On a new computational method for the simulation of periodic structures subjected to moving loads Application to vented brake discs

Introduction

The brake is a major security part of a car. In friction braking systems subjected to very severe conditions, various kinds of defects can appear : honeycomb cracking on the rubbing surface, thru-cracks through the disc thickness, fracture of the elbow of the bowl, wear... A numerical model able to predict these phenomena is an alternative and a complement to expensive bench-tests. The computational approach we develop consists in:

-new numerical strategies suitable for problems involving components subjected to moving loads; -a relevant modelling of the behavior of the material;

-a modelling of the different damage phenomena undergone by the disc, which takes account of the multiaxial and anisothermal characteristics of the loads.

It is essential for the numerical determination of the thermomechanical state of the disc to take into account the main couplings between the different phenomena, the transient characteristic of the thermal history, the inelastic behavior of the material, the non-homogeneous thermomechanical gradients taking place in the disc and the rotation of the disc. The use of classical finite element methods leads to excessive computational times. More precisely, one particularity of the brakes discs is the fact that they are subjected to repeated thermomechanical rotating loads with amplitude varying with the rotations. To simulate a whole braking, dozens of rotations are necessary and dozens of incremental rotations are needed to compute a rotation so that the total computational time is too high. To circumvent this difficulty, algorithms adapted to problems of structures subjected to thermomechanical moving loads have been developed.

The alternative approach consists in using the stationary methods, first proposed by Nguyen and Rahimian [START_REF] Nguyen | Mouvement permanent d'une fissure en milieu élastoplastique[END_REF] and later developed by Dang Van and Maitournam [START_REF] Maitournam | Formulation et résolution numérique des problèmes thermoviscoplastiques en régime permanent[END_REF][START_REF] Van | Steady-state flow in classical elastoplasticity: Application to repeated rolling and sliding Contact[END_REF], which permit to directly calculate the mechanical state of the structure after one rotation or directly the asymptotic state after repeated passes. These algorithms lead to important reductions of the computational time. They can be applied to structures which geometries are generated by the translation or the rotation of a two-dimensional section. Many industrial applications for instance railways [START_REF] Van | On some recent trends in modelling of contact fatigue and wear in rail[END_REF] and brake discs [NGU02A, NGU02B] have been treated with these methods. In a previous paper [START_REF] Nguyen-Tajan T | Une méthode de calcul de structures soumises à des chargements mobiles. Application au freinage automobile[END_REF], we have treated only solid disc. Here, we consider the case of vented discs (figure 1). These structures have a periodic geometry, so that stationary methods cannot be used in their previous formulations. The objective of the paper is to propose an extension of such methods to periodic structures subjected to moving loads and to quickly determine the mechanical state after a given number of rotations by calculating the solution cycle by cycle. First, we present the principle of the method and its formulation in the case of an elastoplastic material with linear kinematic hardening. Then, an example of simulation of a vented disc is given.

The periodic stationary method

Overview of the stationary method

The stationary method was first proposed by Nguyen and Rahimian [START_REF] Nguyen | Mouvement permanent d'une fissure en milieu élastoplastique[END_REF]; Dang Van and Maitournam [MAI89,[START_REF] Van | Steady-state flow in classical elastoplasticity: Application to repeated rolling and sliding Contact[END_REF] developed it in the case of repeated moving loads. The considered structures are generated by the translation or the rotation of a given 2D section. They are subjected to repeated moving thermomechanical loads. Quasi-static evolution and infinitesimal deformations are assumed. The objective of the pass-by-pass stationary algorithm is to directly determine the thermomechanical response of the structure after each pass of the moving loads.

The stationary method relies on the following hypothesis :

-the amplitude and velocity of the loads remain constant during one load pass; -in a reference frame attached to the moving loads, the thermomechanical quantities are stationary (steady-state assumption).

The idea is then to use this frame instead of the one related to the structure and so to use eulerian coordinates. The steady state assumption makes the problem become time independent. Internal variables are therefore directly calculated (without time incremental resolutions) by integration along the streamlines which are known as the hypothesis of small transformation holds: it is as if the constitutive law is non local [START_REF] Maitournam | Formulation et résolution numérique des problèmes thermoviscoplastiques en régime permanent[END_REF][START_REF] Van | Steady-state flow in classical elastoplasticity: Application to repeated rolling and sliding Contact[END_REF].

