100 K.

LII experiment

The LII experiments have been carried out by using a 532 nm laser excitation wavelength after frequency doubling of the fundamental 1064 nm wavelength generated by a Nd: YAG Quantel. The 6 ns laser pulse was cadenced at 10 Hz. The energy of the laser beam was adjusted with an attenuator module. Two prisms were used to direct the laser beam through a circular pinhole with diameter of 850 µm in order to obtain a laser beam with a top hat profile. The laser beam at the exit of the pinhole was sent at the center of the burner using a focus lens with 200 mm focal length. This lens was placed at two times the distance of its focal length between the pinhole and the burner in order to avoid the diffraction patterns of the laser spot and to obtain a tophat profile into the diameter of the flame. The laser beam energy was measured by using a laser pyroelectric energy sensor located just after the burner (no-extinction of the laser was measurable due to low volume fraction of soot and low flame diameter).

The incandescence emission from the flame was collected through the entrance slit of a spectrometer using two achromatic lenses (f1=400mm and f2=200mm) setting a magnification factor of 0.5. A Notch filter 532 ± 9.8 nm was located just before the spectrometer to remove part of the 532 nm laser scattering. The emission signal through the notch filter was collected with an Acton SP300i spectrometer through a 1 mm wide opened slit. A diffraction grating 150 groves/mm, blazed at 800 nm (high transmission in near IR) was used. The center wavelength of the diffraction grating was set at 750 nm allowing to collect the emission spectral range from 609.1 nm to 889.8 nm. The spectrometer has two outputs provided to collect the signal either by a photomultiplier tube Philips XP2020Q (PMT) or by a Roper PIMAX 4 ICCD camera.

Temporal LII signals measured by PMT were triggered by a photodiode detector and typically averaged over 2000 laser shots. 1D spectral measurements were recorded with a temporal detection gate (gate width of the camera) set to 50 ns and centered on the peak of the LII pulse. 1D spectral images were recorded in order to obtain the emission spectra for the chosen wavelength domain or to obtain the flame emission profile. 1D spectral images were obtained by averaging 500 images and systematically corrected from the corresponding average background emission of the flame.

Calibrated lamp

In this work, we propose a new direct method to calibrate the soot volume fraction from the LII signal measured by the ICDD camera. To do so, we used an integration sphere from SphereOptics CSTM-LR-6-M. This sphere consists of a lamp located inside of a cavity, which is covered by white Lambertian substrate (BaSO4). It emitted a black body type radiation in the range of 360 nm to 1000 nm with an adjustable temperature between 2000 and 3300 K by adjusting the voltage of the external power supply module. An optical fiber connected with the sphere directs the light to a calibrated spectrograph, which provides luminance L° spectra as reference. This optical configuration is represented in the Fig. 2. The parameters of the detection system (position of the collimator, gain of the camera) are the same as for LII measurements.

The power P emitted by the orifice of the sphere per steradian (meaning the product of the luminance L° given by the calibrated spectrometer of the sphere by the sphere orifice surface Ssphere orifice and by the wavelength bandwidth ) for different power supply of the tungsten lamp (meaning different color temperatures of black body photons) is according to:

𝑃 = 𝐿° . 𝑆 𝑠𝑝ℎ𝑒𝑟𝑒 𝑜𝑟𝑖𝑓𝑖𝑐𝑒 . 𝜆 eq 1
For the detection system, the response (in count) of one pixel of the CDD could expressed as:

𝑆 𝐶𝐶𝐷 = 𝐿°• ∆𝜆 • 𝑆 1 𝑝𝑖𝑥𝑒𝑙  𝛽 eq.2
where 𝑆 1 𝑝𝑖𝑥𝑒𝑙 (m 2 ) is the surface area of the collected image in the space corresponding to one pixel in the ICCD camera,  (sr) is the collection solid angle from a photon emitted from the sphere to the first collection lens, 𝛽 (count.W -1 ) is the transmission coefficient, which depends on the set up of the experiment and the detected wavelength range.

All calculations in this study have been realized for 1 pixel corresponding to λ = 800.05 nm. The luminance of the sphere L° at 15V and λ = 800.05 nm is 1.2325.10 9 (W.m -2 .m -1 .sr -1 ). The ∆ which depends on the grating of the spectrograph and the camera is 2.74.10 -10 (m). 𝑆 1 𝑝𝑖𝑥𝑒𝑙 can be obtained with 𝑆 1 𝑝𝑖𝑥𝑒𝑙 = 2 × ℎ 𝑠𝑙𝑖𝑡 × 2 × 𝑙 𝑝𝑖𝑥𝑒𝑙 due to the presence of the achromatic lenses system. hslit which is the height of the slit of the spectrograph is 1.19.10 -3 (m). lpixel, the size of 1 pixel is 1.3.10 -5 (m). Thus, S1pixel = 6.19.10 -8 (m 2 ) and SCCD measured by the camera at 15 V after correction by the transfer function is 1013.2 (count). From eq.2, we obtain a value of 𝛽 = 4.8472.10 10 (count.sr.W -1 ).

Results

Temperature profile

Fig. 3 shows the experimental temperature profiles measured in the center line of the diesel et E85 flames. The maximum temperatures of two flames are very similar. However, the temperature profile of E85 flame shifts 100 mm higher by comparing to that of the diesel flame. This shift could be explained by the difference of the mass flow rate of the fuels (145.4 g.h -1 for the E85 and 98.2 g.h -1 for diesel flame).

LII results

Laser fluence determination

The evolution of the LII signal as a function of the laser fluence along the center line of the flame has been studied for the two flames and reported in Fig. 4 (left column). In the diesel flame, the fluence curves shape clearly varies with HAB. This evolution is characteristic of the evolution of the optical properties (Em(λ) notably) of the generated soot particles. At 50mm HAB, the fluence curve is quasi-linear with energy as generally observed for nascent soot particles in laminar flames [START_REF] Mouton | Laser-induced incandescence technique to identify soot nucleation and very small particles in low-pressure methane flames[END_REF]. At 70 mm HAB, the fluence curve starts to bend and to finally leads above this HAB to the typical S shape of fluence curves characteristic of mature soot [START_REF] Mouton | Laser-induced incandescence technique to identify soot nucleation and very small particles in low-pressure methane flames[END_REF]. From HAB equal to 110 and 200 mm, the fluence curves peaks around 100 mJ.cm -2 before decreasing when laser fluence increases due to soot sublimation above this laser fluence. The corresponding temporal decay curve of the LII is reported in the right column of Fig. 4 (Fig. 4c andd) as well as the measured decay-times at 1/e (Fig. 4e) of the LII peak signals. The relationship between the LII temporal decay and soot particle size is complex [START_REF] Michelsen | Laserinduced incandescence: Particulate diagnostics for combustion, atmospheric, and industrial applications[END_REF] and requires the use of LII modeling to interpret the LII signal in terms of primary particle diameter. However, the evolution of the temporal LII decay time is correlated to the diameter of soot particle [START_REF] Michelsen | Laserinduced incandescence: Particulate diagnostics for combustion, atmospheric, and industrial applications[END_REF]. The longer the decay time is larger the soot particle size. In the diesel flame, the decay-times increase from 50 mm to 90mm and remain nearly constant at higher HABs. This evolution indicates that the nascent soot particles which are formed around 50 mm HAB, undergo soot growth process with HABs until 90 mm HAB.

Regarding the E85 flame, we could only determine the fluence curve at 210 nm because of the very weak LII signal, especially for the lower HAB. The quasilinear shape of the obtained fluence curve seems to characterize the formation of nascent soot particles (with low Em(λ) value) undergoing only limited or no surface growth along the flame height. This statement is corroborated by the absence of increase of the LII decay-times reported also in Fig. 4d indicative of nascent soot particles. As can be seen, the corresponding decay-times measured at 1/e of the LII peak signals remain constant for all HABs in the E85 flame and very close the value determined at 50 mm and 60 mm in the diesel flame.

LII imaging of the flame

Regarding the fluence curve, we defined a laser fluence around 54 mJ.cm -2 for the LII measurement in the diesel flame with the ICCD camera. This value allows indeed LII measurements without sublimation issues and an adequate signal to noise ratio. In the E85 flame where no sublimation issue can be established until 250 mJ/cm 2 , we had to increase the laser fluence to 108 mJ.cm -2 in order to get a sufficient signal to noise ratio for the LII measurement.

Fig.5. 2D plots of LII signal detected at 800 nm

The temporal gate width of the camera was also chosen regarding these data. We hence defined a starting gate at the peak of LII signal and a with a gate width of 50 ns, allowing to minimize the variation of temperature between t = 0 ns and t = 50 ns during the measurement of the heated soot particles. In our experimental condition, we have estimated this variation around 8.5 %. Fig. 5 shows the rebuilt LII images obtained from series of 1D spectral measurements centered at 800 nm. We note that the maximum LII signal along the center line of the flames appears at 180 mm of HAB in the diesel flame. The corresponding LII signal intensity is 100 times higher than that the maximum LII signal determined 210mm HAB in the E85 flame.

Absolute soot volume fraction determination

The absolute soot volume fraction has been experimentally determined along the center line of the two flames according to the new auto-calibrated method presented below and described step by step.

Determination of the temperature of the heated soot

The average temperature Tp of the soot particles heated by the laser can be derived from the LII spectrum as below:

ln ( 𝑆 𝐿𝐼𝐼 (𝑡 0, λ) 6 𝐸 𝑚 (𝜆) ) = - ℎ𝑐 𝑘 𝑏 𝑇 𝑝  + ln (48𝜋ℎ𝑐 2 𝑓 𝑣 ) eq.3
where SLII(t0,λ) is the incandescence signal intensity, Em(λ) the absorption function of the particle, Tp the average temperature of soot particles and fv the soot volume fraction.

