Mohammad Irfan Alam

Shaik Subhani

Rajkumar S Pant

Multidisciplinary Shape Optimization of Stratospheric Airships

Keywords: High Altitude Airship, Shape generation scheme, Optimization

This paper describes a methodology for shape optimization of the envelope of an airship for long endurance missions at stratospheric altitudes. An existing shape generation scheme is selected for optimization studies, in which the envelope shape is parameterized by four shape coefficients and envelope length. The values of these shape coefficients are obtained by minimizing the sum of the squared residuals of the coordinates of the baseline shape listed in literature, and their predicted values using the equation of the profile. A composite objective function is formulated which incorporates the value of envelope volumetric drag coefficient (C DV ), circumferential hoop stress (σ hoop ) on the envelope, area of solar array and envelope surface area. The optimization is carried out using an open-source implementation of a robust stochastic algorithm, viz., Genetic Algorithm. The optimum obtained for minimum C DV , minimum σ hoop and the minimum value of the composite objective function are compared.

INTRODUCTION

There is a global interest in design and development of stratospheric airships [START_REF] Epley | Stratospheric Aircraft, Blimps, Balloons and Long Endurance Vehicles[END_REF], which can serve as a long endurance platform for deployment of equipment for several commercial and strategic applications e.g., next generation wireless broadband telecommunications [START_REF] Tozer | High-altitude platforms for wireless communications[END_REF],

digital broadcasting [START_REF] Grace | Broadband Communications via High-Altitude Platforms[END_REF], coastal surveillance [START_REF] Colozza | High-altitude, long-endurance airships for coastal surveillance[END_REF], remote sensing and GPS augmented navigation systems [START_REF] Tsujii | A Navigation/Positioning Service Based on Pseudolites Installed on Stratospheric Airships[END_REF]. These airships are designed to be able to maintain a quasi-stationary position at altitudes of around 20 km, where ambient winds are of low magnitude. Such airships function as low-altitude satellites, but offer much shorter transmission distances and ranges with high resolution, and lesser signal propagation errors. They are much more economical compared to satellites, as they can be relocated or brought down and refurbished with latest equipment.

Several researchers have proposed methodologies and approaches for conceptual design and sizing of stratospheric airships [START_REF] Lobbia | A modular sizing model for high-altitude/long-endurance airships[END_REF][START_REF] Yu | Configurations analysis for high-altitude/long-endurance airships[END_REF][START_REF] Chen | Analysis to Effects on Conceptual Parameters of Stratospheric Airship with Specified Factors[END_REF][START_REF] Alam | A Methodology for Sizing and Optimization of High Altitude Airship[END_REF]. The shape of the envelope is one of the most critical elements in the design of such systems, and envelope shape optimization is a key area of research in this field [START_REF] Zhang | Shape Optimization of Airship based on Constrained Particle Swarm Optimization[END_REF]. Concurrent subspace optimization techniques have also been applied to the conceptual design and sizing of airships [START_REF] Liang | Conceptual Design Optimization of High Altitude Airship in Concurrent Subspace Optimization[END_REF].

Due to long endurance missions, and the high altitude of operation, conventional propulsion systems may not be suitable for high altitude airships. Instead, it is proposed to mount Solar cell on the top of the envelope to meet the power requirements of the airship to maintain station, as well as that of the payload mounted onboard. The excess power generated by these solar cells during the daytime will be utilized to charge the onboard batteries, which then meet the needs during night-time, or occasions when the solar power is insufficient. This paper presents a methodology for shape optimization of an envelope for high altitude airship. On the lines of the work reported by Wang et al. [START_REF] Wang | A methodology for optimisation design and analysis of stratosphere airship[END_REF][START_REF] Wang | An Approach for Shape Optimization of Stratosphere Airships based on Multidisciplinary Design Optimization[END_REF] a composite objective function is devised which takes into account various factors that influence airship performance, including aerodynamics, structures, energy and weight. The envelope shape is parameterized in terms of some geometry related parameters; and the optimum shape that minimizes this composite objective function is obtained. Constraints are imposed on the volume of the airship, to ensure comparability of the design results. Optimal solutions are obtained using an evolutionary technique, viz., Genetic Algorithm

MODELS OF AIRSHIP SHAPE OPTIMIZATION

In the past, drag was often considered in airship optimization. When the coefficient of drag was smaller, the airship shape was considered more optimal [START_REF] Zhang | Shape Optimization of Airship based on Constrained Particle Swarm Optimization[END_REF]. In fact, the practical studies gradually show that many factors restrict the airship shape and resistance is only one of the several important factors, which also include weight, structural strength etc. After screening and contrasting to determine the most important factors on airship, coefficient of drag (C DV ), surface area of the airship envelope (A e ), minimum hoop's stress (σ min ) and area of the solar array (A sa ) are employed in the present study.

Shape Generation Algorithm

Exploring the possibility of better shapes in view of multidisciplinary optimization, a shape generation algorithm was proposed by Wang et al. [START_REF] Wang | A methodology for optimisation design and analysis of stratosphere airship[END_REF][START_REF] Wang | An Approach for Shape Optimization of Stratosphere Airships based on Multidisciplinary Design Optimization[END_REF]. The geometry of the airship envelope is governed by four shape parameters a, b, c, d and length l.

The equation of the airship body is expressed as,

64(y 2 +z 2 ) = a (l-x) (bx-l + ) (1)
Since the complete airship body is obtained by revolving the 2D shape by 360 o about the Xaxis, the 2D shape equation can be transformed as follows:

y = (2)
The reference shape is shown in Fig. 1.

Model of Volumetric drag coefficient

In order to seek the drag of the airship envelope, C DV is calculated as per the formula quoted by Cheeseman in [START_REF] Cheeseman | Propulsion[END_REF].