In fact, we consider a continuous medium subjected to a thermomechanical load moving with a velocity V(t) relatively to a frame R = (O, e X , e Y , e Z ). We adopt the frame R =(O , e x , e y , e z ) attached to the load moving. In this frame, the structure is therefore moving with the velocity -V(t). The material derivative of a tensorial quantity B related to the material is given by :

Ḃ(x, t) = ∂B ∂t (x, t) + ∇ x B(x, t).v(x, t) with : v(x, t) = v r (x, t) -V(x, t)
where x is the geometrical position of the material point in R , v the velocity of the material point relatively to R and v r its velocity relatively to R.

Thanks to the hypothesis of infinitesinal transformation in the reference linked to the solid, the term v r (x, t) becomes negligible compared to V(x, t). Hence, the expression of the material derivative of B becomes :

Ḃ(x, t) = ∂B ∂t (x, t) -∇ x B(x, t).V(x, t) [1]
The assumption of steady state in a frame moving with the loads leads to a timeindependent problem for which all time partial derivatives vanish. So the expression of the material derivative of B becomes :

Ḃ(x, t) = -∇ x B(x, t).V(x, t) [2]
To numerically solve the problem, we use a frame moving with the loads and replace material derivatives in the governing equations (equilibrium, constitutive law and boundary conditions) by expressions as given above.

The periodic stationary method

We consider a structure with a periodic geometry subjected to a repeated moving load. The load moves with a constant velocity V e x . Its intensity is constant or varies periodically. Although we treat here a rotating load, we choose to present the method for translating load; the two cases are formally identical but the notations are less heavy in the case of translation.

By periodic structure (figure 1), we design a structure which is generated by the translation or the rotation of an inhomogeneous material volume (heterogeneous solid made of different materials or containing voids). An elementary heterogeneous volume is called "cell".

Figure 1. The vented disc: an example of periodic structure

Due to this geometrical and material inhomogeneity, the thermomechanical state of each cell depends on the relative position of the load over the cell. The steady state assumption in the load reference no longer holds. On the other hand, the non stationary behavior is assumed to be periodic. The solution method adopted consists in two main features:

-determination of the transient solution in a time period (time necessary for the loading to move along a cell); -use of the steady-state assumption at the cells scale in the reference frame related to the moving load.

So the computations involve two stages: the trial transient elastic solution on a time period will be first sought and then integrations along the streamline associated to the cells are performed (as in the "classical" stationary method).

These two points are used in the formulation of the problem to be numerically solved: on each time interval with a period T (T is the time necessary for the load to cover the distance X equivalent to the length of a cell along e x ), the response is variable; it is T-periodic in the load reference.

In other words, in the load reference, for any physical quantity B and for any point x of the structure:

B(x, t) = B(x -Xe x , t -T ) [3]
This equation allows the transport of the physical quantities from cell to cell along the streamlines, as in the case of the stationary method.

On the other hand, for the transient regime (lasting the time necessary for the load to cover the length of a cell), one has simply Ḃ(x, t) = ∂B ∂t (x, t) and a method similar to the Large time Increment Method [LAD96] is adopted.

Formulation of the periodic stationary method in elastoplasticity

From the equations (2) and (3), we are able to propose a solution scheme for the periodic stationary method and give the discretized equations of the problem. We just consider here a von Mises elastic-plastic material with a linear kinematic hardening (c) and a yield function (f ) of the following form:

f (σ, cε p ) = (devσ -cε p ) : (devσ -cε p )-k = devσ -cε p -k = ξ -k [4]
Let us recall that the steady state at the cell scale is assumed; the solution is then entirely determined by the knowledge of the response over a period (t ∈ [0, T ]). This time interval is discretized in m instants corresponding to the number of positions of the load on a cell. Practically, we have the following two-stage algorithm.

A global stage consisting in calculating the elastic solution over the whole time interval [0, T ] with given internal variables is first carried out: in fact one performs discrete sequence of elastic calculations for all the positions of the load over a particular cell considered as reference.

It is followed by a local stage for the determination of the internal variables by integration along the streamlines, and this is done for all the instants of the interval [0, T ]. This integration scheme using closest point projection, is detailed in the following.