To determine Tp, we first need to record an emission LII spectrum in a spectral range (750-850 mm) within Em(λ) can be assumed as constant [START_REF] Yon | Examination of wavelength dependent soot optical properties of diesel and diesel/rapeseed methyl ester mixture by extinction spectra analysis and LII measurements[END_REF]. In that case, the relation ln(SLII(t0,λ)λ 6 ~-hc/(kb,Tp) can be established. Fig. 6 presents some examples of Tp determination from LII spectra in the diesel et E85 flames. The LII signal were measured in the flame center and corrected from the transfer function and flame emission for the calculation process. Good linear fits are obtained for the diesel and E85 flame, allowing an accurate the heated temperature of the particles for all HAB.

LII signal intensity from soot particles

Soot particles are known to behave as grey body emitter characterized by the following expression:

𝐸 𝑏𝑏 (𝑇 𝑝 , 𝜆) = ∫ (𝑇, 𝜆) 2𝜋ℎ𝑐 2 𝜆 5 1 𝑒𝑥𝑝( ℎ𝑐 𝜆𝑘 𝐵 𝑇 𝑝 )-1 ⅆ𝜆 ⅆ𝑆 𝜆 2 𝜆 1 eq.4
where 𝐸bb is the emittance (W) of an elementary surface dS (m -2 ) emitted over 2 steradian (in "half the space") and defined over a spectral range d. λis the emissity (without dimension).

The absorbing ability α(λ,Tp) of a body represents the ratio of the radiation flux absorbed by the body to the radiation flux incident on the body. According to Kirchhoff's law, the emissivity is equal to the absorption coefficient for the same couple of 𝜆 and Tp values. The emissivity is given in the Rayleigh approximation by, where πdp<< λ

𝛼(𝜆, 𝑇 𝑝 ) = 4𝜋 ⅆ 𝑝 𝐸 𝑚 (𝜆) 𝜆 eq.5
The Kirchhoff's law establishes the relationship between the abilities of emitted and absorbed electromagnetic energy by any physical body. It can therefore be approximated that the heated soot particles are in thermodynamic equilibrium with the encountered radiation. So the absorption coefficient α(λ,Tp) and the emission coefficient (or emissivity) ε(λ,Tp) are equal for the same couple of Tp, λ.

Thus, according to eq.5, the emissivity could be taken into account to define the eq.6 for a defined volume V, which contains Np (m -3 ) soot particles (spherical particles in the Rayleigh approximation, here with the same diameter and a surface of πdp 2 ). The following equation gives the LII signal emitted by Np soot particles: The LII signal from soot particles were measured with the detection system characterized by the collection solid angle  and the transmission coefficient 𝛽. Thus, SLII detected could be expressed as: From eq.9, it appears that to determine the soot volume fraction, the Em(λ) values and corresponding temperatures of soot particles are necessary. In the low laser fluence regime, the Em(λ) absorption function can be expressed by: 𝐸 𝑚 (𝜆) = (𝑇 𝑝 -𝑇 𝑔 ).𝜆 𝑙𝑎𝑠𝑒𝑟 .𝜌 𝑠 .𝑐 𝑠 6𝜋.𝐹 eq.10

𝑆 𝐿𝐼𝐼 (𝑇 𝑝 , 𝜆) = ∫ 𝑁 𝑝 . 4𝜋 ⅆ 𝑝 𝐸 𝑚 (𝜆) 𝜆 . 𝜋ⅆ 𝑝 2 .
where Tg is the temperature of flame, λlaser is the laser wavelength, F the laser fluence, ρc the density of soot particles and cs is the specific heat of soot particles. The density of soot ρc in the diesel flame was extrapolated from 1.3 g.cm -3 for nascent soot to 1.8g.cm -3 for mature soot [START_REF] Betrancourt | Quantitative measurement of volume fraction profiles of soot of different maturities in premixed flames by extinction-calibrated laserinduced incandescence[END_REF]. The value of ρc in the E85 flame was considered constant and equal to 1.3g.cm -3 for all HABs. The value of specific heat of soot particles is taken at 2.3 J.g -1 .K -1 [START_REF] Betrancourt | Quantitative measurement of volume fraction profiles of soot of different maturities in premixed flames by extinction-calibrated laserinduced incandescence[END_REF]. Fig. 7 (a) presents the evolution of the average temperature of soot particles after laser pulse measured in the center line of two studied flames. The temperature of the soot particles in the flame E85 was slightly higher than that in the diesel flame because the laser fluence used for E85 flame was higher than that used for diesel flame. In the diesel flame, the resolution of the LII spectra from 50 mm HAB enable to determine the average temperature of soot particle while Tp could only be identified from 160mm to 240 mm HAB in the E85 flame. Fig. 7 (b) shows the evolution of Em(λ) along the center line of the two studied flames. In the E85 flame, Em(λ) is nearly constant around 0.14 with the flame heights, characteristic of nascent soot particles In the diesel flame, the value of Em(λ) at the beginning of the soot formation is 0.226 which is higher than the value of the E85 flame. This difference might be explained by the turbulence of the diesel flame. The images recorded by camera might be mixture of signal coming from nascent particles formed in the central axis and more mature ones surrounding the flame. Above 120mm HAB, Em(λ) increases with HABs due to the evolution of optical properties of the soot particles with their maturation.

The soot volume fraction profiles determined along the center line of two flames of diesel and gasoline E85 is finally presented in Fig. 8. The experimental results show that the maximum soot volume fraction in the diesel flame is 951 ppb while it is only 13ppb in the flame E85. The method proposed in this study allows to measure the soot volume fraction in very slightly sooting flame. These results highlight that this kind of fuel is a promising bio-fuel for internal combustion engine in regard to the soot formation issues.

4.Conclusion

This work describes a new auto-calibrated method of the detection system allowing a direct determination of the soot volume fraction by LII in flames. We demonstrated here that this method is well adapted for turbulent flame studies and highlight a large dynamic scale in terms of measurable soot volume fraction. This method provides here valuable information about the propensity of diesel and E85 biofuel to generate soot particles. With a produced soot volume fraction rather than 100 times lower than the diesel flame, the E85 appears a promising biofuel.

Fig. 2 .

 2 Fig.2. Schematic of the optical set up for the calibration with sphere

Fig. 3 .

 3 Fig.3. Temperature profiles measured in the center line of diesel et E85 flames

Fig. 4 .

 4 Fig.4. Left column: Normalized fluence curves obtained in diesel and E85 flame. Right column: LII temporal signal measured at different HAB in two flames: (a) diesel flame, (b) E85 flame. For clarity, the peak of LII signals have been normalized to 1 (c, d). (e) LII decay-time measured at 1/e of the LII signal as a function of HABs

Fig. 6 .

 6 Fig.6. Determination of Tp from two LII spectra: (a) Diesel 180mm, (b) E85 210mm

3 6,Eq. 7 1 .

 371 Considering the soot volume fraction fv defined as 𝑓 𝑣 = 𝑁 𝑝 𝜋 ⅆ the LII signal SLII(Tp,λ) in W.m -3 emitted at 4π steradian can finally be expressed as:𝑆 𝐿𝐼𝐼 (𝑇 𝑝 , 𝜆) represents the general equation of the LII signal characterizing the thermal radiation emitted by Np spherical soot particles at the temperature Tp according to their optical properties Em(𝜆) in the investigated wavelength domain. As, the emission spectral range 𝜆, centered on , is very narrow, the expression of the total LII signal emitted at 4π steradian in W.m -3 could be expressed as: 𝜆 . 𝑓 𝑣 eq.8

1 . 9 where 4 .

 194 𝑉 𝑚 . Ω . 𝛽 . 𝜆 . 𝑓 𝑣 eq.Vm is measured volume with 𝑉 𝑚 = 2 × 𝑙 𝑝𝑖𝑥𝑒𝑙 × 𝜋 𝑙𝑎𝑠𝑒𝑟 2 ℎ 𝑠𝑙𝑖𝑡 . The diameter ϕlaser of the 532nm excitation laser beam is 850µm. Thus, Vm = 1.475.10 -11 m 3 .

Fig. 7 .

 7 Fig.7. Evolution of temperature of soot particle (a) and Em(λ) (b) with HAB in two flames of diesel and E85. Laser fluence = 54 mJ.cm -2 for diesel flame and laser fluence = 108 mJ.cm -2 for E85 flame.

Fig. 8 .

 8 Fig.8. Soot volume fraction profile measured in the center line of diesel flame (blue) and of E85 gasoline flame (red).

