J.-M Hartmann
email: jean-michel.hartmann@lmd.polytechnique.fr

C Boulet

H Zhang

F Billard

O Faucher

B Lavorel

Collisional dissipation of the laser-induced alignment of ethane gas. Energy Corrected Sudden quantum model

We present the first quantum mechanical model of the collisional dissipation of the alignment of a gas of symmetric-top molecules (ethane) impulsively induced by a linearly polarized nonresonant laser field. The approach is based on use of the Bloch model and of the Markov and secular approximations in which the effects of collisions are taken into account through the state-to-state rates associated with exchanges among the various rotational states. These rates are constructed using the Energy Corrected Sudden (ECS) approximation with (a few) input parameters obtained independently from fits of the pressure-broadening coefficients of ethane absorption lines. Based on knowledge of the laser pulse characteristics and on these rates, the time-dependent equation driving the evolution of the density matrix during and after the laser pulse are solved and the time dependence of the so-called "alignment factor" is computed.

Comparisons with measurements, free of any adjusted parameter, show that the proposed approach leads to good agreement with measurements. The analysis of the ECS state-to-state collisional rates demonstrates that, as in the case of linear molecules, collision-induced changes of the rotational angular momentum orientation are slower than those of its magnitude. This explains why the collisional decay of the permanent component of the alignment is significantly slower than that of the amplitudes of the transient revivals in both experimental and computed results. It is also shown that, since intermolecular forces within C 2 H 6 colliding pairs weakly depend on rotations of the molecules around their C-C bond, the dissipation mechanism of the alignment in pure ethane is close to that involved in linear molecules.

I. INTRODUCTION

Since detailed and general introductions to the topic of laser-induced molecular alignment can be found in Refs. 1,2, we here only recall studies on the collisional dissipation of the alignment of gases induced by intense and short laser pulses. The pioneering theoretical studies on this subject 3,4 showed that it could be possible to disentangle the effects of rotational population relaxation and pure phase decoherence by using the dissipation of field free alignment. These works, in which a M-independent Energy Corrected Sudden (ECS) model was used to construct state-to-state collisional rates for linear molecules, were extended 5 by introducing an ECS model that explicitly takes into account the dependences on M. As confirmed by comparisons with measurements 6,7 taking this dependence into account is essential for correct predictions of the decays of the permanent and transient components of the alignment. Indeed, due to the propensity of collisions to conserve the orientation of the rotational angular momentum 5 , these decays are different, the dissipation of the permanent alignment being significantly slower than that of the transient, a fact not predicted 5 by the Mindependent model of Refs. 3,4. Besides the M-dependent ECS model, Ref. 5 also proposed, for linear molecules, an original and completely different approach based on requantized Classical Molecular Dynamics Simulations (rCMDS). Its interest was demonstrated by comparisons with experiments 8 and with the predictions of the M-dependent ECS model 5 .

Besides the above mentioned theoretical studies, experiments probing the collisional dissipation of the laser-induced alignment for linear gaseous molecules can be found in Refs.

6,7,9-11. For non-linear molecules, no results were available under conditions for which collisions play a role until some very recent measurements for ethane 12 and CH 3 I 13 and a successful extension of the rCMDS to symmetric-top species 14 . In the absence of a quantum approach for such types of molecules, it is of interest to extend the M-dependent ECS model proposed for linear molecules 5 to symmetric tops. This is the subject of the present paper in which comparisons with measurements for ethane gas are also made. Recall that the ECS approach, presented in more details below, enables to explicitly express rotational state-tostate collisional cross sections (or rates) in terms of the relevant quantum numbers and of a limited set of basic collisional quantities (in the case of a linear molecule, the rates ( 0) K J → for the de-excitation from rotational state J to J=0). This is achieved starting from the Infinite Order Sudden approach that assumes that molecules do not rotate during collisions and correcting for this approximation by introducing "adiabaticity" factors which re-introduce the finite energy spacing between rotational states. The resulting model has the advantage of enabling computations for (complex) molecular systems and (elevated) temperatures (such as pure C 2 H 6 or CO 2 near 300 K) for which rigorous quantum mechanical treatments (e.g. Close Coupling) require prohibitive computer efforts.

The remainder of this paper is organized as follows: The model is presented in Sec. II together with the associated input data needed for practical computations in the case of ethane gas. Comparisons between measured and computed decays of the laser-induced alignment of pure ethane gas are then presented and discussed in Sec. III before concluding remarks and possible directions for future researches (Sec. IV).

II. MODEL AND DATA USED

For reasons explained below, all operators are, or are assumed to be, diagonal versus the rotational quantum number K. The model used here for symmetric-top species is thus, except for the state-to-state rates, a quite straightforward extension of that for linear molecules 5 .

A. Time-dependent alignment

Consistently with what was measured in Ref. 12, we compute the so-called "alignment factor", mean value of the squared cosine of the angle θ between the molecule symmetry axis (along the C-C bond of ethane) and the ( Z ) axis of polarization of the excitation field, i.e.:

] ( ) cos ( )

J K M t JKM t JKM θ θ = ∑ ρ , (1)
where ρ ρ ρ ρ(t) is the time-dependent density matrix and J, K, and M are the rotational quantum numbers. Since the

JMK JMK P J K M JKM J KM T J K M J t t JKM JKM t t J KM JKM θ ρ θ θ ρ θ = ∑ = ∑ ∑ , (2) where ,
θ implies that ' , 1, 2 J J J J = ± ± .
Starting from a gas at equilibrium, where the density matrix ρ ρ ρ ρ(t<0) before the laser pulse is diagonal with terms given by the Boltzmann relative populations (ie: 0 , ' ' ' , ' , ' , '

( 0)

JKM J K M J J K K M M JKM t ρ δ δ δ ρ < =
), the time dependence is obtained from 3,5 :

Coll dt (t) d ] (t) ), t ( [ i ) t ( dt d       + + - = ρ ρ H H ρ L 0 ℏ , (3)
where H 0 is the free molecule rotation Hamiltonian, which is diagonal with elements given by the rotational energies E JKM of the levels, i.e.:

0 JKM JKM JKM E = H . ( 4
)
The Hamiltonian H L , due to the interaction with the linearly polarized laser field ( ) E t , is given by:

2 2 1 1 ( ) [ . ( )]. ( ) || ( )|| (cos 1/ 3) 2 2 t E t E t E t = - = -γ θ - L H α , (5)
in which angle independent terms which do not participate to the dynamics have been removed. In this equation, α is the polarizability tensor of the molecule and ⊥ γ ≡ α -α is the anisotropy of the polarizability. As in Refs. 3-5,15, the dissipative dynamics are treated with the Bloch model and the Markov and secular approximations, so that one has, for pure gas at a total pressure P:

, , , ", , " , ( ", ") ( , ) ", , " , , " ", " " ( ", ") ( , ) , ' ",," ,' ,' ( ",") ( ',) ( )

JKM JKM J K M J K M JKM JKM J M J M Coll J K M J K M J KM J KM J M J M JM J KM JKM J KM J K M J Coll d t P K t dt P K t d t t P K dt → ≠ → ≠ →     = - ∑             + × ∑         = -     ρ ρ ρ ρ ρ , " ( ", ") ( , ) ', , , ' , , ", ( ) ( ) ( ) ( ) 1 ( ) 2
K M J M J M PD J K M J K M JKM J KM JKM J KM J M J M K P t ≠ → ≠  ∑     + - × ∑    γ ρ . (6)
Note that the fact (see Sec. II.B) that ethane-ethane collisions only enable ∆K=0 transitions was taken into account in these equations which are thus not fully general. The , , ', , ' J K M J K M K → are the pressure-normalized rates of population transfer from state JKM to state ' ' J KM . They include two types of processes: the inelastic ones (in which the value of J changes) as well as those resulting from elastic reorienting collisions (in which the value of J is conserved but that of M changes).

, ' PD JKM J KM γ is the pressure-normalized rate of pure dephasing of the ' JKM J KM coherence which describes the effect of elastic collisions that interrupt the phase of the molecule without quenching it.

B. State-to-state collision-induced rotational transfers

For linear molecules, the equations for the construction of the , ', ' J M J M K → within the Infinite Order Sudden (IOS) approximation were given in Ref. [START_REF] Bréchignac | [END_REF]. They have been improved by introducing detailed balance and adiabaticity corrections 17 , leading to the so-called Energy Corrected Sudden (ECS) model. The latter has been extensively and successfully applied, in the spectral domain, to the calculation of line-mixing effects on absorption spectra (see Chapt. IV of Ref. 18). It also enabled, in the time domain, accurate descriptions of the dissipation of the laser-induced alignment in CO 2 gas 6,7 . A similar procedure was used to build-up an ECS approach for symmetric-top molecules, starting from the IOS model of Ref.

