Christophe Coquelet

Albert Chareton

Alain Valtz

Abdelatif Baba-Ahmed

Dominique Richon
email: richon@paris.ensmp.fr

Vapor-Liquid Equilibrium Data for the Azeotropic Difluoromethane + Propane System

Keywords: R32, Propane, VLE, modelistaion, azeotrope calculation, critical point

HAL is

Introduction

In 1987, the modification of the Montreal protocol [START_REF]Montreal Protocol on substances that deplete the ozone layer, United Nations Environmental Program (UNEP), Final Act[END_REF] has prohibited the use and the production of chlorofluorocarbons (CFC's) in industrialized nations. Accurate knowledge of the thermo-physical properties of mixtures containing hydro fluorocarbons (HFC's) and hydrocarbons, which are proposed as alternative refrigerants, is of great importance to evaluate the performance of refrigeration cycles and to determine the optimum composition of new working fluids.

Vapor liquid equilibria are essential for evaluating the thermodynamics properties and then the efficiency for refrigeration systems. This point was predominantly claim during the second IUPAC Workshop (April [START_REF] Mathias | Extension of the Peng-Robinson Equation of State to Complex Mixtures: Evaluation of Various Forms of the Local Composition Concept[END_REF][START_REF] Michelsen | A modified HURON-VIDAL mixing rule for cubic equations of state[END_REF][START_REF] Renon | Local Composition in Thermodynamic Excess Function for Liquid Mixtures[END_REF]2001) on refrigerants (Ecole des Mines in Paris, France), where Dr. J. Morley (DuPont Fluoroproducts, Hemel Hempstead, UK) addressed the question "Are we near an industry standard for refrigerant properties?" He discussed the various important world-wide activities which were taking place to determine accurate thermophysical properties of candidate alternative refrigerant working fluids.

A knowledge of vapor-liquid equilibrium (VLE) data for new mixtures allows a choice of mixtures that offer the most suitable thermodynamic properties. The development of models for representation and prediction of physical properties and phase equilibria as well as the improvement of current equations of state cannot be handled seriously without accurate VLE data.

Using an apparatus based on a static-analytic method, isothermal vapor-liquid equilibrium measurements excluding saturated phase densities on the difluoromethane (R32) + propane binary mixture were performed at temperatures from (278.10 to 343.26) K. The measurements were fitted with the Soave-Redlich-Kwong (SRK) equation of state.

Experimental Section

Materials. Propane is from Messer Griesheim with a certified purity higher than 99.95 vol %. The difluoromethane (R32) was purchased from DUHON (France) with a certified purity higher than 99.99 vol %. Chemicals were used after degassing the fluids to avoid the presence of non condensable.

Apparatus and Experimental Procedures. Most of data have been determined using an apparatus (Figure 1) based on a static-analytic method with liquid and vapor phase sampling. This apparatus is similar to that described by Laugier and Richon [START_REF] Laugier | New apparatus to perform fast determinations of mixture vaporliquid equilibria up to 10 MPa and 423[END_REF].

Remaining data have been determined using a variable volume cell described by Fontalba The equilibrium cell is immersed in a thermo-regulated liquid bath; the temperature is controlled within 0.01 K. For accurate temperature measurements in the equilibrium cell and to check for thermal gradients, two platinum resistance thermometers (Pt100) are inserted inside wells drilled into the body of the equilibrium cell at two different levels (see Figure 1) and connected to an HP data acquisition unit (HP34970A).

These two Pt100's are periodically calibrated against a 25  reference platinum resistance thermometer (TINSLEY Precision Instruments). The resulting uncertainty is not higher than 0.02 K. The 25  reference platinum resistance thermometer was calibrated by the Laboratoire National d'Essais (Paris) based on the 1990 International Temperature Scale (ITS 90). Pressures are measured by means of a pressure transducer (Druck, type PTX611, range: (0 to 6) MPa) connected to the HP data acquisition unit (HP34970A) as are the two Pt100's ; the pressure transducer is maintained at constant temperature (temperature higher than the highest temperature of the study) with a homemade air-thermostat thermally controlled by a PID regulator (WEST instrument, model 6100).

The pressure uncertainty is estimated to be 0.001 MPa, after a careful calibration against a dead weight balance (Desgranges & Huot 5202S, CP 0.3 to 40 MPa, Aubervilliers, France).

The HP on-line data acquisition unit is connected to a personal computer through an RS-232 interface. This complete data acquisition system allows real time readings and storage of both temperatures and pressures during isothermal runs.

The analytical work was carried out using a gas chromatograph (VARIAN model CP-3800) equipped with a thermal conductivity detector (TCD). Peak integrations are done on a computer containing a special card from Borwin through the software developed by Borwin (BORWIN ver 1.5, from JMBS, Le fontanil, France). The analytical column is a HaySep T 100/120 Mesh (silcosteel tube, length: 1.6 m, diameter:1/8" from Restek). The TCD was repeatedly calibrated by introducing known amounts of each pure compound through a syringe in the injector of the gas chromatograph. Taking into account the uncertainties due to calibrations and the dispersions of analyses, the accuracy for vapor and liquid mole fractions is estimated to be 1.0 % over the whole range of concentrations.

The experimental procedure is the following: At room temperature, the equilibrium cell and loading circuit was evacuated down to 0.1 Pa. One of the thermal compressors (TC 1 ) was loaded with R32 while the other (TC 2 ) was loaded with propane.

At the required equilibrium temperature assumed to be reached when the two Pt100 thermometers give the same temperature value within their temperature uncertainty for at least 10 minutes, a volume of about 5 cm 3 of propane was introduced into the equilibrium cell. The vapor pressure of propane (the higher boiling temperature component) was then recorded at this temperature. To describe the two-phase envelope with at least 10 PTxy data points, adequate amounts of the light component (R32) were introduced step by step, leading to successive new equilibrium mixtures. Equilibrium was assumed when the total pressure remains unchanged within 1.0 kPa during a period of 10 min under efficient stirring.

For each equilibrium condition, at least six samples of both vapor and liquid phases were withdrawn using the pneumatic samplers ROLSI TM as described by Guilbot et al. [START_REF] Guilbot | Rapid On Line Sampler-Injector, a reliable tool for HT-HP Sampling and on line GC analysis[END_REF] and analyzed in order to check for measurement repeatability (1%).

Correlations

Isothermal VLE measurements on the R32-C 3 H 8 system were performed in the temperature range from (278.1 to 343.26) K and at pressures up to 5.4 MPa. The critical temperature (T C ), critical pressure (P C ), and acentric factor (), for each pure components are given in Table 1 and are from REFPROP (6). Our experimental VLE data are correlated by means of home-made software, THERMOPACK (7). The original Soave Redlich-Kwong (8) equation of state (SRK EoS) gives good results for VLE of either non-polar or slightly polar mixtures. It is worthy to note that R32 is a polar compound and the use of the Soave alpha function would result in systematic deviations between experimental and calculated vapor pressures. We have used the SRK EoS but with the Mathias-Copeman (9) alpha function with three adjustable parameters, which was especially developed for polar compounds, given by  

2 3 3 2 2 1 1 1 1 1                                        C C C T T c T T c T T c T  (1)
wherec 1 , c 2 and c 3 are adjustable parameters. Mathias-Copeman coefficients are evaluated in our whole temperature range using a modified Simplex algorithm. The objective function is,

2 exp exp 100            P P P N F cal (2)
where N is the number of data points, P exp is the measured pressure, and P cal is the calculated pressure.

In our equation of state approach, we need a mixing rule and an activity coefficient model. For these purposes we have selected the MHV1 (modified Huron-Vidal) mixing rule proposed by Michelsen [START_REF] Michelsen | A modified HURON-VIDAL mixing rule for cubic equations of state[END_REF] where the attractive parameter is calculated from Eq. ( 3) and the molar co-volume from Eq. ( 4):

                     i i i E i i i i i q x P T G b b Ln x q RT b a x b a 1 1 , ,  (3)
  i i i b x b (4)
The reference pressure is P= 0. Michelsen recommends q 1 = -0.593.

The excess Gibbs energy is calculated using the NRTL (11) local composition model.

  i j i j k i k i k k i j i j j i E P T RT Exp x RT Exp x x RT G , , , , , ,                            ( 5
)
where  i,i =0 and  i,i =0, and  j,i ,  j,i and  i,j are adjustable parameters. For our system which belongs to a given polar mixture type it is recommended (11) to use  j,i = 0.3. The  j,i and  i,j are adjusted directly to VLE data through a modified Simplex algorithm using the objective function, 2. We have also measured the vapor pressures of the two pure components. Tables 3 and4 (R32 and propane respectively) report both our experimental data and pressures calculated with our model using the determined Mathias-Copeman coefficients. We have a good agreement between experimental and calculated vapour pressures showing good consistency between experimental data, literature correlations and our data treatment through the RKS EoS + Mathias-Copeman alpha function. The alpha functions are valid between 248 K and the critical temperatures of each component.

                 

B) Vapor-liquid equilibrium:

The VLE data obtained are listed in Tables 5 to 10. At each temperature, we have adjusted the two ( j,i and  i,j ) NRTL parameters. They appear slightly temperature dependent as shown in Figures 2 and3.

Second order relationships are adequate for their representation:

 12 = 0.215T 2 -133.44T + 23579.72 (7)
 21 = -0.139T 2 + 77.35T -8387.20 [START_REF] Soave | Equilibrium constants for modified Redlich-Kwong equation of state[END_REF] The results of modeling are reported in Tables 5 to 9 and plotted in Figure 4.

The mean relative absolute percentage deviations on pressure, MRDP, and the mean relative percentage deviations on vapor phase mole fraction, MRDY, listed in Table 10, are defined by: [START_REF] Mathias | Extension of the Peng-Robinson Equation of State to Complex Mixtures: Evaluation of Various Forms of the Local Composition Concept[END_REF] where U=P or y 1 and N is the number of data points.

         exp exp / / 100 U U U N MRDU cal
We have also calculated the BIAS values which are listed in table 10 and defined by eq [START_REF] Michelsen | A modified HURON-VIDAL mixing rule for cubic equations of state[END_REF]: [START_REF] Michelsen | A modified HURON-VIDAL mixing rule for cubic equations of state[END_REF] where U=P or y 1 and N is the number of data points.

         exp exp / 100 U U U N BIASU cal
An accurate representation of the experimental data is found except at 343.26 K where adjustment and modeling is very difficult. At the mixture critical point the equation of state must calculate identical molar volumes for liquid and vapor phases. However, the SRK cubic equation of state is unable to calculate high-accuracy molar volumes close to the critical region. This may be the main reason for the modeling difficulty here.