Table 1 : Flame conditions

 1

	Flame	Fuel	Air	Nebulization	LVH
		(g.h -1 )	(NL.min -1 )	N2	(MJ.h -1 )
				(NL.min -1 )
	Diesel	98.2	19.6	0.25	4.2.10 -3
	E85	145.4	19.6	0.25	4.2.10 -3


text:
H Q Do

E Therssen

L S Tran

K Sood

L Giarracca-Mehl

X Mercier

Characterization of the impact of ethanol on the formation of soot particles in gasoline turbulent diffusion flames

Keywords: Ethanol, Surrogate gasoline, Soot formation, Laser induced incandescence, Turbulent diffusion flame

The objective of this study was to characterize the impact of ethanol as a fuel additive on soot formation in turbulent diffusion flames for different gasoline mixtures of varying alcohol concentrations. These jet spray flames were stabilized at atmospheric pressure. A TRF mixture (Toluene Reference Fuel) defined as a surrogate representative of the composition of standard gasolines of type SP95 was used as reference flame. To characterize the impact of ethanol on soot formation, 11 flames of TRF mixed with various ethanol mole fraction from 0 to 100% were studied by keeping either the lower heating value (LHV) or the mass flow rate (MFR) constant. Soot volume fraction (fv) were measured by laser induced incandescence (LII). Absolute fv values were obtained by an autocalibrated method requiring a radiation source of known luminance to calibrate the detection system. The experimental results highlight a quasi-linear reduction of the soot formation with the added mole fraction of ethanol, until their complete disappearance for a pure ethanol flame. These results also highlight a stronger effect of ethanol on the soot reduction for ethanol addition with constant MFR characterized by a gradual decrease of the flame height. Experiments with commercial gasoline SP95-E10 and E85 were also carried out. The measured fv profiles show strong similarities with the fv profiles determined for their corresponding surrogates. These results illustrate that the TRF is an appropriate gasoline surrogate for studies aimed at characterizing soot formation. A modeling work, currently in progress, will be investigated to explain the inhibiting effect of ethanol on soot formation kinetics.

Introduction

Ethanol is an attractive alternative fuel with a high octane number (RON/MON = 120/99) for spark-ignited internal combustion engine [START_REF] Dirrenberger | Laminar burning velocity of gasolines with addition of ethanol[END_REF][START_REF] Peralta-Yahya | Microbial engineering for the production of advanced biofuels[END_REF]. The addition of ethanol has shown to reduce the soot formation in gasoline sooting flames [START_REF] Liu | An experimental study on soot distribution characteristics of ethanol-gasoline blends in laminar diffusion flames[END_REF][START_REF] Khosousi | Experimental and numerical study of soot formation in laminar coflow diffusion flames of gasoline/ethanol blends[END_REF][START_REF] Maricq | Soot formation in ethanol/gasoline fuel blend diffusion flames[END_REF][START_REF] Lemaire | Effect of ethanol addition in gasoline and gasoline-surrogate on soot formation in turbulent spray flames[END_REF]. The soot volume fraction decreases when the quantity of ethanol is added to the laminar diffusion flame of gasoline [START_REF] Liu | An experimental study on soot distribution characteristics of ethanol-gasoline blends in laminar diffusion flames[END_REF][START_REF] Khosousi | Experimental and numerical study of soot formation in laminar coflow diffusion flames of gasoline/ethanol blends[END_REF]. Maricq et al. [START_REF] Maricq | Soot formation in ethanol/gasoline fuel blend diffusion flames[END_REF] investigated the impact of ethanol on the particles size distribution function (PSDF) in the laminar diffusion flame of gasoline. They found that substituting a small amount of ethanol in the gasoline had little impact on the PSDF. However, when the ethanol ratio was increased up to 85%, the primary particles constituting soot agglomerates decreased by more than 50% in comparison to that of the reference flame. Lemaire et al. [START_REF] Lemaire | Effect of ethanol addition in gasoline and gasoline-surrogate on soot formation in turbulent spray flames[END_REF] also studied the effect of ethanol addition on the formation of soot and polycyclic aromatic hydrocarbons (PAHs) in turbulent spray flames of gasoline and their surrogates. The advantage of spray flames is that it relies on the use of liquid fuel injection which avoids evaporation issues. Lemaire et al. [START_REF] Lemaire | Effect of ethanol addition in gasoline and gasoline-surrogate on soot formation in turbulent spray flames[END_REF] pointed out that the addition of 10-30% of ethanol to gasoline flames reduces the total soot quantity by 25-81%.

To better understand the role of ethanol in soot reduction, we investigated the soot formation in several atmospheric pressure spray flames of  Corresponding author: hong-quan.do@univ-lille.fr Proceedings of the European Combustion Meeting 2023 gasoline surrogate TRF (Toluene Reference Fuel) with varying alcohol concentrations (0 -100%) and constant lower heating value (LHV) or mass flow rate (MFR). Soot volume fraction (fv) were measured by using auto-calibrated laser induced incandescence (LII). The obtained results provide some valuable information regarding the powerful impact of ethanol on soot reduction. Furthermore, we also highlight the very good mimicry of the SP95-E10 and E85 by the TRF-Ethanol mixtures regarding soot formation.

Experimental set-up

Burner and flame conditions

The turbulent spray flames were stabilized on a homemade burner consisting of a nebulizer (DIHEN-170-AA) [START_REF] Lemaire | Original use of a direct injection high efficiency nebulizer for the standardization of liquid fuels spray flames[END_REF] for liquid fuel's atomization and the oxidation air stabilization system. The atomization equipment plays a major role in the characteristics of the combustion process of twophase flow. Smaller the droplets, faster is the vaporization of the liquid and more effective is the combustion. The liquid fuels were injected by a capillary tube and cut by a high-speed flow gas circulating in an annulus area to create the spray. In this study, we used nitrogen as the nebulized gas. The air flow was injected under a honeycomb structure which allows a better stabilization of the flame. The nebulizer was placed in the center of the honeycomb structure. For all studied flames, the flow rates of N2 and Air were kept constant at 0.25 L.min -1 and 19.6 L.min -1 respectively. The mass flow rate of the liquid fuel for 11 flame TRF-Ethanol are reported in Table 1 and2. The studied mixtures were prepared by mixing 4 pure chemical compounds: iso-octane, toluene, nheptane and ethanol. The mole fraction of the mixtures was verified by using gas chromatography (GC). The uncertainty associated with the mole fractions of each of the compounds was determined to be less than 3%.

Temperature measurement

The vertical centerline temperature profiles of the studied flames were measured with a type S thermocouple (TC S.A., Pt-Pt/10%Rh) having 0.35 mm wire diameter and 1.01 mm bead diameter. The thermocouple was cleaned by placing it in the blue part of the flame after every three measurements in the sooting zone. The thermocouple temperature measurements were corrected from the radiation losses by following the recent and simple method described in Elias et al [START_REF] Elias | Thermocouple-based thermometry for laminar sooting flames: Implementation of a fast and simple methodology[END_REF]. The uncertainty on the temperature was estimated around ± 100K.

Determination of soot volume fraction profiles

Soot volume fraction profiles were determined using laser induced incandescence (LII) measurements carried out by using a laser excitation wavelength at 532 nm. The laser beam passed through a pinhole to provide a top-hat irradiance profile at the position of the LII measurement in the flame. The LII signal was collected at right angle from the laser axis by a system of two lenses (f1 = 400 mm and f2 = 200 mm) associated to a spectrometer Acton SP300i. A diffraction grating 150 groves/mm, blazed at 800 nm (high transmission in near IR) was used. The center wavelength of the diffraction grating was set at 750 nm allowing to collect the emission spectral range from 609 nm to 890 nm. The spectrometer had two outputs providing to collect the signal either by a photomultiplier tube Philips XP2020Q (PMT) or by a Roper PIMAX 4 ICCD camera. A Notch filter centered at 532 ± 9.8 nm was positioned just before the spectrometer to remove part of the intense Rayleigh laser scattering.

The LII signal from soot particles were measured with the detection system characterized by the solid angle of collection  and the transmission coefficient 𝛽. Thus, the detected LII signal could be expressed as: In order to get absolute fv values from the LII signal, we calibrated the detection system by using an auto-calibrated method requiring a radiation source of known luminance. This method also relies on the determination of the absorption function of the particle Em(λ) and the measurement volume Vm which can be defined according to the expression :

𝑉 𝑚 = 2 × 𝑙 𝑝𝑖𝑥𝑒𝑙 × 𝜋 𝑙𝑎𝑠𝑒𝑟 2 4
. ℎ 𝑠𝑙𝑖𝑡 , where lpixel is the size of 1 pixel, ϕlaser is the diameter of laser beam, hslit is the open of slit. Em(λ) has been determined along the vertical centerline of the flame using the low laser fluence methodology [START_REF] Betrancourt | Quantitative measurement of volume fraction profiles of soot of different maturities in premixed flames by extinction-calibrated laser-induced incandescence[END_REF]. This method relies on the determination of the soot heated temperature 𝑇 𝑝 by the laser pulse for different laser energies, connected to the Em(λ) according to the following expression:

𝐸 𝑚 (𝜆) = (𝑇 𝑝 -𝑇 𝑔 ).𝜆 𝑙𝑎𝑠𝑒𝑟 .𝜌 𝑠 .𝑐 𝑠 6𝜋.𝐹 eq.2
where Tg is the temperature of flame, λlaser is the laser wavelength, F the laser fluence, ρc the density of soot particles and cs is the specific heat of soot particles. The density of soot ρc in the sooting flame of this study was extrapolated along the centerline of the flame from 1.3 g.cm -3 (50 mm HAB corresponding to nascent soot) to 1.8 g.cm -3 (210 mm HAB corresponding to mature soot).

Finally, the term Ω . 𝛽 in eq.1 can be obtained from the measurement of calibrated black body emission spectra transmitted from the calibrated integrated sphere. This way, it is possible to calibrated the LII signal issued from the flame into absolute fv values.

Sprays characterization

The structure of the TRF sprays with and without the flame were measured by using the corresponding Mie scattering signals upon 532 nm excitation wavelength. The Mie scattering signal was collected with the same detection system as for LII measurements without the Notch filter 532 ± 9.8 nm placed in front the spectrometer.