19. Recall that the IOS approach is obtained 18,20 from the Close-Coupling model by first making the Centrifugal Sudden (or Coupled States, CS) approximation, ie: by assuming an effective orbital momentum eigenvalue and freezing the centrifugal potential. Then, starting from the CS equations, the IOS freezes the molecular rotation during each collision, which corresponds to neglecting the energy difference between different rotational states. For molecule-atom collisions, one can then separate the collisional cross -sections into "spectroscopic" and "dynamical" factors in a treatment for symmetric-tops 19 that is analogous to the that given In Refs. 16,21 for linear rotors. The "spectroscopic" terms involve 3J and 6J symbols which describe the coupling of the involved angular momenta, while the "dynamical" factors are directly related to the expansion of the angle-dependent scattering matrix elements into spherical harmonics. Note that, while the first depend on the final quantity of interest (e.g. state-to-state rotational cross sections, line-coupling among infrared absorption lines, isotropic or anisotropic Raman transitions, etc), the second, that are "basic" collisional quantities (see below), do not. It is then possible to introduce a correction in order to (approximately) take into account the energy difference between rotational states and the finite duration of collisions. This is achieved by introducing 17 a so-called "adiabaticity factor" in the expression of the IOS state-to-state cross sections, which depends on the spacing between adjacent rotational levels and on an effective duration of efficient collisions.

In addition, detailed balance corrections are also introduced. Before turning to the state-tostate rotational rates , , ', ', ' J K M J K M K → involved in the relaxation of the alignment, recall that the (spectroscopic) ECS model for symmetric tops enables predictions of the relaxation matrix elements and associated line-mixing process 18 . It was successfully tested by looking at the effects of line-mixing among M components of CH 3 F lines 22 (which involve

0 J K ∆ = ∆ = but 0 M ∆ ≠ changes)
as well as at NH 3 spectra at elevated pressures 23,24 (where the absorption shape is sensitive to all possible J ∆ , K ∆ and M ∆ changes). As mentioned above, within the IOS/ECS model, all state-to-state rates (and relaxation matrix elements) can be written 18,19 in terms of basic dynamical factors ( , , ) ' ' ' " " " ' ' ' " " "

i f Q L M M .
l l L M LM L M J K M J K M S J K M Y J K M = ∑ S [
J K M J J K M L J J L K J J M M M M J J L J L Q L K K L → ≤ ≠    = + + ∑    - -       Ω  × +    - Ω     , (7)
where (:::) is a 3J symbol, ( )

J Ω
is the adiabaticity correction 17 discussed below and

|J-J'| L J+J' ≤ ≤
. Note that the fact that only even L values are kept in Eq. ( 7) is an approximation justified by the symmetry of the ethane molecule (which has no dipole moment) and the fact that the quadrupole-quadrupole interaction makes a significant contribution to intermolecular forces in C 2 H 6 pairs. As done for linear molecules 5 , the ECS rates for upward collisional changes are deduced from those computed using Eq. ( 7) by using the detailed balance relation, i.e.:

0 0 ' , , ' , , , , ', ', ' ' '
( / )

J J K M J K M J K M J K M JKM J KM K K < → → = × ρ ρ , ( 8
)
where 0 JKM ρ is the equilibrium relative population of state JKM . The terms ( )

J Ω and
( ) L Ω
, which are introduced 17 in order to take into account the rotation of the molecule during collisions, are given in terms of a "scaling length" c ℓ (or, alternatively, a characteristic collision duration

r c c v / ℓ = τ
with r v the mean relative speed) by:

2 2 r c 2 J , J ] 24 / ) v / ( 1 [ ) J ( - - ω + = Ω ℓ , (9) where , 2 2 ( )
/ J J JKM J KM E E - - ω = -
ℏ is obtained from the energy difference between rotational level J and the nearest inferior level significantly coupled to J by the intermolecular potential [i.e. J-2 by consistency with the above mentioned fact that only even values of L are retained in Eq. ( 7)]. The basic quantities ( , 0, 0) Q L of this model are the rates for the deexcitation from level J,K,M=L,0,0 to J,K,M=0,0,0. They can be calculated from the intermolecular potential but they are more generally 18 modeled using an analytical function whose parameters are deduced from fits of measured data. Let us emphasize that Eqs. ( 7)- (9) enable to calculate the effects of both inelastic and elastic reorienting collisions since they can be used to predict the , , ' , , '

J K M J J K M M K → = ≠ .
Finally, the expression of the pure dephasing rates , ' PD JKM J KM γ within the IOS approximation, derived as done for a linear molecule in Ref. 5, is:

, ' even 0 2 1 (2 1) (2 1) 0 0 2 ' ' ' ' (2 ' 1) ( ,0,0) 0 0 PD JKM J KM L J J L J J L L J K K M M J J L J J L J Q L K K M M ≠     γ = + + ∑     - -         - +     - -     . ( 10
)
It is important to recall that the ECS and IOS models, as written here and widely used for other studies 18 , neglect the influence of the rotational structure of the collision partner (perturber). Strictly speaking they are thus only applicable to molecule-atom interactions. As for pure CO 2 5 this limitation is, for ethane, of small consequences thanks to the small value of the rotational constant B which makes resonance or non resonance effects between rotational changes of the pair of colliding partners relatively small. This implies that adjacent J levels are close to each other so that these effects, which are associated with the molecular nature of the collisional partner (i.e. its rotational energy structure), are weak. Furthermore, the influence of transfers between rotation and translation, which result in changes of the translational distribution with time after excitation of the rotation by the laser pulse in the alignment experiment, are disregarded in the ECS model. However, the latter remains

C. Data used and computational procedure

The data needed for calculations include the energies JKM ( 1) ( ) [ ( 1)] ( 1)

JKM J JK K E BJ J A B K D J J D J J K D K = + + - - + - + - , (11) and 0 , , exp( /
) / exp( / ) JKM JKM JKM B JKM JKM B J K M g E k T g E k T   = - - ∑     ρ , ( 12
)
where T is the temperature, JKM g is the degeneracy of the JKM level, A and B are the rigid rotor rotational constants and D J , D JK and D K describe the effect the centrifugal distortion.

Their values were taken from Ref. 12 together with that of the anisotropy of the C 2 H 6 polarizability (γ=0.7 A 3 ). For the laser pulse, we used the parameters reported in the experimental studies 12,26 .

As widely done in various studies of molecular collisions 18,27 , the basics rates ( , 0, 0) Q L of the ECS model have been represented by the exponential-power law: 00 / 0 ( ,0, 0)

[ ( 1)]

L B E k T Q L Q L L e -β -α = + . ( 13
)
The values of the final set of ECS parameters ( 0 Q , α , β , and c ℓ ) at room temperature have been obtained from fits of the pressure-broadening coefficients of lines of ethane. In the absence of data for isotropic Raman lines, we used values for infrared R Q-lines 28 and wrote:

1 ", , ', , 1 , , ', , ' ( ', , ') ( , , ) , 1,
', 1, ' ( ', , ') ( , , ) 1 ( 21) 2

v J K v J K J K M J K M M J K M J K M J K M J K M J K M J K M J K K - → + → ≠ + → + ≠  γ + ∑ ∑     + ∑    ≃ , (14) in which
", , ', , 1 v J K v J K → + γ is the pressure-broadening coefficient of the ", , ', , 1 v J K v J K → + R Q optical transitions (v" and v' denoting vibrational quantum numbers). Figure 1 shows that a quite satisfactory fit is obtained with the following values of the ECS model parameters: 0 Q =44.2 10 -3 cm -1 /atm (8.32 ns -1 /atm), 0.87 α = , 0.009 β = and 1.4

c = ℓ A, (15)
that we have retained for all computations.

v J K v J K → + γ R Q(J) lines of the ν 9
band of pure ethane 28 (symbols) and those computed using Eqs. ( 7)-( 9), ( 13)-( 15) (lines). The results in black, red and blue are for K=0, K=2 and K=6, respectively.

In the calculations, the conservative values of J max =|K max |=|M max |=50 for rotational states and a time step of 5 fs [to solve Eq. ( 3)] were used. For comparisons with experiments and as done in Ref. 12, the computed alignment factor versus time was convoluted by a Gaussian function (FWHM of 150 fs) which takes into account the finite duration (100 fs) of the probe pulse and the effect of the crossing angle between the two beams. Since the first excited vibrational state (ν 4 ) is significantly populated at room temperature (25%), two calculations of the alignment factor were made using the rotational constants of the ground and v 4 =1 states.

For comparisons with measurements, they were then combined, as done in Ref. (7)] with the pure dephasing rates , ' PD JKM J KM γ [Eq. (10)] show that the latter are more than one order of magnitude smaller, as in the case of pure CO 2 5 . Their contribution was thus disregarded and only the , , ', , ' J K M J K M K → were kept in Eq. ( 6).

J K M J K M K → [Eq.