C) PVT method:

We have used another method to get results especially in the region where a two phase-domain split was found and a poor representation was obtained. This was used to verify the data obtained from the static-analytic method. This second method selected here is the static-synthetic one with a variable volume cell. Herein, we measured only bubble pressures and compared them against the correlations. The uncertainties of the pressure is around 0.004 MPa and 0.1 K for the temperature. As displayed in Table 11, there is a good agreement (less than 1% for relative pressure deviation) between the two experimental methods. We have shown that left hand part of the diphasic envelope at

0            P i x T for i=1 to N-1 (11) 0            T i x P for i=1 to N-1 ( 12
) i i y x  for i=1 to N (13)
An azeotrope behaves like a pure fluid and then its components cannot be separated by simple distillation.

consequently, at equilibrium, EoS mixtures attractive parameters (a) at the azeotrope composition are the same in both the liquid and vapor phases. Conditions satisfying this equality allows computation azeotrope location. This method is suitable with an equation of state for isothermal or isobaric calculation.

Analytically, the advantage of this method is there are no derivatives to calculate. A simple secant method permits to obtain a l =a v at equilibrium where the compositions of the two phases are equal (

i i y x  ).
The computational algorithm is as follow: i) Input composition.

ii) Calculation of a v -a l at equilibrium. iii) Search for another composition where   0

  i l v i a a  at equilibrium.
iv) Use the secant method to obtain third composition where a v -a l =0.

We show in the Table 12 and Figures 6 and 7 the characteristics of the azeotrope (pressure, temperature and composition). Equations ( 14) and [START_REF] Wong | A Theoretically Correct Mixing Rules for Cubic Equation of State[END_REF] give the relation between T, P az and x az (R32).

P az =379.61x az 2 -451.39x az + 134.13

P az = 5.49810 -4 T 2 -0.275T + 35.26 [START_REF] Wong | A Theoretically Correct Mixing Rules for Cubic Equation of State[END_REF] Note that the azeotropic composition of R32 increases with temperature.

E) Comparison with literature Data: Bobbo et al. ( 16) obtained data for this system at lower temperatures but did not reproduce the liquid-liquid equilibrium mentioned by Holcomb et al. [START_REF] Bobbo | VLE measurements and modeling for the strongly positive azeotropic R32 + propane system[END_REF]. We have fitted our model to their data. Then, we obtained two new parameters at each of their temperatures. Equations ( 16) and ( 17) represent the temperature dependence of the parameters obtained for each of our and Bobbo's et al.

temperatures, (248.15 to 343.26 K). Temperature dependence of parameters is continuous (see Figures 8 and9) indicating consistency between the two data sets.

 12 = 0.189T 2 -111.73T + 19375 ( 16)

 21 = -0.098T 2 + 49.78T -3817 (17)
The BIASU and MRDU were also calculated and the results are reported in Table 13.

There's a good agreement between experimental data and calculated data using the parameters  12 and  21 (Eqs ( 16) and ( 17)). Figure 10 gives the predictive curves along with experimental data (the 343.26 K isotherm does not appear in this figure).

F) Supercritical state: At 343.26 K, we have pointed out the disappearance of the phase separation for x R32 between 0.5 and 0.85. The mixture becomes supercritical although the equilibrium temperature is lower than the critical temperature of the lightest component (R32). This isotherm and its two graphical critical end points are shown in Figure 4. An apparatus using the sapphire cell described by Laugier et al. [START_REF] Laugier | Simultaneous determination of vapor-liquid equilibria and volumetric properties of ternary systems with a new experimental apparatus[END_REF] was used to observe the transition. At the critical point, a fog can be observed when the pressure is decreased. We can see in Figure 11 the different steps involving the fog and liquid formation. With this technique, we can record the pressure and the temperature for one composition after several increasing and decreasing of temperature. Two bubble pressures were measured and the results are given in Table 14. The precision for the pressure is 0.004 MPa and 0.1 K for the temperature. A correlating method to represent the critical point locus was established by Van Poolen and al. [START_REF] Van Poolen | Isoplethic method to Estimate Critical lines for Binary Fluid Mixtures from Subcritical Vapor-Liquid Equilibrium: Application to the Azeotropic Mitures R32 + C 3 H 8 and R125 + C 3 H 8[END_REF]. Our critical data are congruent with the correlation, Figure 12 shows a plot indicating the VLE domain including the azeotrope line and the critical line from Van poolen et al..

Conclusion.

In this paper we present VLE data for the Propane+R32 system along several isotherm.

Two experimental methods were used to verify the behaviour of this system. A staticanalytic method and a PVT method were used to obtain the experimental data. The 2)

3)

Figure 11. The different steps to characterize a mixture critical point:

1) mixture in supercritical state;

2) The pressure decreases (beginning of fog formation);

3) The fog leads to a liquid phase. Fog Sapphire cell Piston

  et al. (3) and Valtz et al. (4).

  pressures: Two vapor pressure correlations was used to generate enough data in order to fit the Mathias Copeman coefficients: the Tillner -Roth's (12) correlation for R32, and the Mc Linden's (13) correlation for propane, from 248 K to critical temperatures of the corresponding component. The calculated values of the SRK EoS Mathias-Copeman coefficients are reported in Table

  343.26 K really extends to xR32 about 0.5 while modeling stops at about 0.4. At this temperature there is clearly a modeling problem, not an experimental one. So we have changed the EoS and the mixing rules in order to have the best densities calculation. The Peng Robinson EoS (14) associated with the Wong-Sandler (15) mixing rules may well represent the last isotherm. The Wong-Sandler mixing rules are more adaptable with the third parameter k ij , so in consequence all the densities are better calculated and the experimental data are better represented specially at high pressure. The value of each parameters are given below and the isotherm is plotted on figure 5.  12 = 1317,  21 = 3135, k 12 =0.359. D) Azeotrope line computation: An azeotrope corresponds to an extremum of temperature or pressure. At this point the compositions of both liquid and vapor phases are equal. This can be expressed by,

Figure 2 .

 2 Figure 2.   NRTL Binary parameter as a function of temperature:♦; fitted to isotherm ; __; eq (7).

Figure 3 .

 3 Figure 3.   NRTL Binary parameter as a function of temperature:♦; fitted to isotherm; __; eq[START_REF] Soave | Equilibrium constants for modified Redlich-Kwong equation of state[END_REF].

Figure

  Figure 4. VLE for the R32 (1) + propane (2) system at different temperatures: •; 278.10 K; ▲; 294.83 K; *; 303.23 K; ; 313.26 K ; ■; 343.26 K; +; graphical end points; solid lines, calculated with RKS EoS and MHV1 mixing rules ; dashes lines ---, calculated at 323 K; dashes lines _ _ _, calculated at 333 K ; ♦; Azeotrope location.

Figure 5 .Figure 6 .

 56 Figure 5. VLE for the R32 (1) + propane (2) system at 343.26 K. solid lines, calculated with PR EoS and Wong Sandler mixing rules ;

Figure 7 .

 7 Figure 7. Azeotropic pressure as function of temperature.♦ ; calculated azeotrope ; __; eq[START_REF] Wong | A Theoretically Correct Mixing Rules for Cubic Equation of State[END_REF].

Figure 8 .

 8 Figure 8.   NRTL Binary parameter as function of temperature: ▲; from Bobbo et al.; ▪; this work ; __; eq (16).

Figure 9 .

 9 Figure 9.   NRTL Binary parameter as function of temperature: ▲; from Bobbo et al.; ▪ ; this work ; __; eq (17).

Figure 10 .Figure 12 .

 1012 Figure 10. VLE for the R32 (1) + propane (2) system at all different temperatures with experimental data.

Table 1 .

 1 Critical Parameters and acentric Factors from REFPROP[START_REF] Fontalba | Simultaneous determination of vapour liquid equilibria and volumetric properties up to 45 MPa and 160°C by the static method using a variable volume cell without sampling[END_REF]

	Soave-Redlich-Kwong (SRK EoS) equation of state, with a Mathias-Copeman alpha
	function and MHV1 mixing rules was chosen to conveniently fit VLE data except for the
	critical isotherm at 343.26 K where the Peng Robinson (PR EoS) and the Wong Sandler

isotherm were used. At this temperature, there are two critical points. The azeotrope location is given as a function of temperature (see Figure

11

).

Table 2 .

 2 Ajusted Mathias-Copeman Coefficients

	Coefficients	R32	Propane
	C 1	1.034	0.789
	C 2	-1.454	-0.894
	C 3	4.038	2.716

Table 3 .

 3 Experimental and calculated vapor pressures of R32 (SRK EoS)

	T /K	P exp /MPa P cal /MPa	P
	283.19	1.111	1.108	0.003
	288.21	1.286	1.282	0.004
	293.24	1.481	1.477	0.004
	298.26	1.697	1.692	0.005
	303.27	1.935	1.931	0.004
	308.28	2.197	2.194	0.003
	313.30	2.485	2.485	0.000
	318.28	2.801	2.802	0.001
	323.30	3.147	3.153	-0.006
	328.31	3.526	3.536	-0.010
	343.26	4.892	4.905	0.013

Table 4 .

 4 Experimental and calculated vapor pressures of Propane (SRK EoS)

	T /)	P exp /MPa P cal /MPa	P
	277.17	0.536	0.535	0.001
	283.22	0.638	0.638	0.000
	288.26	0.734	0.734	0.000
	293.27	0.838	0.839	0.001
	298.30	0.955	0.955	0.000
	302.27	1.055	1.055	0.000
	308.80	1.236	1.236	0.000
	311.80	1.326	1.326	0.000
	313.24	1.370	1.371	-0.001
	318.22	1.537	1.536	0.001
	323.22	1.716	1.715	0.001
	328.26	1.911	1.911	0.000
	333.29	2.120	2.122	-0.002
	338.31	2.346	2.350	-0.004
	343.26	2.591	2.593	-0.002
	348.31	2.852	2.859	-0.007
	353.41	3.134	3.149	-0.014

Table 5 .

 5 Vapor-liquid Equilibrium Pressures and Phase Compositions for R32 (1) + Propane (2) Mixtures at 278.10 K

	Experimental data			Calculated data
	P exp /MPa	x 1	y 1exp	P cal /MPa	y 1cal	P	y
	0.553	0.000	0.000	0.550	0.000	-0.003	0.000
	0.727	0.043	0.236	0.726	0.243	-0.001	-0.007
	0.936	0.124	0.419	0.944	0.431	0.008	-0.012
	1.109	0.262	0.526	1.121	0.544	0.012	-0.018
	1.189	0.424	0.596	1.197	0.599	0.008	-0.003
	1.201	0.474	0.610	1.208	0.611	0.007	-0.001
	1.209	0.516	0.622	1.216	0.620	0.007	0.002
	1.215	0.563	0.634	1.222	0.631	0.007	0.003
	1.218	0.583	0.639	1.223	0.635	0.005	0.004
	1.220	0.608	0.646	1.225	0.641	0.005	0.005
	1.221	0.628	0.651	1.226	0.646	0.005	0.005
	1.222	0.673	0.664	1.226	0.658	0.004	0.006
	1.221	0.680	0.666	1.226	0.660	0.005	0.006
	1.214	0.756	0.693	1.217	0.687	0.003	0.006
	1.205	0.791	0.711	1.208	0.704	0.003	0.007
	1.131	0.909	0.805	1.129	0.801	-0.002	0.004
	1.023	0.975	0.921	1.016	0.923	-0.007	-0.002
	0.956	1.000	1.000	0.950	1.000	-0.006	0.000

Table 6 .