We denote by j the position of the load on the reference cell, j ∈ {1, ..., m}, ε p j the plastic deformation of the current point of the cell (n). (.) j denotes quantities at a point of the cell (n), for the j position of the load while (.) j (n -1) denotes quantities at the homologous point of the preceding cell (n -1), for the jth position of the load. Within, the periodic stationary method, the plastic deformation ε p is calculated as follows:

If j = 1 we define ξ * j = devσ j-1cε p j-1 + 2μΔ(devε) j , one has: -if ξ * j > k, plastification occurs, so

ε p j = ε p j-1 + 1 2μ+C 1 -k ξ * j ξ * j -if ξ * j ≤ k, no plastification occurs, so ε p j = ε p j-1 If j = 1 , we define ξ * 1 = devσ m-1 (n -1) -cε p m-1 (n -1) + 2μΔ(devε) 1 one has: -si ξ * 1 > k, plastification occurs, so ε p 1 = ε p m-1 (n -1) + 1 2μ+C 1 -k ξ * j ξ * j -If ξ * 1 ≤ k, no plastification occurs, so ε p 1 = ε p m-1 (n -1)

Figure 2. Calculated positions of the load

This algorithm has been implemented in the code Castem 2000 for a von Mises elastic-plastic material with a linear kinematic hardening.

Application to a vented disc

In this section, we present an application of the periodic stationary method to the vented disc (figure 1). Instead of making a realistic simulation of the braking in which thermal effects are proeminent, we choose to illustrate the different kinds of results that can obtained with this method in the case of purely mechanical problems.

The dimensions of the disc are the following: external radius R e = 133 mm, internal radius of rubbing surfaces R i = 86.5mm, thickness of these surfaces e = 13 mm. The disc constitutive material is cast iron assumed to be, at room temperature, a von Mises elastic-plastic material with a linear kinematic hardening. Its characteristics are: Young modulus E = 110000MPa, Poisson coefficient ν = 0.3, yield limit in traction σ y = 90 MPa, hardening modulus h = 90000 MPa. The figure 3 shows the adopted mesh and the applied loading. The loading consists in two distributions of hertzian pressure (prescribed at the contact zones between the disc and the pads) with the maximum pressure equal to 500 MPa. This pressure is greater than the ones encountered during real brakings but here, as thermal effects are not taken into account, we choose a greater pressure just for illustration of the capabilities of the method which is interesting only in inelastic cases. Eight load positions are used for the simulation. They are represented with different colors on figure 3. Thanks to the periodicity of the solution in the cells "away" from the load, the mesh is truncated; only five cells are represented.

Figure 3. Hertzian pressure distributions on the two surfaces of the vented disc : the eight considered load positions are represented

The evolutions of equivalent plastic deformations during the first pass of the loading are shown on figure 4 for the eight positions of the load. The load is moving in the anti-clock-wise. One can notice that the solution is transient and depends on the relative position of the loading to the cell.

On the first of figures 4, we observe a plastic deformation induced backwards by the moving loads.

On figure 5, one can see the equivalent plastic deformations during the first pass of the loading. The calculation of five successive passes of the loading show that the mechanical stabilized state is reached quickly. The stabilized state is defined by the periodicity of the mechanical response at any material point. On figure 7, we plot the evolution of equivalent plastic deformations along a constant radius streamline: one can then see that the stabilized state is a plastic shakedown. One can also notice that backward, the plastic deformation becomes periodic, with a period equal to the length of a cell (0.08m). On figure 6, we show the equivalent stresses in the limit state obtained for the fifth pass of the loading.

Conclusion

In this paper, an extension of the stationary methods to periodic inelastic structures subjected to repeated moving loads is presented. It is based on the hypothesis of the periodicity of the response in a reference frame moving with the loads and the use of an approach similar to the Large Time Increment Method. It permits the directly determination of the mechanical state during a whole pass of the loading and therefore the determination of the limit state in the case of repeated moving loads. Even though only the capabilities of this method have be shown, it is clear that it reduces considerably the computational times and accordingly allows the simulation of complicated structures such as vented discs and the determination of asymptotic state of such structures subjected to repeated loads.

Figure 4 .Figure 5 .Figure 6 .

 456 Figure 4. Equivalent plastic deformations during the movement of the load along a cell

Figure 7 .

 7 Figure 7. Evolution of equivalent plastic deformations along a streamline for the five first passes of the loading: case of a plastic shakedown

Mac Lan Nguyen-Tajan -Habibou Maitournam Luis Maestro

	PSA Peugeot Citroën, Direction de la Recherche, Route de Gisy
	F-78943 Vélizy-Villacoublay
	maclan.nguyen@mpsa.com
	LMS, UMR 7649, Ecole Polytechnique, F-91128 Palaiseau cedex
	habibou@lms.polytechnique.fr
	Stagiaire de l'ENSTA

ABSTRACT. The purpose of the paper is to present a new numerical method suitable for the computation of periodic structures subjected to repeated moving loads. It directly derives from the stationary methods proposed for cylindrical and axisymmetrical structures. Its mains features are the use of a calculation reference related to the moving loads and the periodic property of the thermomechanical response. These methods are developped by PSA and the Ecole Polytechnique, in order to design vented brake discs. In this paper, a brief description of the algorithm is first given and examples of numerical simulations of a vented brake disc are treated.

