Wanda Zhao
email: wanda.zhao@ls2n.fr

Anatol Pashkevich
email: anatol.pashkevich@imt-atlantique.fr

Damien Chablat
email: damien.chablat@cnrs.fr

Alexandr Klimchik
email: a.klimchik@innopolis.ru

Mechanics of compliant serial manipulator composed of dual-triangle segments

Keywords: component, compliant manipulator, stiffness analysis, equilibrium, robot buckling, redundancy

published or not. The documents may come

I. INTRODUCTION

Currently, compliant serial manipulators are used more and more in many applications (such as inspection in constraint environment, medical fields etc.), because of their sophisticated motions and low weights. Conventional compliant manipulators are usually composed of rigid links and compliant actuators, like hinges, axles, or bearings. However, there is a lot of research in this area dealing with some new mechanical structures [1] [START_REF] Albu-Schaffer | Soft robotics[END_REF][3] [START_REF] Howell | Compliant Mechanisms[END_REF], which achieve compliant motions through tensegrity mechanisms. And one of them will be studied here.

In general, the robotic manipulators are usually classified into three types [START_REF] Robinson | Continuum robots -a state of the art[END_REF], conventional discrete, serpentine, and continuum robots. The first one is made of traditional rigid components. The second one uses discrete joints but combine very short rigid links with large density joints, which produce smooth curves and make the robot similar to a snake or elephant trunk [START_REF] Chirikjian | Kinematically optimal hyperredundant manipulator configurations[END_REF]. While the continuum robots do not contain any rigid links or joints, they are very smooth and soft, bending continuously when working [START_REF] Yang | Synthesis and analysis of a flexible elephant trunk robot[END_REF]. Many researchers have done studies on serpentine and continuum robots in recent years, designed flexible mechanisms for many Manuscript received Sep, 2020; revised Sep 25, 2020; accepted Oct 9, 2020.

applications [8]. However, the pure soft continuum robot received little attention, as its small output force and design difficulty. Thus, combining rigid and elastic or soft components becomes a popular practice in designing a robot manipulator. The typical earlier hyper-redundant robot designs and implementations can be date back to the 1970s [START_REF] Anderson | Tensor arm manipulator[END_REF], which includes a series of plates interconnected by universal joints and elastic control components for pivotable action to one another. [START_REF] Gravagne | Kinematic transformations for remotely-actuated planar continuum robots[END_REF] [START_REF] Cieślak | Elephant trunk type elastic manipulator -a tool for bulk and liquid materials transportation[END_REF] [START_REF] Hutchinson | P o s t b u c k l i nTgheory[END_REF] Nowadays, a very promising trend in designing compliant robots is using a series of similar segments based on various tensegrity mechanisms, which are composed in an equilibrium of compressive elements and tensile elements (cables or springs) [START_REF] Skelton | Tensegrity systems[END_REF] [START_REF] Moored | Analytical predictions, optimization, and design of a tensegritybased artificial pectoral fin[END_REF]. Some kinds of tensegrity mechanisms have been already studied carefully. Such as [START_REF] Arsenault | Kinematic, static and dynamic analysis of a planar 2-DOF tensegrity mechanism[END_REF], the authors dealt with the mechanism composed of two springs and two lengthchangeable bars. They analyzed the mechanism stiffness using the energy method, demonstrated that the mechanism stiffness always decreasing under external loading with the actuators locked, which may lead to "buckling". And in [START_REF] Furet | Kinematic Analysis of Planar Tensegrity 2-X Manipulators[END_REF] [START_REF] Furet | Kinematic Analysis of Planar Tensegrity 2-X Manipulators[END_REF], the cable-driven X-shape tensegrity structures were considered, the authors investigated the influence of cable lengths on the mechanism equilibrium configurations, which may be both stable and unstable. The relevant analysis of the equilibrium configurations stability and singularity can be seen in [START_REF] Wenger | Kinetostatic analysis and solution classification of a class of planar tensegrity mechanisms[END_REF].

A new type of compliant tensegrity mechanism was proposed in our previous papers [START_REF] Zhao | Stiffness Analysis of a New Tensegrity Mechanism based on Planar Dual-triangles[END_REF] [START_REF] Zhao | The Stability and Stiffness Analysis of a Dual-Triangle Planar Rotation Mechanism[END_REF]. It is composed of two rigid triangle parts, which are connected by a passive joint in the center and two elastic edges on each side with controllable preload. The stiffness analysis of a basic dual-triangle was carried on, and the stable condition of the equilibrium was obtained. The results also showed that there may be a buckling phenomenon. Usually, while designing a robot, researchers always try to avoid buckling, but such behavior can make improvements in some fields [START_REF] Yamada | A compact jumping robot utilizing snap-through buckling with bend and twist[END_REF]. So this phenomenon must be taken into account. In this paper, we study a compliant serial manipulator composed of the dualtriangle segments mentioned above, concentrate on the equilibrium configurations and their transformations under the loading, which may be either continuous or sporadic that leading to buckling phenomenon. Both loaded and unloaded stiffness model of this manipulator were analyzed. The simulation of the manipulator behavior after buckling was obtained, which provides a good base of the design and relevant control algorisms of such manipulator

II. MECHANICS OF DUAL-TRIANGLE MECHANISM

Let us consider first a single segment of the compliant serial manipulator. It consists of two rigid triangles connected by a passive joint whose rotation is constrained by two linear springs as shown in Fig. 1. It is assumed that the mechanism geometry is described by the triangle parameters (a1, b1) and (a2, b2), and the mechanism shape is defined by the central angle, which is adjusted through two control inputs influencing on the springs L1 and L2. Let us denote the spring lengths in the non-stress state as 0 1 L and 0 2 L ,and the spring stiffness coefficients k1 and k2.

To find the mechanism configuration angle q corresponding to the given control inputs 0 1 L and 0 2 L , let us derive first the static equilibrium equation. From Hook's law, the forces generated by the springs are 0 ( )

i i i i F k L L   (i =1, 2)
, where L1 and L2 are the spring lengths |AD|, |BC|. These values can be computed using the formulas

2 2 1 2 1 2 ( ) 2 cos( ) i i i L c c c c      (i=1,
2). Here   . The torques M1=F1·h1, M1=F2·h2 in the passive joint O can be computed from the geometry, so we can get

2 2 i i i c a b   (i=1,
0 1 1 1 1 1 1 2 1 0 2 2 2 2 2 1 2 2 ( ) (1 ( )) sin( ) ( ) (1 ( )) sin( ) M q k L L c c M q k L L c c            
where the difference in signs is caused by the different direction of the torques generated by the forces F1, F2.

Further, taking into account the external torque Mext applied to the moving platform, the static equilibrium equation for the considered mechanism can be written as M1(q)+ M2(q)+Mext =0.

Let us now evaluate the stability of the mechanism under consideration. In general, this property highly depends on the equilibrium configuration defined by the angle q, which satisfies the equilibrium equation M(q)+ Mext =0. As follows from the relevant analysis, the function M(q) can be either monotonic or non-monotonic one, so the single-segment mechanism may have multiple stable and unstable equilibriums, which are studied in detail [START_REF] Zhao | Stiffness Analysis of a New Tensegrity Mechanism based on Planar Dual-triangles[END_REF] [START_REF] Zhao | The Stability and Stiffness Analysis of a Dual-Triangle Planar Rotation Mechanism[END_REF]. As Fig. 2 shows, the torque-angle curves M(q) that can be either monotonic or two-model one, the considered stability condition can be simplified and reduced to the derivative sign verification at the zero point, i.e.

  0 0 q M q    (2)
which is easy to verify in practice. It represents the mechanism equivalent rotational stiffness for unloaded configuration with q=0.