Results and discussions TRF flame jet characterization

The structure of the TRF sprays with and without the flame are presented in Fig. 1. We observe that the liquid fuel droplets in the TRF flame disappear at 20 mm HAB while the liquid fuel droplets evaporate completely at HAB = 70mm in TRF cold jet. Impact of ethanol on the temperature profile Fig. 2 shows the impact of ethanol on the temperature profile of TRF flame in the case of constant LHV (Fig. 2a) and in the case of constant MFR (Fig. 2b). In both cases, we observe that ethanol substitution does not change the maximum temperature reached in both flames as shown in Table 1 and 2. In the case of constant LHV (Fig. 2a), the increasing ethanol concentration (from 0 to 100%) shifts the temperature profile to the burnt gas zone. This observation could be explained by the increase of mass flowrate of the fuel.

In the case of constant MFR, the temperature profile shifts towards the nebulizer when the quantity of ethanol increases in the TRF mixture. This observation may be caused by keeping the mass flow rate of mixture leading to decrease of their LHV. The reduction of LHV reduces the flame power meaning decrease in the flame height.

Impact of ethanol on soot formation

LHV constant Fig. 3 shows pictures of the 6 TRF-Ethanol flames in the case of constant LHV. The parameters of the camera to take these pictures have been kept identical for the whole flames. When the quantity of ethanol in the mixture increases, we observe that the flame height increases while the orange color decreases and even disappears completely in the 100% ethanol flame. The 2D imaging of the LII signal rebuilt from the 1D spectral measurements carried out in the 6 flames are reported in Fig. 4. From these images, we could determine the evolution of fv along the vertical centerline for the whole flame. This data is reported in Fig. 5 and highlights the impact of ethanol on the soot volume fraction profile in the various TRF flames. The maximum soot volume fraction in the reference TRF flame is about 664 ppb at 130 mm. We observe that the substitution of 20% ethanol in mole (TRF-E) slightly decreases the soot volume fraction (562 ppb) which continues to decrease with increasing ethanol concentration in the mixture. The highest value of fv in the TRF-E85 flame corresponding to 85% ethanol in volume or 93.1% in mole in the mixture, is only 9 ppb. Finally, we note that the soot particles disappear completely (no measurable LII signal) in the flame with 100% ethanol. All these experiments were carried out with identical flowrates of N2 and air for all studied flames but variable ethanol flowrates. It is known that the increase of the mass flowrates of the fuel decreases the efficiency of the nebulizer for the atomization of the injected fuels leading to a reduction of the combustion efficiency [START_REF] Lemaire | Original use of a direct injection high efficiency nebulizer for the standardization of liquid fuels spray flames[END_REF] and an increase in the soot formation. However, we clearly observe a strong reduction of the soot formation with the increase of the mass flow rate in the case of ethanol indicating the strong chemical effect of ethanol to inhibit the formation of soot in the TRF flame.

MFR constant

Fig. 6 shows the pictures of the 6 TRF-Ethanol flames (from 0 to 100% ethanol) stabilized for an identical mass flow rate equal to 98.2 g.h -1 . In this case, we observe that the orange color and the flame height decrease with increase of ethanol. We also reported in Fig. 7 the corresponding 2D LII imaging determined for these flames. The decrease of soot signal in the case of constant MFR is faster than in the case of constant LHV. The soot particles disappear completely (no measurable LII signal) in the flame TRF-E85*.

Comparison between the surrogate and real fuel

The soot volume fraction profiles of the TRF-E, TRF-E* and TRF-85 flames were compared with that of their real fuels and shown in Fig. 9. The soot particles were not detected in the flame TRF-E85*, thus, the comparison was not realized for this flame. The soot volume fraction profiles of TRF-E, TRF-E* and TRF-E85 are quite similar with that of their corresponding real fuels. Thus, the surrogates used in the present study are good and well suited to investigate the impact of ethanol on the soot formation in gasoline flame.

Discussion of the kinetic impact of ethanol on soot formation.

Fig. 10 shows the maximum soot volume fraction values determined in the whole flame plotted versus the mole fraction of ethanol in the TRF mixtures. In both cases (constant MFR or LHV), we observe a quasi-linear reduction of the soot formation with respect to the mole fraction of ethanol. These results were also observed in the laminar diffusion flame of gasoline published by Khosousi et al [START_REF] Khosousi | Experimental and numerical study of soot formation in laminar coflow diffusion flames of gasoline/ethanol blends[END_REF]. Besides, we also observe in Fig. 10 that the reduction of the soot volume fraction is more efficient with substitution of ethanol with constant MFR than that with constant LHV. This difference in efficiency is very probably related to the mass flow rate of mixture in the case of constant MFR lower than that of LHV constant. The kinetic impact of ethanol on soot reduction in gasoline and gasoline surrogate flames has been discussed in literature [START_REF] Lemaire | Effect of ethanol addition in gasoline and gasoline-surrogate on soot formation in turbulent spray flames[END_REF][START_REF] Xu | Experimental and modelling studies of the effects of methanol and ethanol addition on the laminar premixed low-pressure nheptane/toluene flames[END_REF]. Lemaire et al. [START_REF] Lemaire | Effect of ethanol addition in gasoline and gasoline-surrogate on soot formation in turbulent spray flames[END_REF] pointed out that the soot reduction is due to the combined effects of dilution and oxygen contained in ethanol leading to oxidize the soot particles faster. Xu et al. [START_REF] Xu | Experimental and modelling studies of the effects of methanol and ethanol addition on the laminar premixed low-pressure nheptane/toluene flames[END_REF] suggested that adding alcohol can inhibit the formation of PAHs due to massivelyproduced HO2 and OH radicals from alcohol.

Conclusion

In this work, we carried out a series of experiments aimed to characterize the impact of ethanol on the soot formation in different turbulent diffusion flames of gasoline. Two approaches have been carried out to investigate the impact of ethanol by keeping the lower heating value of fuel constant or by keeping the mass flow rate of fuels constant. In both cases, we observed a quasi-linear reduction of soot volume fraction in the TRF flame with increasing of ethanol added but with a stronger efficiency in the case of constant MFR. Moreover, we have also an excellent agreement between the experiment carried out with commercial fuels E10, E10* and E85 and their corresponding surrogates which therefore validate these surrogates for the soot formation studies related to these commercial fuels.

We also showed that the centerline temperature profiles of all these flames highlight similar maximum values. This point therefore indicates the fv reduction is mainly related to the chemical effect of ethanol, for which a modeling work will be soon performed to lead to a deeper understanding of this process.

.

  𝑆 𝐿𝐼𝐼,𝑑𝑒𝑡𝑒𝑐𝑡𝑒𝑑 (𝑇 𝑝 , 𝜆) = 12𝜋 ℎ𝑐 2 𝐸 𝑚 (𝜆) 𝑉 𝑚 . Ω . 𝛽 . 𝜆 . 𝑓 𝑣 eq.1 where λ is the emission wavelength, kb the Boltzmann constant, c the light speed, h the Planck constant. Tp the average temperature of soot particles determined on the LII spectrum. 𝜆 is the emission spectral range. fv is the soot volume fraction.

Fig. 1 .

 1 Fig.1. Liquid droplet distribution measured by Mie scattering in TRF flame (left) and TRF cold jet (right)

Fig. 2 .

 2 Fig.2. Impact of ethanol on the temperature profile of TRF flame in the case of LHV const (a) and in the case of MFR const (b)

Fig. 3 .Fig. 5 .

 35 Fig.3. Pictures of the 6 TRF-Ethanol (0-100%) flames with constant LHV

Fig 6 .Fig. 8 .

 68 Fig 6. Pictures of the 6 TRF-Ethanol (0-100%) flames with constant MFR

Fig. 9 .

 9 Fig.9. Comparison of the soot volume fraction profiles obtained with the commercial fuel E10, E10* and E85 with their surrogates.

Fig. 10 .

 10 Fig.10. The impact of ethanol on the maximum soot volume fraction of TRF flame

Table 1

 1

	Flame

. Experimental conditions for the 6 flames with same LHV. xiso-octane, xtoluene, xn-heptane, xethanol are the mole fraction of iso-octane, toluene, n-heptane and ethanol in the mixture. Tmax is the maximum measured temperature by using thermocouple

Table 2

 2

. Experimental conditions for 6 flames with same mass flow rate of fuel MFR. xiso-octane, xtoluene, xn-heptane, xethanol are mole fraction of iso-octane, toluene, n-heptane and ethanol in the mixture Tmax is the maximum measured temperature by using thermocouple. * symbol indicates the flames with MFR constant

Acknowledgements

This work was supported by the Agence Nationale de la Recherche through the OFELIE project (ANR-20-CE05-0047) and the LABEX CAPPA (ANR-11-LABX-0005). Financial and technical supports from the CERLA was also greatly appreciated.


Edith Ackermann

Françoise Decortis

Stéphane Safin

enhanced spaces for intergenerational learning Literature review and theoretical approach

This document has two main objectives. First it aims to explore the current literature on intergenerational learning in public spaces. Second it seeks to define a relevant theoretical approach to embraces intergenerational learning in public spaces enhanced by technology. It contains three main parts. In the first part we will state the stage, that is define what we mean by places, who the participants are and how digital technologies can be used. In the second part, we describe our sources and resources to progress iteratively in defining our theoretical approach. The third part is dedicated to key dimensions and themes to go further in researching for intergenerational learning in public spaces.

INTRODUCTION

This document has two main objectives. First it aims to explore the current literature on intergenerational learning in public spaces. Second it seeks to define a relevant theoretical approach to embraces intergenerational learning in public spaces enhanced by technology. It contains three main parts. In the first part we will state the stage, that is define what we mean by places, who the participants are and how digital technologies can be used. In the second part, we describe our sources and resources to progress iteratively in defining our theoretical approach.

The third part is dedicated to key dimensions and themes to go further in researching for intergenerational learning in public spaces.