III. RESULTS AND COMPARISONS WITH MEASUREMENTS

A. Dissipation of the transient alignment

A comparison between the measured alignment factor for pure ethane gas at P=0.69 bar and initially at 295 K 26 and those computed with the ECS approach at the same pressure P and for collision-free conditions (P=0 bar), are plotted in Fig. 2 for a broad range of delays ∆t after the pulse. Note that, in the birefringence experiments of Refs. 12 and 26, the probe laser measures the change ∆n(∆t) of the refractive index that is induced by the pump pulse. This change is proportional 12 to the so-called alignment factor 2 cos ( ) 1/ 3 t θ ∆but the proportionality factor leading to the signal delivered by the photodiodes in the experiment is not known. The results are thus presented in arbitrary units and the calculated results in Figs.

2a and 2b have been multiplied by a constant for the best match with the measured amplitude of the first revival in Fig. 2c. As can be seen, the influence of collisions (i.e. of pressure) on the decay of the revivals amplitudes, that can be deduced from the comparison of Figs. 12a and12b, is significant. Furthermore, the comparison of the results in Figs. 12b and12c gives a first indication of the quality of the ECS quantum model. Note that the permanent alignment is here negligible due to the weak intensity of the pulse (recall that, for moderate intensities, the magnitude of the permanent alignment scales with the square of the intensity while those of the revivals increase linearly 5 ). The quality of the ECS model for the dissipation of the alignment revivals is confirmed by Fig. 3 which displays detailed views of measured and computed alignment factors around some of the revivals. Both the shapes and the magnitudes are quite well reproduced by theory (note the large change of the y-axis scale from Fig. 3a to Fig. 3f) which slightly overestimates the decay with time of the revivals peak to peak amplitude. Let us note that one must be cautious when drawing conclusions on the model quality by a direct comparison, such as the one displayed in Fig. 3, between one single experimental recording of the alignment and the predictions for the following reasons: (i) the first is that measurements carry uncertainties, in particular because the intensity of the alignment pulse, as seen by the probe through the spatial overlapping of the two beams, may vary during the numerous shots needed to determine the alignment factor for different delays. Indeed, a slow drift in the pulse intensity induces a bias in the decay with time of the revivals amplitudes. (ii) The measured shapes and amplitudes of the alignment revivals are affected by the finite duration of the probe and non zero angle between the two pulses. These somehow act like a low-pass filter whose effects are taken into account in the calculation (see Sec. II.C) by convoluting the predicted timedependent alignment factor by a Gaussian function. This is obviously approximate and induces errors that affect the shape of the calculated alignment within the revivals (all the more that the revival shows numerous and narrow structures). According to these elements, carrying an analysis of the detailed differences between measured and calculated results in Fig. 3 and drawing conclusions from a comparison for a single alignment trace and pressure is, in our opinion, risky. However, the analysis of numerous experimental results for different pressures enables to deduces 12 a density normalized time constant for the decay of the amplitude of the alignment revivals. As shown by the values given in Table 1, the ECS model underestimates this time constant, a result which is consistent with what is indicated by Fig. 3, i.e. the fact that calculations overestimate the decay of the revivals amplitude with increasing delay.

10.

12. 14.

16.

-

B. Dissipation of the permanent alignment

A comparison between measured alignment factors recorded at pressures of 2 and 6 bar for more intense laser pulses which make the permanent alignment significant and measurable and the associated predictions is plotted in Fig. 4. As can be seen, the quantum ECS model quite well reproduces the decays of the permanent alignment with time, confirming the interest of this approach for the modeling of the changes of the rotational angular momentum magnitude as well as orientation. Note that the apparent inconsistency in the differences between measurements and computations at 2 and 6 bar results from experimental errors (likely mostly on the zero level of the signal) and not from the fact that the model does not well describe the effect of increasing pressure. Indeed, while the time constant of the predicted exponential decay of the permanent alignment is inversely proportional to pressure, as it should be for the considered moderate pressures for which collisions are binary, the experimental values deviate from this rule. However, these inconsistencies are within the uncertainties of the measurements and scatter of the results obtained for various pressures which can be seen in Fig. 5 of Ref. 12 and lead to the error bars given in the Table 1.

C. "Gyroscopic" effect

In order to go further, we determined from the ECS-computed alignment traces, the density normalized time constants driving the collisional decays of the amplitudes of the particularly when considering that no parameter was adjusted in the calculations in order to improve the agreement. In fact, tests show that it is possible to simultaneously lower P τ and increase T τ by lowering the ECS parameter α while increasing 0 Q [see Eq. ( 13)] at the price of a slight degradation of the ECS-predicted broadening parameters displayed in Fig. 1, however well within experimental uncertainties.

The values in Table 1 also show that measurements as well as computations reveal that the collisional dissipation of the permanent component of the alignment is significantly slower than that of the revivals amplitude. A similar situation was observed and predicted for linear molecules5-7,11 and explained by a "gyroscopic effect" 5 resulting from the fact that collisions, while they change the rotational speed (i.e. the value of J), tend to conserve the direction of the rotational angular momentum (i.e. the value of M/J). In the case of ethane, the situation is similar, as shown by the state-to-state rates plotted in Fig. 5, since the collisional cross sections for the (J,K,M)→ (J',K,M') change have a maximum for M'/J'≈M/J. Note that, as discussed in Sec. II.C, the C 2 H 6 -C 2 H 6 intermolecular potential is close to that for a pair of linear molecules. It is thus not surprising that Fig. 5

D. Discussion on the models

For a system like pure ethane at room temperature, rigorous "first principle" quantum mechanical methods cannot be used to predict the decay of the alignment even though an accurate intermolecular potential is available. 25 The reason for this is that the number of significantly populated rotational states and of collisionally opened channels that need to be taken into account, as well as that of the state-to-state rates that are needed are by far too large for calculations to be tractable yet. One thus has to rely on approximate models. From this point of view, only the ECS approach described in this paper and the requantized Molecular Dynamics Simulations (rCMDS) presented in Ref. 14 have been proposed so far, which have different interests and weaknesses. The rCMDS have the advantages of directly using an input intermolecular potential, of taking into account the rotation-translation transfers and thus the eventual influence of the progressive heating of the translational motion during the collisional dissipation, and of correctly treating (at least classically) molecular pairs. In contrast, the ECS approach relies on knowledge of the basic rates which in many cases cannot be calculated and are approximately modeled (e.g. Eq. ( 13)] with parameters for the determination of which some measurements (e.g. Fig. 1) are needed. Furthermore, rotation-translation transfers are disregarded and the collision partner is treated as an atom with not rotational degree of freedom. However, within these approximations, the ECS approach is quantum and thus correctly describes the Raman transitions induced by the pump laser and the coherences in the wave-packet that they generate. Furthermore, going beyond the rigid rotor model and taking into account effects such as centrifugal distortion with this model is quite straight forward. In contrast, the requantization of classical simulations as proposed in Refs. 5 and 14 remains some kind of "trick" that is not fully satisfactory and has its limits, particularly when the kinetic temperature becomes comparable with the rotational constants. Furthermore, it is not possible to correctly introduce centrifugal distortion effects. Even though the collisional decay of the alignment may be well predicted within a rigid rotor approach, the shapes of the revivals are not correctly predicted as shown in Ref. 14. Hence the ECS and rCMDS have different interests and drawbacks but they are complementary. In order to explain this complementarity, let us consider the case where one needs to predict the dissipation of the alignment of a pure gas of linear or symmetric top molecules, for instance. If only an intermolecular potential is available, with not other data from which the ECS basic rates can be determined, rCMDS is the only solution. On the opposite, if there is no potential available but some line broadening measurements have been made that can be used for the determination of the ECS parameters, rCMDS cannot be made and the ECS model is the only applicable one.