C DV = (3)
Where, l is the envelope length D is the maximum diameter

The Reynolds Number can be estimated using Eq. ( 4) as:

Re = (4)
Where,

D is the maximum diameter of the envelope

Re is the Reynolds number v is the velocity of wind ρ is the density of air μ is the dynamic viscosity of air

Model of surface area

The surface area of the envelope 'A e ' can be calculated using Eq. ( 5) as:

A e = 2π (5)

Model of Minimum Hoop Stress

Several researchers have estimated the circumferential hoop stress σhoop by assuming the airship body to approximate a thin cylinder with hemi-spherical ends. In this study, the pressures are obtained by considering the Elastic Engineering theory. A generalized moment equation is derived based on the Elastic theory with an assumption of linear distribution of mass along the length of the airship.

In order to maintain positive internal pressure, the minimum inner pressure (ΔP) consisting of static pressure (P static ), Munk pressure (P dyn ) and internal differential pressure (P diff ) are calculated using Eqns. ( 6) to (9) as:

ΔP = P static + P dyn + P diff (6)
P static = 4.227ρ a r gc λ2

P dyn = 2ρa v 2 Ve (k 2 -k 1 )(sin 2α)/π r gc 3 (7)
P diff = 1.722gρ a Rλ sinα (9) (8)
Where, g is the acceleration due to gravity r gc is the radius of the envelope at the mass center λ=l/D is the envelope fineness ratio k 1 and k 2 are the Munk inertial factors of longitudinal and transverse directions, which are 0.33 and 0.77, respectively α is the angle of attack (assumed to be 6 degrees) R is the maximum radius of the envelope.

The static pressure is caused by static bending moments, Munk pressure caused by dynamic bending moments and internal differential due to differential gradients.

The hoops stress can be calculated using Eq. ( 10) as:

σ hoop = ΔP.D/2 (10)

Model of Power requirement

The total power requirement (P total ) of an airship consists of payload systems (P payload ), control systems (P ctrls ) and propulsion systems (P thrust ). The payload power and the control systems power are assumed to be constant at 10 W and 11 kW, respectively. P total = P thrust + P payload + P ctrls [START_REF] Liang | Conceptual Design Optimization of High Altitude Airship in Concurrent Subspace Optimization[END_REF] The energy used for propulsion system can be calculated as,

P thrust = D total v/ƞ prop (12)
Drag 'D' acting on the airship can be obtained using Eq. ( 13) as:

D = ρ a v 2 C DV V 2 /3/2 (13)
Where, v is the speed of the airship ƞ prop is the propulsion system efficiency C DV = volumetric drag coefficient, and V = envelope volume, estimated using Eq. ( 14) as:

V = π (14)
The total energy Q total is estimated using Eq. ( 15) as:

Q total = P total t day + P total t night /ƞ convert [START_REF] Garg | Solar Panel Area Estimation and Optimization for Geostationary Stratospheric Airshipˮ[END_REF] Where, t day and t night are the duration of day and night time respectively and ƞ convert is the conversion efficiency for storing the energy.

Model of Solar Area requirement

The surface area of the solar array can be calculated in numerous ways. In an approach developed by Garg et al. [START_REF] Garg | Solar Panel Area Estimation and Optimization for Geostationary Stratospheric Airshipˮ[END_REF], the solar panels are considered to be mounted symmetrically or asymmetrically with respect to the three planes, also they can be placed in discrete patches or continuously on the surface of the airship hull. In their study, the solar panels were assumed to be placed on the top surface of the airship. The orientation of the solar panel is defined by two parameters, the height h from the equilateral plane/geometric axis of the airship and the width w along the span length of the airship.

In order to estimate the solar energy incident on the airship, the available solar panel area was resolved into three perpendicular planes. The angles of the incidence for respective planes were analytically determined and the incident energy was resolved in three perpendicular planes i.e., XY, YZ and ZX planes. The power calculated for each plane was added, and the total power estimated was being integrated to determine the total energy incident on the airship for a given day and given orientation of the solar panel.

Liang et al. [START_REF] Liang | Conceptual Design Optimization of High Altitude Airship in Concurrent Subspace Optimization[END_REF] have suggested an approach in which the actual geometry of the airship can be considered for solar array area estimation. But, this approach can work only for simple geometries, and is not feasible for complex geometries.

In the present study an approach similar to Liang et al. [START_REF] Liang | Conceptual Design Optimization of High Altitude Airship in Concurrent Subspace Optimization[END_REF] is adopted. But for simplicity, the airship geometry is assumed to approximate a cylinder. The radius of the envelope at the mass center r gc is taken as the radius of the cylinder.

Elementary solar area (dA) can be calculated using Eq. ( 16) as:

dA = r gc dξdx (16)
Where, dx is elementary length along length and dξ is angular width of elementary area of solar panel along circumferential direction.

So, total area of solar array (A sa ) required can be estimated by using Eq. ( 17) as: ξ

To find the total length of solar panel x s and included angle ξ, as a limit of Eq. ( 17), energy supplied (Q sup ) can be equated to total energy required (Q total ) as in Eq. (18) as:

Q sup = Q total (18)
Where, Qsup can be calculated by Eq. (19) as:

Where, and are solar conversion efficiency and normal solar irradiance values respectively calculated by Global Irradiance Model explained by Ran et. al [START_REF] Ran | A Comprehensive Global Model of Broadband Direct Solar Radiation for Solar Cell Simulation[END_REF] for the date of Aug. 08. And is angle between surface normal vector and I n.. Integral of Eq. ( 19) was integrated for the whole day time (t day ) to get total power supplied.

SHAPE OPTIMIZATION OF AIRSHIP

Several attempts have been made to optimize the shape of the airship envelope. Zhang et al.

[10] have carried out multidisciplinary optimization using a weighted composite function.

The designer can input the weighting parameters to optimize airship shape according to different design requirements. The objective functions considered for minimization are C DV , σ hoop and the envelope slenderness ratio l/D. An improved Constrained Particle Swarm Optimization (CPSO) algorithm was used by them to solve the airship shape optimization problem.