II LA PIAZZA : STATING THE STAGE

Defining our research object "La Piazza, Technology enhanced public spaces for intergenerational learning" starts along three axes : what places ? who are the concerned participants? what is the social environment ? and how digital tools can be used to enrich social relations. Defining our theoretical approach to embraces intergenerational learning on the other hand emerges from three types of sources and resources that we will explore in a second time.

1 What ? Places, Convivial Space, Transitional

Zone, Living Stage

Third-places, as defined by Oldenburg, are "great good places between home and work" where people from different ages and walks of life come together to turn the habitual into the extraordinary [Oldenburg, 1989 1 )]. Examples of third places include cafes, theatres, public squares, museums, and concert halls. They also include dedicated locations for passing events or celebrations, such as carnivals, fairs, markets, or circus. Third places are important to intergenerational learning in that they bring together folks who wouldn't otherwise meet, to do things they wouldn't ordinarily do! Transitional zones in Winnicott's sense [2], these spaces in-between afford a mental elbow-room (Spielraum in German) for social actors to safely explore, recast, play out, and ultimately work through otherwise unspoken aspects of their lives, thus inventing new potentials, or virtualities, together. Third places are both convivial "piazzas" and living stages.

A "piazza" is fore and foremost a convivial space: a place where it feels good to be together. It is also a transitional zone, or third-place where people, like actors on a stage, play out and unveil aspects of their "personae" otherwise untapped.

Lastly, a "piazza" is a living memory p(a)lace, structured by the community and reflective of the changing identities and dreams of its members.

Picture;1a and 1b: Piazza as playground and living stage (source google images)

Our objective in reviewing the relevant literature is to help identify some of the spatial and relational qualities that make for a good piazza and to build a vocabulary that captures the evocative and holding powers and ambient qualities of place, beyond mere functionality. Here we aim to identify some of the relational qualities and socio-cultural dynamics that are conducive to collateral learning. Get a handle on the selforienting techniques that people, young and old, invent for themselves to play, learn, grow, belong, and be loved. The team imagines scenarios for the "piazza" of the future, and proposes to augment these scenarios, using digital technologies. Three questions drive the inquiry: 1. How to mediate/enhance people's sense and experience of place? 2.

How to merge digital and physical in the design of sensorially-rich and stimulating places? 3. What technologies for what purpose?

Our objective is to help identify which types of technological tools may best suit which contexts and to build a vocabulary for the design and evaluation of digitally enhanced event/ambient spaces.

III SOURCES AND RESSOURCES

To define our theoretical framework we used an iterative approach based on practices and writings on intergenerational learning programs, a priori field studies and a posteriori process concept design. On one axis (figure 1), field studies allow to define the more important issues or dimensions describing the context. On a second axis, process concept design allows to explore these Figure 1. An iterative approach to define our intergenerational learning theoretical approach

In the following, we will explore sequentially -Citizenship where for instance elderly offer their skills and experience and young offers sense of responsibility and support.

-Social exclusion: older and young are not contributors and considered as part of economic society, IG brings these two groups together to challenge this stereotype -Synergy: when older and younger are bring together a new relationship is created, synergy, generations recognise their similarities and the way they are excluded from social trend.

In recent years, there has been a proliferation of isolated and local intergenerational practices. In the USA, shared intergenerational website programs are developed to provide new opportunities for learning that engage both young and older while creating stronger intergenerational relationships (Arfin, 2002 ; Steinig and Peterson, 2002 7 ). However, little research has been completed on these experiences. What has been done has been deemed vague and fragmented. Therefore it is increasingly important for intergenerational programs to demonstrate their effectiveness to policy makers in addressing individual, social, and community problems.

Research about intergenerational practices can be classified in two main streams.

On the one hand, focus is on the significance of intergenerational engagement in terms of impact on human development outcomes. In this regard, some good

Context and place

It has become commonplace to distinguish between apprenticeship (learning within community) vs. school teaching, and informal vs. formal learning, and these distinctions call for further attention to intergenerational learning.

Intergenerational learning occurs in three kinds of places:

-In families, -In formal settings (like school),

-In communities creating informal settings. (Gadsen & Hall, 1996). 12 In the La Piazza Project, we focus on the third places-between school and home (see hereafter)-while not neglecting the two others when relevant.

The sense of place is nowadays the subject of many studies,which is not surprising in the context of mondialization and people mobility.

There is not a single "sense of place"

13

; instead, we bring to the places we live a whole set of cultural preconceptions that shape the way we respond to the place, and reshape the place to fit those preconceptions. Various definitions are given which illustrate the diversity of understanding the sense of place. Most of them associate with the concept sense of place, notions such as place attachment, topopilia, insidedness, and community sentiment.

-"Place attachment is the symbolic relationship formed by people giving culturally shared emotional/affective meanings to a particular space of piece of land that provides the basis for the individual's and group's understanding of and relation to the environment.... Thus, place attachment is more than an emotional and cognitive experience, and includes cultural beliefs and practices that link people to place as explained by anthropologist Setha Low, "Symbolic Ties that Bind: Place Attachments in the Plaza") 14 .

-"Sense of Place is the particular experience of a person in a particular setting (feeling stimulated, excited, joyous, expansive, and so forth)"

Why intergenerational learning is highly relevant?

Much of the rationale in education literature is based on a societal need and historical evolution of generations' separation: The case is made that generations are much farther apart today in spatial, emotional and cultural terms than before.

Groups begin to be institutionally segregated (e.g. pediatric definition, social security added the notion that demand of generations was different).

Theories of aging stress the need for elderly people to be more connected with society. Alias, being engaged in meaningful activities, together with others, is a condition for their wellbeing. On the other hand, the increased development of a "youth culture" with a life of its one is seen as evidence of the widening gap between young and old (Loewen, 1996). In short, retirement villages entrench the elderly on one end of the generational spectrum, while MTV and the advertisement industry generate a "youth culture" and entrench the younger generations at the opposite end of this spectrum.

What makes Intergenerational learning programmes (IGP) successful?

Loewen (1996) gathers the most effective elements from approximately twenty programmes of IGP into five categories serving as criteria for intergenerational programmes:

-Curriculum based: by basing IG within the school curriculum two things happen -the activity is given value, and devoted significant time to; -the activity is constructed by the teacher from an "optimal learning perspective".

-Relationship based: a structure is required. Also programmes need time for personal connections to be developed between students and adults -Reciprocal relations: to achieve optimal learning, both adults and adolescents can offer expertise, and the learning process should be as dynamic as possible. In the best programmes the lines between those served and those serving are blurred to the point of irrelevance.

-Community based: involving students in a community of practice, based on real community issues.

-Authentic work: final product relevant and worthy of great mental and physical energy, not only focused on the pleasure of meeting. actors 20 in Liège, we have identified five categories of issues essential to understand IG practices. These actors were referring mainly to two important intergenerational programmes that recently took place in Belgium. At first we will describe these activities and then we will discuss key issues 21 . in the light of early interviews with our IG actors in the site of Liège.

Intergenerational programmes in Liège

« Digestions: memory and transmission » an Exhibition in MAMAC (September -October 2005). The goal was to create a link between youngsters and elders across several events focused on joint exploration of the archives of the « Cirque Divers ». Dimensions of the project include.

-The creation of a convivial space for exploring the archives and a meeting point between youth and elders: "apero-archives" -At the same time, establishing collaborations with three schools that have included work on these archives within the class curriculum.

-Turning the exploration of the archives into an authentic "labor of love", or a work of inspiration, geared toward the creation of art works, to be exhibited at the museum.

-Invitation of young artists « heirs » chosen by the older artists who had participated to the "Cirque Divers" activities.

-Conferences specifically dedicated to the intergenerational issue: feminism today, social movements post-68…

20 Michel Antaki, organiser of the exhibition « Digestions: Memory and Transmission », founder director of the "Cirque Divers", an important Belgian cultural place in 70-80 years. He's currently the director of the non-profit association "D'une certaine gaité" organisation of permanent education in cultural domain.

Werner Moron, artist, specialized in intergenerational cultural activities, in cultural workshop for youth, especially in the framework of the "youth houses federation" 21 In the next section we will refine our classification system taking into consideration other sources and resources (readings, design process, other sites observation) to identify dimensions for IG learning.

Intergenerational artistic workshops. Starting from the will to connect generations around art and the artistic creation, and to address the issue of the public in the arts, the interviewee leaded several activities :

-Implication of youths from a Youth House for the exhibition « biennium of photography » in order to let them show to adults who they are and the type of places where they do evolve together.

-Artistic animations at schools and other organizations.

-Animation of intergenerational activities for the promotion of a cultural centre in Belgium. The objective of the workshops is to attract neighbours to contemporary art exhibitions in a Cultural Centre thanks to a work that engages younger and older audiences. Target groups are youth (10 years old) and elders (70+). This one-year lasting work consists in learning to act using symbolic expression such as theatre or paintings and engaging in the live of the Cultural Centre and the community (city) by expressing themselves.

What these projects have in common is that they are not confined into one place (school or museum, or neighbourhood), that they evolve over time, and that they don't feel "fake"-This element of authenticity or genuine and mindful engagement in an endeavour that is meaningful and inspiration is a key to the success of any intergenerational program. Below, a first look at some of the key issues emerging from the interviews, and related questions that need further exploration.

Time, Rhythm and Space

As outlined by one interviewee (artist, practitioner in intergenerational work), a key to success is to take the time to reflect on the issue of time(s

Time, Rhythm -"Take your time"

Several issues appear relevant:

-Time of meeting (may be experienced differently by younger/elderly) -Levels of tolerance for "filled" time versus empty time (may vary)

-Rhythms and routines, or the pace of things (may vary)

-Times of preparation and of result (meddling about vs. show and tell)

-"Structure": prepared, organized

Person in the world-find your voice

As a member of a socio-cultural community, a person's identity has also much to do with becoming an active and respected member of a group -whose opinion matters to the individual. Role of elderly in society -place of younger in society

Quotes from interviews

-NETWORKS

To initiate intergenerational activities, it is necessary to use preexisting networks. To attract youth, they have to be guided by an existing structure. « In every transmission, the path has to be indicated » The encounters can create new networks, facilitating intergenerational meetings.