IV. CONCLUSION

This paper presents the first quantum model for calculations of the collisional dissipation of the laser-induced alignment of a gas of symmetric-top molecules. It is based on a kinetic equation describing the time evolution of the density matrix, in which the effects of intermolecular collisions are taken into account through state-to-state rates constructed using the Energy Corrected Sudden approximation. This approach is applied to ethane gas for which measurements of the alignment have been made recently. The associated comparison between predicted and measured time-dependent alignment signals demonstrates the quality of the model for the decays of both the permanent and transient components of the alignment. The analysis of the computed state-to-state collisional rates shows that they are the largest when the orientation of angular momentum associated with the rotation of the molecule symmetry axis is conserved (i.e. M/J practically does not change). This explains the experimentally and theoretically observed fact that the permanent alignment decays more slowly than do the alignment revivals amplitudes. It is important to note that the present paper only provides a limited test of the ECS model for the collisional dissipation of symmetric-tops molecules. Indeed, as discussed in this paper, 0 K ∆ ≠ transitions play a negligible role in the case of pure ethane whose behavior is thus close to that of a linear molecule. It would thus be of interest to find a molecular system (including a symmetric-top molecule and an eventually different one in which it is diluted) for which the situation is different and that could be investigated experimentally. This may not be so easy since two constraints should be satisfied. The first is that the sensitivity of intermolecular forces to rotation of the molecule around its symmetry axis should be important. The second is that the anisotropy of the polarizability of the molecule should be sufficient to enable a significant degree of alignment using current and reasonable laser pulse intensities. In any case, one should remember that the proposed ECS model has limitations that may not make it suitable for more complex systems than pure ethane, for two main reasons. The first is that the collision partner is treated as an atom so that resonance effects (appearing when each molecule of the colliding pair makes a rotational change) occurring in molecule-molecule collisions are not taken into account, The second is the use of approximate corrections of the IOS model, through the adiabaticity factor, in order to take into account the fact that molecules do rotate during collisions. These have moderate consequences when the rotational constant is small but may lead to significant errors when it is not the case (e.g. NH 3 , PH 3 , CH 3 D or linear molecules such as HCl and HF).

  applicable here since, thanks to the (moderate) laser-pulse energies in the experiments 12,26 used below for the test of the model and to the small value of the anisotropic polarizabiliy of ethane. These make the increase of the rotational energy induced by the interaction of ethane molecules with the excitation field relatively small. The collision-induced rotation-translation transfers thus only slightly change the translational motion and have very small effects on the decay with time of the alignment (see Ref. 5 for a discussion of this issue in the case of CO 2 which has a much larger anisotropic polarizabiliy).

E and the equilibrium relative populations 0

 0 JKMρ of the rotational levels, the C 2 H 6 anisotropy of the polarizability, the characteristics of the laser pulse, and the parameters of the ECS model [the ( , 0, 0) Q L for Eqs. (8) and (10) and c ℓ for Eq. (9)]. The values of JKM E

Fig. 1 :

 1 Fig. 1: Measured self-broadening coefficients for the ", , ', , 1 v J K v J K → +

Fig. 2 :

 2 Fig. 2: Alignment factors predicted under collision-free conditions (a) and at a pressure of 0.69 bar (b) together with the measured values at 0.69 reproduced from Fig. 2 of Ref. 26 (c).

Fig. 3 :

 3 Fig. 3: Comparison between the measured (red circles, from the experiments of Ref. 26) alignment factor at 0.69 bar and 295 K and that predicted using the ECS model (blue line). Panels (a),(b),(c),(d),(e), and (f) display the results obtained around the revivals centered atT rev /2, and 3T rev /2, 6T rev /2, 9T rev /2, 12T rev /2 and 15T rev /2, respectively (

Fig. 4 :

 4 Fig. 4: Measured (red circles, from the experiments of Ref. 12) and computed (blue lines) alignment factors in pure ethane initially and 295 K and pressures of 2 bar (lower panel) and 6 bar (upper panel).

Fig. 5 :

 5 Fig. 5: Pressure normalized rates , , ', , ' J K M J K M K

  permanent ( P τ ) and transient ( T τ ) components of the alignment, as done in Refs. 5,12. The values obtained are reported in Table 1 with those retrieved from experiments 12 and predictions of requantized Classical Molecular Dynamics Simulations 14 . As can be seen the overall consistency between experimental and computed values is quite satisfactory,

Table 1 :

 1 Density-normalized time constants of the collision-induced decay of the amplitudes of the permanent ( Pτ ) and transient ( T τ ) alignments.

	looks very similar to Fig. 9 of Ref. 5

Acknowledgements: This work was supported by the Conseil Régional de Bourgogne under the PhotCom PARI program, the European Union (FEDER program), the Labex ACTION program (No. ANR-11-LABX-01-01).


Directeur

Gabriel Huard

Keywords: interaction apprenant-enseignant (n.f.), interaction pédagogique (n.f.) teacher-student interaction, student-teacher interaction

assignments; homework devoirs (n.m.plur.); travaux (n.m.

Bureau de la traduction

Le Bureau de la traduction offre un large éventail de services à des clients du gouvernement qui doivent communiquer dans plusieurs langues ou organiser des événements à l'intention de participants de langues différentes. Le Bureau est renommé pour la grande qualité de ses services, qu'il s'agisse de traduction, d'interprétation, de services linguistiques ou de terminologie.

vii

Avant-propos

Le XXI e siècle s'ouvre sur la société du savoir et de l'intelligence, sur la transmission fulgurante des derniers acquis technologiques, scientifiques et pragmatiques aux coins les plus éloignés du village planétaire, sur l'échange ininterrompu de savoirs, d'expériences, de compétences et de biens à l'aide de conduits ultra-sophistiqués tels l'inforoute ou le cyberespace.

Les administrations publiques demeurent les principales responsables de l'éducation des jeunes, mais tout comme les entreprises privées, elles se consacrent dans une proportion croissante à la formation professionnelle de leurs propres employés, devenue la condition sine qua non de leur productivité, de leur compétitivité et de leur progrès. D'où l'attention portée ces dernières années aux « organisations qualifiantes » et aux « entreprises apprenantes ». L'éducation des jeunes et des adultes, dispensée à l'école, à l'université ou en milieu de travail prend ainsi une place grandissante du côté de l'offre et de la demande, tant dans le service public que dans le secteur privé, et entraîne le développement d'un très grand marché mondial de services et de contenus éducatifs qui déborde les méthodes et les techniques traditionnelles de l'enseignement à distance, par correspondance, en privé ou en salle de classe pour s'installer sous les appellations apprentissage en ligne, autoformation à domicile, université virtuelle ou cyberenseignement dans les intranets d'entreprise, les réseaux scolaires ou

Foreword

The 21st century ushers in a knowledgebased and intelligence-driven society in which the latest scientific, technological and practical advances very rapidly reach the farthest corners of the global village, and where the non-stop exchange of knowledge, experience, skills and goods relies on ultrasophisticated channels of communication such as the information highway and cyberspace.

In this society, public administrations retain the primary responsibility for educating the young, and just like the private sector, they are devoting a growing share of their energy to developing and upgrading the skills of their own employees. On-the-job learning has become an essential requirement for productivity, competitive strength and progress, and has given rise to the concept of learning organizations.

The education of children and adults, whether offered at school, in university or in the workplace, is playing an increasingly large role in the supply and demand cycle in both the public and private sectors contributing to the development of a huge global market for educational content and services. These services go beyond traditional methods and techniques such as distance learning, in-class or private lessons, correspondence courses, and into the new realm of e-learning, home-based selftraining, virtual universities and online tutoring using business intranets, school and university networks, the Internet or the World Wide Web. viii universitaires, l'Internet ou le Web. Sensibilisée à cette problématique depuis quelques années dans le cadre du projet de cybergouvernement appelé Le gouvernement en direct, la fonction publique canadienne s'est taillé une place de choix parmi les administrations publiques modernes qui investissent massivement dans le développement professionnel de leurs employés et dans la démocratisation de l'accès au savoir spécialisé grâce au virtuel.

Le ministère des Travaux publics et des Services gouvernementaux compte parmi les entités fédérales les plus dynamiques en matière de mobilisation des employés à la formation professionnelle, comme l'a témoigné le lancement officiel de L'Année de l'apprentissage en ligne le 10 septembre 2002 (http://source.tpsgc.gc.ca/dgrh/training/imp/l aunch2002-f.html). C'est dans ce cadre riche en promesses pour l'avenir que le Bureau de la traduction -principal instrument gouvernemental en matière de communication efficace dans les deux langues officielles du Canada -est fier de mettre ce premier lexique bilingue de l'apprentissage en ligne à la disposition de notre ministère, de la fonction publique fédérale et du grand public canadien, marquant ainsi sa propre contribution au fascinant foisonnement d'activités éducatives qu'est la transmission virtuelle du savoir à l'aube du troisième millénaire.

The Canadian public service became involved in these issues a few years ago as it set in motion the cybergovernment project known as Government On-Line. Today, it ranks among the modern public administrations that invest massively in the professional development of their employees and in the democratization of virtual access to specialized knowledge.

The Department of Public Works and Government Services is among the most dynamic federal entities when it comes to employee enrolment in professional training, as seen on September 10, 2002, at the official launch of the Year of E-Learning (http://pwgsc.gc.ca/hrb/training/imp/launch2 002-e.html). Within this very promising framework, the Translation Bureau -a primary government agency for ensuring effective communication in Canada's official languages -is proud to make its first bilingual glossary on e-learning available to our department, the federal public service and the Canadian public, as a token of its contribution to the multitude of learning activities brought about by the virtual transmission of knowledge at the dawn of the third millennium.