 6 Vapor-liquid Equilibrium Pressures and Phase Compositions for R32 (1) + Propane (2) Mixtures at 294.83 K

	Experimental data			Calculated data
	P exp /MPa	x 1	y 1exp	P cal /MPa	y 1cal	P	y
	0.874	0.000	0.000	0.874	0.000	0.000	0.000
	0.926	0.008	0.049	0.922	0.050	-0.004	-0.001
	1.123	0.046	0.206	1.121	0.216	-0.002	-0.010
	1.206	0.064	0.261	1.202	0.269	-0.004	-0.008
	1.406	0.123	0.370	1.413	0.385	0.007	-0.015
	1.693	0.264	0.508	1.699	0.511	0.006	-0.003
	1.840	0.439	0.584	1.851	0.586	0.011	-0.002
	1.897	0.599	0.645	1.908	0.641	0.011	0.004
	1.900	0.618	0.650	1.911	0.648	0.011	0.002
	1.906	0.694	0.684	1.913	0.678	0.007	0.006
	1.903	0.731	0.699	1.908	0.695	0.005	0.004
	1.897	0.759	0.713	1.900	0.709	0.003	0.004
	1.880	0.802	0.746	1.881	0.735	0.001	0.011
	1.715	0.941	0.877	1.710	0.875	-0.005	0.002
	1.677	0.957	0.903	1.672	0.903	-0.005	0.000
	1.547	1.000	1.000	1.542	1.000	-0.005	0.000

Table 7 .

 7 Vapor-liquid Equilibrium Pressures and Phase Compositions for R32 (1) + Propane (2) Mixtures at 303.23 K

	Experimental data			Calculated data
	P exp /MPa	x 1	y 1exp	P cal /MPa	y 1cal	P	y
	1.255	0.027	0.126	1.253	0.130	-0.002	-0.004
	1.492	0.073	0.258	1.495	0.270	0.003	-0.012
	1.824	0.165	0.404	1.833	0.413	0.009	-0.009
	2.076	0.287	0.503	2.090	0.506	0.014	-0.003
	2.262	0.456	0.590	2.272	0.583	0.010	0.007
	2.311	0.535	0.615	2.320	0.615	0.009	0.000
	2.317	0.564	0.630	2.332	0.626	0.015	0.004
	2.336	0.646	0.665	2.352	0.661	0.016	0.004
	2.340	0.694	0.689	2.353	0.684	0.013	0.005
	2.345	0.705	0.695	2.352	0.689	0.007	0.006
	2.318	0.794	0.747	2.320	0.740	0.002	0.007
	2.226	0.890	0.824	2.218	0.821	-0.008	0.003
	2.094	0.953	0.916	2.084	0.905	-0.010	0.011
	1.937	1.000	1.000	1.929	1.000	-0.008	0.000

Table 8 .

 8 Vapor-liquid Equilibrium Pressures and Phase Compositions for R32 (1) + Propane (2) Mixtures at 313.26 K

	Experimental data			Calculated data
	P exp /MPa	x 1	y 1exp	P cal /MPa	y 1cal	P	y
	1.496	0.017	0.075	1.497	0.077	0.001	-0.002
	1.608	0.034	0.133	1.613	0.138	0.005	-0.005
	2.344	0.198	0.412	2.363	0.417	0.019	-0.005
	2.540	0.272	0.475	2.555	0.472	0.015	0.003
	2.720	0.367	0.530	2.730	0.526	0.010	0.004
	2.844	0.468	0.583	2.859	0.575	0.015	0.008
	2.931	0.582	0.639	2.949	0.631	0.018	0.008
	2.940	0.605	0.649	2.960	0.642	0.020	0.007
	2.952	0.622	0.658	2.966	0.651	0.014	0.007
	2.964	0.710	0.705	2.975	0.699	0.011	0.006
	2.923	0.799	0.761	2.934	0.756	0.011	0.005
	2.880	0.844	0.797	2.887	0.792	0.007	0.005
	2.685	0.947	0.901	2.677	0.906	-0.008	-0.005
	2.491	1.000	1.000	2.483	1.000	-0.008	0.000

Table 9 .

 9 Vapor-liquid Equilibrium Pressures and Phase Compositions for R32 (1) + Propane (2) Mixtures at 343.26 K

	Experimental data			Calculated data
	P exp /MPa	x 1	y 1exp	P cal /MPa	y 1cal	P	y
	2.591	0.000	0.000	2.593	0.000	0.002	0.000
	3.139	0.065	0.146	3.165	0.148	0.026	-0.002
	3.499	0.113	0.226	3.519	0.220	0.020	0.006
	3.964	0.188	0.310	3.977	0.297	0.013	0.013
	4.222	0.237	0.345	4.225	0.333	0.003	0.012
	4.442	0.282	0.375	4.423	0.360	-0.019	0.015
	4.702	0.345	0.420	4.658	0.388	-0.044	0.032
	5.009	0.432	0.472	5.003	0.432	-0.006	0.040
	5.077	0.457	0.480	5.075	0.457	-0.002	0.023
	5.451	0.858	0.849	5.451	0.858	0.000	-0.009
	5.413	0.876	0.866	5.415	0.873	0.002	-0.007
	5.308	0.911	0.901	5.313	0.900	0.005	0.001
	5.259	0.924	0.915	5.267	0.912	0.008	0.003
	5.201	0.939	0.930	5.208	0.927	0.007	0.003
	5.049	0.972	0.965	5.058	0.964	0.009	0.001
	4.940	0.992	0.989	4.951	0.989	0.011	0.000
	4.892	1.000	1.000	4.905	1.000	0.013	0.000

Table 10 .

 10 Mean Relative Absolute Deviations in Pressure, MRDP, Vapor Phase Compositions, MRDY, and Bias using the Soave-Redlich-Kwong Equation of State with

	MHV1 Mixing Rules
	T /K BIASP /% MRDP /% BIASY /% MRDY /%
	278.10	0.25	0.50	-0.18	0.96
	294.83	0.10	0.33	-0.59	1.18
	303.23	0.22	0.43	-0.32	1.24
	313.26	0.14	0.26	0.02	1.15
	343.26	0.09	0.26	1.93	2.31

Table 11 .

 11 Bubble Point Data Measured by the PVT method and Calculated by SRK + MHV1 + NRTL Models

	T /K	P exp /MPa	x 1	P cal /MPa	y 1cal	P
	287.53	1.533	0.439	1.542	0.593	-0.009
	323.25	3.455	0.439	3.482	0.542	-0.027
	333.04	4.186	0.439	4.207	0.509	-0.021
	343.10	3.876	0.173	3.884	0.284	-0.008
	343.18	4.821	0.388	4.780	0.388	0.041
	333.49	4.090	0.388	4.109	0.477	-0.019
	342.15	4.874	0.406	4.823	0.406	0.051
	333.49	4.129	0.406	4.156	0.487	-0.027
	295.38	1.869	0.465	1.890	0.594	-0.021
	303.67	2.278	0.465	2.302	0.586	-0.024
	313.02	2.817	0.465	2.841	0.574	-0.024
	323.35	3.497	0.465	3.532	0.556	-0.035
	333.17	4.251	0.465	4.278	0.524	-0.027
	337.85	4.629	0.465	4.641	0.493	-0.012
	340.42	4.739	0.465	4.698	0.465	0.041
	332.75	4.404	0.866	4.391	0.838	0.013
	323.16	3.572	0.866	3.570	0.824	0.002

Table 12 .

 12 Composition and Pressure of the Azeotrope (R32) at Each Temperature (MHV1 Mixing Rules)

	T /K	x az exp	P exp /MPa	x az cal	P cal /MPa	P	x
	278.10	0.663	1.221	0.653	1.226	-0.005	0.010
	294.83	0.679	1.906	0.666	1.914	-0.008	0.023
	303.23	0.683	2.342	0.674	2.354	-0.012	0.009
	313.26	0.702	2.961	0.684	2.977	-0.016	0.018
	323.00			0.694	3.699
	333.00			0.705	4.580

Table 13 .

 13 Mean Relative Absolute Deviations in Pressure, MRDP, Vapor Phase Composition, MRDY, and Bias using the Soave-Redlich-Kwong Equation of State with MHV1 Mixing Rules T /K BIASP /% MRDP /% BIASY /% MRDY /%

		248.15	-0.18	0.26	0.46	0.63
	Bobbo	254.15	-0.11	0.45	-0.03	0.74
	and al	273.15	-0.05	0.41	1.20	1.21
		294.91	-0.08	0.36	0.96	1.05
		278.10	0.39	0.42	-0.09	0.74
	This work	294.83 303.23 313.26	0.37 0.27 0.12	0.38 0.33 0.16	-0.25 0.03 0.29	0.79 0.19 0.75
		343.26	0.12	0.25	2.60	2.91

Table 14 .

 14 Critical Points Measured by the PVT Equipment with a Sapphire Variable

	Volume Cell
	T /K	P /MPa	x R32
	342.50	5.210	0.527
	344.00	5.532	0.866

C: Carrier Gas; EC: Equilibrium Cell; FV: Feeding Valve; LB: Liquid Bath; PP: Platinum Probe; PrC: Propane Cylinder; PT: Pressure Transducer; RC: Refrigerant Cylinder; SM: Sampler Monitoring; SW: Sapphire window; TC 1 and TC 2 Thermal Compressors; Th: Thermocouple; TR: Temperature Regulator; VSS: Variable Speed Stirring; VP: Vacuum Pump.

  4. VLE for the R32 (1) + propane (2) system at different temperatures: •; 278.10 K; ▲; 294.83 K; *; 303.23 K; ; 313.26 K ; ■; 343.26 K; +; graphical end points; solid lines, calculated with RKS EoS and MHV1 mixing rules ; dashes lines ---, calculated at 323 K; dashes lines _ _ _, calculated at 333 K ; ♦; Azeotrope location.