Definition of self / identity

"Me seen through others", we are the way the others perceive us. These mirroring effects contribute to define the role of people in definition of self/identity. Intergenerational work, and transmission, is a mean for elders to have a role in society, to define themselves a new identity. This is also done through a mirror: how elders understand they are viewed by younger, what they can read in younger eyes and inversely.

Groups and belonging (appartenances) reciprocities

This relate to expectations and ideas that each generation has regarding the other Transmission in the arts offers new ways to work together, to learn ropes that are not taught in school. Youth are an amazing resource when it comes to pragmatic (technological) problems « They have a natural ease to make things » and a different rapport to technologies (graphics, communication). « In fact they feed me […] They have access to new networks, they apprehend the current world differently, all of which enriches me".

Mediations

Mediating tools are several, for instance oral versus written transmission. The practitioners we met talk about cultural bath.

-"Cultural bath": different approaches to expressing one's thoughts and feelings, using available cultural tools. different modes of communicating (colours, smells, etc), and styles of learning and speaking -"literacy" : different levels of fluency in the usages of cultural media.

Different genres of writing (computer-literacy versus "alphabetisation")

"CULTURAL BATH"

In the artistic activities, the idea is to create "cultural baths". The introduction of the notion of audience is another kind of requirement that allows deep reflections.

Imaginary journeys

-"TRAJET RÉEL -TRAJET RÊVÉ": REAL JOURNEY -DREAMED JOURNEY

The idea is to do a work with the young people on "trajet réel -trajet rêvé" « once that one made the observation of a trivial reality (trajet réel), one can convene his imaginary (trajet rêvé) » « They have to know from where they start to express themselves, and be conscious of that ». Often the youth "borrow their identity" «They regurgitate, in the framework of the expression, MTV pre-formatted discourses ». It is a responsibility to understand who the young is really. want, what we want to be and where we want to go.

-ANCHORING -GROUNDING: CENTERING, SELF-ORIENTING « Before working the expression, it was a question of seeing who they were, in what they were anchored. See why they did not express their own day-to-day, but were constantly out of them, in the reference »

Process concept design

The co-design session leaded by University of Siena consisted in a brainstorming session based on participants' experience and was articulated around ideageneration techniques: attribute listing, to create vignettes, collection of elements, to start concept production; and exquisite corpse, for the production of concepts. The cards below are the outcome of this co-design activity aimed at the production of personal stories. The emerging cards offer a visual and textual encapsulation of 8 concepts to be used as inspirational materials by researchers Concept-cards -clothes fight [1]; what do you eat now? [2]; traces and trails [3]; on the road again [4]; flag our nation [5]; shadow games [6]; summer challenges [7]; and virtual summit [8].

1. Clothes fight describes a role-playing game where people can "put themselves in other people's shoes". They dress up to stretch their identities;

2. What do you eat now builds on the power of food to draw people! Gastronomic habits activate a narrative flow when a food is encountered in a public space like a market;

3. Traces and trails lets players drop memories in a public space and share them with passers-by, marking a territory with their traces;

4. On the road again describes a labyrinth where players find tokens left by previous explorers (sounds, pictures) and drop their own, to be found by others;

5. Flag our nations lets players explore the social meanings of cultural symbols, such as flags, and engage in building their own special flag or totem to represent their communities;

6. Shadow games merge physical and virtual to capture people's shadows as they cross or mingle in a shared area;

7. Summer challenges offer engaging ways for players to solve a problem of interest to all, and where the contribution of each is fundamental to reach a shared goal;

8. Virtual summit is similar to 7 in the form of a treasure hunt. Players are set to reach a goal (mountain top). They join forces to succeed in their adventure.

These concepts have been inspiring material for the definition of key dimensions of IG learning.

Further theoretical explorations

Concepts cards drive us to further explore the literature and to dimensions that appear relevant. v Places can help to build identity, as freedom spaces, as self-being spaces, allowing introspection and also as spaces having marked the course of live (places associated with milestones moments). These places grow in signification throughout the social relation that take place in it. Therefore identity creation is a process that relates self and places.

Time/place

v Places can operates as bridges to the past through remembrances of recurring past events andparticularly important events. Throughout the places people can make connexions between a collection of past and present feelings and experiences.

v Places can be spaces of security or community membership.

People develop various meanings (negative, positive or ambivalent) in relation to several places (from a room to a country). The combination reflects our way to be in the world. Relations to places are dynamic and represent evolving identities and personal development. People choose places that are congruent to their way of living.

Place relation is bi-directional : it is throughout their usage that they acquire meaning.

A space gains meaning when it triggers recordings of its use at several times.

Moments acquire evocating potentialities when we can mentally link them to places. When urban places keep traces of past uses they gain in evocating power due to the fact that it contains, it embraces all these different times. When a place is able to signal how it was used over time, then it becomes more interesting.

And similarly when a place offers immediate capacity to appreciate past activities it increases in density. Therefore from an experience point of view, time and space cannot be distinguished and from a design point of view it is important that these dimensions enters into resonance in order to enrich the experience.

Identities and pile worlds

Younger and elder have different world views, different experiences, and perspectives and sharing views is not always straightforward.

They have also different access, and different keys to access this world -Who is allowed or able to go where?

As Boltansky and Thevenot27 show, we are all actors in society living in a world which comprises various levels, a king of "world piles", each world having its own values that circulate simultaneously. Indeed in a given context for all type of action, the agreement or disagreement between actors will depend if the actors succeed in finding a compromise which corresponds with the values underlined ideas of justice and honesty. Six worlds are identified such as the inspiration world, the domestic world, the opinion world, the business world and the industrial world. For instance lets take the inspiration worldwhich is characterised by the will to discover, to imagine, to dream.

Mediations

The socio-constructivism gives interesting insight here through Social mediations.

Vygotsky28 describes what he calls the law of semiotic mediation, that is we learn through the experiences of others. For example we may learn something and create visual images about Sahara without having been there but only by listening others telling their experience and memories. Social memories and social practice take here all its substance because it allows the construction of imagination.

But there are also other mediating tools which are maybe more unknown. Using territories as a media to communicate experience, interests, emotions, etc.

See also Vygotsky. A construction of fantasy may constitute something effectively new and which doesn't correspond to any object / concept yet really existing. But once this product of imagination is crystallised into an image, once it is externalised, it becomes a thing among other things, it starts to exist in the world and to act on other things.

Imagination and creativity

Imaginary "journeys" : displacement & reality shifts -imagination / simulacrum simulations recall the definition Vygotsky gives to imagination. Imagination is no antithetic to reality but a mere exploration of it and imagination exploits traces of events in new forms. The creative activity of imagination depends on the richness and variety of previous experience made by an individual because fantasy constructions are composed of the material supplied by experience.

IV KEY DIMENSIONS AND THEMES

Recurring themes from literature review, interviews and concept cards have been grouped into five dimensions to be taken into account when designing or facilitating events and spaces for intergenerational learning.

Space-time

Take your time and find your place. In their everyday lives, people don't usually separate time and space the way scientists do. The word "chronotope" (Greek for time/space) captures the notion that, in human experience, place is tied to events, i.e., evocative of what happened in it over time. Conversely, timely events are associated with, and evocative of, place. Intergenerational learning calls for dedicated space/times that enable shifts between private and public, comfort and challenge, "connivence" and inclusiveness (like-minded and extraneous). Time and place are experienced differently at different ages, and so are levels of tolerance for "filled" versus, "empty" time/space (noisy/silent, crowded/void, fast/slow).

Traces and trails / routines and rituals

Keep track and come back. In Casey's words, "Who we are is where we are and when we are" [4]. Finding one's way around (navigating) and keeping a bearing (having a direction or destination) are needed for people to exist, physically and mentally, in time and space. Traces and trails are self-orienting device to help people in transit-or minds in motion-be grounded and able of return. So are routines and rituals. They also convey an identity to place itself (genius loci), and stimulate a sense of belonging by the people who contributed to the construction of its identity.

ME ++ (self-expansion, personal growth)

  and 2 b ;Growing in connection (source google images) Looking into the spatial and relational qualities of existing-and imagined-piazzas provides a useful lens to rethink learning in informal settings, in this case trans-generational learning. Three questions drive this part of the inquiry: 1. How to create a climate conducive to meaningful encounters between young and old. 2. Why encourage such encounters? What features of the environment, ambient qualities, and cultural activities are likely to foster collateral learning?

  2 Event spaces of the future (source google images)

  dimensions in different contexts, to build a vocabulary for visioning digitally enhanced ambient spaces and to project them into "what if" scenarios, what if these dimensions would be supported by information technologies. This back and forth movement between context and concepts occurs iteratively.

  Rydmark and McCrea (2002) 10 explore the uses of technology in intergenerational learning from two perspectives: A Swedish program in which seniors interact with school-age children using computers; and a USA program that uses distance education to teach professionals how to develop intergenerational programs. The project "Seniors in Schools" aims at creating new meeting-points for schoolchildren and senior citizens. The goal is to get the old life-experienced generation to interact with the younger IT-generation. The seniors engaged in the project visited local schools and participated in school activities. The exchange of knowledge between project participants was thought to be a vital force for understanding of computers, life-long learning and history. Langford (2002) 11 explores the dynamics of intergenerational projects using different art forms (Photography -Creative writing -Drama Design), and stresses the role of artists who work with young and older people. Her study is based on practical experience of intergenerational arts projects in the East End and other parts of London. This includes work with frail nursing home residents, elders with dementia and Bengali elders.