Introduction

Le Lexique de l'apprentissage en ligne regroupe plus d'un millier de termes spécialisés dans chacune des deux langues officielles. Ces termes désignent trois catégories de concepts : les concepts relatifs à la pratique des activités éducatives (structuration et livraison de savoirs, conception de programmes d'études et maniement d'outils pédagogiques, méthodes d'apprentissage et de tutorat, etc.); les concepts relatifs aux acteurs qui s'y consacrent (apprenants, enseignants, aideenseignants, fournisseurs de services, éditeurs et fournisseurs de contenus, etc.); et les concepts traitant des moyens et des lieux privilégiés où se déroulent ces activitiés (universités et classes virtuelles et traditionnelles, audio-et visioconférences, cybersespaces, babillards électroniques, postes de travail en ligne, etc.).

Le lecteur reconnaîtra plusieurs termes empruntés au vocabulaire de l'enseignement traditionnel, ainsi que de nombreux termes propres à l'informatique et à la télématique, indispensables à la communication dans le domaine décrit. Il s'apercevra aussi qu'un nombre considérable de désignations présentent un caractère néologique prononcé souvent motivé par le besoin de distinguer les concepts sous-jacents de leurs parents traditionnels : l'apprentissage en classe ou en présentiel se distingue de l'apprentissage en distanciel, même s'ils coexistent dans le nouveau concept de l'apprentissage mixte, la réalité virtuelle se distingue de la réalité physique, et l'Internet du Web. Il constatera que l'interaction en ligne peut inclure à la fois l'activité en direct et en différé, que l'instruction peut être envisagée dans la

Introduction

The E-Learning Glossary contains over a thousand specialized terms in each official language. These terms designate three sets of conceptual clusters. The first set covers educational practices, such as structure and delivery of knowledge, curriculum design, use of pedagogical tools, learning and teaching strategies. The second set deals with the players, namely learners, teachers, teachers' aids, service providers, content designers and developers. The third set covers the ways and means by which educational activities take place, including virtual and traditional universities and classrooms, audio-and video-conferences, cyberspaces, electronic bulletin boards, and online workstations.

Readers will recognize many terms borrowed from the vocabulary of traditional education, and some others from computer science and telematics, which are indispensable to communication in the e-learning field. Readers will also notice that there are a large number of newly coined words, often used to better distinguish new concepts from their traditional counterparts. Thus, classroom learning is contrasted with distance learning and with online learning even though they co-exist in the new concept of blended learning. Similarly, virtual is contrasted with brick-and-mortar, and the Internet is distinguished from the Web. Readers will discover that online interactions may include both live and delayed activities, that instruction can be seen from the perspective of the learner, the x perspective de l'apprenant, du système tutoriel aussi appelé logiciel de tutorat et tutoriel, ou encore de l'enseignant et même du cyberenseignant. Le domaine de l'apprentissage en ligne étant relativement nouveau, le lecteur s'apercevra bien vite d'un autre fait frappant, à savoir, que l'emploi des termes dans cette spécialité est encore flottant et qu'il s'enrichit très rapidement d'appellations inattendues, accrocheuses, aussi bien que d'appellations lourdes ou longues. Soucieux de préserver la concision et la cohérence du lexique, nous avons évité l'énumération répétitive des variantes orthographiques, grammaticales ou lexicales en les regroupant sous une seule entrée principale. En anglais, nous avons ainsi retenu l'orthographe des mots communs (adviser, behavioural, -centred, counsellor, etc.) du Gage Canadian Dictinary, mais nous avons adopté la graphie online dans toutes les entrées concernées suivant le seul usage attesté dans la documentation de spécialité, tout en signalant, dans les entrées principales online, offline les graphies on-line, on line et off-line, off line trouvées dans les dictionnaires courants. Dans le cas de online, nous avons ajouté les synonymes spécialisés cyber-, network-centred, virtual pour rendre en ligne, en réseau, cyber-, virtuel. Ce faisant, nous avons tenu compte des prédilections de l'usage spécialisé : p.ex., apprentissage en ligne est plus fréquent en français que cyberapprentissage mais apprentissage virtuel est rarement utilisé; université virtuelle est très fréquent, mais université en ligne est quasi-inexistant, tandis que cours en ligne et cours virtuel sont interchangeables dans tous les contextes. L'ordre des synonymes reflète autant que possible leur fréquence d'emploi.

En français, le souci de lisibilité et de simplicité a inspiré le recours à la seule forme masculine tout au long du lexique tutor, the tutoring software, the teacher or even the online teacher. In any event, it is clear that e-learning is a relatively new specialized field, that its vocabulary is still unsettled and that it may well acquire unexpectedly expressive terms as well as cumbersome ones.

For the sake of conciseness and consistency, we have avoided the repetition of spelling, grammatical and lexical variants in all entries by listing them once only, in the main entry. In English, we have retained the spelling given in The Gage Canadian Dictionary for common language words, such as adviser, behavioural, -centred, and counsellor, but we have adopted the spellings online and offline throughout the Glossary, since they are preferred in e-learning documentation. However, we have added to their main entries the variants on-line and on line, off-line and off line found in current dictionaries. In the case of online, we have included its synonyms network-centred, cyber-, and virtual. The presence of these synonyms elsewhere in the Glossary takes into account their preferred usage among specialists of the field. For example, the term e-learning, i.e. electronic learning, is more common in English than online learning and virtual learning, whereas cyberlearning is nearly nonexistent. At the same time, online course and virtual course are interchangeable in all contexts. The order in which synonyms are listed usually reflects their frequency of use.

In French, the desire for simplicity and readability led us to use the masculine form exclusively, because it is grammatically xi pour son caractère non marqué grammaticalement, l'emploi alternatif du singulier et du pluriel dans contenu(s), formation(s), connaissance(s) et savoir(s) tel qu'attesté dans la documentation dépouillée, et l'élimination du trait d'union dans la graphie des mots composés où se rencontrent deux voyelles, usage reconnu par le Petit Robert (p. ex., téléapprentissage, microordinateur). Certains synonymes (p.ex., sponsoring pédagogique, e-apprentissage) portent des marques d'usage géographique (EURope, CANada).

Le Lexique de l'apprentissage en ligne fera sans doute l'objet de nombreuses actualisations, puisqu'il marque le début d'un dialogue avec le lecteur dans l'effort de consignation et de normalisation de l'usage qui caractérise tous les travaux terminologiques à la Direction de la terminologie et de la normalisation du Bureau de la traduction.

Le lecteur est prié de nous envoyer ses commentaires et suggestions à l'adresse suivante : Direction de la terminologie et de la normalisation Bureau de la traduction Travaux publics et Services gouvernementaux Canada Ottawa (Ontario) K1A 0S5 CANADA Par téléphone : (819) 997-9727 Par télécopieur : (819) 953-8443 Par courriel : termino@tpsgc.gc.ca unmarked, to alternate the singular and plural in the entries containing the terms contenu(s), formation(s), and savoir(s) as recorded in specialized usage, and to eliminate the hyphens between vowels in compound words, as recommended in the Petit Robert dictionary for such entries as téléapprentissage and microordinateur. Certain synonyms (e.g. sponsoring pédagogique, e-apprentissage) bear geographic labels (EURope, CANada).

The E-Learning Glossary will undoubtedly be updated since its present edition is but a starting point for a dialogue with the reader in an effort to record and standardize usage. Such a dialogue is part and parcel of the ongoing terminology work done in the Terminology and Standardization Directorate of the Translation Bureau.

Any comments and suggestions should be sent at the following address: The comments and suggestions provided by my fellow terminologists -Diane Nolet, François Mouzard, Yolande Bernard, Charles Skeete, Marie-Josée Préseault and Natalie Cécile Ranger -have been very valuable in helping to improve the quality and content of the E-Learning Glossary. Once again, Diane Lafrance did most of the documentary research and prepared the bibliography. Martine Racette edited the introductory pages in French and Barbara Collishaw and Linda P. Collier translated them into English. Claudine Poirier helped by scanning documents, recording the data on TERMIUM ® records and proofreading the manuscript. Rachel Laflamme designed the cover of the Glossary, and formatted the electronic and paper versions. Their contribution is hereby gratefully acknowledged.

xv

Guide d'utilisation

User's Guide

Pour alléger la présentation du lexique et en faciliter la consultation, nous avons adopté les règles suivantes :

Les entrées sont classées suivant l'ordre alphabétique absolu.

Les synonymes, les variantes et les abréviations sont séparés du terme principal par un point-virgule.

La nature grammaticale et le genre des termes français sont indiqués entre parenthèses de même que les éléments orthographiques facultatifs.

Les chiffres en exposant distinguent les différentes acceptions d'un terme.

Abréviations

(adj.) adjectif (n.f.) nom féminin (n.m.) nom masculin (plur.) pluriel (v.) verbe

[CAN] Canada

[EUR] Europe

To streamline the glossary and facilitate its use, the following rules have been adopted:

Entries are arranged in strict alphabetical order.

Semicolons are used to separate synonyms, variants and abbreviations from the main entry.

Parentheses are used to indicate the part of speech and the gender of the French terms; they also enclose an optional spelling variant.