Some attempts have also been made to minimize the envelope surface area and the solar array area, in addition to above objective functions. Wang et al. [START_REF] Wang | A methodology for optimisation design and analysis of stratosphere airship[END_REF][START_REF] Wang | An Approach for Shape Optimization of Stratosphere Airships based on Multidisciplinary Design Optimization[END_REF] have used a composite objective function which minimizes the volumetric drag coefficient, Hoop stress, surface area of the airship envelope and area of the solar array. The same set of objective functions were used in the present study.

Design Vector

The design vector consists of four shape coefficients a, b, c, d and the length of the airship l.

Thus the design vector is described as

X D = (a, b, c, d, l).
The appropriate values of the shape coefficients a,…d for the reference shape shown by Wang et al. [START_REF] Wang | A methodology for optimisation design and analysis of stratosphere airship[END_REF][START_REF] Wang | An Approach for Shape Optimization of Stratosphere Airships based on Multidisciplinary Design Optimization[END_REF] are obtained by Newton's least squared method, in which the sum of the squared residuals is minimized. The residuals are obtained by obtaining the difference between the ordinate of the reference shape (obtained by digitizing Fig. 1) and their predicted values using Eq. ( 2). The values for the shape parameters are validated by comparing the envelope surface area and envelope volume with that of the reference shape of length of 194 m listed in [START_REF] Wang | A methodology for optimisation design and analysis of stratosphere airship[END_REF][START_REF] Wang | An Approach for Shape Optimization of Stratosphere Airships based on Multidisciplinary Design Optimization[END_REF].

Constraints imposed while obtaining optimum shape

The volume of the airship is fixed to be 250,000 m 3 , to enable a fair comparison of various envelope shapes. Appropriate side constraints on the values of design variables are imposed taking into account the shape and length of airships in general. Also, the solar cell coverage area is constrained to be less than 45 % of the Envelope surface area. An additive penalty function approach is used to handle the constraints [START_REF] Metropolis | Equation of state calculations by fast computing machines[END_REF].

Objective functions for Optimization

Several objective functions can be selected for determining the optimum envelope shape, e.g., minimum volumetric drag coefficient, minimum hoop stress and a composite objective function incorporating more than one objective function. To consider the influences of various factors on the optimization of the shape, a composite objective function involving C DV , A e , σ min and A sa is devised as follows:

F comp = (17)
Where C DV,ref , A e,ref , σ min,ref and A sa,ref are the values of these parameters corresponding to the reference shape.

INPUT PARAMETERS AND DESIGN VARIABLES

The input parameters consist of the initial values of the shape coefficients, user requirements and the design constants. The input parameters are summarized in Table 1. The input design variables are consistent with the mission scenario shown in Table 1 and the parameters discussed in subsystems.

RESULTS

In this section, the results after performing optimization using Genetic Algorithm (GA) are presented. Firstly, we optimized the airship envelope shape using the objective function as envelope C DV . An improvement of ~1.8 % in C DV is noticed in comparison with reference value. Then, the airship envelope shape is optimized for minimum hoop stress σ hoop . The optimal solution obtained is seen to have ~15% lower σ hoop compared to the reference shape.

CONCLUSIONS

It is seen that the results obtained by GA are slightly better than those reported by Wang [START_REF] Wang | A methodology for optimisation design and analysis of stratosphere airship[END_REF][START_REF] Wang | An Approach for Shape Optimization of Stratosphere Airships based on Multidisciplinary Design Optimization[END_REF] for all the three objective functions. It has been observed that, GA shows a good convergence to find the optimal solution for given constraints. It is also observed that the numerical values of the four shape parameters (viz., a, b, c and d) are very sensitive. For the given constraints, many combinations of design values to imaginary solution. To take care of the same, an additional penalty functions were imposed, to overlook the values which results in imaginary output of the shape function. The methodologies explained have some limitations especially in solar area calculation and structure modelling. There is a need to develop an all-encompassing methodology consisting of different models, which would be able carry out sizing and arrive at the more realistic optimal configuration fulfilling any given requirements with low cost, high payload capability, and least size and weight.

Figure 1 .

 1 Figure 1.Reference shape for the envelope[START_REF] Wang | A methodology for optimisation design and analysis of stratosphere airship[END_REF][START_REF] Wang | An Approach for Shape Optimization of Stratosphere Airships based on Multidisciplinary Design Optimization[END_REF]

Fig. 2

 2 Fig. 2 shows the optimized shape for minimum hoop stress, and minimum drag in comparison with reference shape. The comparison of optimized shape and reference shape for F comp listed in Eq. (17), is shown in Fig 3.

Figure 2 .Figure 3 .

 23 Figure 2. Comparison of profile for Min. CDV, Min. σ hoop with Reference shape

TABLE I :

 I Input Parameters

	Input Parameter	Value
	Design Altitude	20,000 m
	Maximum design speed, v	25 m/s
	Payload mass	1000 kg
	Power required by Payload	10 kW
	Power required by Control Systems	11 kW
	Ratio of C DV , total / C DV , env	2
	Propulsive efficiency	90 %
	Solar array efficiency	9 %
	Energy factor	1.2

TABLE II :