Let us also consider in detail the symmetrical case, for which a1=a2=a, b1=b2=b, k1=k2, 0 i L = 0 L . Then as follows from the mechanism geometry, to distinguish the monotonic and non-monotonic cases presented in Fig. 2, we can omit some indices and present the torque-angle relationship as well as the stiffness expression in more compact forms:

  0 12 1 0 12 1 2 2 2 cos sin cos( 2)s 2 cos cos cos c in( 2) ( ) ( 2 ) s ) o ( 2 M q ck c q L q M ck c q q L q                  (3)
it is also necessary to compute M'(q) for unloaded equilibrium configuration q=0, that let us obtain the condition of the torque-angle curve monotonicity:

  0 2 2 1 ( ) L b a b   
for the further analysis.

III. MECHANICS OF SERIAL MANIPULATOR

A. Manipulator Geometry and Kinematics

Let us consider a manipulator composed of three similar segments connected in series as shown in Fig. 3, where the left hand-side is fixed and the initial configuration is a "straight" one (q1=q2=q3=0). This configuration is achieved by applying equal control inputs to all the mechanism segments. For this manipulator, it is necessary to investigate the influence of the external force Fe=(Fx, Fy), which causes the endeffector displacements to a new equilibrium location ( , ) ( 6, )

T T x y x y b    
, which corresponds to the nonzero configuration variables (q1, q2, q3). It is also assumed here the external torque Mext applied to the endeffector is equal to zero. It can be easily proved from the geometry analysis that the configuration angles satisfy the following direct kinematic equations 2 2 2 2

x b bC bC bC y bS bS bS

       (4)
where

  123 1 2 3 cos C q q q    ,   123 1 2 3 sin S q q q    ,   12 1 2 cos C q q   ,   12 1 2 sin S q q   , 1 1 cos C q  , 1 1 sin S q 
. These two equations include three unknown variables, and it allows us to compute two of them if the third one was known. For instance, if the angle 1 q is

L L  ( 0 0 q  ).
assumed to be known, the rest two angles 2 q , 3 q can be computed from the classical inverse kinematics of the two-link manipulator as follows  

3 3 3 3 1 2 1 1 3 atan 2 atan( ) atan( ) 2 2 q S C bS y bS q q x b bC b bC         (5)
where

    2 2 2 2 3 1 1 2 2 5 4 C x b bC y bS b b           , 2 3 3 1 S C   
. The latter expressions provide two groups of possible solutions, which correspond to the positive /negative configuration angles 3 0 q  and 3 0 q  . To find a stable manipulator configuration under the loading, let us apply the energy method. It is clear that the end-effector displacement caused by the external loading leads to the deflections of mechanism springs, which allows us to compute the manipulator energy as

  3 2 2 0 1 1 1 2 ij ij i j E k L L      (6)
where ij L and o ij L are the spring lengths in current and initial (unextended) states respectively. The above energy can be expressed via one of the three variables q1, q2 or q3.

Assuming that variable q1 is chosen as an independent one, the desired stable configurations can be found by computing local minima of the energy function

1 1 ( min q E q  (7)
Examples of such energy curves 1 ( ) E q for several typical cases are presented in Fig. 4.

B. Manipulator Stiffness Behavior

An alternative way to compute the configuration angles q1, q2, q3 at the equilibrium state is based on the torque equation Me(q1)=0, which is implicitly used in the energy method. The latter is illustrated by combined plots of the energy-torque curves computed for the initial "straight" configuration presented in Fig. 5, which shows that the max/min of the energy E(q1) correspond to zeros of the torque Me(q1)=0. Further, to find the external forces corresponding to this end-point location, it is necessary to use the force-torque equilibrium equation 0

M J F T q   (8)
where M=(Mq1, Mq2, Mq3) T , F=(Fx, Fy, Me) T . They denote the internal torques Mq1, Mq2 and Mq3 in all manipulator segments and the force/torque at the end-point. In this equation, the internal torques can be computed using the previously derived expression from section II, 2 2 0 2 ( )sin sin(0.5 ) ; 1,2,3

qi i i M k b a q bL q i         (9)
and the Jacobian matrix Jq can be computed using the standard technique for the three-link manipulator presented as follows bS bS bS bS bS bS bC bC bC bC bC bC

                  J ( 10
)
where S and C with corresponding indices have the same meaning as in [START_REF] Howell | Compliant Mechanisms[END_REF]. Assuming that the Jacobian is nonsingular (i.e. the loaded manipulator is already out of the straight configuration), the external force/torque can be expressed directly as

T q    F J M
, where the transport inverse matrix -T q J can be computed analytically. Then we can get the following expression

1 12 1 12 1 12 1 12 1 2 2 3 23 3 2 23 3 1 2 2 q x y q e q M F C C C C F S S S S M bS bS bS bS bS bS M M                                  (11)
The latter allows us to rewrite the system of the equilibrium equation (4) in the following extended form    

3 1 23 3 2 2 23 q3 2 2 0 2 2 0 2 0 q q b bC bC bC x bS bS bS y S M S S M S S M                    (12)
whose solution (q1, q2, q3) may correspond to either stable or unstable equilibriums of the manipulator configuration. Then, using expressions Fx (q1, q2, q3) and Fy (q1, q2, q3) obtained from [START_REF] Cieślak | Elephant trunk type elastic manipulator -a tool for bulk and liquid materials transportation[END_REF], one can get the external loading (Fx , Fy) corresponding to the end-effector position (x, y), which finally allows us to generate the desired forcedeflection curves. Examples of such curves for several case studies are presented in Fig. 6, where it is assumed that under the loading the manipulator moves along with x-axis, i.e. var x   , 0 y   . As follows from this figure, in general cases (Fig. 6a), the force-deflection curves are quasi-linear, but some of them may do not pass through the zero point. The latter means that the corresponding manipulator possesses very specific particularity known as the "buckling" property [START_REF] Zhao | Stiffness Analysis of a New Tensegrity Mechanism based on Planar Dual-triangles[END_REF][20] [START_REF] Yamada | A compact jumping robot utilizing snap-through buckling with bend and twist[END_REF], for which the configuration angles may suddenly change while the external force increasing gradually. Besides, in the case presented in Fig. 6b, there is the "jumping" phenomenon, because of the unstable geometrical parameters of the manipulator segment (see section II and stable condition ), and the manipulator suddenly changes its shape even for extremely small loading.

To compute the critical force 0

x F of the buckling, let us assume that the configuration angles (q1, q2, q3) are small enough but not equal to zero. This allows us to derive a linearized stiffness model in the neighborhood of qi=0 (i=1, 2, 3). Under such assumptions, the first and second equations from (3.15) can be presented in the following form ( 0.5 ) 2 ( 0.5 )

x y b q q q b q q q         (13)
which allows us to present the condition δy=0 as q1+q12+ q123/2=0. Applying similar linearization to the third equation from [START_REF] Hutchinson | P o s t b u c k l i nTgheory[END_REF], one can get the additional relation of the configuration angles 2 2 1 3 2 2 3 3 0 q q q q q q     , which ensures the equality Me=0. Further, combining these two obtained relations and considering q2 as an independent variable, it is possible to express q1, q3 in the way

1 1 2 q q    , 3 3 2 q q    , where     1 3 21 11 20; 21 1 4          (14)
The latter gives us four possible manipulator geometric configurations corresponding to the static equilibrium, two with U-shape and two with Z-shape (see Table 1).

The corresponding external forces Fx, Fy can be linearized for small configuration angles, which yields

2 2 0 1 3 2 2 2( ) ( 2 ); 0 2 x y k F b a bL q q q F bq            (15)
Further, taking into account ( 13) the desired critical force can be expressed in the following way -+ + U-shape:

q 1 q 2 q 3
Stable + --U-shape:

q 1 q 2 q 3
Stable Case of "-√" -+ -Z-shape:

q 1 q 2 q 3
Unstable + -+ Z-shape:

q 1 q 2 q 3
Unstable Figure 6. Force-deflection curves and stiffness coefficients for the "straight" initial configuration.