MD Laurent Bonello
email: laurentbonello@yahoo.fr

PhD Marc Laine

MD Laurence Camoin-Jau

PhD Corinne Frere

PLATELET REACTIVITY: JOURNEY TO THE END OF THE NIGHT

We read with great interest the paper by Stratz et al. (1) on a new automated method to quantify reticulated platelets through several markers, including the immature platelet count (IPC), to predict platelet reactivity (PR). In this well-designed study, the authors observed, using a validated platelet assay, that IPC correlated with ontreatment PR in patients with stable coronary artery disease under clopidogrel and prasugrel. Among several parameters, absolute IPC appeared to be a strong independent predictor of PR. They conclude that IPC was a simple and inexpensive tool to easily assess the on-treatment PR.

However, the study has some limitations. First, in stable coronary artery disease patients the rate and clinical impact of HTPR (High on-Treatment Platelet Reactivity) are reduced [START_REF] Tantry | Consensus and update on the definition of ontreatment platelet reactivity to adenosine diphosphate associated with ischemia and bleeding[END_REF]. Second, the correlation between IPC and PR, although significant, was only observed in the clopidogrel and prasugrel 30-mg groups. Third, very few patients had HTPR (n = 4 of 300), which does not allow to evaluate the sensitivity and specificity of IPC. Indeed, 2 of these 4 HTPR patients had an IPC in the same range as good responders, suggesting a low specificity. Finally, results regarding IPC remains conflicting because studies in acute coronary syndrome with a moderate correlation between IPC and PR under prasugrel and no correlation under ticagrelor (3). Therefore, concluding that IPC may become useful to predict PR seems premature.

An automated, easy-to-perform, rapid, inexpensive, and standardized method to predict PR would be of interest. However, it must be acknowledged that the determination of IPC is not a routine but an optional parameter that is only available in labs using XE-Series Sysmex (Sysmex Europe GmbH, Norderstedt, Germany) hematology analyzers. Furthermore, it is not a platelet function assay and it only reflects thrombopoiesis and the rate of platelet turnover that are contributors rather than predictors of PR for drugs with short-lived active metabolites such as clopidogrel.

Because identifying the factors involved in HTPR is of major interest, studies have investigated its mechanisms, which include intrinsic PR, platelet turnover, body mass index, diabetes, genetic polymorphisms, and more importantly acute coronary syndrome. However, the factors contributing to HTPR differ between patients and may vary over time. Therefore the end-product PR under therapy, which was constantly associated with adverse outcome across several large studies, appeared more relevant than all these individual factors to determine the clinical outcome and predict both bleeding and ischemic events under P2Y 12 -adenosine diphosphate receptor antagonists [START_REF] Tantry | Consensus and update on the definition of ontreatment platelet reactivity to adenosine diphosphate associated with ischemia and bleeding[END_REF].


Mathieu Bourgais

Patrick Taillandier

Laurent Vercouter

An Agent Architecture Coupling Cognition and Emotions for Simulation of Complex Systems

Keywords: Cognitive Agent, Emotions, Multi-Agent Simulation, Evacuation

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

Introduction

These last years, multi-agent simulation has become an important tool, especially in the field of social sciences [START_REF] Hickmott | Agents bdi et simulations sociales[END_REF]. It enables to simulate situations with humans at a large scale more easily than with traditional simulations.

To ensure the quality of results obtained with digital simulations, these ones have to reproduce correctly the actors' behavior, that implies not only the use of a cognitive architecture [START_REF] Balke | How do agents make decisions? a survey[END_REF][START_REF] Hickmott | Agents bdi et simulations sociales[END_REF] but also to take into account their emotions [START_REF] Nair | The role of emotions in multiagent teamwork[END_REF][START_REF] Adam | Simulation of the emotion dynamics in a group of agents in an evacuation situation[END_REF]. However, using such a cognitive and emotional architecture requires a high level in computer sciences and more particularly in Artificial Intelligence. Moreover, as the studied systems are often composed of thousands of entities, the computation time of the proposed tools is a true concern.

This paper proposes an agent architecture integrating at the same time a cognitive and an emotional dimension, that aims at being used by all types of user -even non computer scientists -and at simulating several thousands of agents. This architecture is implemented in GAMA [1, 14], a multi-agent software for modeling and simulating complex systems. The present work consists in upgrading the existing cognitive architecture in GAMA [START_REF] Caillou | A simple-to-use bdi architecture for agent-based modeling and simulation[END_REF] and in integrating an engine that will simulate emotions in the agents.

This article is structured as follow: Section 2 is a state of the art on the existing cognitive and emotional architectures in the field of multi-agent simulation. Section 3 presents the cognitive architecture. Section 4 is dedicated to the presentation of the developed emotional module. Section 5 discusses an example of use of the new architecture and at last Section 6 serves as a conclusion.

2 Related Works

Cognitive multi-agent simulations

A lot of cognitive architectures have been presented in the field of multi-agent simulations. Indeed, it has been shown that adding cognition to agents increases the realism of simulations [START_REF] Balke | How do agents make decisions? a survey[END_REF][START_REF] Hickmott | Agents bdi et simulations sociales[END_REF].

One of the most used architecture in this domain is the BDI architecture [START_REF] Bratman | Intentions, plans, and practical reason[END_REF]. It has been developed using modal logic [START_REF] Cohen | Intention is choice with commitment[END_REF] to define without ambiguity the concepts of beliefs, desires and intentions and the logical links between these concepts.

The BDI architecture has been implemented in different frameworks to ease the development of cognitive agents. A classical framework is the Procedural Reasoning System (PRS) [START_REF] Myers | User guide for the procedural reasoning system[END_REF] that is composed of three steps : a perception that gives information about the environment to the agent, a central interpreter that deliberates between desires and finally the execution of the action selected. Inspired by PRS, other frameworks have been developed such as JACK [START_REF] Howden | Jack intelligent agents-summary of an agent infrastructure[END_REF] that has been used in different commercial use (in video games for example). JADE [START_REF] Bellifemine | Jade-a fipa-compliant agent framework[END_REF] is another framework enabling the development of BDI agents in multiagent systems whose most advanced version is Jadex [START_REF] Pokahr | Jadex: A bdi reasoning engine[END_REF]. Unfortunately, these frameworks are developed for a public expert in computer science.

The BDI architecture has also been included in multi-agent modelization and simulation software in order to be more accessible. An extension of NetLogo [START_REF] Wilensky | Netlogo: Center for connected learning and computer-based modeling[END_REF] proposes a simplified BDI architecture for educational purposes [START_REF] Sakellariou | Enhancing netlogo to simulate bdi communicating agents[END_REF]. Agents have beliefs, intentions and ways to answer to intentions. Sing and Padgham [START_REF] Singh | Opensim: A framework for integrating agentbased models and simulation components[END_REF] went further by connecting a multi-agent platform with an existing BDI framework (JACK or Jadex for example). In the same spirit, an application connecting the Matsim platform [START_REF] Balmer | Multi-agent systems for traffic and transportation engineering[END_REF] with the GORITE BDI framework [START_REF] Rönnquist | The goal oriented teams (gorite) framework[END_REF] has been proposed. These works, more generic, are also developed for a public expert in computer science.

Another integration of the BDI architecture has been initiated in the GAMA software [1]. The developed architectures have been created to be complete as most as possible and available to a non expert public. It gives agents a beliefs base, a desires base, an intentions base and a reasoning engine. It also offers low computation time enabling the simulation of thousands of agents. The limit of this work is that it does not provide tools to connect the cognitive engine with the environment of the agent. The present article is based on this later work.

Emotional multi-agent simulations

In parallel with propositions of cognitive architectures, researches were lead to add emotions to agents [START_REF] Gratch | A domain-independent framework for modeling emotion[END_REF][START_REF] Adam | Simulation of the emotion dynamics in a group of agents in an evacuation situation[END_REF]. Various works have shown that the addition of emotions to a multi-agent system permitted to increase the realism of observed results [START_REF] Nair | The role of emotions in multiagent teamwork[END_REF][START_REF] Hickmott | Agents bdi et simulations sociales[END_REF].

Emotional theories have been developed first by James and Lange [START_REF] Carl | The emotions[END_REF] who worked on a physiologic origin of emotions. Their theory explains that the human nervous system creates a physiological answer to events perceived. Emotions are then the answers created physiologically.

Afterwards, researches have been lead to show the cognitive origin of emotions. Arnold [START_REF] Arnold | Emotion and personality[END_REF] and Lazarus [START_REF] Craig | Emotion and adaptation[END_REF] discussed the fact that it is the appraisal of a situation that creates emotion. Over that psychological definition, Ortony, Clore and Collins [START_REF] Ortony | The cognitive structure of emotions[END_REF] defined a typology of emotions (the OCC typology) based on the appraisal of different situations. This model represents twenty emotions created to be used in artificial intelligence.

Different implementations of emotions have then been proposed for agents. DETT (Disposition, Emotion, Trigger, Tendency) [START_REF] Van Dyke | A model of emotions for situated agents[END_REF] is based on the OCC model by considering the perception of a situation as the trigger of the creation of emotions. Other works such as eBDI [START_REF] Jiang | Ebdi: an architecture for emotional agents[END_REF] integrated emotions to a BDI architecture. This emotional module creates primary emotions from perception of the environment and secondary emotions are created by cognition. These emotions are then used to influence the cognitive deliberation with a control loop to minimize the impact of a selected action on the emotion base. However, these integrations are not made easy to use for a non expert public.

Finally, various works have been done on the study of emotional contagion. The emotional contagion is the process wherein the emotions of a person influence the emotions of an other person or a group of persons [START_REF] Sigal | The ripple effect: Emotional contagion and its influence on group behavior[END_REF]. As explained in the theoretical studies of Bosse [START_REF] Bosse | A multi-agent model for emotion contagion spirals integrated within a supporting ambient agent model[END_REF] and Barsade [START_REF] Sigal | The ripple effect: Emotional contagion and its influence on group behavior[END_REF], emotional contagion is a social influence. Therefore, it is important to integrate it to the present work to enable modelers to socialize cognitive agents. In their work, they revealed the existence of two types of emotional contagion: an unconscious form and a conscious form. These theories have been partially integrated in a cognitive architecture based on eBDI [START_REF] Saunier | Une architecture mixte agent/environnement pour le calcul dynamique des émotions[END_REF] by adding a decreasing intensity to emotions and an unconscious contagion. However, this work does not implement the conscious contagion.

Presentation of the cognitive module

Our architecture is based on the one developed previously for GAMA [START_REF] Caillou | A simple-to-use bdi architecture for agent-based modeling and simulation[END_REF][START_REF] Grignard | Gama 1.6: Advancing the art of complex agent-based modeling and simulation[END_REF], that aims at letting modelers use the BDI theory to define their cognitive agents. It also fosters the ease of use for a non expert public and a low computation time. In this section, we propose an extension for this architecture that links cognitive agents with their environment. The cognitive architecture with our improvements is summarized in figure 1.