 II Key Output Parameters

	Parameter	Reference	Minimum	Minimum	Minimum
		Shape	C DV	σ hoop	F Comp
	Shape Parameter, a	7.447	1.5398	9.5719	9.2203
	Shape Parameter, b	2.072	2.8010	1.7511	1.6417
	Shape Parameter, c	9.010	6.7470	5.6779	5.9622
	Shape Parameter, d	7.981	2.9808	4.7935	4.4432
	Envelope Length (m)	194.0	208.47	175.109	175.004
	Envelope Area (m 2 )	23211	25153	23212	23280
	Envelope Vol. (m 3 )	234640	250010	249990	249990
	Envelope Dia. (m)	50.12	47.87	53.32	52.844
	Slenderness ratio	3.870	4.355	3.2839	3.3117
	Reynolds No. (10 6 )	30.03	32.27	27.11	27.09
	Envelope C DV	0.01965	0.0192	0.0206	0.206
	Static Pressure (Pa)	138.67	168.85	106.54	107.54
	Dyn. Pressure (Pa)	36.55	43.80	32.05	32.78
	Diff. Pressure (Pa)	15.07	16.197	13.605	13.60
	Total Pressure, (Pa)	190.30	228.85	152.20	153.92
	Hoop Stress (Pa)	4769.7	5477.7	4057.94	4066
	Total C DV	0.03930	0.0385	0.0413	0.0412
	Tot. power req. (kW)	149.48	152.28	161.80	161.49
	Tot. energy req. (kWh) 4593.8	4679.9	4972.3	4962.7
	Solar array area (m 2 )	6189.90	6305.84	6699.94	6686.96
	Solar Coverage ratio	0.2667	0.2507	0.289	0.2872
	% Improvement	----------	1.78	14.9	1.6
	compared to baseline

Proceedings of ICTACEM 2014 International Conference on Theoretical, Applied, Computational and Experimental Mechanics December 29-31, 2014, IIT Kharagpur, India


Neuroscience, labeled as « Sistine Chapel of science » by James G. Ballard, has been receiving a lot of public attention in France for the past thirty years. Since L'Homme neuronal (Neuronal Man) by JP Changeux [START_REF] Changeux | L'Homme neuronal[END_REF], numerous popular neuroscience essays have become best-sellers. As a matter of fact, the non-fiction best-seller of this autumn in France is also inspired by neuroscience. Neuroscience is nowadays a legitimate discourse in French society, from anticrime policies to mental health issues, from the intellectual field to the education field, from marketing to communication, and so on. People are often convinced of this legitimacy via popular science. Therefore, my object of study is : what is really transmitted through neuroscience popularization ?.

I have worked on popular neuroscience in several ways : studies on celebrated French authors such as Jean Pierre Changeux, on cultural go-betweens like publishers and journalists. This research resulted in a book published in 2014 [START_REF] Lemerle | Le singe, le gène et le neurone: du retour du biologisme en France[END_REF]. I am currently working on the reception in France on Paul D. MacLean's theory of the triune brain. But I'm also working on events and « live » popularization, and that will be my topic today.

In this research, I try to understand what is happening in the course of a science popularization process and, in a first part, I will introduce the hypothesis that one of the most common features of science popularization lies in its use of metaphors and analogies. I will also introduce some of the most used of them in a popular neuroscience event that I have been attending for two years, and some consequences of this fact in terms of public understanding of neuroscience.

However, these metaphors at the SdC are less numerous than one would expect. In a second part, I'll try to explain this surprisingly narrow range of metaphors by identifying several factors in their uses in popularization discourses.

The « Semaine du Cerveau »

First, a few words about the fieldwork. The « Semaine du Cerveau », which I will call SdC from now on, is the French edition of the « Brain Awareness Week » (BAW), launched in 1996 by the Dana Foundation in the US, as a campaign dedicated to advancing public awareness about the progress and benefits of brain research.

It was launched in France in 2000 and it is run by 700 volunteers from all the major French research institutes in neuroscience. It is held every March. In 2016, it involved 34 French towns and attracted 35 000 people (more than 8 000 people in Paris only).

It consists in open houses at neuroscience labs, lectures on brain-related topics, exhibitions about the brain in museums and unversities, displays at libraries, movies and debates in theatres and community centers, classroom workshops… It provides a rich material to study the ways neuroscience is popularized. The SdC has another interest, which is being an event entirely managed by scientists and scientific institutes staff, without any cultural go-betweens. The core of the SdC initiative lies in the fact that it is thought as an encounter between researchers and the public.

Popularizing implies using metaphors

What SdC popularizers do I have counted more than 250 events organized by the SdC in the Paris region since 2008, dealing with more than 300 topics. Perception is the most frequent subject (the five senses, the inner ear, and s.o.), followed by general presentations on the history of neurosciences, on memory and aging, on sleep, on neurodegenerative diseases, and other medical conditions (strokes, mental health...).

When you attend the SdC or talk with the researchers involved in it, you may find four or five main ways of popularizing. I will develop only one of them : using specific rhetorical techniques, especially analogies, metaphors, or, according to the people I spoke to, « parallels » or « images ».

Why do metaphors seem so important to produce narratives on neuroscience topic in extra-scientific contexts ? This idea has already been formulated more than 20 years ago in various studies on popular science [START_REF] Mcrae | The Literature of Science : Perspectives on Popular Scientific Writing[END_REF]. In his book about the writing of popular science, Yves Jeanneret stressed that metaphors are useful to scientific popularizers because they allow the public to grasp scientific concepts thanks to ordinary ways of talking [START_REF] Jeanneret | Écrire la science: formes et enjeux de la vulgarisation[END_REF]. But he also stressed that metaphors are in fact surely necessary because of the way our mind operates. Metaphors might be a kind of natural way of thinking, according to George Lakoff and Mark Johnson. Then they might be one of the best way to convey messages.

The most influential framework for the study of metaphor is currently provided by Lakoff and Johnson's conceptual metaphor theory (or the cognitive theory of metaphor). I won't detail here this theory, which has been mentioned a lot of times since yesterday. I'd like just to stress that a lot of the metaphors used at the SdC can be analysed as combinations of primary metaphors which can make pretty sense to a non-specialist audience.

The SdC metaphors

So, what kind of metaphors are used by SdC popularizers and what does it tell us about the way scientific discourses make their way to public spheres ? I'm well aware of the fact that I'm going to tell you about metaphors in French, and that may be an hurdle during a presentation in English. Fortunately, all the metaphors that I listed have their adequate counterparts in English.