RÉSUMÉ. Cet article porte sur le développement d'une nouvelle méthode de résolution numérique adaptée au calcul de structures périodiques soumises à des chargements mobiles et répétés. Il s'inspire directement des méthodes stationnaires développées pour les structures cylindriques ou axisymétriques. Cette méthode repose sur les principes suivants : le repère de calcul est lié au chargement et non plus à la structure, et la réponse thermomécanique de la structure y est supposée périodique. Cette méthode a été développée par PSA Peugeot Citroën et l'Ecole

Polytechnique dans le cadre du dimensionnement des disques de frein ventilés. Dans cet article, on donnera une brève description de l'algorithme puis la simulation mécanique d'un disque de frein ventilé illustrera la méthode. KEYWORDS: periodic steady state algorithm, cyclic moving load, brake disc, thermomechanics. MOTS-CLÉS : algorithme stationnaire périodique, chargement mobile cyclique, disque de frein, thermomécanique.


Raul Ramos

Diego Scoca

Rafael Borges Merlo

Francisco Chagas Marques

Luiz Fernando Alvarez

Fernando Zagonel
email: zagonel@ifi.unicamp.br

Study of nitrogen ion doping of titanium dioxide films

Keywords: nitrogen ion doping, titanium dioxide, Anatase, transparent conducting oxide, diffusion; electronic transport

This study reports on the properties of nitrogen doped titanium dioxide (TiO 2 ) thin films considering the application as transparent conducting oxide (TCO). Sets of thin films were prepared by sputtering a titanium target under oxygen atmosphere on a quartz substrate at 400 or 500°C. Films were then doped at the same temperature by 150 eV nitrogen ions. The films were prepared in Anatase phase which was maintained after doping. Up to 30at% nitrogen concentration was obtained at the surface, as determined by in situ x-ray photoelectron spectroscopy (XPS). Such high nitrogen concentration at the surface lead to nitrogen diffusion into the bulk which reached about 25 nm. Hall measurements indicate that average carrier density reached over 10 19 cm -3 with mobility in the range of 0.1 to 1 cm 2 V -1 s -1 . Resistivity about 3.10 -1 cm could be obtained with 85% light transmission at 550 nm. These results indicate that low energy implantation is an effective technique for TiO 2 doping that allows an accurate control of the doping process independently from the TiO 2 preparation. Moreover, this doping route seems promising to attain high doping levels without significantly affecting the film structure. Such approach could be relevant for preparation of N:TiO 2 transparent conduction electrodes (TCE).

Introduction

The increasing demand of energy efficiency and cost-effectiveness for display and energy technologies pushes continuously towards the search of new materials to surpass industry standards. In flat panel displays, light emitting devices and some solar cells, efficiency is linked to the performance of the transparent conducting electrodes (TCEs) used which allows front electrical contacts and simultaneously letting visible light in or out of the device. While tindoped indium oxide (ITO) is an industry standard TCE, it presents a high cost linked to indium scarcity. Most alternatives available today, such as ZnO or SnO 2 , has interesting niche applications. New and better TCEs, both in terms of cost and efficiency, are of great interest for several wide or niche applications.

Since titanium oxide (TiO 2 ) doped with niobium has been proposed as TCE by Hasegawa group see refs. [1,2], several studies discussed the optical and electrical properties of TiO 2 doped with Nb, Ta, W, and N [3,4,5,6]. Moreover, it has been shown that, by doping TiO 2 with nitrogen, it is possible to reduce its optical gap and favor catalytic activity with visible light, with considerable interest for water splitting, among other applications [7,8]. Since then, several studies explored the properties of nitrogen doped titanium oxides (mainly Anatase and Rutile) prepared in various ways with respect to its optical, catalytic and transport properties.