Superscript numbers distinguish between the different meanings of a single term. bibliothèque de cas (n.f.) VOIR casothèque (n.f.) bibliothèque de contenus (n.f.) content library bibliothèque de corrigés (n.f.) VOIR base de corrigés (n.f.) bibliothèque de didacticiels (n.f.) VOIR didacthèque (n.f.) bibliothèque de fiches-outils (n.f.) learning-sequence library bibliothèque d'exercices et mises en situation (n.f.)

Abbreviations

drill-and-practice library bibliothèque électronique (n.f.) 1 ; bibliothèque numérique (n.f.); infothèque (n.f.) electronic library 1 ; e-library 1 ; digital library; digitized library bibliothèque électronique (n.f.) 2 ; bibliothèque virtuelle (n.f.); bibliothèque en ligne (n.f.); cyberthèque (n.f.) electronic library 2 ; e-library 2 ; online library; cyberlibrary; virtual library bibliothèque en ligne (n.f.) VOIR bibliothèque électronique (n.f.) 2 bibliothèque numérique (n.f.) VOIR bibliothèque électronique (n.f.) 1 bibliothèque réutilisable (n.f.) VOIR logithèque réutilisable (n.f.)

bibliothèque virtuelle (n.f.) VOIR bibliothèque électronique (n.f.) conception axée sur l'apprenant (n.f.) learner-centred design conception de contenu pédagogique (n.f.) VOIR conception de parcours d'apprentissage (n.f.) conception de contenus pédagogiques (n.f.) VOIR conception pédagogique (n.f.) conception de didacticiels (n.f.); conception de logiciels éducatifs (n.f.) courseware design; educational software design conception de l'interaction didacticielle (n.f.) courseware interaction design conception de logiciel(s) d'apprentissage (n.f.)

learning-software design conception de logiciels éducatifs (n.f.) VOIR conception de didacticiels (n.f.) conception de parcours d'apprentissage (n.f.); conception de contenu pédagogique (n.f.)

learning-path design conception de ressources didactiques (n.f.) learning-resource design conception de story-boards didacticiels (n.f.) courseware storyboard design conception d'interactions (n.f.) interaction design conception en ligne (n.f.) online design conception graphique (n.f.) graphics design conception pédagogique (n.f.); conception de contenus pédagogiques (n.f.) educational content design; instructional content design conduite au travail (n.f.); comportement au travail (n.m.) on-the-job behaviour conférence audiographique (n.f.) VOIR audioconférence (n.f.) conférence par ordinateur (n.f.); téléconférence par ordinateur (n.f.); conférence virtuelle (n.f.); cyberconférence (n.f.) one-on-one; one-to-one; person-to-person; P2P industrie de la connaissance (n.f.) VOIR industrie du savoir (n.f.) industrie de la formation (n.f.) training industry industrie de la formation en ligne (n.f.) e-training industry industrie de l'éducation en ligne (n.f.) VOIR industrie de l'enseignement en ligne (n.f.) industrie de l'enseignement en ligne (n.f.); industrie de l'enseignement virtuel (n.f.); industrie de l'éducation en ligne (n.f.) online education industry; e-learning industry; online learning industry industrie de l'enseignement en ligne (n.f.) VOIR industrie de l'enseignement virtuel (n.f.) industrie de l'enseignement virtuel (n.f.) VOIR industrie de l'enseignement en ligne (n.f.) industrie de l'enseignement virtuel (n.f.); industrie du cyberenseignement (n.f.); industrie de l'enseignement en ligne (n.f.)

computer
e-teaching industry industrie du contenu (n.f.) content business; content industry industrie du cyberenseignement (n.f.) VOIR industrie de l'enseignement virtuel (n.f.) industrie du savoir (n.f.); industrie de la connaissance (n.f.)

U

université classique (n.f.); université réelle (n.f.); université traditionnelle (n.f.); université en dur (n.f.) traditional university; physical university; bricks-and-mortar university; real university université d'entreprise (n.f.); université d'industrie (n.f.) corporate university; industry university; in-house university université d'industrie (n.f.) VOIR université d'entreprise (n.f.) université en dur (n.f.) VOIR université classique (n.f.)

université en ligne (n.f.) VOIR université virtuelle (n.f.)

université ouverte (n.f.); université sans murs (n.f.) open university université réelle (n.f.) VOIR université classique (n.f.)

université sans murs (n.f.) VOIR université ouverte (n.f.)

université traditionnelle (n.f.) VOIR université classique (n.f.)

université virtuelle (n.f.); université en ligne (n.f.); e-université (n.f.)

virtual university; electronic university; e-university; online university univers virtuel (n.m.) VOIR environnement virtuel (n.m.)

V validation des acquis (n.f.) VOIR validation des savoirs acquis (n.f.) validation des savoirs acquis (n.f.); validation des acquis (n.f.) acquired knowledge validation; background knowledge validation valise de formation multimédia (n.f.); valise multimédia (n.f.)

Other Translation Bureau Publications

The Translation Bureau has a special mandate to create a standardized terminology for the Government of Canada. We produce more than 100 glossaries in a variety of specific fields. By reducing research time, our terminology tools can significantly improve your productivity. ! Cumulative Index

  (s) (n.m.) VOIR transfert de savoir(s) (n.m.) transfert de savoir(s) (n.m.); transfert de connaissance(s) (n.m.) knowledge transfer transmis par satellite VOIR diffusé par satellite transmission de l'enseignement (n.f.); prestation éducative (n.f.) delivery of instruction transmission des connaissances (n.f.) VOIR transmission du savoir (n.f.) transmission du savoir (n.f.); transmission des connaissances (n.f.) knowledge dissemination; knowledge distribution transmission Web (n.f.) VOIR diffusion sur le Web (n.f.) transmiweb (n.m.) VOIR diffusion sur le Web (n.f.) travail collaboratif sur le réseau (n.m.) VOIR travail collectif en réseau (n.m.) travail collectif (n.m.) VOIR travail de groupe (n.m.) travail collectif en réseau (n.m.); travail d'équipe en ligne (n.m.); travail collaboratif sur le réseau (n.m.) online teamwork; online collaborative work; networked teamwork travail de groupe (n.m.); travail collectif (n.m.) group work; team work travail d'équipe en ligne (n.m.) VOIR travail collectif en réseau (n.m.) travail en ligne (n.m.); e-travail (n.m.) electronic work; e-work travaux (n.m.plur.) VOIR devoirs (n.m.plur.) tuteur (n.m.) VOIR enseignant-tuteur (n.m.) tuteur en ligne (n.m.); e-tuteur (n.m.) e-tutor; online tutor tuteur informatisé (n.m.); système tutoriel (n.m.) automated tutoring system; computer-based tutor; computerized tutor; computer tutor tuteur intelligent (n.m.) VOIR système tutoriel intelligent (n.m.) tuteur personnel accessible par courrier électronique (n.m.) VOIR tuteur personnel disponible par courriel (n.m.) tuteur personnel disponible par courriel (n.m.); tuteur personnel accessible par courrier électronique (n.m.) e-mail personal tutor; individual online tutor; personal e-mail tutor tutorat (n.m.) tutoring; tutorial instruction tutorat à distance (n.m.) VOIR télétutorat (n.m.) tutorat à la carte (n.m.) VOIR tutorat individualisé (n.m.) tutorat asynchrone (n.m.) asynchronous tutoring tutorat asynchrone en ligne (n.m.) VOIR tutorat virtuel en différé (n.m.) tutorat asynchrone par courriel (n.m.) e-mail asynchronous tutoring; e-mail delayed-response tutoring tutorat axé sur les conséquences (n.m.en classe virtuelle avec visio (n.m.) tutorat en ligne (n.m.) e-tutoring; online tutoring tutorat en tête-à-tête (n.m.); tutorat individuel (n.m.) one-on-one tutoring; one-to-one tutoring; person-to-person tutoring; P2P tutoring; individual tutoring; personal tutoring tutorat en tête-à-tête virtuel (n.m.) VOIR tutorat individuel en ligne (n.m.) tutorat frontal par webcam (n.m.) VOIR tutorat via visioconférence en face-à-face (n.m.) tutorat générique (n.m.); tutorat standard (n.m.); tutorat non personnalisé (n.m.) generic tutoring tutorat individualisé (n.m.); tutorat à la carte (n.m.) individualized tutoring tutorat individuel (n.m.) VOIR tutorat en tête-à-tête (n.m.) tutorat individuel en ligne (n.m.); tutorat individuel virtuel (n.m.); tutorat en tête-à-tête virtuel (n.m.); cybertutorat privé (n.m.) one-to-one e-tutoring; person-to-person e-tutoring; P2P e-tutoring; P2P online tutoring tutorat individuel synchrone (n.m.) VOIR tutorat synchrone individuel (n.m.) tutorat individuel virtuel (n.m.) VOIR tutorat individuel en ligne (n.m.) tutorat individuel virtuel en direct (n.m.) VOIR tutorat synchrone individuel (n.m.) tutorat juste-à-temps (n.