Among the most recurring metaphors, we have :

brain as a black box or a fortress which has to be opened ; that is to say : full of secrets that must be discovered. We have here a rather traditionnal rethoric in popular science : the «wonder of science ». The brain is often introduced as the most mysterious thing in the world.

nervous impulses described as flowing electricity and the like : axons and dendrites as electric wires, myelin as insulating material which makes easier electric circulation.

brain organization as neural highways and nervous impulses circulating in these roads, following signs, etc..

at last, the famous computer metaphor, although not the most frequent and whose expression can vary : brain as a super computer, analysing data taken from the environnement in order to proceed thoughts and actions ; brain as a global positioning system...

What are the main conceptual metaphors at stake ?

The metaphors that I just listed can be understood via several conceptual metaphors identified by Lakoff and Johnson (Lakoff and Johnson 1999, 45 et sq.) First, the ORGANIZATION IS PHYSICAL STRUCTURE metaphor. The concept that is meant (the target domain) is « relationships unifying the brain ». It is expressed with the source domain of physical structure such as a building (fortress, black box) or a road.

In the case of the « fortress », there is another conceptual metaphor that can be identified : UNDERSTANDING IS GRASPING, but in a specific way, stressing on the difficulty to reach what is to be understood. This leads to another primary metaphor : KNOWING IS SEEING. We can guess it from the fortress metaphor : once you break in, you will see the truth. But this also the case for the « black box » metaphor : we have to open the box, light up what is plunged into darkness and so we'll have access to the secrets of thought, the emergence of thought.

Another dimension may be implied by this metaphor : « black box », in French and in English as well, means also a flight recorder in an aircraft. This may be analysed as a complex mapping with two conceptual metaphors : THINKING IS MOVING (which can illustrated with expressions such as « to jump to conclusion ») and THE MIND IS A MACHINE. Here, the brain is referred to as a device regulating the course of human thinking (and the rest). This is consistent with another metaphors used during the SdC : the metaphors of the brain-computer and of the brain-GPS.

The social and cultural impact of metaphors used in popular science

Why is it so important to pay attention to these metaphors ? In my opinion, because they can have a great impact on basic, extra-scientific narratives concerning the brain. Reuse of these metaphors can be conventionnal or more creative, but it is sure that numerous entailments of these metaphors can be then found in the social world.

Latent meanings of a metaphor can be unfolded in order to convey interpretations going beyond the original purpose. Think of the computer metaphor, which can be developped according to ideas of self-empowerment : the exploitation of all the potentialities of the machine that is in our skulls, the conviction that we only use 10% of our brain, that we can program or reprogram our brain, and the like.

I can also mention the highway metaphor as it is interpreted in by a famous French personnal development coach : talking of « neuronal highway », she explains that « the more a road is taken, the more we are likely to take it », in order to suggest that changing behavior is very hard.

My hypothesis is that these metaphors set a large part of the layman understanding of neuroscience and of the basic principles of brain operations. But on the other hand, the meaning of these metaphors is not fixed and may vary according to specific contexts, or, to speak with Hans Robert Jauss's words, according to the « horizon of expectations » (Erwartungshorizont) of the public.

Social determinations of the uses of metaphors

The SdC popularizers are aware of the risks inherent in the use of metaphors. They are in fact rather cautious when it comes to metaphors. This led me to think about the existence of constraints on the use of metaphors among the scientists involved in the SdC. Four types of influences can be mentioned :

The sociocultural contexts

Cultural habits have beyond any doubt an influence on the popularizers' choice and use of metaphors. As many historians showed us [START_REF] Hadot | Le voile d'Isis: essai sur l'histoire de l'idée de nature[END_REF]) [START_REF] Eamon | Science and the Secrets of Nature : Books of Secrets in Medieval and Early Modern Culture[END_REF] [START_REF] Pesic | Labyrinth : A Search for the Hidden Meaning of Science[END_REF], the idea of nature as a hidden reality which has to be unveiled and deciphered can be found from Antiquity to present-day representations.

Nowadays, these representations of nature can survive through the cultural clichés used and reused by the media, to which neuroscientists and popularizers are exposed as much as ourselves. For instance, using the « black box » metaphor is something very common in the French newsmagazines.

The scientific context

Kövecses writes that « if there are universal metaphors as « underlying » layer of cultural experience, some other metaphors may also be culture-specific. » Among others, « the subculture of science and its various subgroups provide an interesting example of how metaphorical source domains change over time. This is one of the most obvious cases of metaphor variation. » (Kövecses 2005). As a matter of fact, Cornelius Brock, in his study on the metaphors used in neuroscience, notes that « the brain appears to be an unstable organ that has been compared to a wide and variable range of objects » [START_REF] Borck | Toys Are Us. Models and Metaphors in in Brain Research[END_REF] This instability could explain the gap between the media and the neuroscience field when it comes to brain metaphors. The media can keep on using metaphors that have proven inaccurate according to neuroscience. In our case, the popularizers of the SdC choose their metaphors in relation not in relation with the media, but in relation with the state of the art in neuroscience. Their terminology depends on what is considered legitimate in this specific field.

There can be of course common ground between media discourse and popularizers' discourse. For instance, the metaphors of the black box and the fortress keep on working, not only because of a general cultural context inherited from ancient past, but also because this ancient past is relevant to the history of brain science, in so far as this history, according to Nikolas Rose and Joelle Abi-Rached, is an history of the will of rendering the invisible visible or, in other terms, an history of the formation of a certain clinical gaze which strives to make visual the interior world of the human mind. (Rose and Abi-Rached 2013, see chap. 2) In the majority of cases, SdC popularizers pay carefully attention to the scientific plausibility and the legitimacy of the metaphors, images, parallels, analogies, that they use.