Nitrogen doped TiO 2 has already been synthetized by reactive sputtering and by post treatments with ammonia or ion implantations, among others. Using electron cyclotron resonance plasma sputtering under O 2 and N 2 gases, H. Akazawa showed that it is possible to continuously control carrier concentration and obtained films with a resistivity of 0.2 cm with a maximum transparence in the visible of about 80%, but the films were frequently amorphous, while large crystalline grains might favor better conductivity at similar transparency [4,6]. Using reactive d.c. magnetrons sputtering in an Ar+O 2 +N 2 gas mixture, N. Martin et al. obtained about 25cm with about 30% transmission, depositing TiN x O y . Again, in this study, crystal structure was difficult to control and, besides Rutile and Anatase, even Ti 3 O 5 was observed [9]. In another work by J.-M. Chappé et al., also using d.c. reactive magnetron sputtering, prepared TiO x N y films with visible light transmittance ranging from very low to nearly 80%, with a resistivity ranging from 10 -3 cm to 50 cm and with a complex crystal structure where Anatase was not the majority phase present [10]. Given the inherent difficulty in controlling independently composition and crystal structure/quality in reactive sputtering, splitting the processes in two parts is an interesting alternative. In this approach, Anatase or Rutile samples can be prepared and doped a posteriori with nitrogen by, for instance, ion implantation or NH 3 gas [11,12,13]. Using this approach, H. Shen et al. showed that implantation with 200 eV nitrogen ions successfully doped Anatase nanoparticles and enhanced photocatalytic efficiency without changing the crystal structure [13].

Considering that ion doping of TiO 2 could be relevant for TCE preparation, in this work, we deposited Anatase thin films at 400 and 500°C and then doped by low energy nitrogen ion implantation at 150eV from a simple laboratory ion gun. Such process allows doping pure Anatase thin films with controllable nitrogen amounts and following closely its properties. By heating the sample during the ion implantation, we could allow the diffusion of nitrogen from the surface into the bulk, thus developing a dopant profile. The results indicate that low

Experimental Methods

Sample preparation was performed in two sequential steps. First, a Ti target was sputtered using an ion beam (Ion Beam Deposition) to grow a thin film on amorphous quartz substrate. Argon was used as inert gas for bombarding the Ti target at an energy of 1.5keV. During the deposition, a partial pressure of 2.510 -2 Pa of oxygen was maintained (chamber base pressure was about 210 -4 Pa). Such partial pressure results in Anatase films with well-defined x-ray diffraction peaks [14]. During the deposition, Argon partial pressure in the chamber was about 110 -2 Pa. During a second step, nitrogen ions were implanted at low energy, 150 eV, into the thin film surface. The ions were produced in a Kaufman cell fed with 5 sccm of Nitrogen and 0.5 sccm of hydrogen, resulting in 2.110 -2 Pa and 2.110 -3 Pa partial pressures in the chamber respectively (Argon and oxygen were not used in this step). Such sample preparation was performed in a custom-built system that features two ion guns (one pointing to a sputter target and the other to the sample holder) in one vacuum chamber that is directly connected to another chamber for in situ X-ray Photoemission Spectroscopy analysis. More details of the deposition system and its capabilities can be found in references [15] and [16]. Hydrogen was used in analogy with ref. [17] (see also references there in) to remove oxygen from the surface to make it more reactive for incoming nitrogen. Indeed, the formation enthalpy favors TiO 2 over TiN [18] and in principle residual oxygen gas and water vapor in the vacuum chamber could keep the surface partially oxidized preventing nitrogen intake. The ion gun points perpendicularly to the sample surface and is located about 30 cm from the sample. The samples were prepared at different substrate temperatures (for both steps): 400 and 500°C and with different implantation times: 0, 10, 30 and 60 minutes. Film thickness was evaluated by perfilometry and it ranges from 70 to 100 nm.

Just after preparation, samples were in situ analyzed in UHV by X-ray Photoemission Spectroscopy (XPS) using Al K radiation. Spectra were fitted using Avantage software. Average inelastic mean free path for Anatase and kinetic energies from 900-1100 eV are estimated as about 2 nm [19]. X-ray diffraction (XRD) was performed using Cu Kand keeping incidence angle at 1°. In this geometry, the average penetration depth is estimated as 0.05 m for Anatase [START_REF] Noyan | Residual Stress: Measurement by Diffraction and Interpretation[END_REF]. Sheet resistance was measured using 4-probe technique. Mobility, resistivity and carrier concentration were determined by Hall measurements using the Van der Pauw method in an Ecopia-3000 device using a 0.55 T permanent magnet. For Hall measurements, indium was used to provide ohmic contacts. Optical transparency measurements were performed in an Agilent 8453 device which uses a CCD detector.