-

  who can teach what to whom? What are the social identifier, what are their world views ? Opportunities for knowing from each other -creation of a dialogue Reciprocity of learning: mutual learning previously structured or incidental Michel Antaki talks of "transmission" as a unilateral dialogue. The youth is there to learn, and the elder to teach. The roles get loosened, and sometimes revered, through joint artistic creations. For him, youth are mainly a resource for the teaching of techniques. « By teaching me the technique, (the youngster) sees how I learn it, and at that moment there is an exchange. That makes me ask questions about the technique, about his life, and I reflect about myself (…) I talk about transmission because that's how intergenerational exchanges mostly work: a one-way dialogue".

  ways in which people feel and think about space, how they form attachments to home, neighbourhood, and nation, and how feelings about space and place are affected by the sense of time. He suggests that place is security and space is freedom: we are attached to the one and long for the other.As shown byManzo (2005) 26 , attitudes and meaning linked to places depend on the experiences lived in these places. Places are not significant by themselves but through experiences-in-places. Several factors make places meaningful:

  Belong and be loved -Mingle and share. As a member of a socio-cultural community, a person's identity has much to do with becoming an active and respected member of a group. It also has to do with being able to negotiate differences. Intergenerational encounters are a means for old-timers and newcomers to reshape their roles in society, define a new identity for themselves, and regain a voice as a group.Dream it up and make it happen! The future belongs to those who invent it! Making dreams come true is a key to both personal and societal growth. Envisioning possibilities, or gauging what is in terms of what could be, opens new horizons and sheds different light into one's reality. Imagination naturally occurs in make-believe activities, such as storytelling, or play. Creativity reigns in the mind of the artist.

Older people and youth engaging together in informal learning activities (e.g. leisure, recreation, art festivals, exhibitions, sports).

	1 "Intergenerational activities are defined as bringing together the old and Practices and writings on intergenerational -Note that in la Piazza project, we focus on the fourth type. young generations in order to close the gap between them."
	learning programs They require to study IG practices referring to human life span developmental
	Another definition has been proposed by Oduaran 3 : psychology (Eriksson), and focusing on several issues such as :
	We found interesting to start defining intergenerational learning by looking at "Intergenerational programmes form a system, an approach and practice
	Intergenerational programmes and their definitions. Based on these various in which all generations, irrespective of age, race, location and socio-
	inputs, we will later on build up a definition that will best suit our orientation economic status bind themselves together in the process of generating,
	within La Piazza JEIRP. There are several definitions of Intergenerational promoting and utilizing ideas, knowledge, skills, attitudes and values in
	programmes. Some come from the International Consortium on Intergenerational an interactive way for the improvement of self and community".
	Program (ICIP, UNESCO):
	"Intergenerational programmes are vehicles for the purposeful and Within this definition, the benefits and contributions of IG practice are studied at
	ongoing exchange of resources and learning among older and younger three levels: -individual human development; -community development; and -
	Context generations for individual and social benefits" (Hatton-Yeo & Ohsako, development of the society.
	2000 2 ).
	What these definitions have in common is their focus on IG and on the
	Theoretical assumption that human development and learning is a life long process.
		approach
	According also to Loewen 4 :
	"Intergenerational learning program should bring young and old
	Concept design together in similar numbers so that each may get to know the other, see
	the other in action and learn form one another".
	Within this definition there are four types of IGP: Finally according to Granville & Ellis (1999), 5 Newman (1997)	6
	-Older people serving children and youth (e.g. tutors, mentors, resource
	persons, coaches, friends, grandparent raising a grandchild)
	-Children and youth serving older people (e.g. friendly visitors, 3 Oduaran, A., Intergenerational approaches to sustainable community development in Botswana
	and Nigeria, a paper presented to UNESCO symposium 'Intergenerational strategies for sustainable companions and tutors, etc) community development in developing countries', at the First ICIP conference Connecting
	-Older people and youth collaborating in service to their community (e.g. Generations -A Global Perspective, Keele, 2002
	environmental and community development projects) 4 Loewen, J. (1996). Intergenerational learning : what if schools were places where
	adults and children learned together. Report. EDRS.
	5 Granville, G. & Ellis S. (1999). Developing Theory into Practice : researching intergenerational
	exchange. Education and Ageing, vol 14 N° 3, 231-248.
	10

1. Current practices and writings on intergenerational learning programmes 2. Reflections from field studies and concept cards :what we learned from our sites, how concepts cards allowed us to further explore literature.

3. Further theoretical explorations that drive us to define dimensions and themes.

According to these authors various characteristics are essential to the success of IGP (InterGenerational Program): -to demonstrate mutual benefits for participants; -to establish new social roles and/or new perspectives for young and old participants; -to involve multiple generations and include at least two nonadjacent and non familial generations; -to promote increased awareness and understanding between the younger and the older generations and the growth of self esteem for both generations; -to address social issues and policies relevant to those generations involved; -to develop intergenerational relationships.

  work has been done in charting out how various intergenerational endeavours contribute to the cognitive development and social and emotional growth of young and older adult participants of such initiatives. Intergenerational learning through play has been studied byDavis, Larkin and Graves (2002)

8

. The assumption here is that play is universal, and thus a good way for all to learn about themselves and the world. Shared play experiences are important in building mutually beneficial relationships among younger and older generations, and they contribute to cognitive growth, improved social skills, physical development and emotional wellbeing. The study shows how older adults can be involved in children's play; appropriate toys and materials, and play games in ways that bring generations together successfully. On the other hand a broader theoretical framework for understanding the significance of planned intergenerational exchange starts to emerge at the community level. Intergenerational program specialists in several countries are now considering outcome variables, which include impact upon community institutions and settings. Kaplan (2002) 9 for instance explored the intersection between domains of intergenerational programming and community development, and investigated program strategies for bringing young people and senior adults together to collaboratively study neighbourhood development issues and explore and pursue civic involvement possibilities. Efforts to facilitate meaningful intergenerational exchange within community participation endeavours are highlighted, as well as broadening the base of professional participation in the intergenerational studies field to community planners, architects, geographers, and anthropologists as well as gerontologists, child development specialists, and educators. Steinig, S. & Peterson, J. (2002). Intergenerational shared sites and services for children, youth and families. First ICIP International Intergenerational Conference, Connecting Generations, a global perspective. April 2-4 Keele University, UK. 8 Davis, L., Larkin, E. & Graves, S.B. (2002). Intergenerational Learning through Play. International Journal of Early Childhood, 34(2). p 42-49 9 Kaplan, M. (2002). Impact of intergenerational programmes on community initiatives and settings. First ICIP International Intergenerational Conference, Connecting Generations, a global perspective. April 2-4 Keele University, UK.

  Sense of Place. Boston, MA: CBI Publishing Co., Inc.-"Topophilia is the affective bond between people and place or setting." Such ties vary in intensity, subtlety, and mode of expression. Responses to the environment may be aesthetic, tactile, or emotional." Yi-Fu sense of place is something that we ourselves create in the course of time. It is the result of habit or custom.... A sense of place is reinforced

		Tuan 16 ,
	-	"A by what might be called a sense of recurring events." Landscape
		Architecture/History: John Brinckerhoff Jackson, A Sense of Place, a
		Sense of Time	17
	-"By sense of place , we mean people's subjective perceptions of their
		environments ant their more or less conscious feelings about those
		environments. Sense of place is inevitably dual in nature, involving
		both an interpretive perspective on the environment and an emotional
		reaction to the environment.... Sense of place involves a personal

according to the Environmental Psychologist, Fritz Steele 15 , -"Spirit of Place : the combination of characteristics that gives some locations a special feel' or personality (such as a spirit of mystery or of identity with a person or group)." -"Setting: a person's immediate surroundings, including both physical and social elements." 12 Gadsen, V. L. & Hall, M. (1996) Intergenerational Learning : a review of literature. Philadelphia, PA : National Center on Fathers and Families. 13 Cross (2001 12th Headwaters Conference, Western State College, November 2-4, 2001. 14 Low, S. 1992. Symbolic Ties that Bind: Place attachment in the plaza. In: Altman, I. and Low, S., (eds). Place Attachment. New York, NY: Plenium Press. 314 p. 15 Steele, F. 1981. orientation toward place, in which one's understanding of place and one's feelings about place become fused in the context of environmental meaning." Sociology: David Hummon, "Community Attachment: Local Sentiment and Sense of Place" 18 ..

2 Reflections from field studies and concept cards

  Based on case studies in four sites (Cosmo Caixa / MAMAC / Space Signpost,

	Bristol Harbourside Cultural Quarter, Computer Club House, Viborg 19 ) a first
	series of themes emerged, mostly from interviews, which helped researchers
	narrow down some of the characteristics that make for great good third places,
	including safe havens; dream spaces; room for symbolic exchanges and play;
	room for personal expression, mutual respect and empathy. All these dimensions
	are drivers in informal learning and community building. They play a key-role in
	inter-generational learning.

Making use of interaction design, or co-creation methods (as leaded by University of Siena), researchers and site participants joined forces to imagine new forms of integrated third-places (the piazzas, cafes, market-places of tomorrow). Based on first-hand experience, and drawing from diverse expertise, the team drafted a handful of innovative concepts cards. Participants were encouraged to merge digital, physical, and virtual to generate engaging and "futuristic" event-spaces.