What kind of scientifically legitimate metaphors are at the popularizers' disposal ? According to Richard Boyd, you have basically two kinds of metaphors : pedagogical metaphors, which play a role in the teaching of explication of theories which already admit of nonmetaphorical formulations. (Boyd 1993, 485) And « theory-constitutive metaphors » which are used by scientists to express « theoretical claims for which no adequate literal paraphrase is known. » (id., 486). We can find them in young disciplines, for instance molecular biology in the first half of the 20 th century [START_REF] Keller | Expliquer la vie: modèles, métaphores et machines en biologie du développement[END_REF] or in computer science and cognitive psychology, from which Boyd quotes, among others, the example of the brain being termed as « a sort of « computer » » (Boyd 1993, 486) This computer metaphor constitutes here an interesting case. At first, it is a theoryconstitutive metaphor, with a story closely related to the development of neuroscience. As Cornelius Borck showed it, the computer has been « the most powerful brain model of the twentieth century », since Alan Turing's works and the interdisciplinary evolution of cybernetics after the end of World War II [START_REF] Borck | Toys Are Us. Models and Metaphors in in Brain Research[END_REF]. This comparison then vanished by the end of the 1990's, to the benefit of other images such as neural networks or plasticity. This is why the computer metaphor is less and less used by the SdC popularizers, whereas it is still very popular in the media.

Another striking example is the highway metaphor that I mentionned before. This metaphor can be considered as a theory-constitutive one, which can found in recent articles in The Scientific American and Science, related to the mapping of the circuit of the brain, which have been described as « a grid-like pattern of fibers crossing at right angles », « superhighways, (…) analog of the streets and avenues in New York City » (Mitra 2012) [START_REF] Wedeen | The Geometric Structure of the Brain Fiber Pathways[END_REF] The popularizers' skills, capitals and positions Beyond sociocultural and scientific contexts, the popularizers' performances depend also on more personal parameters such as skills, training and biographical trajectories, which make popularizers more or less comfortable with the use of metaphors.

Researchers usually want to be scientifically accurate and are rather sober in terms of metaphors. All of them use metaphors, without necessarily theorizing about it. They cling to the few controlled metaphors that I already mentioned. Of course, the longer they have popularized neuroscience, the better they can talk about popularization and its constraints.

Scientific mediators have a professional point of view on science popularization. Sometimes their lack of commitment in research may drive them to be less cautious in their choice of terminology, because their main purpose is to interest their audience. A less accurate message is not a real problem. Flashy metaphors are welcome. They often are more innovative and may sometimes argue with scientists who may find theirs ideas a bit weird : using toys, models, plasticine, games and so on.

Another hypothesis is that the social position of the popularizers may also affect the way they engage in their activity and thus their recourse to metaphors. Depending on whether or not you are a researcher, whether or not you are at the beginning of your career, whether or not you are dominant, you may be more or less audacious, your metaphor may be more or less commonplace. The more you will be close to the research, the more you will tend to use accurate and therefore scarce metaphors. The more you will be a respected member of the scientific establishment, the less you will tend toward extravaganza.

Of course, this is a very general outline, and it has to be replaced in the context of a public event of science popularization, which deals above all with the public image of science.

An implicit representation of the audience

A final aspect of the question is the representation of the public among science popularizers.

The full understanding of the metaphors and analogies used by the SdC popularizers often requires some prior conceptual knowledge. If you compare the brain to a computer, you expect people to roughly know how a computer works. This is what Hugh Petrie and Rebecca Oshlag call interactive metaphors, in contrast to mere comparative ones [START_REF] Petrie | Metaphor and Learning[END_REF].

Hence, we can talk of implicit representations of the public among the popularizers. These implicit representations can also be guessed via the use of the black box-or the fortressmetaphor. This kind of metaphor is likely to work for a certain kind of public that can share the same interest and curiosity for the brain secrets.

Sociological studies have established that, in France, this interest and curiosity spread mainly in certain social groups, mostly upper and middle class, mostly medical and social workers, teachers, human resources manager, etc. These results have been confirmed by a survey that I have made on the SdC audience in 2016. By saying this, I do not mean that popular neuroscience is only for educated people, but, in a more Bourdieusian approach, that this kind of science popularization is more likely to attract people with high cultural capital, and that this reality is implicitly taken into account by the science popularizers, who, by choosing their style of popularization, also choose or anticipate, somehow, a certain kind of audience.

Conclusion

If, according to Andreas Musolff, « Media discourse continuously makes creative and eclectic use of science terminology -often to the point of contradicting the views of scientific experts on the subject matter in question. » [START_REF] Musolff | Popular Science Concepts and Their Use in Creative Metaphors in Media[END_REF], this is, in my opinion, mainly due to the fact that the media discourses are mostly based on popular science, rather on scientific litterature. Although they hardly could do otherwise, this can lead to more uncontrolled entailments than scientific popularization may have imagined at first. Anyway, it makes the study of the underlying metaphors in popular science all the more necessary.

We have seen that the importance of metaphors is due to cognitive reasons and that the content and significance of the metaphors in question are basically sociocultural. From that, one can conclude that a narratology of science popularization could draw a great benefit from the study of the social conditions of formation and use of metaphors.

  the Uses of Metaphors in Popular Neurosciences Sébastien Lemerle (Univ. Paris Ouest / Cresppa-Csu)


Beyond Neuronal Man: Interdisciplinary Research on the Social Uses of Neuroscience in France

Sébastien Lemerle

Université Paris Ouest Nanterre La Défense Centre de recherches sociologiques et politiques de Paris / CSU

The study of the social uses of neuroscience in France is a part of a larger story, the history of the relations between neuroscience and social science, which began forty years ago.

I shall then outline the main steps of this history, until the late 2000's. Then I shall go back to the study of the social uses of neuroscience, by presenting a modest experience that we have been conducting at the MSH PN since 2010. My presentation will develop three points.