  Finally, let us compare the U-shape and Z-shape equilibrium configurations for their static stability. It can be easily proved that for the small configuration angles qi, the end-effector deflection δx can be expressed in the following way

    
for Z-shape. The latter means that for the similar deflections δx, the U-shape has the smaller configuration angles qi than the one of Zshape, which ensures smaller energy in agreement with [START_REF] Yang | Synthesis and analysis of a flexible elephant trunk robot[END_REF].

Let us consider now when the manipulator initial configuration is non-straight, which corresponds to the angles ( 0 0, 1,2,3

i q i  
). Similar to the above section, the equilibrium is defined by three equations [START_REF] Hutchinson | P o s t b u c k l i nTgheory[END_REF], which are derived from the direct kinematics and the zero external torque assumption Me=0. It can be proved that the energy curves have the "∞-shape" similar to the straight configuration considered before. However, depending on the initial end-effector location (x, y), these energy curves may be non-symmetrical and can be even discontinuous and include cusp points. Typical examples of such curves corresponding to the end-point location T T ( , ) (5.5 , 0)

x y b  are presented in Fig. 7, where the discontinuity caused by the geometric constraint is visible. In particular, the energy curve of cases (a) consists of two separate U-shape parts that yield two symmetrical stable equilibriums and four unstable ones. Such separation is caused by the geometric constraints max i i q q  . However, the energy curves for the case (b) cannot be treated in the same way, because the combination of a, b, 0 i L provides non-monotonic torque-angle curves for the segments and even separate parts of the manipulator are unstable here. It should be stressed that in the cases (a), each segment of the mechanism is statically stable. It should be also noted that there are some unfeasible sections (black lines) inside of the curve, where at least one of the angles q2 or q3 is out of the allowable geometric limits.

The above-presented case studies, corresponding to the end-effector initial position T T ( , ) (5.5 , 0)

x y b  , can be also illustrated by the force-deflection curves presented in Fig. 8. As follows, there is no buckling phenomenon in the case (a), the curve is quasi-linear and passes through the zero point. Besides, the buckling detected in the case (b) cannot be observed in practice because of the nonstability of the separate manipulator segments.

To evaluate the manipulator stiffness matrix for the non-straight configuration, let us first find the joint torques for all manipulator segments using the method from section II,

    2 2 0 1 0 2 2 ( )sin( ) cos( 2) sin( 2) cos( 2) sin( 2) ; 1,2,3 qi i i i i i i i M k b a q kL a q b q kL a q b q i        (18)
and compute the derivatives providing equivalent stiffness coefficients in the joints "blue curves" ─ feasible configuration with q3>0; "green curves" ─ feasible configuration with q3<0; "black curves"─ unfeasible configuration; "red point •"─ stable equilibrium; "black point •" ─ unstable equilibrium.. This allows us to apply the VJM method and to express the unloaded stiffness matrix of the considered manipulator as

qi qi i K dM dq    2 2 0 1 0 2 2 ( )cos( ) cos( 2) sin( 2) 2 sin( 2) cos( 2 ) 2; 1, 2, 3 qi i i i i i i i i K k b a q kL b q a q kL a q b q i             (19)
  1 0 1 T F o qo o    K J K J (20)
where the subscript "o" denotes the variables corresponding to the unloaded initial configuration. Further, if we express the 2x3 submatrix of the [START_REF] Gravagne | Kinematic transformations for remotely-actuated planar continuum robots[END_REF] for this configuration as

11 12 13
21 22 23 2 3 o J J J J J J         J (21)
The desired compliance matrix of the unloaded mode can be expressed analytically in the following way

T q q q F o qo o q q q J J J K K K J J J K K K                    C J K J ( 22
)
where 1 2 3 ( , , )

qo q q q diag K K K  K
is the matrix of size 3×3.

For the loaded mode, the manipulator stiffness matrix can be computed using the extended VJM technique proposed in [START_REF] Chen | Conservative Congruence Transformation for Joint and Cartesian Stiffness Matrices of Robotic Hands and Fingers[END_REF]. Within this technique, let us assume that there is a non-negligible deflection ( , , ) q q q q      . As follows from the equilibrium equation T =  M J F , the corresponding variation of the joint torque can be expressed as

T T d d              J M q F J F q (23)
where the part T d dq J , which includes the Jacobian derivative, can be rewritten as

3 T T 1 i g i i d q d q                        J J q F = F K q q (24)
where g K is the 3×3 matrix describing the influence of loading F on the manipulator Jacobian J

1 2 3 3 3 T T T g q q q                  J J J K F F F (25)
that can be also written in the extended form as

J F J F J F J F J F J F J F J F J F J F J F J F J F J F J F J F J F J F                             K (26)
Further, after expressing the virtual joint torque variation as

q     M K
q and its substitution to (23), the variable  q can be presented as  

1 T q g        q K K J F (27)
which allows us to find the end-effector deflection    J q 

, and finally to obtain the desired loaded compliance and stiffness matrices

    1 T 1 1 T F q g F q g            C J K K J K J K K J ( 28
)
It is worth mentioning that all the Jacobian and the joint stiffness matrices Kq, Kg must be computed for the loaded equilibrium configuration, which is different from the initial unloaded one (It requires relevant solutions of the non-linear equations considered above).

To illustrate the importance of the loaded stiffness analysis, the obtained expressions were applied to several cases study, which focusing on the manipulator stiffness changing under the external loading. For all considered cases, it was assumed that the initial manipulator configuration is a non-straight one, with the endpoint location (x0, y0)=(5.5b,0). Under the loading the configuration angles corresponding to the external force F=(Fx, Fy) T were computed from (11) numerically (using Newton's Method). There are three combinations of the geometric parameters a/b ϵ{0.75; 0.9; 1.1}, relevant results are presented in Figs. 9 and 10. As follows from these figures, in most cases the manipulator stiffness essentially changes if the external loading is applied. In particular, the manipulator resistance in the x-direction becomes lower and lower while the force Fx is increasing (see Fig. 9a). In contrast, the resistance in the y-direction with respect to the force Fy becomes higher and higher while this force is increasing (see Fig. 9b). These results are also confirmed by the Kxx and Kyy plots presented in Fig. 10, which show an enormous loss of x-direction resistance under the Fx loading (it can be treated as a "quasi-buckling", see Fig. 10a for the stiffness coefficient Kxx). On the other side, while increasing the force Fy, the stiffness coefficient Kyy is very small at the beginning, then it is increasing until reaches the maximum value, and then it is decreasing (see Fig. 10b). In this figure, an evolution of the manipulator configuration under the loading are also presented, with relevant stiffness coefficients Kxx and Kyy plots (corresponding to the case a/b=0.75). They demonstrate the above mention results from the geometrical and physical point of view, which are corresponded to the stiffness coefficient and force relation. There are four representative configurations presented here, which showing the shapes of all segments and their position with respect to the joint limits. As follows from them, the observed sudden change of the stiffness (see Figs. 9 and 10) occurs if one of the segments is close to its joint limits, where the equivalent rotational stiffness coefficient is very low. Hence, in practice, it is necessary to avoid applying too high loading, or the manipulator will approach its joint limits and lose stiffness.

Therefore, as follows from the above study, the mechanical properties of a serial manipulator based on dual-triangle segments have several particularities, which are different from a classical serial structure composed of rigid links and compliant components. These particularities must be obligatory taken into account in control algorism, for ensuring desired motions of such manipulator, which is in the focus of our future research.