Basis of the cognitive architecture

In this architecture, the knowledge is represented by a data type called predicate. We consider a predicate to be a tuple <Name, Values, Priority, Truth> with the following elements :

-Name (mandatory) : the name of the predicate.

-Values (optional) : a map containing the values stored by the predicate.

-Priority (optional) : a real priority value to compare two predicates.

-Truth (optional) : a boolean value that indicates if the predicate is true or false.

Depending on the context, a predicate can be a belief, a desire or an intention, and can be used in the reasoning steps of choosing the current intention and choosing the current plan. These steps follow the principles of the BDI theory that is to say an intention is chosen in function of the beliefs, desires and intentions of the agent and then a plan is selected to answer this intention according to the agent's beliefs. The reasoning engine is detailed in the paper [START_REF] Caillou | A simple-to-use bdi architecture for agent-based modeling and simulation[END_REF].

This architecture gives a cognitive behavior to agents but does not link this behavior with the agent's environment. This is the challenge of adding a perception, inference rules and a lifetime to predicates.

Tools to connect the architecture to the environment

The perception module creates beliefs representing the perceptions of the agent.

It contains multiple parameters to be adaptable to various situations :

-A perception area around the agent. The modeler can give a particular geometry (it can be complex and defined according to the vision of the agent) or just a perception distance.

-The agents that will be possible to perceive. The modeler can indicate precisely which agents will be detected in the area of perception. -A boolean condition to activate the perception.

Then, the modeler indicates which information of the perceived agents will become beliefs for the perceiving agent.

The definition of inference rules consists in parametrizing the transformation of beliefs and desires according to the perceived world. A rule can add or delete beliefs or desires according to the state of the corresponding bases. The inference rules get a lot of parameters, all optional, to be adjustable to any situation :

-A belief to activate the rule.

-A desire to activate the rule.

-The belief created by the rule.

-The desire created by the rule.

-The belief deleted by the rule.

-The desire deleted by the rule.

-A boolean condition to activate the rule.

Finally, a lifetime is added to predicates which become a tuple <Name, Values, Priority, Truth, Lifetime>. It is optional and decreases automatically of 1 at each step with the predicate degradation module of the figure 1. This mechanism enables to indicate that a belief or a desire will not exist any longer after a certain number of time steps.

With these tools, the cognitive architecture gets its own dynamic and is connected to the environment of the agent. An experiment has been carried out with three computer scientists and three geographers who were invited to test the architecture through an exercise. The six modelers said the architecture was easy to use which is a good point. The details of the experiment can be find on the site : http ://acteur-anr.fr/experiment.html 4 Adding emotion through cognition

Presentation of the emotion type

We have chosen to base the emotion module on the OCC theory [START_REF] Ortony | The cognitive structure of emotions[END_REF]. The main contribution of the present work consists in the implementation of this emotion system in the core of our cognitive architecture in order to propose to modelers a tool to easily create emotional agents.

According to the OCC model, an emotion is a valued answer to the appraisal of a situation. On that statement, we create the emotion type as a tuple <Name, Predicate, Intensity, Decay> with the following elements :

-Name (mandatory): the name of the emotion.

-Predicate (optional): the predicate, identified by its name, that represents the fact about which the emotion is expressed.

-Intensity (optional): a real positive value of the intensity of the emotion.

-Decay (optional): a real positive value which will be subtracted from the intensity value at the end of each time step.

So, for example, an agent can simply be happy (which corresponds to the tuple <"happy">), an agent can express hope about a fact A (which corresponds to the tuple <"hope", A>) or an agent can express fear about a fact B with an intensity of 3.8 and a decay value of 1.2 (which corresponds to the tuple <"fear", B, 3.8, 1.2>).

We add to the cognitive architecture of GAMA an emotion base that will contain instances of the emotion type. In this base, only one emotion with a same name and a same predicate can exist. So, if an existing emotion is added again to the base, the emotion base only keeps one emotion and, adds the two intensity values and keeps the minimum decay value so that an ephemeral emotion does not put to end a more sustainable emotion.

Creation of emotions by and for cognition

To take into account emotions in the behavior of agents, we modified the cognitive architecture as described by figure 2.

Fig. 2. Schema of the developed architecture with the addition of emotions

To integrate emotions into the cognitive architecture, in addition to the emotion base mentioned previously, we add a base of uncertain expected events that will be referred thereafter as the uncertainty base. The main contribution of this article is about the emotion base which will be managed with different tools.

Concerning the uncertainty base, it is for the moment managed manually by the modeler.

To manage the emotion base, we modify the inference rules previously defined in order to take into account emotions. The modeler can, thanks to the definition of those rules, change the emotion base according to the agent mental states or change the belief base or desire base according to the agent emotions.

The use of inference rules to create emotions from cognition requires knowledge in emotions theory from the modeler. We also offer for non expert researchers the possibility to use emotions with the computation emotion module presented in figure 2. This module will automatically, with no intervention from the modeler, create emotions according to the mental states of the agent.

The automatic creation of emotions according to the mental states of the agent is based on the OCC model [START_REF] Ortony | The cognitive structure of emotions[END_REF] and its logical formalism [START_REF] Adam | Emotions: from psychological theories to logical formalization and implementation in a bdi agent[END_REF], which has been proposed to integrate the OCC model in a BDI architecture.

According to the OCC theory, emotions can be split into 3 groups: emotions linked to events, emotions linked to people and emotions linked to things. For the moment, we only focused on emotions linked to events that are the easiest to integrate in a generic way as the concept of events is represented in the existing architecture with the type predicate.

The eight emotions automatically created by our computation module have the following definition, according to the logical formalism [START_REF] Adam | Emotions: from psychological theories to logical formalization and implementation in a bdi agent[END_REF]:

-Joy(P) <"joy",P> = Belief(P) & Desire(P) -Sadness(P) <"sadness",P> = Belief(P) & Desire(not P) -Hope(P) <"hope",P> = Expect(P) & Desire(P) -Fear(P) <"fear",P> = Expect(P) & Desire(not P) -Satisfaction(P) <"satisfaction",P> = Hope(P) & Belief(P) -Disappointment(P) <"disappointment",P> = Hope(P) & Belief(not P) -Relief(P) <"relief",P> = Fear(P) & Belief(not P) -Fear confirmed(P) <"fear confirmed",P> = Fear(P) & Belief(P)

The terms Belief(P), Desire(P) and Expect(P) have the following definitions:

-Belief(P) : indicates that the fact P belongs to the belief base of the agent.

-Desire(P) : indicates that the fact P belongs to the desire base of the agent.

-Expect(P) : indicates that the fact P belongs to the uncertainty base of the agent.

The emotions created by the computation module are created without intensity nor decay value as there is no generic way to define them. If the modeler wants to use intensity, he/she will have to add it manually.

Note that the creation of some emotions will automatically remove other ones. The creation of fear confirmed or of relief will replace the emotion of fear while the creation of satisfaction or of disappointment will replace a hope emotion. Moreover, according to the logical formalism [START_REF] Adam | Emotions: from psychological theories to logical formalization and implementation in a bdi agent[END_REF], the creation of satisfaction and relief leads to the creation of joy and the creation of disappointment and fear confirmed leads to creation of sadness.

Once the decisional process of the agent has been carried out, the architecture deteriorates the emotions according to the decay value of each emotion. The operation done here is only a subtraction that corresponds to the degradation of an intensity of an emotion during one time step. If an intensity reaches zero, the emotion is removed from the base.

With these tools, the agent can now express emotions according to its mental states, it can use these emotions to influence its deliberations and these emotions can dynamically evolve with their decay rate.

Emotional contagion module

In our architecture, emotional contagion is seen as an emotional perception. The emotional contagion is thus defined as the process wherein the emotions of an agent are influenced by the emotions of agents nearby. The module of emotional contagion is then placed inside the perception module, as seen on the figure 2, to actualize the emotion base before starting the reasoning phase.

The unconscious emotional contagion corresponds to the fact that an emotion is automatically copied when perceived in another agent. In our work, the unconscious emotional contagion has multiple parameters to be adaptable on various situations:

-The emotion that must be detected to be copied (mandatory).

-A real value of charisma between 0 and 1 corresponding to the strength of the transmission from the perceived agent (optional). -A real value of receptivity between 0 and 1 corresponding to the capacity to receive an emotion for the perceiving agent (optional). -A real threshold between 0 an 1. If the product between charisma and receptivity is greater or equal to the threshold, the emotional contagion is activated (optional). -A boolean value to activate the emotional contagion (optional).

By default, the charisma value and the receptivity value is 1 and the threshold is 0.25 in order that if the value of the two variables are 0.5, the contagion happens. With that system, if the charisma is just under a mean value (under 0.5), the receptivity will have to be above the mean value, and vice versa. If the modeler wants another threshold, he/she can change it easily.

Let's take an example. An agent A have a charisma value of 0.5 and a receptivity value of 0.6 and an agent B have a charisma value of 0.7 and a receptivity value of 0.2. The threshold for the emotional contagion stay by default at 0.25. If agent A is contaminated by agent B about an emotion E, the emotional contagion will happen (0.7 * 0.6 ≥ 0.25). Agent A will copy emotion E and the intensity of E will be multiplied by the charisma value from B and the receptivity value from A. In the case of a contamination of B from A, the contagion will not happen (0.5 * 0.2 < 0.25).

The conscious emotional contagion corresponds to the fact that an agent creates a new emotion if she perceives a certain emotion in another agent. The created emotion can be different from the perceived emotion, contrary to the unconscious emotional contagion. The conscious emotional contagion has also multiple parameters to be adaptable to various situations:

-The emotion that must be detected to activate the contagion (mandatory).

-The emotion that will be created by the contagion (mandatory).

-A real value of charisma between 0 and 1 (optional).

-A real value of receptivity between 0 and 1 (optional).

-A real threshold between 0 an 1 (optional).

-A boolean value to activate the emotional contagion (optional).

Example case

Introduction of the example case

The architecture developed in this work has been used on the example case of drivers in a crisis situation such as an industrial hazard.

The situation is the following one: on the studied area, a factory of chemical products is on fire and some products are spread into the air. If a driver smells the toxic gas, she will think it is possible that a catastrophe happened so she will go to a shelter. Some drivers will not be afraid by the gas but when they will see the fire, they will panic and go to the shelters twice faster than the normal speed.

Over that situation, we add the fact that if a driver sees other drivers fleeing, she will have a probability to flee herself.

This example uses at the same time the cognitive architecture and the emotional engine to simulate the behavior of thousands of agents.