Resistance versus temperature measurement was performed for the sample deposited at 500°C and implanted for 60 minutes (at the same temperature). The measurement was carried out in a CTI Cryodine closed-cycle helium refrigerator in the temperature range from 80 K to 300 K. The electrical data was acquired using a Keithley model 2602A SourceMeter and the indium contacts previously used for Hall measurement, in the van der Pauw geometry. A constant current of 10 A was applied between two contacts and the voltage was measured between the other two, in a parallel configuration. A complete thermal loop was carried out to confirm the reproducibility of the data. Sample's morphology was studied by Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). TEM analysis was performed in a JEOL 2100F TEM equipped with a Field Emission Gun (FEG) operating at 200 kV with an energy resolution of about 1 eV. EELS was obtained using a Gatan GIF Tridiem installed in this TEM and Gatan Digital Micrograph routines were used for quantification. The data were acquired in Scanning Transmission Electron Microscopy (STEM) mode in the form of spectrum lines (the electron beam is focused on the sample and a spectrum is acquired for each position along a line forming a bidimensional dataset). Topographic images of the sample's surface were taken with an Innova Bruker Atomic Force Microscope (AFM) in non-contact mode.

Results and Discussions

Composition and Structural characterization

The effectiveness of the ion implantation at 150 eV was demonstrated by the presence of large amounts of nitrogen at the surface, as observed by in situ XPS. Figure 1 shows XPS spectra for the sample prepared at 500°C for 60 minutes, with similar results for all other samples. Main features observed by XPS are expected for TiO 2 and for TiN. In situ XPS on TiO 2 samples grown at 400 and 500°C (not shown) are similar to those in ref [14] and [START_REF] Scoca | [END_REF], typical for Anatase film close to stoichiometry. It must be noted that absolute binding energies are not accurately known due to some degree of uncontrolled spectral shift that is attributed to sample charging. From the indicated decomposition into several proposed chemical bounds, it is possible to observe that nitrogen concentration is similar to that of oxygen and that a TiO x N y alloy was created at the surface (TiN and TiO 2 components are observed in the Ti 2p spectrum). It is noteworthy in Figure 1(c) the presence of two XPS peaks for N 1s, one, smaller, at higher binding energy, and another, bigger, close to 396 eV (that is in turn composed of two peaks). Such smaller and bigger peaks are attributed to interstitial nitrogen and substitutional nitrogen, respectively [12,13,22,23]. In our case, interstitial N accounts to about 10% of the total amount of nitrogen observed on the surface, a much lower value when compared to ref. [8], which used NH 3 as nitrogen source, or ref. [13], which used 200 eV nitrogen ions without hydrogen. Therefore, depending on the incorporation route, different chemical locations are possible. This difference is relevant since depending on nitrogen site different diffusion mechanisms apply [12]. To evaluate if hydrogen was significantly affecting N 1s spectra, a sample was prepared without hydrogen gas during the implantation step. N1s peaks for samples prepared with and without hydrogen at 500°C and implanted for 60 minutes are shown in Figure 2. The spectra show that even without hydrogen the peak is still present and with similar (although smaller) ratio with respect to main N 1s peak. This shows that it does not depend on presence of hydrogen during the nitriding process, in contrast to literature suggestion [24]. However, as discussed below, total nitrogen concentration is smaller without hydrogen, indicating that hydrogen contributes to nitrogen incorporation at the surface, possibly by removing oxygen. [ To support the given interpretation of XPS results, SRIM simulations have been performed [25,[START_REF]The Stopping and Range of Ions in Matter[END_REF]. Simulations considered nitrogen ions (N+) on Anatase. Average penetration depth is about 0.9 nm while 90% of implanted nitrogen ion reaches a depth within 1.7 nm. These simulations indicate that XPS is probing exactly the implanted region and hence is suitable to investigate the nitrogen intake by the sample from the ion beam.