IV. CONCLUSION

The paper focuses on the compliant serial manipulator composed of a new type of dual-triangle tensegrity mechanism, which is composed of rigid triangles connected by passive joints. In contrast to conventional cable-driven mechanisms, here there are two lengthcontrollable elastic edges that can generate internal preloading. So, the mechanism can change its equilibrium configuration by adjusting the initial lengths of the elastic components.

The energy method was used to find the equilibrium configurations for different combinations of geometrical and mechanical parameters. The results show that both stable and unstable equilibriums may exist, and the manipulator shape will be an essential evolution if the external loading is applied. Some analytical results are presented, which allow us to find the manipulator shape under the loading and to estimate the stability of the corresponding configuration.

The manipulator stiffness analysis for both loaded and unloaded mode was done using the VJM method, and the relations between the end-effector deflection and the external force were obtained. Similar to the single dualtriangle segment, the buckling phenomenon occurs if the manipulator initial configuration is straight. Besides, for the non-straight initial configuration, the sudden change in deflection was also observed in some cases, which was treated as quasi-buckling. These particularities of the manipulator stiffness behavior were also observed in simulation.

The obtained results allowing to predict manipulator complicated behavior under the loading, and to avoid the buckling or quasi-buckling phenomenon by proper selection of the mechanical parameters, which will be used in the future for the development of relevant control algorisms and redundancy resolution.

Figure 1 .

 1 Figure 1. Geometry of a single dual-triangle mechanism.

Figure 3 .

 3 Figure 3. The torque-angle curves and static equilibriums for 0 0 1 2L L  ( 0 0 q  ).

Figure 2 .

 2 Figure 2. The torque-angle curves and static equilibriums for 0 0 1 2

Figure 4 Figure 5 .

 45 Figure 4. Energy curves

0 xF

 0 shape. It is worth mentioning that the obtained expression allows us to derive the static stability condition for the straight configuration. In fact, this configuration is stable if and only if 0  , which is equivalent to

  the monotonicity of the torque-angle curves for the manipulator segments.

Figure 7

 7 Figure 7. Energy curves

Figure 8 .

 8 Figure 8. Force-deflection curves and stiffness coefficients for "non-straight" initial configuration with different parameters (a, b, L o ) and displacement     , 2,0 x y b    .

Figure 9 .Figure 10 .

 910 Figure 9. Force-deflection relations of three-segment mechanism for non-straight initial configuration with     , 5.5 , 0 o x y b  .

TABLE I .

 I

		POSSIBLE MANIPULATOR SHAPES IN STATIC EQUILIBRIUM
	q1	q2	q3	Geometric configuration	Stability
	Case of "+√"

ACKNOWLEDGMENT

This work was supported by the China Scholarship Council ( No. 201801810036 ).


Thomas Lacroix

Eds Rainer Bauböck

Thomas Faist

Diasporic Identity, Transnational Agency, and the Neoliberal Reconfiguration of Global Migration

Keywords: Diaspora, transnationalism, globality, methodological nationalism, neorealism

This book is the latest step in the long-standing dialogue between two

incorporated micro-level activities in their analysis while, conversely, research on transnationalism has paid growing attention to the importance of macro-level dynamics and actors such as states. In 1999, Robin Cohen and Steven Vertovec's book and in particular their landmark "Introduction" heralded this convergence. Since then, diasporic groups are commonly perceived as a specific category of transnational formation. Admittedly, diasporas differ from other transnational communities, owing to an enduring group consciousness forged through cross-borders ties and practices. Although Diaspora and Transnationalism endorses this view, it also reveals new perspectives on the scholarship not only in the two related fields, but others as well. Indeed, since the early 2000s, the concepts of diaspora and (to a lesser extent) transnationalism have permeated the vocabulary of policy makers. The growing number of diasporic policies formulated by states and intended to attract the economic favor of their expatriate groups has led some academics to revisit common assumptions and theories about the making of transnational and diaspora groups. In consequence, new theoretical stances have emerged. Diaspora and Transnationalism reflects the current re-composition of the academic debate.

The book is divided into three sections that explore the theoretical, conceptual, and methodological frameworks of the two approaches. This opus is an effort to shed new light on diaspora and transnationalism by redrawing the margins that separate and juxtapose them. The project that underpins this work is one of redefinition, of pointing to the content of the concepts at issue and exploring possible combinations. At first sight, no common ground emerges from this collection of papers. In many regards, this book appears as a series of monologues on diaspora, transnationalism, and sometimes (but not always) their relationships. The aim of the book is not to weave together an overarching theory. Nevertheless, its merit is to provide a panoramic view of the variety of themes, perspectives, and methods through which the relationship of diaspora and transnationalism is currently addressed by students of migration.

In the first place, the book illustrates the convergence between the two fields, which is partially related to the growing politicization of the notion of diaspora. In an attempt to provide a theoretical justification for this convergence, Thomas Faist argues that diaspora and transnational studies share the same epistemological terrain, one that lies between methodological nationalism and globalization studies. In addition, several other articles (by Valentina Mazzucato, Koen Jonkers, Kathrin Kissau, Uwe Hunger, Laura Morales, and Laia Jorba) show how recent methodological innovations have provided common methodological tools for the study of diasporas and transnational phenomena. But, in the second place, Diaspora and Transnationalism reflects persistent past and recent academic quibbles. Several contributions make the case that contemporary diaspora formations are an outcome of state efforts to engage with their nationals living abroad. In contrast, transnationalism appears as a grassroots process that escapes from state control (see Rainer Bauböck). In this respect, the book is strongly marked by a recent neorealist turn in migration studies (that will be discussed later; it illustrates the current re-evaluation of the role of the state in the formation of cross-border social entities. In this essay, I will successively present the two opposite trends that characterize contemporary debate on diaspora and transnationalism: one characterized by convergence that is demonstrably present in some areas, but also another trend of persistent divergence between certain academic stances.

Theoretical, Epistemological, and Methodological Convergences

Diaspora and Transnationalism as Two Facets of the Same Coin: From Utilitarian to Scholarly

Discourses

In the 2000s, the terms diaspora and transnationalism crossed the border that usually separates the scholarly-academic and policy worlds; this crossing was accompanied by the conceptual distortions such moves frequently involve. The chapters by Weinar, Koinova, and Waterbury explore the use of these terms by public officials and civil society actors. This use is primarily driven by utilitarian considerations. For Waterbury, states develop diasporic policies either to support development plans, muster political support, or to reassert a national myth (136). Migrants' remittances are becoming the new "mantra" of development stakeholders [START_REF] Vertovec | Remittances: The New Development Mantra?[END_REF]. For example, the African Union defines the African diaspora as the "peoples of African origin living outside the continent, irrespective of their citizenship and nationality and who are willing to contribute to the development of the continent and the building of the African Union" (Waterbury 79). Myra Waterbury fills a gap in the literature on diaspora engagement policies by documenting "kin state policies." These policies target still-territorialized populations that found themselves in a foreign country not because they moved but in the wake of border redefinitions after World War I. Interestingly, the term diaspora is also used to name these populations in Eastern European countries. This use is underpinned by political strategies. For example, in Serbia, discourses about the diaspora justify irredentist and nationalistic ambitions.

The Serbian Unity Congress, which acted as the official representative of US-based Serbians, has provided constant support to nationalist parties in Serbia during the nineties (Koinova, 159).

Maria Koinova (chapter 8) shows how the term is instrumentalized to enable the diaspora to pursue a political agenda in the origin country. The chapter unravels the underpinnings of such discourses and shows how, behind the promotion of democratic values and procedures, diaspora groups strive to achieve particularistic political aims in their land of origin.

The thriving literature produced by international, state, and civil society organizations on the matter pays little regard to the definitional criteria usually deployed by academics, such as "spatial dissemination, collective identity, integration, intensity of mobility," and so forth.