Implementation of the example

We focus on the implementation of the behavior of drivers. Each driver gets a random value for charisma and receptivity and a boolean value that indicates if the driver will flee only with the fear of a catastrophe (and not necessarily with the belief of a catastrophe). Initially, the driver agents desire to move randomly.

The reasoning cycle of the agent starts with the perception of her own environment. An example of implementation of the environmental perception of the cloud gas is given in Figure 3. The modeler indicates the target that will be perceived and a distance for that perception and he/she indicates that if the "hazard" agent is perceived, the driver agent should add the uncertainty about a catastrophe and the desire that there is no catastrophe.

On the other side, the perception of other drivers is an emotional perception that will occur through emotional contagion. The figure 4 shows an example of implementation for the unconscious contagion of the fear confirmed emotion.

We then define inference rules to create the agent's desires. Figure 5 shows the implementation of a rule to remove the intention to move randomly and to add the desire to go to a shelter if the agent has the belief of a catastrophe. Finally we implement plans that will be used by the agent to face hers intentions. On the figure 6, the activation of the plan is conditioned by the presence in the emotion base of the fear confirmed emotion. The complete model can be find on the following website : https://github.com/mathieuBourgais/ExampleModels.

Discussion

The goal of this example is not to propose an accurate representation of drivers' behavior in a crisis situation but to show how the tools we have developed can be used for such a simulation.

The major challenge of our architecture is to be easy to use, especially for non computer scientists. The codes shown as examples illustrate the simplicity of implementation for the perceptions, inference rules or emotional contagion.

One of the main advantage of our work is its emotion computation module. On the previous example, the modeler never needs to indicate how to create emotions. They will be automatically created according to the cognitive state of the agent. The modeler just has to indicate the changes of the cognitive states such as adding beliefs or uncertainties. Then, the modeler can use the emotions inside inference rules or plans.

Another advantage of this architecture is its adaptability. A more skilled modeler can, for example, use charisma and receptivity values to modulate the emotional contagion or create new emotions using inference rules. The architecture proposes a lot of tools to easily create complex behaviors for agents.

Concerning the computation time, the experiments carried whith our example on a computer with a dual core processor and 4GB of RAM showed that it takes less than 50ms per step for 500 driver agents, which is quite fast. With 5000 agents, it takes less than 400 ms per each step which is an acceptable time.

Conclusion

In this article, we have presented a cognitive architecture for multi-agent simulations coupled with an emotional module enabling the modeler to define agents with social features. Our architecture features tools to connect agents' cognition and their environment such as perception or inference rules, an emotion type and an emotion engine to automatically create emotions from cognition, and an emotional contagion module.

In the future, we plan to lead experiments with modelers of different fields to test the ease of use of the architecture. We also want to facilitate the use of the uncertainty base in the cognition process. Finally, in order to enrich the possibilities of developping social agents, we plan to add social norms to the architecture while keeping in mind the low computation time and the ease of use.

Fig. 1 .

 1 Fig. 1. Schema of our cognitive architecture

Fig. 3 .Fig. 4 .Fig. 5 .

 345 Fig. 3. Implementation of the perception of the cloud gas

Fig. 6 .

 6 Fig. 6. Implementation of a plan

Acknowledgment

This work is part of the ACTEUR ("Spatial Cognitive Agents for Urban Dynamics and Risk Studies") research project funded by the French National Research Agency.


Malvina Apostolou
email: malvina.apostolou@gmail.com

Urban eco-acupuncture methods: case study in the city of Athens

Keywords: small-scale urbanism, urban acupuncture, sustainability, Athens, public spaces, green spaces, reuse

The urban acupuncture theory is related to the creation of small-scale neuralgic interventions in the city that can have a direct impact on the urban morphology and life. Citizen's desires are taken into account in a situational and cultural context that focus on the social cohesion of the urban environment ; via the implementation of sustainable key points in the city, a network of interventions is established that would function as cores of potential energy healing the area. After a brief presentation of the points of the urban acupuncture approach, the second part focuses on the city of Athens as a model for the implementation of three proposed case studies of this theory. The three small-scale interventions aim at the social enhancement, environmental upgrade and creation of functional public spaces, via the activation of missing links in a dense and decaying urban tissue.

INTRODUCTION

The contemporary cities are facing a transformation; a mutation that demonstrates that the traditional methods and tools are inadequate for our perception for the new urban phenomena. The rapid changes in the city have an impact on the urbanity, sociological and spatial. The priorities in the conceptual approach of the design such as land use, mobility, environment, must be re-arranged and enhanced. A long list of urbanisms [START_REF] Kim | Learning from Adjectival Urbanisms: The Pluralistic Urbanism In 102nd[END_REF] are formulated during the last sixty years, attempting to identify the problems of urbanisation and excessive urban sprawl by promoting solutions. The notions included in the definition of those urbanisms are related to sociology, politics, ecology, mobility, infrastructure, sustainability and energy; they gradually transfer their interest from a top-down to a bottom-up system of design; they use community participation, principles of social cohesion, by implementing new codes or combining the existing ones; total design and total architecture, usually being derived from top-down methods and a single, central vision is being replaced. In Collage City a critical analysis of the origins and ideologies of Modernist city planning is presented. In a Post-Modern reaction to the total-design approach, the urban design is considered through fragmentation applied strategically in order to allow the flexibility, adaptation and self-development of the city ; through bricolage that produce a functioning network of pocket utopias. [START_REF] Rowe | Collision City and the Politics of 'Bricolage' Collage City[END_REF] For there exists a great chasm between those, on one side, who relate everything to a single central vision, one system less or more coherent or articulate, (...) and, on the other side, those who pursue many ends, often unrelated and even contradictory, connected, if at all, only in some de facto way, for some psychological or physiological cause, (...); these last lead lives, perform acts, and entertain ideas that are centrifugal rather than centripetal, their thought is scattered or diffused, moving on many levels, seizing upon the essence of a vast variety of experiences and objects for what they are in themselves, without consciously or unconsciously, seeking to fit them into, or exclude them from, any(...) unitary inner vision. [START_REF] Berlin | The Hedgehog and the Fox[END_REF] The holistic approach by acupuncture strategies and micro grids give the ability to respond to the risks of the 21st century and challenge the conventional infrastructure planning and design. The re-conceptualisation of the networks of infrastructure consist a response to an increased service demands from rapid urbanisation on the one hand and the imperatives for ecological and carbon footprint reduction on the other (4). The interdependencies of diverse, multiple, and even contradictory layers -energy, water, waste, information technology, mobility, social inequalities, political instability-point out the essentiality of the integration of multiple urban systems in locally oriented experimental approaches with the synergy of interdisciplinary visions. The boundaries of dipolar notions such as private-public, centre-periphery, built-void, city-nature, planned-spontaneous, permanent-temporal (5) are blurred and intersecting, thus creating interpenetrations that emerge new significations. For example, Infrastructural Urbanism (1960s) with its mega-structures and futuristic cities, Parametric Urbanism as a replacement of modernism by a computer-generated script, Splintering Urbanism [START_REF] Graham | Splintering Urbanism: Networked Infrastructures, Technological Mobilities and the Urban Condition: Networked Infrastructures, Technological Mobilites and the Urban Condition[END_REF] as the fragmenting experience of the city by the use and non-use of infrastructures, including information technologies are only some of the adjectival urbanisms. Others include Emergent, Digital, Disconnected, Networked, Green, Ecological, Sustainable, Clean, Environmental, Traditional, New, Walkable, Participatory, Do It Yourself, Micro-, Pop Up ,Temporary, Everyday, Bricolage (a term applied to urban design by Colin Rowe and Fred Koetter in their book, Collage City (1979), to oppose the modernist assumption that existing cities should be demolished and their established communities displaced [START_REF] Barnett | A Short Guide to 60 of the Newest Urbanisms[END_REF].) At the same time, the adjectives describing the morphology or identity of the cities -like compact, diffuse, polycentric, linear, organic, sustainable, dense, ecological, intelligent, hybrid, digital, autonomous etc-are being also enriched while diverse notions and descriptions of urbanisms appear.

THE THEORY OF URBAN ACUPUNCTURE

The traditional urbanism has therefore expanded its skills and has enriched its approaches by working on the intangible dimension of places already built in order to generate desired uses. In this perspective, temporal interventions are transfiguring the social and urban reality by redefining the urban act. [START_REF] Pradel | Mettre en scène et mettre en intrigue : un urbanisme festif des espaces publics[END_REF]The dimensions of sustainability, time, public space, participation and new technologies are playing an important role as far as the emergence of the participatory urbanism is concerned. The stimulation of the social is also among the basic aims of the urbanism that is 'acupuncture'. The intervention in the city is like a therapy that focuses on the time and the public space, searching at the same time for a validation by the collective use. Explorations in micro-urbanism challenge the idea that space and size are related terms. Small scale strategic and neuralgic interventions are envisaged as key generators for new spatial conditions and habits. It is a concept and a strategy to deal with the complexity of the modern urbanity, suggesting a city design process that goes from the micro to the macro. (9)

Principles of the concept

The basic principle of this urban socio-environmental theory (10) is that the healing of strategic points-parts of the city can operate as cores that gradually heal the whole; it consists of small scale targeted interventions that progressively transform the larger urban context. The origins of the concept are related to the method of acupuncture: thus, the application of pressure in specific points of the body in order to treat diseases or reduce pain. In a similar way, the urban acupuncture pinpoint areas in need of repair; the sites are chosen after a social, ecological and economic analysis of the wider context and through an interaction with the local community. Alike the action of the healing of the body, the urban acupuncture is a strategy that aims at the relief of the 'body' of the built environment. The small-scale interventions are socially catalytic in the urban fabric; they release energy flows of relief by responding to localised needs. In other words, the revitalisation of the whole (city) is being achieved by the treatment and healing of the consisting parts (strategic points). This approach, localised and communitarian, uses the methods of punctual manipulation of the urban energy flows in order to promote an ecologically sustainable development and reinforce the social coherence. The perception of the city as a living organism is therefore integrated with the notion of environmentalism and ecological urbanism, and correlated to the participatory and the pop-up urbanism. In periods when economic and environmental crisis have a significant impact on the depreciation of the built environment as well as the void , the public space is more and more marked by the emergence of a participatory urbanism ; groups of citizens that activate, use, occupy, share, remix the elements that define their involvement with the city and the parts of it that are in a decay ; the neighbourhood, the blocks, the vacant spaces are becoming their field of reflexion, action, reactivation and reuse. Participatory urbanism promotes thus a new relation, attitude, method for citizens to become involved with their city. (11)

Representatives and applications of the concept

Manuel Casagrande views cities as organisms in which different overlapping layers of flows are determining the actions of the citizens as well as the development of the city. By mixing environmentalism and urban design in the method of punctual manipulation of the urban energy flows he aims at the creation of an ecologically sustainable urban development towards the Third Generation City: the organic ruin of the industrial city that becomes true when the city recognizes its local knowledge and allows itself to be part of nature. ( 12) Manuel de Sola Morales' comprehension of urban acupuncture includes the perception of the project as a means of transforming neighbouring area. To act with punctures, pressures, injections is to distribute energy through the skin. It is the epidermis of the urban fabrics that enables us to transform internal metabolisms of its organism. It is the urban matter that transmits to us, at its most sensitive points and its most neutral zones, the qualitative energy that accumulates collective character on certain spaces, charging them with complex significance and cultural references and making them semantic material, social constructions of intersubjective memory. (13) The urbanistic form can at times be that of the whole urban fabric, that of the major morphological orders or that of the primary structure of the city. Sometimes, too, it is the areas of growth, the extensions and suburbs that have served to create urban forms of their own; in other instances, however, it is the smaller-scale civic elements that, due to their location or form, assume certain urban transcendence. But whatever their size, moment or function, urbanistic forms endow the city with that wealth of signification that human thought is capable of producing in its endeavour to master an economic and social process -urbanizationand give it a chosen form and image. [START_REF] De Solà-Morales | Ten lessons on Barcelona[END_REF] Finally, for Jaime Lerner, the detached activities of living, working and leisure in a metropolitan area result in dormitory cities and inactive neighbourhoods; the urban acupuncture method is related to mixing and integrating compatible urban functions so as to effectuate changes.