  virtuel (n.m.) vêtement cybernautique (n.m.) VOIR combinaison RV (n.f.) vidéo-apprentissage (n.m.) VOIR apprentissage par vidéo (n.m-à-face (n.f.); visioconférence en tête-à-tête (n.f.); face-à-face par visio (n.m.); tête-à-tête avec visio (n.m.) face-to-face videoconference; F2F videoconference; one-to-one videoconference; one-on-one videoconference; person-to-person videoconference; P2P videoconference vidéocourriel (n.m.) VOIR courriel vidéo (n.m.) vidéocourriel sur Internet (n.m.) VOIR courriel vidéo sur Internet (n.m.) vidéotutorat en face-à-face (n.m.) VOIR tutorat via visioconférence en face-à-face (n.m.) vidéotutorat frontal en ligne (n.m.) VOIR tutorat via visioconférence en face-à-face (n.m.) .m.) VOIR réalité virtuelle (n.f.) Autres publications du Bureau de la traduction Le Bureau de la traduction a un mandat bien spécial, soit celui d'uniformiser la terminologie utilisée au gouvernement du Canada. Nous publions plus de 100 vocabulaires et lexiques dans une grande diversité de domaines. Nos outils terminologiques réduiront votre temps de recherche, ce qui vous permettra d'accroître votre productivité. Bulletins de terminologie ! Administration correctionnelle ! Administration publique et gestion ! CFAO mécanique ! Constitutionnel (Lexique) ! Couche d'ozone ! Électronique et télécommunications ! Enseignement assisté par ordinateur ! Financement et assurance à l'exportation (Financiamento y Seguro a la Exportación) ! Génie enzymatique ! Génie génétique ! Géologie : gîtologie ) métallogénie ! Gestion des déchets nucléaires (Gestión de desechos nucleares) ! Gestion des finances publiques ! Guerre spatiale ! Industries graphiques ! Intelligence artificielle ! Langage Ada ! Lexique de la Stratégie d'information financière (SIF) ! Lexique de la ZLEA ) Zone de libre-échange des Amériques (Glosario del Alca -Área de Libre Comercio de las Américas)

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trainer; training agent; training instructor; training officer agent de formation (n.m.); encadreur (n.m.); formateur (n.m.); moniteur (n.m.) trainers' trainer; teacher trainer formateur de maîtres (n.m.); formateur de formateurs (n.m.); formateur d'enseignants (n.m.) trainer training; coach training; coaching training; teacher education; teacher training formation de formateurs (n.f.); formation de moniteurs (n.f.); formation de maîtres (n.f.); formation d'enseignants (n.f.) trainer training program SEE train-the-trainer program training acquisition acquisition de la formation (n.f.); appropriation de la formation (n.f.) training agent SEE trainer training by e-mail SEE training via electronic messaging training CD-ROM SEE educational CD-ROM training coaching system système de pilotage de la formation (n.m.) training content contenu de formation (n.m.) training curriculum curriculum de formation (n.m.) training-delivery organization; training organization organisme de formation (n.m.) training delivery via Internet prestation de formation via Internet (n.f.); prestation de formation en ligne (n.f.) training department; training division service de formation (n.m.) training designer SEE training developer training developer; training designer concepteur de formations (n.m.)

Remerciements

Acknowledgments

formation à distance (n.f.); téléformation (n.f.); formation distancielle (n.f.)

distance training; teletraining formation à domicile (n.f.) VOIR formation professionnelle à domicile (n.f.) formation à la carte (n.f.); formation personnalisée (n.f.); formation sur mesure (n.f.)

customized training; custom training; made-to-measure training; tailored training formation à l'enseignement (n.f.) training in education formation assistée par ordinateur (n.f.) VOIR formation informatisée (n.f.)

formation asynchrone (n.f.) asynchronous training formation asynchrone en ligne (n.f.); formation en ligne à réponse différée (n.f.); formation différée en ligne (n.f.); formation différée en réseau (n.f.) asynchronous e-training; asynchronous virtual training; delayed-interaction e-training; delayed-response online training; delayed-time e-training; delayed-time online training formation au management (n.f.) VOIR formation de cadres supérieurs (n.f.)

formation au processus (n.f.); formation opératoire (n.f.)

process training formation automatisée (n.f.) VOIR formation informatisée (n.f.) formation aux NTIC (n.f.) NICT training formation avec instructeur (n.f.); formation présentielle (n.f.); formation en présentiel (n.f.); formation traditionnelle (n.f.); formation en salle de classe (n.f.)


Franck Quaine
email: franck.quaine@gipsa-lab.grenoble-inp.fr

Anton Dogadov

Christine Serviere

Nicolo Celadon

Nicolò Celadon

Marco Gazzoni

Integration of High

Keywords: Biomechanical model, HD-sEMG, finger extensor mechanism, muscle, blind source separation

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

INTRODUCTION

The understanding of muscle coordination in human finger is essential for many application fields, such as muscle computer interface, movement simulation and surgeries. Biomechanical modeling is widely used to characterize the force sharing across the muscles. However, the models result in ill-posed problems since the number of muscles crossing the joints exceeds the number of degrees of freedom of these joints. To solve this problem, one advanced method [START_REF] Vigouroux | Unsing EMG data to constraint optimization procedure improves finger tendon tension estimations during static fingertip force production[END_REF] includes the intra muscular electromyographical (EMG) signal as additional inequality constraints into the optimization procedure. This method is attractive, but it presents some limitations mainly due to the great spatial selectivity of the recordings. Finally, since it is invasive, this technique is not suitable for daily life and sport applications. We propose a new finger biomechanical model and the introduction of high density surface EMG (HD-sEMG) into the optimization procedure. We focused on the extension movement of the index and little finger because of their high level of biomechanical independence. A complex tendinous structure of the extensor mechanism was developed as elastic elements (Fig. 1). To simulate the deformation of the mechanism, the potential energy of the system was minimized using the Quasi-Newton method.

The HD-sEMG signals were recorded in a monopolar configuration using a 64-channel electrode grid (8x8 electrodes, 10 mm inter-electrode-distance, LISiN, Italy) placed on the dominant arm (Fig. 2) The electrode configuration allowed acquiring signals from the Extensor Indicis and Digiti Minimi muscle. Ten subjects were asked to perform cyclic isometric extensions of index, little, and index+little at different force levels (30%, 50% and 70% of the maximum voluntary force). Blind source separation of mixtures of signals of active muscles was performed in order to separate contributions from different muscles. Figure 3 shows the muscle activity distribution detected with the HD-sEMG system. It is possible to identify distinct areas of activity for index and little finger, and one merged activity area in the case of simultaneous extensions of the two fingers. The preliminary results show that the proposed methodology is promising to overcome the limits of classical approaches, and open new perspective in the understanding of biomechanics and motor control of hand movement.

Figure 1 :

 1 Figure 1: Biomechanical description of Index finger extensor mechanism model.

Figure 2 :

 2 Figure 2: Experimental setup. 3D force sensors were used to measure the extension forces. A 64-channel electrode grid was used to record HD-sEMG.

Figure 3 :

 3 Figure 3: HD-sEMG Root Mean Square (RMS) maps calculated over a 500-ms data window. The RMS maps were interpolated with a factor of 10.


Azim Premji

Impact of Computer Aided Learning on Children with Specific Learning disabilities A Report on study carried out by The Spastics Society of Karnataka

Annexure

]This document is a summary of the findings, interpretations and conclusions from the study conducted by The Spastic Society of Karnataka on behalf of Azim Premji .oundation. Azim Premji .oundation is not liable for any direct/indirect loss or damage whatsoever arising from the use or access of any information, interpretation and conclusions that may be printed in this report. INTRODUCTION

Background

The issues of the disabled are becoming a part of the national education system and the planning and management of education programmes is to be seen in the context of individual learners (disabled) from the viewpoint of access, survival and success. Though a number of baseline studies have been conducted in the District Primary Education Programme (DPEP) districts, the achievement levels of disabled children have not been commented upon. Children with learning disability cannot be rehabilitated in regular schools if they are not given extra attention by teachers or do not have the teaching -learning methodology tuned to their disability. Computer technology provides the answer for many of these students. Recent advances in computer technology have much to offer students with learning disabilities, both as tools for instruction in school and as tools for life that can be used to compensate for specific impairments.

Learning is the process of acquiring and retaining knowledge so that it may be applied in life situations. Learning can become a nightmare when there are memory problems, difficulties in following directions, trouble with visual or auditory perception of information and an inability to perform paper-and-pencil tasks. Persons with learning disabilities have specific problems related to language (dyslexia), writing (dysgraphia) and mathematics (dyscalculia) in spite of having near normal or above normal IQ and not having any serious sensory disability, emotional disturbance, brain pathology etc. Millions of children have been labelled as learning disabled. These children often tend to be years behind their classmates in developing academic skills which can lead to dropping out of school. Attempts are being made to use technology to the advantage of the learning disabled. This research explores the effectiveness of computer aided learning in improving the learning outcomes of these children.