Furthermore, the political use of diaspora and transnationalism does not establish any conceptual distinction between the terms. It is true that transnationalism and its lexical field are far less present in this politicization literature. However, when it is present, it is generally used to qualify the cross-border networks and practices of diaspora groups. In this perspective, the two terms are used to shed light on two facets of the same phenomenon. While diaspora designates a group sharing a political identity, transnationalism is used to refer to the actual practices of migrants.

The two concepts are a lens focused on the same object, namely, the cross-border socialities produced by migration. The difference between the two words is of focus, not of nature.

If academic definitions, as argued by Weinar, have never really informed stakeholders' discourses, the contrary is certainly less true. The author notes the recent enlargement of scholarly definition of the concept of diaspora. For example, Van Hear, Vertovec, and Pieke (2004, 3) see diasporas as people on the move with multifarious linkages maintained with the homeland. In this context, Weinar is right to state that "this formulation makes diasporas hardly distinguishable from a transnational view on migrant communities" (76).

Against this backdrop, the introductory chapter of Thomas Faist appears as an attempt to ground the correspondence between the two concepts into a rigorous epistemological framework.

Due to the nature of their object, the study of diaspora and transnationalism can be seen as critiques of methodological nationalism and global studies. The latter, although standing at two opposite scales of the sociological spectrum, tend to convey a homogenized (not to say essentialist) portrait of social life, be it territorially bounded within state borders (for methodological nationalists) or utterly deterritorialized (for scholars of globalization). The concepts of diaspora and transnationalism represent a response to uni-scalar approaches. They assert the multi-polarity of social processes beyond state borders while each "pole" remains firmly rooted in local settings. What makes these socialities distinctive compared to non-migrant ones, beyond their cross-border dimension, is their dialectic nature. In effect, diaspora and transnational communities are social entities forged between distant origins and localized settlement, between sameness and otherness, mobility and sedentarity, locality and globality. As put forward by Thomas Faist (16), diasporas and transnationalism are two "glocal" phenomena. 1

Arguably, transnationalism and diaspora are two approaches that thrive on an epistemological territory bounded by "nationally focused" studies on the one hand and by "global studies" on the other (14-6). Indeed, "methodological nationalism" has been the target of transnational and diaspora experts for nearly a decade now (Wimmer and Glick Schiller 2003).

Transnational studies, deeply infused with behaviorism since the onset, are particularly reactive to any form of essentialism and methodological nationalism. The latter is accused of conveying an essentialist conception of society whose limits would be "naturally" congruent with the state's. Peggy Levitt and Nina Glick Schiller (2004) identify three forms of methodological nationalism: (1) ignoring or disregarding nations as a political and social construct; (2) taking for granted that the boundaries of the nation-state define the unit of analysis; (3) restricting the study of social processes to the political and geographic boundaries of a particular nation-state. The study of migrants engaged in maintaining cross-border practices and social ties challenges the conception of society as a strictly bounded and self-sufficient arena.

Whether the battle against methodological nationalism can be won is another matter. In a context where statistics are produced by national institutions, the quantitative picture of the world is still almost exclusively focused on nation-states. Furthermore, there is a growing acknowledgment that states and territorially bounded institutions such as political parties, religious organizations, village communities, and so forth do play a role in the formation of diasporas and transnational phenomena. In fact, migrants do not always challenge-they often also reproduce and utilize-an array of societal hegemonies (whether racial, gender, ideological, or class hegemonies) in the transnational space. There is therefore an implicit acknowledgment that bounded societies do matter as a unit of production of globalized hegemonies. Dismissing (disqualifying?) the concept of society (Touraine 2007) under the dubious assumption that it colludes with a statist ideology would deprive us of the opportunity of analyzing the production of major social patterns and their transposition into migrant social groups. Furthermore, as mentioned earlier, there is an ongoing reassessment of the role of the state in cross-border social processes. States and societies continue to remain prevailing structural forces of social processes.

In a similar vein, Thomas Faist emphasizes the discrepancies between global and migration studies. For Faist, the literature on migrant cross-border exchanges and socialities offers little comfort to those who hope for and advocate or claim to see the emergence of a global consciousness, or a global normative framework that is linked to the promotion of "postnational" human rights [START_REF] Nuhoglu | Limits of Citizenship. Migrants and Postnational Membership in Europe[END_REF]. "Diaspora and transnational concepts, in contrast to global and world theory concepts, often start from the observation that, while there is less of a requirement of physical and geographical proximity for social life, there is still no clear tendency towards universalisation" (15). However, the relationship between diaspora and transnational studies, on the one hand, and global studies on the other, is far less confrontational. Although arguably distinct, these academic fields stem from the same historical context, marked by the success of the neoliberal political economic agenda and the fall of the Soviet bloc. These academic fields emerged to account for the multi-polarization of the world and the rise of non-state actors on the international scene. The concept of transnational relations was tailored in a critical perspective of the realist paradigm of International Relations 2 (Keohane and [START_REF] Nye | Transnational Relations and World Politics[END_REF]. In this perspective, diasporic groups were identified, along with multinational corporations and nonprofit organizations, as actors responsible for the growing complexity of World Politics (Keohane and Nye 1972, 19). In addition, transnationalism and diaspora studies and global studies share a range of assumptions. Chief among them is the idea that the technological revolution and the ensuing "time-space" compression have changed the rules of the social game. Finally, they point to the importance of local identities as an inherent aspect of globalization. In this regard, globalization thinkers such as Luhman, Beck, Giddens, or Castells have criticized the idea of a world as a unified "McWorld." In their works, globalization is depicted as polycentric rather than a-centric (Laïdi 2007).

The state-centered and global paradigms continue to exert a strong influence on migration scholarship. Rather than two opposite external boundaries delimiting the epistemological territory of post-migration studies, it would be fairer to depict them as two forcefields polarizing the academic debate. If the global paradigm has been dominant in the 1990s and early 2000s, there now seems to be a move toward a greater (re)consideration of the role of state actors.

2. Methodological Innovations

The last terrain on which the encounter between Diaspora and Transnational Studies has occurred is the one of methodology. A body of innovative methodologies delineates what could be called a "methodological glocalism" as opposed to the "methodological nationalism" and "methodological cosmopolitanism" that characterize alternative approaches to social phenomena.

Students of cross-border practices have developed a multipurpose tool-kit likely to overcome the challenges posed by the nature of the research object. The first of these challenges is the multiscalar dimension of migration processes. They span several local settings scattered over the world. Migrants interfere with authorities and existing arrangements at the local, national, or even regional levels. The difficulty is to render the interrelations between processes happening at each of these levels. The second challenge is induced by the scarcity of statistics on "glocal" processes. The measure of flows and the intersection between local and cross-border processes are two key features poorly appraised by existing data. For this reason, students of transnational and diasporic entities have, for long, relied almost exclusively on ethnographic research. The Simultaneous Matched Sample (SMS) methodology elaborated by Valentina Mazzucato (chapter 11) exemplifies the sophistication of multisited ethnography at its best. This approach is based on the parallel and nearly simultaneous investigations of migrant and origin communities by two different research teams. Migrants and their relatives in the place of origin are interviewed on a monthly basis over a year. This provides the possibility of observing the immediate causes and consequences of migrant behaviors in both origin and destination communities. The merit of this approach over classic multisited ethnography is to grasp the simultaneity of cross-border processes. In doing so, the SMS methodology implicitly refers to globalization as a time-space compression of social affairs. In addition, the SMS enables the investigators to collect a fair amount of information that enables researchers to envisage quantitative extrapolations. The third interest of the approach is to grant an equal attention to events in sending and receiving areas.