It is important to have an integrated view of the city. It is like the Turtle embodying life, work and movement. If the turtle's shell is divided into different parts, it will die. (...) There is an absolute need to integrate compatible urban functions within the city. [START_REF]the project weltstadtwho creates the city? , initiative of the goethe-institut and the german federal ministry for the environment, nature conservation, building and nuclear safety (bmub), interview with[END_REF] Sustainability Water LA is a program that promotes an urban acupuncture approach to water sustainability in Los Angeles aiming at a climate resilient city. The strategies concern the capture, conservation and reuse of the local water resources in order to face the climate challenges of the city-wasted waters, and periods of drought and storms. The micro-scale approach to environmental regeneration focuses on the land use and develop tools of small bottom-up interventions from the part of the citizens and the local community groups, such as rain tanks, rain gardens, parkway retrofits, greywater systems, infiltration trenches and permeable paving. The program was conceived by the River Project and activates a network of collaboration between nonprofit, public and private groups; engagement of the community and the residents.( 16) In a project of Manuel Casagrande, the method of Urban Acupuncture is being applied in the scenery of the community gardens coexisting with surrounding industrial surfaces of a 'Third Generation City', Taipei: punctual interventions in the surface of the city aim to establish a contact between the urban collective conscious and the life-providing systems of nature. [START_REF] Casagrande | Paracity: Urban Acupuncture, Public Spaces Bratislava, International Conference[END_REF] The networks of illegal community gardens and urban farms of Taipei are the needles that transform the industrial city in an organic machine. Their spontaneous, unofficial and selforganized character represents an anarchy through gardening. The urban farms -emerged in abandoned construction sites and ruined housing areas, empty city-blocks or flood banks of the rivers-tend to occupy empty spots of the city, to dominate the no-man's land. (18) According to M. Casagrande, this transformation in Taipei is an inside-the-city result of self-organized punctual interventions; it makes the city readier for a larger change (19) of urban ecological restoration process. In his project Ruin Academy (Taipei, Taiwan 2010 -) the occupation of an abandoned 5-story apartment building in central Taipei is effectuated, with the interior walls and windows removed in order to grow vegetables inside the house; the building is penetrated with holes to let rain inside and promotes a communitarian living.

Time

Power is what keeps the public realm, the potential space of appearance between acting and speaking men, in existence. (...) The word itself, its Greek equivalent dynamis, like the Latin potentia indicates its potential character. ( ... )While strength is the natural quality of an individual seen in isolation, power springs up between men when they act together and vanishes the moment they disperse. (...) The calamities of action all arise from the human condition of plurality, which is the condition sine qua non for that space of appearance which is the public realm. Hence the attempt to do away with this plurality is always tantamount to the abolition of the public realm itself. (...) [START_REF] Arendt | Mayor sets out to transform L.A. streets through 'urban acupuncture[END_REF] The event stimulates the assembly and activates the urban act. It gives a possible temporality to the function of a place by hosting the spirit of a collective use that influences its identity. Such operations in the city's fabric usually demonstrate a political will to change the citizen's view on abandoned or less visited neighbourhoods by inviting them to their discovery or reoccupation. Collective spaces are being transformed into temporal public spaces, where the event is articulated between a time and a place. Public squares are hosting events for a preorganized period of time, under the existence of a specific theme, with free entrance. For example, the Plaisirs d' Hiver (Winter Wonders) in Brussels, are temporal events that take place during five weeks -in the end of November until the first days of January-in the city ; streets, squares and vacant public spaces become hubs that host ephemeral events and actions. The streets leading to the heart of Sainte-Catherine area and the Place de la Monnaie are narrow; Christmas lighting becomes the link with the Grand Place of the city center; the Christmas chalets at the crossroads are forming articulations between different places and create an atmosphere of flânerie. The fest allows a different perception of the public spaces; they are not any longer only the receptor of meetings; the public space is the scene of an urban theatre, of exchanges, of attendance. A public Market is being adopted to the space and host multiple uses; the events are forming a narration, they explore the temporality of the ephemeral, where a meeting point/passage/corner is stimulating the social and mobilising the imaginary, repeated in every seasonal change of winter. Another rhythm and time is created within the time of the city ; the selected area in dynamically impacting its surrounding as the focal points that are being revitalised provide new energy to the city during the process.

Public space Park(ing)

Day is an annual worldwide event where citizens and artists are collaborating and participate in the transformation of parking spots into temporary public parks; a critical debate on the creation and allocation of the public space. In this way, new forms of public urban spaces are being created in neighbourhoods that lack public open spaces, consisting of interventions and experiments such as bench typologies, urban farms, installations, and acts with a political and social significance. The most significant challenge of this bottom-up and participatory intervention concerns the revaluation and redefinition of the space in order to accommodate needs of the community. In addition, the emergence of the cultural expression and the socialising process marks temporarily the urban territory and transforms its connotations. Moreover, the Great Streets initiative, envisaged by Los Angeles city mayor Eric Garcetti, concerns among others the transformation of the streets through the approach of urban acupuncture. The re-conceptualisation of the street is projected to be effectuated by the transformation of mayor boulevards into hubs of neighbourhood; the focus will be on the creation of a sense of community by the implementation of amenities and pedestrian spaces in selected areas of the city. More specifically, 15 major thoroughfares scattered throughout the city are selected, as the parts of the city where their small local changes could improve the overall street life, to reduce the traffic congestion and boost economic activity. The project envisages that bike racks, plazas, crosswalk upgrades and other amenities could draw in pedestrians and attract new businesses. (21) Urban Acupuncture is the method of choice of the mayor of Los Angeles as 'the city lacks the money and the space to add the types of transportation that would significantly reduce traffic congestion.' Instead, he hopes that this kind of treatment will bring 'enough amenities to a neighbourhood so that residents stay closer to home and, quite possibly, avoid using their cars altogether.'

CASE STUDIES OF URBAN ACUPUNCTURE APPLICATION IN THE CITY OF ATHENS

As a significant majority of locations in the city of Athens present a considerable lack of green and open spaces, in addition to an intensely evident impact of the economic crisis in the urban and social tissue; the city has been selected as a model for application of the urban acupuncture approach through key studies. The research area selected, the northern part of the wider centre of Athens, between Aharnon and Patission streets is an area that has sustained remarkable changes in its composition during the last decades. Its aging and abandoned building reserve, closed shops, low land value, absence of functional public spaces in combination with the lack of social and environmental capacitors lead to a decay. Moreover, the 6th municipal district where the research is concentrated, is the most overpopulated of the municipality of Athens. The transformation of its character and identity and the generation of social conflicts reflect the general economic and social crisis of the last years. Small scale interventions in neuralgic points are considered to be of a direct significance in order to provide the missing links that would activate the area as well as the environment in which it is prescribed. Thus, three small-scale interventions aim to contribute in the social cohesion and the environmental upgrade of the district through an urban acupuncture approach, while integrating green spaces and water surfaces in the highly dense fabric.

The reference to a 'stasis' in urban passages, indicates a notion of reactivation of the deactivated points in the city that ordinarily are only passed-by ; as well as the reuse of an area that is currently under the status of lethargy. The application of the concept of urban acupuncture here is aiming at a creation of a wider energy flow in the area that would result in its gradual heal by implementing an approach with a low ecological footprint and economic cost.

Method

In the first place, a cartography of the empty sites, vacant and abandoned spaces, the assortment of residents' interviews, as well as a research of the land use, the density and age of the local population have been established; the terrain of the study was northern of Omonoia, between Aharnon and Patission streets, and Victoria Square and Agiou Meletiou street [START_REF] Apostolou | Stasis in three urban passages[END_REF]. The collection of information -apart the bibliographic research-concerning the everyday life, the social composition and structures, was effectuated after encounters and exchanges with the residents. In the second place, the selection of the sites that the urban acupuncture would be implicated has been developed: leftover spaces between buildings, in blocks characterised by a strong presence of children end elders are chosen, in order to be revived through the implementation of structures aiming to accommodate and inspire the temporal use, the interaction of the residents and the passengers, the generation of the nature. The programs hosted and the new use of the points selected are fruits of a thorough analysis and comprehension of the deficiencies in the urban fabric, the lack of social cohesion and the environmental degradation. More specifically, the residual vacant spots are programmed to host public, semi-public and private uses, applied in the context and the land uses that already exist. The proposed interventions use the existing dynamics of the urban environment and are developed in tree axes: the soil, the walls, the roof of the existing voids and buildings; after having taken into account the urban identity of the area and the sociological, economical and environmental context. The land uses that are proposed, the use of materials, the type of vegetation, are selected in such a way as to respond to a sustainable approach through the time. The trees that already exist are maintained and reinforced. The acupuncturing method, developed after the examination of the area's present identity in a micro as well as a macro scale, treats the notions mentioned above: public space, time, sustainability in a social context.