The Technology Initiatives Division at Azim Premji .oundation has launched programmes for use of computers in rural schooling. Presently, experiments are under way in some schools in rural Karnataka. The programme Computer Aided Learning (CAL) envisages deployment of computers as a media to impact learning competencies and to create an attractive environment in the school. The state government provides the computers in schools and the required hardware while the .oundation provides the content for learning. The .oundation has developed several software content designed to aid the classroom learning process in specific areas such as mathematics, language and environment sciences. The Spastic Society of Karnataka conducted a research study on analyzing the impact of computer aided learning on children with specific learning problems in rural elementary schools of Karnataka.

This report provides key findings extracted from the research study.

Objectives

The aim of the study was to assess the effectiveness of computers in enhancing learning for children with learning disabilities. Specifically, the hypotheses for the study were i. The computers will enhance learning for the children in the target group.

ii. The computers will enhance Meta cognitive aspects (self analysis, synthesis and decision making) among the target group.

Methodology

A screening exercise was first carried out in September 2002 followed by a baseline study in December 2002. An endline follow up study was carried out in January 2004. .our schools with Computer Aided Learning Centres in Anekal Taluk of the Bangalore rural district were selected for the study. These were Thindlu, Hebbagodi, Bannerghatta and Ballur. The universe comprised all the students from class two, three, four and five in these schools.

Children from the relevant classes were screened through psychological and psycho-educational assessment to identify those children with reading, mathematics or written expression substantially below that expected for their age, schooling and level of intelligence. The children identified were ruled out for any signs of visual, hearing, or motor disabilities, or mental retardation. Out of 1,010 children from the four selected schools, 70 children were identified as children with problems in learning.

The eclectic approach to data collection involved formal and informal assessment of the children. Psychological testing of children was done to rule out mental retardation and psycho educational to rule out defects in IQ. The psycho educational testing involved testing the children in Language and Mathematics as per diagnostic instruments used for children who were inefficient or slow learners. Interviews were conducted with concerned class teachers and observations of the children were made in the classroom and the Computer Aided Learning Centre. The anthropometric measurements were done to identify the current health status of the target group to rule out any effect of physical deformity. A team consisting of medical and paramedical professionals carried out anthropometric measurements of all the school going children under study (target group). The task of collecting relevant information about the ecological aspects of the target group was carried out by a team of educators. A team of investigators, consisting of research consultant, educators, psychologists and therapists performed the educational and psychological evaluation of the target group to understand the current level of performance.

Tools for data collection used included The Binet-Kamath Test of Intelligence (Indian Adaptation) and various Educational Evaluation. The details are provided in the annexure.

The terms used

An explanation for some of the frequently used terms in the report is given below.

Learning disabilities: Specific learning disability (LD) means a disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, which may manifest itself in an imperfect ability to listen, think, speak, read, write, spell, or to do mathematical calculations. The term includes such conditions as perceptual handicaps, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia. The term does not include children who have problems that are primarily the result of visual, hearing, or motor disabilities, or mental retardation, emotional disturbance, or of environmental, cultural, or economic disadvantage.

Slow learner: This is a term used to describe a child whose learning ability in all areas is delayed in comparison to children of the same chronological age. These children are not considered learning disabled because there is no discrepancy between cognitive expectations and academics achievements. The major problem with these children is LOGICAL REASONING.

Age: It refers to the chronological age of the child.

Ecological aspects: This includes socio economic status, the type of family, and the education of parents as gathered by a structured interview schedule.

Academic performance: The percentage of marks in the subjects as recorded from the previous years record and the values from the teacher rating scales.

Meta cognitive aspects: It is the self analysis of his / her learning style and skill.

.INDINGS

Children with Learning Problems

A total of 1,010 students formed the universe of children in classes three to six in the concerned schools. Of these, 73 children were identified as having learning problems representing a proportion of over 7.2%. The school wise details are given below. As seen in the figure, a significant number of children (64%) show great improvements in the area of reading. At the time of the baseline test, the children were seen to perform below grade level reading and when tested at the end line they were seen to demonstrate grade level reading abilities.

While some improvement is seen in spelling, areas of comprehension, written work and numerical reasoning show only marginal improvement. .igure 2: Impact on Meta Cognition of Target Group

Most of the children (88.1%) show improvement in Social Intelligence which measures practical common sense understanding of everyday social situations and acceptance of conventional standards of behavior. There is also significant improvement in Visual Motor Coordination (78.6%) that involves the sensory perception (visual), their interpretation in the brain, along with the ability to voluntarily control muscles and relate them to manipulative skills of handling raw material. As is seen in reading, there is improvement in many children (26.2%) in Language which implies that there is improved ability of the children to use language to communicate their mental images to another person as well as to understand language meanings and functions. Non Verbal Reasoning (42.9%) is another area of improvement where children are seen to perceive and analyze patterns better and experience enhanced comprehension abstract units non-verbally Marginal improvement is seen in the areas of Meaningful Memory (childs ability to recall organized knowledge of the world, the verbal world of words and how they are used). Conceptual Thinking (logical processes, intellectual maturity, ability to handle abstract ideas, to see relationship and the ability to generalize) and Numerical Reasoning (powers of arithmetic reasoning, one ability with numbers and numerical operations and taps concentration attention skills) show relatively lower improvement under 15%.

CONCLUSIONS

The findings of the study show several areas where computer aided learning has had a significant beneficial impact on the children with learning problems. At the same time, there has little or no improvement in some other areas.

Specifically, improvements are seen in the following 1. Most children show improvement in visual motor coordination, social intelligence and non verbal reasoning.

2. There is tremendous improvement in social behavior, attention, language (oral) and communication and motivation.

3. The computer aided learning has had a positive impact in promoting the reading skills of the children, especially automaticity in reading. Generalized reading capabilities increased in nearly all the children. Improvements were also seen in aspects of speed and expression, accuracy and clarity.

4. To an extent, technology has enhanced language processing and memory of the children. This was seen through improvements in spelling which is defined as a visual and auditory processing ability.

However, the following areas do not show much improvement.

1. There was no clear impact on higher order comprehension of factual information. i.e. analytical thinking and reasoning skills. The children require guidance in using the curriculum software that is meant to improve comprehension and concept understanding skills.

2. Numerical reasoning and thinking skills need improvement. Intensive application and coaching is required as number work involves analytic thinking and reasoning.

Very few children have shown improvement in written expression but accessing the Computer Aided Learning

Centre has improved their motivation to write and use a variety of words. Improvement is seen in ideation (i.e. content and vocabulary) and the length of sentences.

In sum thus, the use of technology does show beneficial impact on the children with specific learning disabilities. .urther improvement in other areas is possible by providing orientation and suitably training the teachers concerned.

Table 1

 1 Impact of CALCThe impact of CALC has been assessed for the children identified as having specific learning problems. While the table above indicates 45 such children, the assessment could be carried out for only 42 children over the study period. All subsequent data and findings hence relate to these 42 children.

	: School wise Distribution of Slow learners and Children(class 3 through class 6)
		having specific Learning Problems
	(* Slow Learners -Children having global learning problems and an IQ less than 90. ** Specific learning problems -Children whose IQ is normal or above normal and have only specific learning problems-Like problem in reading, comprehension.) godi Banner-ghatta TOTAL Total number of Children 258 122 483 147 1010 Children identified as slow learners* 7 9 5 7 28 Children having specific learning problems** 10 8 13 14 45 Number of Children with learning problems 17 17 18 21 73 2.2 Ballur Thindlu Hebba-% of the Total 6.6 13.9 3.7 14.3 7.22
			Ballur Thindlu Hebba-	Banner-	Total Improve-
					godi	ghatta		ment %
	Number of children	10	8	13	11	42
	Reading	Pre test	5	5	8	7	25
		Post test	5	4	3	4	16	64.0%
	Comprehension	Pre test	6	5	13	11	35
		Post test	1	1	2	2	6	17.1%
	Spelling	Pre test	8	5	12	11	36
		Post test	3	0	2	3	8	22.2%
	Written work	Pre test	6	7	13	11	37
		Post test	0	1	1	2	4	10.8%
	Number work	Pre test	10	8	11	10	39
		Post test	1	0	1	1	3	7.7%

(Pre test: children below grade level. Post test: children showing improvement from the pre test)

Table 2 :

 2 Academic Performance of the Target Group .igure 1: Impact on Academic Performance of Target Group

Table 3 :

 3 Meta Cognitive Aspects of the Target group as tested through The Binet Kamath Test (The numbers indicate the number of children who have shown improvement)

ANNEXURE Tools for data collection

A.