Although transnational scholars generally acknowledge the importance of multisited investigations, most research nevertheless presents a bias toward the receiving context. Finally, beyond its technical aspect, the SMS methodology must demonstrate its practical added value compared to classical approaches. The author argues in favor of this added value by listing findings that, it is argued, are more adequately addressed by this approach. Among them stand the transformation of the behavior of migrants over time, the behavior and discourses of migrants during holidays in the place of origin, and the relations between internal and international migration.

I must admit that I have not found these arguments fully convincing. The findings listed in the chapter could have probably been carved out by a committed PhD student following a sample of migrants and spending a reasonably long period in sending areas. My second reservation is that the SMS methodology is dependent on the willingness of migrants to let researchers interact with their family back home. This is not always the case, especially in areas where the political context remains sensitive. Ultimately the choice of the SMS methodology depends on the willingness to accept the drawbacks of team work for the prospect of getting improved data. This choice must be balanced with the personal sensitivity of researchers, the quality of scientific partnerships in the case study country, and the difficulty of undertaking individual research in sending areas. The SMS approach certainly does not mark the end of individual ethnographic research, but its success is illustrative of the importance of multisited methodologies and quantitative/qualitative mixed methods in the "methodologically glocal" toolkit of both transnational and diaspora studies.

The lack of available data on post-migratory cross-border processes such as the density of associational or entrepreneurial partnerships, of long-distance family ties, of political debates and cultural events is partly circumvented by the recourse to network and Web analysis. The study of migrant associations in Spain undertaken by Laura Morales (chapter 14) within the framework of the LOCALMULTIMODEM 3 program is based on the detailed analysis of the spatial distribution of organizational networks in and outside the host country. A similar approach to the study of migrant associations has been carried out through the European research program TRAMO. 4 Other studies have developed the analysis of Internet Web sites; their content and interconnections are increasingly used to map virtual diasporas. The chapter of Kissau and Hunger (chapter 13) on the Russian, Kurdish, and Turkish diasporas gives an example of this flourishing strand of research (see also Kuah-Pearce 2008;[START_REF] Faist | Les Diasporas: Communautés Globales de l'Ere Digitale[END_REF]. It shows how different diaspora groups use Internet tools in innovative ways that reflect their positioning and structuring between the host and origin countries. Finally, Koen Jonkers (chapter 12) uses another untapped material resource, publication databases, in order to track transnational academic collaborations. The author highlights the extent, directions, and forms of academic partnerships between Chinese and overseas scholars. Thanks to this approach, he challenges the notion of brain drain, showing that highly skilled expatriates interact to a relatively high degree with their former home system.

Divergence: Old Debates, New Perspectives

This reading of Diaspora and Transnationalism reveals a shift in the debate between transnational and diaspora scholars. In addition to the long-standing opposition between social constructionist (here represented by Glick Schiller) and positivist (Dahinden, Bruneau) approaches to diasporas, a new perspective has emerged. In effect, the multiplication of diaspora policies has made credible a neorealist interpretation of the emergence of diaspora groups (Bauböck). The realist paradigm of International Relations posits the state as the exclusive actor on the international scene. From the seventies onward, this paradigm has been harshly criticized by theorists pointing the growing importance of non-state actors pursuing their own international agenda (Keohane and [START_REF] Nye | Transnational Relations and World Politics[END_REF]. The collapse the Soviet Union in the late eighties was perceived as opening an era of turbulence (Rosenau 1990) characterized by the surge of non-state actors challenging the nation-state hegemony. Since the early 2000s, a growing number of scholars have attempted to reassess the role of the state within the globalization process. I here name this scholarly tendency neorealism. Against this backdrop, a growing body of works shows how the formation of a diasporic identity is the product of performative effects of policy makers' and civil society actors' actions and discourses. In the late 1990s, the issue of diasporic policy was a minor concern in the scholarship (Cohen and Vertovec 1999). In contrast, it occupies over a quarter of Diaspora and Transnationalism. Three chapters (4, 7, and 8) address the topic through different angles while the concluding chapter seeks to incorporate these findings into a wider theoretical framework on diaspora formation. Interestingly, this new line does not divide diaspora and transnational experts but seems to traverse both academic fields. The section below presents successively the three distinct conceptions that polarize current academic debates.

Transnational Social Fields: A Social

Constructionist Perspective on Transnationalism and Diaspora

As mentioned in the introduction, the authors of Diaspora and Transnationalism generally second the idea that diaspora tends to be a specific category of transnational formation.

There is, however, an exception that challenges this line of thought. Nina Glick Schiller presents a conceptual framework called "the global power perspective," which, while heavily relying on the concept of transnational social field, dismisses the identity-focused concepts of diaspora and transnational community. The author defines transnational social field as follows: "Transnational social fields are networks of networks that link individuals directly or indirectly to institutions located in more than one Nation-State. These linkages are part of the power dynamics through which institutionalized social relations delineate social spaces" (112). Alongside states, a number of institutions affect the structuration of migratory social fields. These are financial conglomerates, NGOs, religious organizations, treaty-based organizations, and corporations. This approach highlights the structuring power of these global institutions and the variety of strategies adopted by migrants to respond to it.

According to the author, students of transnational community and diaspora tend to focus on identity formation and reproduction strategies:

"[…] scholars of transnational migration and diaspora have often bound their unit of analysis of study along the line of national or ethnic identities. They have generally failed to link their description of migrant local and trans-border connections to analyses of new flexible modes of capital accumulation and the contemporary neo-liberal restructuring of space, self and modes of legitimation"

(111).

The study of transnational social fields, she argues, has a stronger theoretical purchase insofar as it displaces the focus from identity to agency, highlighting the bearing of state (and non-state actors') policies on cross-border dynamics. By focusing on the diversity of linkages that migrants maintain with other migrant and non-migrant groups, this approach is more likely to unveil the intertwining between state policies, symbolic hegemonies, and migrant strategies. It is worth noting that Glick Schiller's essay in this volume, unlike Thomas Faist's, draws a nuanced parallelism between migration and globalization studies. Although she acknowledges that the world system and other Braudelian world-scale theories maintain an unjustified distinction between global and local level processes (113-4), she summons authors such as Ulrich Beck or Manuel Castells to support her critique of methodological nationalism and other identity-focused approaches. Her social constructionist approach is therefore firmly related to the paradigm of globalization. The author links transnational processes to the neoliberal re-configuration of the world order in which capitalist forces have constrained states' capacities but have given more space to individual people's agency.

From Transnational to Diaspora Formations:

Unraveling the Spatial/Identity Condition of Migrants

The two first conceptual chapters of Diaspora and Transnationalism present two ways of posing the problem of the difference between transnational groups and diasporas. Michel Bruneau and Janine Dahinden see the origin of the formal distinction in long-term identity processes at the local and multinational levels. According to them, transnationalism and diaspora formations are two ways of overcoming a tension between identity and spatiality inherent to the condition of migrancy. Dahinden argues that a continuum links diaspora and transnational groupings. Diaspora groups (called "localized diasporic transnational formations" (sic)) are firmly anchored in the settlement countries and maintain little more than a shared subjectivity with the origin society or other parts of the diaspora. At the other end of the spectrum, transnationally mobile communities are weakly embedded in the society of arrival but are engaged into constant cross-border practices and circulation. Half way between these two archetypes stands a range of "localized and mobile transnational formations" that entertain a good level of incorporation in the place of arrival while sustaining more or less dense back-andforth movements. According to the author, the passage from one social configuration to the other is explained by integration and the legal context. The emergence of diasporas is the result of a shrinking of migrant spatiality offset by sustained efforts to preserve a shared identity. Compared to transnational communities, diasporas represent a step toward integration. But Janine Dahinden also acknowledges the role of legal restrictions to immigration and to the duration of stay in the destination country and the subsequent agency of migrants who strive to cope with these constrains. Precarious legal statuses tend to force contemporary migrants to limit their stay and remain transnationally mobile. In the most extreme cases of agency deprivation (for refugees or undocumented people), circulation is not an option anymore. This category of people, called the transnational outsiders by the author, tends to privilege localized invisibility. She, however, does not dismiss the relative importance of identity processes in the formation of actual cross-border communities. Paul Boccagni's chapter on Ecuadorians in Italy documents the case of a "localized diaspora transnational formation" in the making. He highlights how, in absence of regular visits paid to the place of origin, long-distance ties sustained between the transnational household and relatives in the original home nurture a sense of continued belonging to the origin country.