Calls for collaboration end up in philosophical soliloquies

In 1972, two social scientists, named Edgar Morin and Massimo Piatelli-Palmarini, organized, with the help of famous biologists such as Jacques Monod, a symposium entitled « L'unité de l'homme », which aimed to build bridges between social science and biology. Among the contributors, we can mention people like David Premack, Paul D. MacLean, Humberto Maturana or Jean-Pierre Changeux. One of the three volumes of the proceedings of the symposium 1 has been entirely dedicated to the brain, although rather in a cognitivist way than really neuroscientific. This sociological interest for neuroscience came from mavericks such as Morin. All of this must be put in the context of great discussions initiated by Foucault at the end of Les mots et les choses, concerning « the end of man » or the end of the absolute, universal notion of man. Human nature was a concept rather disqualified in the French intellectual avant-garde at that time. Bourdieu and Passeron, in their 1970 Reproduction, also denied to biology any influence on social phenomena. And one can say that some people, as Morin, tried to revive this notion in order to contest the supremacy of this avant-garde connected to critical structuralism, but also to Marxism.

Neuroscience really began to draw public attention in France in 1983, thanks to a book written by a prominent neuroscientist, Jean-Pierre Changeux. This book, L'homme neuronal (Neuronal man), inaugurated a long serie of neuroscientific best-sellers in France, by Jean-Didier Vincent Oliver Sacks or Antonio Damasio. Neuroscience became trendy, especially in the intellectual and journalistic fields.

Jean-Pierre Changeux has been one the most brilliant figures celebrated at that time. He perfectly summed up a rather popular opinion in the 1990's that «fierce ideological oppositions have contributed to the disastrous divide between the reflections on brain and human and social science. These three last decades have been dominated in France by three systems of analysis which have neglected too much our brain : structuralism (…), marxism (…) and psychoanalysis. »2 But, paradoxically, at the same time, he did not pay much attention to social scientists and he preferred debating with famous philosophers, such as Paul Ricoeur in a book published in 19983 .

In my opinion, the general tonality of this two works, L'unité de l'homme and Neuronal Man, paved the way for discussion for at least two decades in a very specific manner. I mean that discussion focused on great theoretical propositions, leaning towards anthropology and philosophy, which blurred what sociologists could really do with or think of neuroscience.

At the same time, neuroscience established its legitimacy by gaining more and more importance in the French cognitive science field, at the expense of computer science and human and social sciences.

As a result, neuroscience may have appeared engaged in a kind of imperialist momentum. One could even speak of a kind of general mistrust, all the more so neuroscience, backed by the public authorities, proclaimed as scientific avant-garde, was regularly evoked to delegitimize critical thinking, from Marxism to Foucault or Derrida (this is a gross outline, forgive me). Anyway, calls for collaboration fell flat.

The growing interest of social scientists in two specific fields

French sociologists began in fact to cope with neuroscience only in the late 1990's. Bourdieu alluded to the possible links between his habitus theory and neuroscience in his 1997 book, Méditations pascaliennes. Others, wanting to promote a « cognitive sociology » inspired by the theory of rational individual of Raymond Boudon, tried to take into account some neurocognitive approaches, before dismissing them.

At the same time, Brigitte Chamak, a sociologist who is also a trained neuroscientist, published an article on neuro and cognitive science history in France, but in Social Studies of Science, which is not, as you know, a French journal.

In fact, more and more people thought that neuroscience deserved a real discussion.ButBrigitte Chamak's work has been a kind of exception. When they accepted to talk of or with neuroscience, sociologists rather adopted the same great, large, anthropological, epistemological questions that I evoked before.

During the 2000's, more and more books and articles have been indeed produced about the relations between life science and social science, about social cognition, about the debate between naturalism and constructivism, about the neuro-turn of social sciences and so on4 . They mainly dealt with theoretical issues, as a heritage of the history that I previously described, and one can see that as the sign of a sort of domination of neuroscientists, who set the terms of the discussion.

On the other hand, we can mention, at the same period, a real attention for neuroscientific approach among sociologists working on autism, psychiatry and mental health, such as Brigitte Chamak or Alain Ehrenberg, who wrote an important article about the « cerebral subject » in 20045 . Thus, the scene is set until the late 2000's. A symposium held in 2010 in the EHESS on the « human sciences in a neuronal era » was typical of these two orientations: one half of the symposium was devoted to an overview of the spreading of the prefix neuro in several human and social sciences (linguistics, philosophy, history, economics) (it resulted in a special issue in the Revue after the publication of a report on the learning to read, which suggested that teachers be trained in neuroscience, along with other knowledges. Gilles de Robien's interpretation of the report strongly opposed "real science", that is to say neuroscience in De Robien's mind, and "so-called science", that is to say methods inspired by education science. De Robien's interpretation of course created another controversy.

-In 2009, several seminars on the uses of neuroscience in public policy were held at the Centre d'analyse stratégique, connected to the Prime Minister administration. The topics were the uses of neuroscience in legal proceedings, public health prevention, and so on6 .

All of this made some of us want to go beyond mere epistemological debates. This is my third point. We wanted to have a clearer vision of the social implications of the life science, outside the realm already investigated of mental health and to get rid, at least momentarily, of epistemological debates. We wanted to see if people were concerned in the various uses of biology in everyday life, at school, in the working field, in courts, and so on. In order to do that, we set up a workshop entitled "The social uses of brain science, in May 2012. This was a rather successful workshop, which ended with people strongly debating. We had presentations from several colleagues from human and social science, history, criminology, who met neuroscience in their own research, and also from a neuroscientist, Catherine Vidal, and from a sociomedical scientist, Rebecca Jordan Young, from Barnard College (New York).

We tried to keep this multidisciplinary orientation in two other workshops (the later was held in November 24), although we have not yet succeeded in turning it into a real interdisciplinary one. One of our goals for the next workshop, probably in 2016, would be to invite more neuroscientists. Moreover, a special issue "Biology and sociology" is to be published in the European Journal of Social Science in 2016, with some of the contributions of the workshops, for instance Rebecca Jordan Young on neuroscience and gender, Patrice Pinell on psychiatry, Stanislas Morel on neuroeducation.