Comparing and contrasting the outcomes of the two approaches (fragments of interviews and concept cards) has been instrumental in refining and articulating emerging dimensions.

Several issues that appear relevant for understanding technology enhanced public spaces for intergenerational learning. Based on interviews with art and IG 19 -see

Chabert, A. & Barajas, M. (2006)

. Technology-enhanced public spaces for intergenerational learning : Case studies, Kaleidosocpe D 38-3-1. 75 pages. .Barajas, M., Magli, R., Owen, M., Safin S., Toccafondi, G. and Molari, G., "La Piazza" -Convivial Spaces for Inter-generational Learning: Which role can learning technologies play?. In "Current developments in computer-assisted education (

2006

)" (Eds. A. Mendez-Vilas, A. Solano Martin, J. Mesa-Gonzalez, J.A. Mesa Gonzalez). Publisher: FORMATEX, Badajoz, Spain.

  "If one wants to do an intergenerational work, one needs to reflect on the issue of time. There are individual times that are different between generations. One needs to design collective time, to create rhythms.

	" Aperitif-archives. Convivial space for encounters, discoveries,
	questionings. It's an informal setting, broad-minded in a dedicated
	space (agora) focusing on conviviality and freedom of exploration."
	2.1.2	Person and Identity
	2.1.2.1	Being in the world -keep in touch
	Construction of Identity involves the whole person. Being in touch with what
	one feels, perceives, understands, likes, is a key to a person's identity formation.
	Here the issues concern:
	-Dedicated space (agora)
	-Public and private areas: Niches and nooks?
	-The art of distancing: How close? how far?
	-Thresholds and boarders: Fixed? Adjustable? Tight? Permeable?
	DESIGN OF A SPACE
	20

One needs intra and intergenerational moments. If people are put together too quickly, one can loose something in the richness of the encounter. Intergenerational activities are not simple in terms of speed of result. It is inversely proportional to the demands of the current era. «These projects must have a disproportionate ambition in time, history, and at the same time a very great humility in terms of result. It is necessary to find money to give oneself time, to find funding without having to justify this time » 2.1.1.2 Space, Place -"Find your place"

  The work consists in identifying what remains when all the preformatted influences have been taken away. The remaining part is our self, our identity. It is a strong base to situate ourselves in our places, in our live, in relation to our friends, our families, our fears… Starting from that point it is possible to really dream i.e. defining what we

  Tell your tale and find your voice. Identity formation is about staying in touch with what one feels, perceives, understands and likes. It also involves an ability to speak one's mind, and be heard. To Bruner, stories happen to those who know how to tell them[5]. Early on, children learn to tell their tales to those willing listen, and they soon become silent if their gift is not heard. People, young and old, speak in a hundred languages to express themselves (words, gestures,

	humour, music) [6]

[START_REF] Oldenburg | The great good place: Cafes, Coffee Shops, Bookstores, Bars, Hair Salons, and Other Hangouts at the Heart of a Community (Paperback)[END_REF] The great good place: Cafes, Coffee Shops, Bookstores, Bars, Hair Salons, and Other Hangouts at the Heart of a Community (Paperback)

Hatton-Yeo, A., & Ohsako, T. (2000), Intergenerational Programmes: public policy and research implications: an international perspective, UNESCO Institute for Education, Hamburg & Beth Johnson Foundation, Stoke-on-Trent.

Newman, S. (1997). Intergenerational Programs: Past, Present, and Future. Wahington :Taylor & Francis

Arfin, P. (2002). An observational research project, research methodology and issues. First ICIP International Intergenerational Conference, Connecting Generations, a global perspective. April 2-4 Keele University, UK.

Rydmark, P. & McCrea, J. (2002). Intergenerational learning using technology. First ICIP International Intergenerational Conference, Connecting Generations, a global perspective. April 2-4 Keele University, UK.

Langford, S. (2002). Intergenerational arts projects. First ICIP International Intergenerational Conference, Connecting Generations, a global perspective. April 2-4 Keele University, UK.

[START_REF] Yi-Fu | Space and place, the perspective of experience[END_REF]. Space and place, the perspective of experience. University of Minesota Press.

Jackson, J.B. (1994). A Sense of Place, a Sense of Time.. Yale University Press

Hummon, D. (1992). Community Attachment: Local Sentiment and Sense of Place. Plenum Press

Note: reflection below come from experiments with young people in an art school.

[START_REF] Yi-Fu | Space and place, the perspective of experience[END_REF]. Space and place, the perspective of experience. University of Minesota Press.

Manzo, L.C. (2005). For better or worse: Exploring multiple dimensions of place meaning. Journal of Environmental Psychology. 25(1). pp. 67-86

Boltansky and Thevenot (1991). De la justification: les économies de la grandeur. Paris, Gallimard.

Vygotsky, L. (1986). Thought and language. Cambridge, MA : MIT Press

Eco,, U. (1990). Travels in hyper reality. San Diego : Harcourt Brace Jovanovich..

But this is has to do with journeys toward others and coming back to self. Travel in hyper reality (Eco 29 ). Displacement and dreams to see others, see what is there and also what could be there. Social practices and social memories play also a role here given that through intergenerational interactions and dialogues one may live in imagination past and present events.

6

From experiential qualities to design guidelines (table 2)


est destinée au dépôt

Etude multi-échelle de la permittivité diélectrique de couches minces diélectriques : application aux nanocomposites silice / nanoparticules d'argent élaborés par plasma

Christina Villeneuve-Faure, Kremena Makasheva, Charles Rigoudy, Laurent Boudou, G. Teyssedre

To cite this version:

Christina Villeneuve-Faure, Kremena Makasheva, Charles Rigoudy, Laurent Boudou, G.

  Dans cette étude, nous caractériserons la permittivité diélectrique d'une couche mince nanocomposite, élaborée par procédé plasma et composée d'une matrice en silice et d'un plan de AgNPs situé à différentes distances de la surface (Figure 1.a) [2, 5]. L'objectif est d'étudier et de comprendre l'influence de la position du plan d'AgNPs sur la permittivité diélectrique de l'ensemble. Pour cela, la permittivité diélectrique sera mesurée à l'échelle macroscopique par spectroscopie diélectrique et à l'échelle nanométrique par EFM [4-5]. La cartographie de permittivité obtenue par EFM montre une augmentation de la permittivité, par rapport à celle de la silice, entre les AgNPs alors qu'une diminution est observée au-dessus de ces dernières (Figures 1.b et 1.c). Ce phénomène est d'autant plus marqué que le plan d'AgNPs est proche de la surface (Figure 1.d). Cette évolution est dû à un phénomène d'écrantage induit par les AgNPs qui a été démontré par une modélisation électrostatique du champ électrique par éléments finis. Ce phénomène induit une augmentation de la permittivité, par rapport à la silice, pour un plan de AgNPs situé à moins de 20nm de la surface.

Figure 1 :

 1 Figure 1 : (a) Image TEM en vue sur la tranche de la structure présentant un plan de AgNPs enfouis dans une matrice de SiO2. Image EFM (b) de topographie et (c) de permittivité diélectrique pour un plan de AgNPs situé à 7 nm de la surface. (d) Evolution de la permittivité en fonction de la position du plan de AgNPs. Les lignes en pointillés montrent les résultats obtenus par spectroscopie diélectrique pour une couche de silice thermique et une couche de silice élaborée par plasma.

échelle de la permittivité diélectrique de couches minces diélectriques : application aux nanocomposites silice / nanoparticules d'argent élaborés par plasma Christina VILLENEUVE-FAURE, Kremena

  Les couches minces diélectriques nanocomposites apparaissent prometteuses pour améliorer les performances et la fiabilité des micro-et nano-systèmes. En effet, la nature des nanoparticules (métalliques, semiconductrices ou diélectriques), leur concentration ainsi que les paramètres d'élaboration permettent d'obtenir des propriétés diélectriques accordables. En particulier les nanoparticules d'argent (AgNPs) sont d'un grand intérêt pour leur multifonctionnalité allant des applications biocides aux mémoires et au stockage de l'énergie[1][2]. Pour optimiser les performances, il est nécessaire de caractériser les propriétés électriques, et leur évolution sous contrainte électrique, aussi bien à l'échelle macrométrique que nanométrique. Concernant l'échelle nanométrique les techniques dérivées de la microscopie à force atomique (AFM) sont particulièrement adaptées. Elles permettent par exemple de caractériser les courants de fuite dans les oxydes de grilles (Conductive AFM, C-AFM), l'état de charge aux interfaces oxyde/semiconducteur dans les composants MOS (Kelvin Probe Force Microscopy, KPFM) ou bien la permittivité diélectrique dans les micro/nanocomposites (Electrostatic Force Microscopy, EFM)[2][START_REF] Celano | Electrical Atomic Force Microscopy for Naoelectronics[END_REF][START_REF] Riedel | [END_REF].

	MAKASHEVA, Charles RIGOUDY, Laurent
	BOUDOU and Gilbert TEYSSEDRE
	LAPLACE (Laboratoire Plasma et Conversion d'Energie) ; Université de Toulouse; CNRS, UPS, INPT, Toulouse

Teyssedre. Etude multi-échelle de la permittivité diélectrique de couches minces diélectriques : application aux nanocomposites silice / nanoparticules d'argent élaborés par plasma. 24e Forum des Microscopies à Sonde Locale, Apr 2023, Obernay, France. pp.195. hal-04310859

Etude multi-

Remerciements

Ce travail a été soutenu par la Région Midi-Pyrénées, contrat n° 10051265 et par le programme IDEX Actions Thématiques Stratégiques -ATS 2015 de l'Université de Toulouse, projet SEPHIR (2016-066-CIF-D-DRVD).