Although adopting a similar point of departure, Michel Bruneau's analysis follows an opposite direction. A geographer, Bruneau sees in the formation of diasporas primarily a process of several multi-polarizations: first a spatial stratification that emerges as the different poles of the expatriate community in various countries of settlement get increasingly interconnected; then an identity polarization that develops as the gradual embedding into the receiving areas brings about a process of hybridization. At the same time, the common engagement in a set of practices strengthens a shared subjectivity between diaspora members. Diaspora groups, as Rogers Brubaker ( 2005) has argued elsewhere, can therefore be distinguished according to the "category of practice" that underpins the production of "groupness." Bruneau differentiates commercial, political, and racial/cultural diasporas. This process is often mediated by the territorial embedding of community buildings and areas. Places of worship, shopping areas, community centers, monuments, museums foster the sense of belonging to the same social entity. In contrast to diasporas, transnational groups are characterized by the duality of their identity and the bipolarity of their circulation between the host and source countries. Contrary to Dahinden, Michel Bruneau sees diasporas as a step away from assimilation. Diasporic groups are the result of a deployment of both their shared sense of belonging and practices at a scale beyond the compound formed by arrival and origin settings. The work of Karsten Paerregard on the Peruvian diaspora complements this analysis by focusing on the class behaviors within the same group. The author shows that only the upper class has developed truly diasporic strategies. The Peruvian mestizos have established networks between the different parts of the diaspora in North and Latina America as well as in Europe. These actors display a stronger sense of belonging to the same group than working-class migrants. The mobilization of the latter group is restricted to a translocal arena encompassing the places of arrival and origin. The formation of diaspora groups, he concludes, is facilitated by higher social, political, and financial capitals obtained through incorporation.

Beyond their opposite line of thought, Bruneau and Dahinden adopt a definition of transnationalism and diaspora as two related but distinct realities. Both share the view that the difference is a consequence of temporal and spatial processes. Transnational groups become diasporas in the wake of a long-term integration process into local settings and of a transformation of their cross-border embedding. This approach differs from the neorealists' insofar as it posits the emergence of diaspora groups as the consequence of autonomous processes of social differentiation and not, as will be shown below, on the intervention of political actors. This stance, as opposed to the social constructionism of Glick Schiller, can be regarded as positivist insofar as it conceives a positive existence of diaspora and transnational groups, each of them characterized by a set of specific features such as mobility patterns and group consciousness. In a sense, this approach contradicts the idea of globalization as a timespace compression. Time and space continue to matter, even for supranational-scale phenomena.

The authors depart from the globalization paradigm. Both draw a perspective on cross-border phenomena equidistant from methodological nationalism and cosmopolitanism.

Diaspora and Transnational Groups: A Neorealist Perspective

Away from the constructionist stance of Nina Glick Schiller and the positivist idea of autonomous production, Rainer Bauböck argues that transnationalism and diasporas are social formations produced by contingent factors. Bauböck sees transnationalism as an outcome of the multiplication of citizenship statuses at the local, national, and international levels. The transnational character of migration is favored by the growing varieties of dual citizenship, denizenship, and an array of short-term immigration statuses. Transnationalism is therefore the consequence of the evolution of migration regimes. Migrants' mobility is the response of the growing precariousness of migration statuses. When possible, migrants opt for dual citizenship in order to preserve their freedom of circulation in a context of border closing. In contrast, diasporas are transnational communities organized and mobilized by political actors. Group consciousness forms along the lines of hegemonic narratives of belonging. Narratives of states and diasporic civil society actors tailor diasporic imaginings that fit into utilitarian and political objectives. As mentioned earlier, sending states rely on diasporic sentiments to enhance remittances and investments of expatriates. But diaspora mobilization can also serve to support homeland political interests and lobby the governments of receiving countries. Agnieszka Weinar, Myra Waterbury, and Maria Koinova (chapters 4, 7, and 8) give ample illustration of this. The narratives conveyed by civil society actors are not necessarily less hegemonic than the ones proposed by states. As put forward by Koinova (chapter 8), despite the promotion of democratic and pluralist values that often underpins their objectives, civil society actors tend to disregard cultural, gender, or political diversity, both within the diaspora and the homeland.

Bauböck and other authors following the same line of thought remain mute on the structural consequences that these discourses have on the morphology of transnational groups. Even when he acknowledges the spatial and identity distinctiveness of diaspora groups, Bauböck argues that they are explenanda (factors to be explained) rather than explenandum (causal factors). Bauböck, in line with Bruneau and Dahinden, argues that transnational groups and diasporas present distinct features. However, for him, transnationalism and diaspora formation are spurred by contingent factors (the mutation of migration and citizenship regimes on the one hand, political strategies of states and civil society actors on the other) rather than by social dynamics of integration and cross-border embedding. These phenomena are less the responses to an identity/space conundrum than to the mutation of state and politics in the context of globalization (155).

Conclusion: Diaspora and Transnationalism as Social Constructs

Diaspora and Transnationalism brings to the fore new lines of division along which the current scholarly debate on migrant social formations (increasingly infused with non-academic considerations) is taking place. Next to the positivist conception of transnationalism and diaspora and its constructionist critique, a new school of thought argues that diasporas are less an outcome of intertwined identity processes and cross-border practices than of an evolution of legal and political opportunity structures. The supporters of this conception focus on the formulation and implementation of diasporic policies and agendas by a range of actors: international organizations, volunteer organizations, NGOs, governments of receiving and origin countries, and so forth.

At the fringes of academic and policy spheres, a new strand of works moves away from the aforementioned theoretical considerations. A growing number of experts see transnationalism and diaspora as two facets of the same cross-border coin. In this respect, diaspora is the name given to any group of expatriate financial remitters to their place of origin. This highly ascriptive definition of diaspora pays little attention to the social morphology and internal diversity of migrant social formations. Does this perspective mark the obsolescence of the concept of diaspora? The dangers of the gradual widening of its definition have already been pointed out [START_REF] <jrn>brubaker | The 'Diaspora' Diaspora[END_REF], but recurrent calls to stick to a more restrictive definition have fallen short in the face of the contagious influence of policy-oriented research. This trend could rapidly lead to its abandonment in the social sciences literature. In this context, the cross-fertilizing fields of transnational and diaspora studies may open an avenue to stimulate conceptual innovations. By mapping the current debates, Diaspora and Transnationalism implicitly highlights the gaps that impede the emergence of an overarching framework of analysis. One striking absence of this book is any chapter proposing an empirical description of the evolution of a group from a transnational to a diasporic form. The diachronic comparison of the same migrant groups over at least two periods of their history would shed light on the emergence of new characteristics and the demise of others. Such an approach would highlight either the shrinking (Janine Dahinden) or the enlargement (Michel Bruneau) of cross-border ties paralleling the emergence of diasporic identities. The use of archive analysis (of public or civil society organizations) and oral history are methods insufficiently used by students of migration. In addition, the different chapters of the book display a clear-cut disconnection between studies of macro-level politics and micro-level social dynamics. For this reason, I fully second Thomas Faist's call (13) for a more integrated approach to social structures and migrants' agency. Finally, as shown in this article, there is in the social sciences a growing account of the influence of the legal and policy contexts in the formation of cross-border social entities. But more remains to be done on the influence of nonpolitical factors such as the de-structuration of community agrarian systems, of the reconfiguration of patriarchal systems and, more generally, of the surge of individualism in departure areas. Addressing such an issue would lead scholars not only to revisit existing common approaches to cross-border phenomena but also the broader architecture of migration studies, so far strongly polarized analyses of development and integration (Glick Schiller and Faist 2010). We can hope that Diaspora and Transnationalism will contribute to a surge of combined analysis of societal and transnational processes.