Following the procedures detailed in references [START_REF] Scofield | [END_REF] and [28], we used XPS results to calculate the elemental concentrations of surface components. The results are shows in Figure 3 for samples prepared at 400 and at 500°C with implantation times ranging from 0 to 60 minutes. It is observed that in the first few minutes of implantation, a significant nitrogen concentration builds up at the surface and after the concentration increases yet to reach about 33at.%. This is explained by the high reactivity of the nitrogen ion beam and the low diffusion coefficient of nitrogen into the interior of the thin film. In such scenario, we consider that a high nitrogen concentration builds up during the first moments and is maintained by the ion beam creating a high nitrogen chemical potential at the surface. This nitrogen concentration will be the driving force for nitrogen diffusion into the thin film. The extent of the diffusion will depend mainly on the temperature but also on several details of the thin film microstructure, such as vacancies, grain boundaries, stress, and so on. This process is in tight analogy to the plasma or ion beam nitriding of steels at low temperatures where nitrogen diffusion is also slow [29,30]. It is important to note that for both studied temperatures, with sufficient nitriding time, the surface builds a titanium oxynitride alloy with stoichiometry close to TiO 1 N 1 (note such result applies only at the outer 2 nm of the thin film surface). It is also interesting that the sample prepared without hydrogen had a nitrogen concentration of only 25at.% while the sample prepared with hydrogen in the same conditions (500°C -60 minutes) had 33at.% of nitrogen at the surface. Again this indicates that hydrogen may favor oxygen removal opening sites for nitrogen chemical adsorption and reaction, even if nitrogen arrives at 150eV at the surface and the sample is in high vacuum. X-ray diffractograms are shown in Figure 4 for samples prepared at 400 and 500° without nitrogen implantation and implanted for 10, 30 and 60 minutes, as before. It is observed that all samples display peaks associated with Anatase phase with considerable intensity indicating the crystalline nature of the thin films. Moreover, implantation with Nitrogen and Hydrogen does not disturb the crystal structure, similarly to what has been reported in the literature for 200eV nitrogen implantation into Anatase thin films [13]. The position of the Anatase (101) peak remains within (25.30±0.05)° for all diffractograms while reference Anatase ( 101) is expected at 25.33° according to ICSD 9852. It must be noted that samples are kept at deposition temperature during the implantation and are therefore annealed what could affect their crystalline structure. It is also noteworthy that peak ratios do not agree with expected values for Anatase powder and hence the films should have some texture [31]. Transmission Electron Microscopy was applied to determine the extent of nitrogen diffusion into the film from the surface. For that, we considered only the sample prepared at 500°C for 60 minutes, considering that other samples would have a shallower nitrogen penetration depth. Figure 5 shows a cross-section of the sample. Apart from the amorphous quartz substrate and the protective coating used for FIB lamella preparation, we can observe the N implanted TiO 2 thin film in two layers, on top a layer that apparently has been modified by the implantation/diffusion process and on the bottom the pristine Anatase film. HRTEM images indicate the presence of atomic planes and grains from bottom to top of the thin film, again confirming the Anatase film preserved its crystal structure even after nitrogen shallow implantation (shallower than 2nm from SRIM simulations) and subsequent diffusion. Electron energy loss spectroscopy was used to detect nitrogen and determine its profile in the sample cross-section. Figure 6(a) shows the profiles of nitrogen, oxygen and titanium from the surface to the interior of the thin film. The detection of nitrogen was difficult due to sample damage: apparently the electron beam removed nitrogen during beam exposure. For this reason (and also because of diffraction and thickness effects were not taken into account), the results in Figure 6(a) may underestimate the original concentration (due to damage even in reduced dose measurements) or other systematic error (due to the other mentioned effects). However, it can accurately be considered semi-quantitatively to measure the diffusion depth.

In Figure 6(a), a complementary error function fitting is added to the nitrogen profile as a thin line. Despite the noise, it is clear that nitrogen is detected down to 25 nm or so (where estimated nitrogen concentrations decreases to 10% of its surface value). The presence of nitrogen is also clear in the fine-structure of Titanium and oxygen absorption edges, shown in Figure 6 (b). Again, a transition from one edge shape to the other is observed around 30 nm from the surface. Moreover, it is interesting to note that the obtained nitrogen profile didn't affect the crystal structure as observed by RH-TEM (Figure 5 (b)), that is, no amorphous layer was found despite the observed nitrogen concentration. Indeed, in some studies, the presence of nitrogen in reactive sputtering leads to amorphous N:TiO 2 films [4]. Atomic force microscopy was used to gather a broader idea of the growth and also a clearer picture of the surface before and after ion implantation. The average surface roughness is about 1 nm for all samples, indicating a smooth growth of TiO 2 Anatase thin film by reactive sputtering and also that implantation at 150eV does not induce surface roughening. Illustrative results, for samples growth at 400°C without implantation and implanted for 30 minutes, are shown in Figure 7. Without implantation, the surface shows small grains having about 40-60 nm in diameter, but the height difference from peak to valley is just about 3 nm. After implantation, crystal grains are partially revealed, as indicated by arrows in Fig. 7(b), and their diameter is in fact about 200 to 300 nm, a result more consistent with TEM observations. As we consider that the ion implantation at 150eV or the annealing time didn't change the crystal structure, grains should have diameters in the hundreds of nanometers from the beginning of the deposition, but ion polishing was necessary to reveal the actual grains to preferential sputtering of different crystal orientations [32]. From XRD, XPS, TEM and AFM results, it is possible to form the following picture of the implantation process: the ion beam is highly reactive and, with the help of hydrogen, creates a high surface chemical potential which is, together with the process temperature, the driving force for nitrogen diffusion into the thin TiO 2 film. Considering that a roughly constant nitrogen concentration builds up in the first minutes, a diffusion coefficient of nitrogen on anatase at 500°C can be calculated as approximately 210 -8 m 2 s -1 , considering the solution of Fick's second law for a constant surface concentration. R. G. Palgrave et al. fond similar values (2.5310 -8 m 2 s -1 ) at 675° for rutile and also, analyzing very accurate nitrogen concentration profiles, reported different diffusion coefficients, indicating more than one diffusion route [12]. Moreover, they show that interstitial nitrogen diffuses much faster than substitutional nitrogen. In this case, the quantitative concentration of nitrogen obtained by EELS should be compared to the interstitial nitrogen concentration, which, from our in situ XPS results, is about 3at.%, meaning a better agreement between EELS nitrogen concentration near the surface and XPS results. It must be noted that since only about half to one third of the film is actually doped, the average nitrogen concentration is probably closer to 1-2at.%.