First case study, Kalymnou street, Athens

During the cartography of this area, a remarkable lack of areas hosting leisure and cultural activities for the residents was observed. Moreover, there is a high density of children and elders. This acupuncturing intervention aims at the creation of meeting points for the nearby inhabitants during the summer and the winter, intended to, enhance the sense of a neighbourhood, to invite the inhabitants to use the space and enhance their social bonding. This block contains two vacant plots facing each other. The intention here was to unify those two empty spaces so as to create the widest public space possible. Thus, the road that separates the plots become their connector ; on the second hand, a diagonal axe structures the space so as to unify it visually, to define its uses and to permit a permeability in the horizontal and vertical axe. In the first plot that is the smallest one, an open unit -a public library is proposed as a structurepassage-shelter that guides the user in the hidden garden in the interior of the block. The diagonal axe is distinguishing here the passage -in the form of ramp so as to facilitate the access of elderly or handicapped residents and the baby trolleys-from the slightly raised reading area and the bookshelves. In the opposite plot, the diagonal axe-continuation distinguishes also the uses proposed: one the one hand a Square is being created; a tall and big tree defines its space -reminding the Platanus in the middle of the traditional public squares. On the second hand, the axe is structured in a closed unit -a greenhouse; an urban garden as a participatory public space. In this intervention as well, the space can be used totally as well as partly, in the diverse seasons and by a variety of age groups. Finally, the lateral walls of the opposite blocks of flats, the boundaries of the walls that define the public and semi public space, are treated as parts of the scenery of the intervention; climbing plants are developed in their surfaces.

Second case study, Ithakis street, Athens

In this block, two vacant leftover and fragmented spaces, as well as a pedestrian street compose the scenery. The proposal consists of the creation of a public space, connecting two roads and creating axes. Thus, the two vacant parcels are proposed to be connected so as to create a linear passagepathway that involves the staying, connecting it at the same time with Eftichias pedestrian street. The concept applied consists of the creation of three surfaces-rooms, as distinct entities of urban subspaces that are however part of the whole synthesis; to define the stay, the planting, the materials, the subspaces are created as superposed layers along the pathway. The first and the third subspaces have medium-height vegetation, while the second subspace, in the center of the space created, symbolises the void : the Square; it is a reference point; a meeting place of the residents with a water point setting a scene and defining the limit with the semi public gardens. Linear elements (benches, axes of passage with different materials, rows of trees) are organising the uses of the space and structuring the boundaries of the public and the semi public gardens of the surrounding block of flats. The limited space that is provided, in combination with the essential lack of public and green spaces in the area have contributed to the application of this concept that unifies separate zones by diffusing their boundaries: the parts of the synthesis can be read distinctly and also holistically; moreover, the uses combine the public character and the regeneration of the nature.

Third case study, Broadway Passage, Kefallinias street, Athens

Broadway is one of the first multiplex in Athens; it was created in the 1970's and comprised two cinemas, two theatres, an entertainment centre and 17 shops. Today, only 2 theatres and 4 shops are still operating. Its current state is characterised by the intermediate state of no use. This passage reflects areas of the city of Athens where a previous glory is replaced by a decline and abandonment under the circumstances of the general economic depression. Broadway passage has been for years a point of reference in the social and cultural life of the Athenians. In the context of implementing alternative economic models, the intervention in this point of the city focuses on the retrieval of a common space by the elaboration of the coexistence, participation, communication of the inhabitants, and the creation of the place as a meeting point for the public; the use and activation of the spaces abandoned, and principally the reopening of the open air cinema on the roof of the building are aimed to host the stay as well as temporal or permanent actions. Furthermore, the conversion of the building's envelope to a vertical garden contributes in the energy performance of the building that is situated in the middle of a block and surrounded by other buildings. The vertical garden consists of an alternative method to enter natural elements in this highly dense area and in particular in this block where there is no possibility to create a garden in the ground.

CONCLUSIONS

After the reinterpretation of the response of large scale projects of urban design to the necessities and challenges that the contemporary city is facing, a new approach of urbanism has been emerged. When the design of cities in an era of environmental and economic uncertainties is concerned, the method of urban acupuncture could provide the city cores of energy that would progressively contribute in its revitalization and reuse by the urban dwellers. The bottom up approach of this type of urban design demonstrates the residents and the users of the space as participators at the decisions being taken thus achieving a social enhancement in a context of a more localised and community approach.

In spite of its early promise, its frequent bravery, urbanism has been unable to invent and implement at the scale demanded by its apocalyptic demographics.(...) 'The' city no longer exists. As the concept of city is distorted and stretched beyond precedent, each insistence on its primordial conditionin terms of images, rules, fabricationirrevocably leads via nostalgia to irrelevance.(...)Now we are left with a world without urbanism(...) If there is to be a 'new urbanism' it will not be based on the twin fantasies of order and omnipotence; it will be the staging of uncertainty; it will (...) be concerned with (...)the irrigation of territories with potential; it will (...) aim (...) for the creation of enabling fields that accommodate processes that refuse to be crystallized into definitive form; it will (...) be (...) about expanding notions, denying boundaries,(...) about discovering unnameable hybrids; it will (...) be obsessed (...) with the manipulation of infrastructure for endless intensifications and diversifications, shortcuts and redistributionsthe reinvention of psychological space. Since the urban is now pervasive, urbanism will never again be about the new only about the 'more' and the 'modified.' It will not be about the civilized, but about underdevelopment. Since it is out of control, the urban is about to become a major vector of the imagination. Redefined, urbanism will (...) be a way of thinking, an ideology: to accept what exists. [START_REF] Koolhaas | What Ever Happened to Urbanism?[END_REF] The three case studies of small scale interventions in the city of Athens presented above has been developed after an in situ research of the characteristics synthesising the present status of the area; thus, as a surgical operation that impregnate the existing dynamics of the city with potentials that accommodate the use and the interaction of the inhabitants is proposed; with the social, environmental and economic dimensions taken into consideration. The small scale approach is expected to activate deactivated points of the city and result in a large scale mutation.


Élodie Masson

Ugo Scemama

A Lignères

Audrey Benyamine

Pascal Rossi

Kathia Chaumoitre

Brigitte Granel
email: bgranel@ap-hm.fr

E Masson

U.-A Scemama

M.-A Lignères

Une infiltration péri-rénale gauche

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L'histoire

Un homme, âgé de 81 ans, vivant en institution, était hospitalisé en urgence pour une douleur abdominale associée à une constipation (pas de selles depuis 4 jours). Ses antécédents notables étaient une hypertension artérielle, un accident vasculaire cérébral ischémique sans séquelle, une fibrillation auriculaire et des troubles cognitifs. Ses traitements comprenaient : bisoprolol, lercanidipine, fluindione et paroxétine. À l'examen, les constantes hémodynamiques étaient conservées, sans fièvre. L'abdomen était tendu avec une matité sus pubienne. On notait aussi un important météorisme et une défense du flanc gauche. Le toucher rectal confirmait le fécalome. Il n'y avait pas de signes de décompensation cardiaque. La biologie objectivait une insuffisance rénale aiguë sévère (clairance de la créatinine : 8 mL/min/1,73 m2selon Chronic Kidney Disease Epidemiology Collaboration) et un syndrome inflammatoire (CRP > 350 mg/L) avec hyperleucocytose à polynucléaires neutrophiles, sans anémie. L'INR était à 6. La conduite thérapeutique immédiate consistait à la mise en place d'une sonde urinaire permettant l'évacuation de 4 litres d'urines hématuriques, une hydratation intraveineuse pour prévenir le syndrome de levé d'obstacle et la réalisation de lavements rectaux, ramenant des selles. Un traitement antibiotique par céphalosporine de troisième génération était débuté dans l'hypothèse d'une porte d'entrée infectieuse urinaire ou digestive. L'examen cytobactériologique urinaire confirmait par la suite une infection à Klebsiella pneumoniae sensible à la ceftriaxone. Les hémocultures restaient stériles. Aux urgences, devant l'INR élevé, l'insuffisance rénale aiguë et les urines hématuriques, la fluindione était suspendue et 2 mg de vitamine K était administrée. Le premier scannerabdominal sans injection retrouvait un épanchement périrénal et pararénal postérieur et antérieur gauche, de densité liquidienne avec sédiment dense, sans dilatation significative des cavités excrétrices urinaires. L'uroscanner était secondairement réalisé après normalisation de la fonction rénale (Fig. 1).

Le diagnostic

Un urinome.

Les commentaires

L'urinome est une rare condition correspondant à une extravasation d'urine encapsulée dont l'origine, traumatique ou spontanée, est toujours liée à un facteur obstructif. Sa principale cause est l'obstacle urétéral sur lithiase [START_REF] Porfyris | Spontaneous rupture of renalpelvis as a rare complication of ureteral lithiasis[END_REF]. D'autres causes d'urinome sont rapportées dans la littérature : obstruction sur néoplasie rectale [START_REF] Garg | Spontaneous rupture of the renal pelvispresenting as an urinoma in locally advanced rectal cancer[END_REF], traumatique sur choc abdominal [START_REF] Bogdanovic | Successful surgicalreconstruction of ruptured renal pelvis following blunt abdominal trauma[END_REF], manipulation iatrogène lors d'une endoscopie urétérale [START_REF] Bannowsky | Iatrogenic fornix rupture caused during retrograde manipulationof the ureter: a case report[END_REF], et sur syndrome de la jonction pyélo-urétérale, avec un diagnostic prénatal possible pour cette dernière cause [START_REF] Stathopoulos | Prenatalurinoma related to ureteropelvic junction obstruction: poor prognosis of theaffected kidney[END_REF]. L'originalité de notre observation est la cause de l'obstruction secondaire à l'important globe vésical surfécalome. La rupture des voies excrétrices permettrait de lever la surpression sur le parenchyme (effet « pop-off » ou « soupape ») et protégerait ainsi le rein. Ceci est bien décrit dans les cas d'urinomes sur obstacle sous vésical avec constitution d'ascite urinaire. Les complications de l'urinome sont d'ordre mécanique ou infectieux.

Le diagnostic est réalisé par scanner (images réalisées au moins 6 minutes après l'injection du produit de contraste), l'échographie étant moins performante. Le traitement repose essentiellement sur la levée de l'obstacle (s'il existe) et la protection de la voie excrétrice lésée (dérivation des urines et mise en place d'une sonde JJ par voie percutanée ou naturelle). Le drainage percutané de l'urinome est parfois associé si son volume est très important. La chirurgie à ciel ouvert est nécessaire en cas de rupture urétérale importante [START_REF] Bogdanovic | Successful surgicalreconstruction of ruptured renal pelvis following blunt abdominal trauma[END_REF].

Fig. 1 .

 1 Fig. 1. Vue coronale du scanner au temps veineux (a) montrant un épanchement liquidien périuretéral gauche (flèches). Au temps tardif, le scanner montre l'extravasationde produit de contraste au sein de l'épanchement liquidien péri-rénal et urétéral, confirmant l'origine urinaire de celui-ci (flèches) en coupe coronales (b) et axiales (c). Aucune obstruction urétérale n'était visualisée incluant l'uretère pelvien (flèches) et la vessie (d).