Notes

1.

The term glocalization was popularized by Robertson (1992, 173-4) to describe how global pressures and demands are made to conform to local conditions. Here, the global is modified by its contact with the local. Thus, there is no homogenizing force at work here but rather new and various possibilities for fusion and creativity (Cohen and [START_REF] Kennedy | Global Sociology[END_REF].

2. This paradigm is posited on the idea that nation-states pursuing their particular interests are the exclusive actors on the international arena.

  3. Multicultural Democracy and Immigrants' Social Capital in Europe: Participation, Organisational Networks and Public Policies at the Local Level (LOCALMULTIMODEM). The Spanish program was funded by the Spanish Ministry of Science and Education and by the Seneca Foundation of the Region of Murcia. See www.um.es/capsocinmig. accessed 20/02/2013. 4. Diffusion and Context of Transnational Migrant Organizations in Western Europe (TRAMO). The Program was funded by the Volkswagen Foundation. The study group includes the Department of Sociology of the University of Bochum (coord.), the University of Granada, the International Migration Institute of Oxford University and the University of Warsaw accessed 20/02/2013 2001, http://www.ruhr-uni-bochum.de/tramo/en/index.shtml.


Review of "Watson, N. J., Jarvie, G., & Parker, A. (Eds.). (2020). Sport, Physical Education, and Social Justice: Religious, Sociological, Psychological, and Capability Perspectives. Routledge.

Author: Alessandro PORROVECCHIO Affiliation: Univ. Littoral Côte d'Opale, Univ. Lille, Univ. Artois, ULR 7369 -URePSSS -Unité de Recherche Pluridisciplinaire Sport Santé Société, F-59383 Dunkerque, France, alessandro.porrovecchio@univ-littoral.fr

Abstract:

In this review I analyse the book "Sport, Physical Education, and Social Justice: Religious, Sociological, Psychological, and Capability Perspectives", edited by Nick J. Watson, Grant Jarvie and Andrew Parker, published by Routledge in 2020. After a first introduction in which I illustrate some traits of my experience that led me to be interested in these themes, I propose a brief summary in which I emphasize the main issues and theoretical approaches proposed by its 11 chapters. To conclude, I illustrate what I believe to be the main strengths and weaknesses of this book: the ability to embrace the complexity of the issues dealt with on the one hand, on the other perhaps the lack of pragmatism, and the absence of the issue of "health", which however is strongly linked to each of the topics analysed.

Review of "Watson, N. J., Jarvie, G., & Parker, A. (Eds.). (2020). Sport, Physical Education, and Social Justice: Religious, Sociological, Psychological, and Capability Perspectives. Routledge.

There is no doubt that the issue of social justice, today, is very important. Moreover, it is at the heart of many of my concerns: as a PhD student I used to discuss with my supervisor about the need for a committed, militant sociology. As a researcher, then, I began to converge towards a socially responsible sociology: I wanted to be the bearer of these "messages in the bottle" mentioned by Horkheimer and Adorno in Dialektik der Aufklärung. I approached the issue of social justice, such as John Rawls' works, applying them in the field of health. And then, a few years ago I was recruited in my current university, in an environment in which social inequalities affect the local population, especially the younger generations. In this university, I lecture on social health inequalities and social justice in the areas of adapted physical activities and nursing sciences.

I found this book while trying to explore the link between physical activity and social justice. The first things that struck me were the "religious perspectives" mentioned in the title. If the reference to capabilities was obvious and quite common in the field of sport and social justice, the connection with religious perspectives was quite new for me. The book became even more appealing when I realized that two of three editors had dealt with issues related to religion too. Nick Watson was founder of the Global Congress on Sports and Christianity. Andrew Parker was Professor of Sports Ministry at Ridley Hall Theological College (Cambridge, UK). Grant Jarvie was the closest to the issues of equality and social justice. My first impression of a religion-focused book was initially confirmed by the Editorial. Not that I was sorry: I considered this as a further indicator of originality.

Deepening the reading, the work seems more balanced. If in the first chapter, the (Christian) religious dimension is still central, in the second -a position statement, such as the following chapters, up to the ninth -it is more nuanced, and the topic of Judaism appears more like a cultural one, despite the references to ancient core texts. The author proposes a historical excursus of the relationship between Jews, sport, and discrimination.

The three following chapters, moving away from the more theological framework of the previous ones, enter the merits of the relationship between sport for development and peace (SDP) and the theory/practice of social justice. Chapter three deals more with capability approach as a framework for the construction of the common good, while the fourth, basing in a psychological approach, analyses some participatory local sport programs, providing postulates encapsulating the characteristics of high-quality critical sport for development, and drawing on principles of decolonization. Similarly, the following chapter, provides a critical sociological approach (à la Charles Wright Mills), hypothesising that sport-based programs can have a positive impact going beyond the world of sport itself if mobilized through a transformative approach addressing fundamental issues of global underdevelopment and inequality.

Chapter six to nine are more education-centred. Garratt and Kumar's one, rooted on a Foucauldian approach, criticises the historical dominance of children's engagement in competitive sports in schools and the elision between physical activity and physical education, that, in the authors' view, may have served to perpetuate the status quo. It concludes with a case study of positive practice, interesting but perhaps too short. This negative view of the competitive practices is partially questioned in the seventh chapter, in which -starting from a wide range of definitions -the authors suggest that "character education in a competitive and democratic sport team contexts can promote social justice by impacting the development of athlete's character" (p. 112). Chapter 8 offers a figurational sociological approach to understand issues relating to bullying in school based physical education. Basing in an Eliasian approach, it addresses mainly gender and sexuality-based bullying, while the issue of racism and racial inequality is at the core of the following chapter, drawing from work in the tradition of critical race theory, stressing the political dimension of sports too.

The last two chapters deal more with societal issues. Jarvie and Ahrens' chapter refers most of all to Amartya Sen's theoretical frame and focuses on the experience of The Homeless World Cup Foundation, and Street Soccer Scotland, one of its partner organizations, and on their actions for social integration and development of capability. The last chapter, analyses the role of sport protest under Donald Trump's presidential administration, proposing two examples. The first one, highly visible, is Colin Kaepernick's well known case, and his struggle against racism. The second one, less recognised, is New England Patriot's members' refusal to meet the president, and their fight against sexism.

This book, that is addressed to a wide range of readers (undergraduate, postgraduate, researchers, practitioners, general public), has several interesting aspects. Among these, it addresses the relationship between physical activity (sport, physical education) and social justice through both microscopic (individual experience, psychological dimension, educational relationship) and macroscopic (social, societal, cultural, and religious) frames. Furthermore, it proposes a strong interdisciplinary dimension, crucial to address the complexity of the issues analysed (capability, social justice, sport, racism, etc.).

We come to the (few) weaknesses of this book: first, it tries to propose potential strategies for social justice action, without entering a pragmatic dimension, often limiting itself to proposing some examples, analysing them basing on some specific theoretical perspective, and then describing their positive effects. Furthermore, none of the chapters focuses on the health dimension, which however is strongly linked to each of the issues analysed, especially that of social justice. But these are certainly weaknesses that do not affect the overall quality and originality of this one-of-a-kind book, which I warmly recommend.


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