What kind of results can we get from these three workshops, which gathered twenty colleagues coming from neuroscience, sociology, philosophy, anthropology, education science or history ? First, as far as we know, there are few works on the social impacts of neuroscience in France, except in the mental health field. Thus, Brigitte Chamak recently conducted a project granted by the French National Research Agency (ANR) : "The social life of neuroscience", focused on autism and patients organizations and which resulted in a book this year : Neuroscience et société. Several specialists from social science and life science collaborated on the book, including Nikolas Rose and Joelle Abi-Rached.

Second, the other kinds of works where neuroscience is studied, are large investigations, where neuroscience is just one aspect of the whole thing.

Moreover, the topics of these works are few. One can mention the issue of youth and more specifically the issue of education and school, especially school failures. A quarter of the presentations in all our workshops dealt with these topics.

Another important topic can be mentioned: gender. There is at the CNRS an interdisciplinary thematic network on gender, including social scientists and life scientists. I really think that childhood and youth are topics more and more legitimate for interdisciplinary research and you can also consider that this topic has strong connections to the field of mental health. The best example of that is the recent launching of a large-scale study, the "Elfe" project, involving researchers from many different backgrounds, including neuroscience and social science, who will follow the lives of 18 000 children born in 2011, from the day they were born up to their 20th birthday. They will be exploring every aspect of these children's lives, in order to measure the impact of their family circumstances, living conditions and the environment on their physical and psychological development, health and socialization. This "Elfe" project is managed by a joint unit, which was set up under an agreement between the National Institute for Demographic Third, when they exist, studies on the social uses of neuroscience are conducted by social scientists alone, and often by social scientists who are not trained in biology, except few people like Brigitte Chamak. This can be a real difficulty. Since you can expect that people working on China, speak Chinese, you can expect from people who study social applications of neuroscience, to have a kind of biological training. Unfortunately we do not have many sociologists of that kind. We therefore need interdisciplinary team, involving biologists and social scientists. I look forward to having news from this Elfe project. An epidemiologist at INSERM (Marie-Aline Charles), is the director of this joint unit. She is assisted by a deputy director (Bertrand Geay), Professor of Education at the University of Picardy. Around thirty people currently work within the Elfe unit, including Sandrine Garcia, one of the colleagues who came to our workshops. Indeed cooperation does not always go without saying. For instance, in the education field, there are still more controversies than collaboration between very pervasive neuroscientists who would like to convince everyone that teaching is a science and education scientists who strike back by showing that teaching is a social practice.

Finally, for the time being, we mostly find, on one hand, neuroscientific projects ignoring social scientists' works, even when they study questions with obvious social dimensions. And, on the other hand, we have critical studies by social scientists.

As a conclusion, I would say that the situation of interdisciplinary research is yet far from being clear. When programs exist, what role for social sciences in them ? Supplement of soul or real contributor ? But the issue of interdisciplinary research is also linked to the other issue that I evoked, concerning the social uses of neuroscience. I am convinced that it is an indispensable aspect of interdisciplinary research. We need neuroscientists or sociologists with neuroscientific skills to study these social uses, as well as neuroscientists need social scientists to fulfill this kind of work. The goal could be to get the indispensable reflexivity which will enable us to, I hope, more fruitful collaborations.

Thank you for your attention.

  d'histoire en sciences humaines in 2011) ; the other half was devoted to the uses of neuroscience in the realm of psychiatry and psychology, for instance, how neuroscience can be used in the treatment of hyperactivity or of obsessivecompulsive disorders. This kind of investigation could have led to other social uses of neuroscience, but for a while most of the discussions seemed to remain theoretical. If you were sympathetic with naturalistic approach, you could talk epistemology. If you were in a critical and anti-reductionist mood, you could work to reveal the flaws of neurotheories of social phenomena. But few investigations dealt with other kind of concrete situations, whereas, at the same time, new topics appeared which began to catch the eye of journalists and various specialists. I will mention a few of them: -In 2006, a report of the National Institute of Health and Medical Research (INSERM, Institut national de la santé et de la recherche médicale) on the « conduct disorders in children and teenagers », aimed to provide a set of tools in order to identify problematic individuals among very young children and aroused a huge controversy, -In 2006, Minister of Education, Gilles de Robien had a quarrel with teachers

3

  Trying to go beyond Neuronal ManIn 2010, the historian Carole Reynaud Paligot and I began to coordinate at the Maison des Sciences de l'Homme Paris Nord a research topic, that we called « The biologization of the social : discourses and practices ». Carole has been working for years about French racial ideologies and politics in 19th and early 20th century France. I have worked on biologism in contemporary France, especially among intellectuals and cultural industries.

  Studies (INED), the National Institute for Health and Medical Research (INSERM) and the French National Blood Service (EFS).

L'unitédel'homme,3vol.Paris,Seuil,1974.

Jean-PierreChangeux,Raisonetplaisir,Paris,OdileJacob,1994.

Jean-PierreChangeux,PaulRicoeur,Cequinousfaitpenser,Paris,OdileJacob,1998.

See Michel de Fornel and Cyril Lemieux (dir.), Naturalisme versus constructivisme, Paris, EHESS, 2008 ; Bernard Lahire and Claude Rosental (dir.), La Cognition au prisme des sciences sociales, Éd. des Archivescontemporaines, 2008 ; Revuefrançaisedesociologie,décembre2010,etc.

AlainEhrenberg,«Lesujetcérébral»,Esprit,,novembre2004,p.130-155.

A « note de veille » thus indicated that the neuroscience project could not be anymore summed up in a mere brain science project, as neuroscience had now numerous impacts in various social spaces, arousing false hopes and fantasies.