Electrical characterization

Very generally, the effect of nitrogen implantation and diffusion into the Anatase thin film can be monitored by 4 probe electrical resistivity measurements. Such results, converted into sheet resistance, are shown in Figure 8 (a). It is observed that sheet resistance drops by 7 orders of magnitude and reaches 54.7k/. These results are in close agreement with resistivity, , as measured by van der Pauw method using indium contacts, shown in Figure 8(b). The films resistivity could be as low as 310 -1 cm, for the sample prepared at 500°C and implanted for 60 minutes (average nitrogen concentration about 1-2%). This resistivity is about 10 fold lower than reported for TiO 1.88 N 0.12 (4at.% of nitrogen) prepared by plasma-assisted molecular beam epitaxy [33]. Moreover, the presented results are very similar to N:TiO 2 prepared by electron cyclotron resonance and by reactive sputtering in refs [4,6] (with slightly lower light transmittance, see below) but higher than TiO 2 doped with Nb, Ta or W, which may show resistivity much lower than 10 -2 cm [5,34,35]. In Figures 8 and9 the symbols cover the estimated uncertainty bars. Mobility and carrier concentration results are shown in Figure 9. Highest carrier concentration is observed for sample implanted at 500°C and for 60 minutes and reaches up to 610 19 cm -3 . Mobility values measured are always lower than 1 cm 2 v -1 s -1 (and just above 0.1 cm 2 v -1 s -1 ), which is much lower (at least by one or even two orders of magnitude) than usual TCOs like ITO or SnO 2 [36]. Such mobility is however similar to reported to Nb doped TiO 2 [34]. Note that resistivity and carrier concentration values are calculated considering the full film thickness and, as EELS Nitrogen profile showed (Figure 6(a)), nitrogen concentration is far from homogenous along the thin film. If one takes into account that nitrogen is present in about one third of the films (30 nm instead of 90 nm), then carrier concentration would be in such region and in average about 210 20 cm -3 (it should be higher close to the surface). Such corrected carrier concentration starts to be similar to values obtained in the literature as 310 20 cm -3 for Ta:TiO 2 and 10 21 cm -3 for Nb:TiO 2 [35,34]. Industry standard TCEs have again similar carrier concentration values, such as 1.510 20 cm -3 for FTO, or about 20 21 cm -3 for ITO and AZO [37,38,39]. Similarly, sheet resistance (or resistivity) in the doped region would be 3 fold smaller than in the thin film average. Moreover, nitrogen concentration gradient may explain low mobility since the region more relevant to electrical measurements has higher carrier concentration, which in turn may reduce mobility. The temperature dependence of the resistance is shown in Figure 10 (a) for the sample prepared at 500°C and implanted for 60 minutes. A very small hysteresis was observed. Failure to fit data in an Arrhenius plot (LnR vs. 1/T) denoted that the resistance is not governed by thermal activation, contrary to plasma-assisted molecular beam epitaxy N:TiO 2 samples that contained mostly substitutional nitrogen [33]. However, the resistance scales as LogR α T -1/2 , as shown in Figure 10 (b). This suggests that the conduction mechanism close to room temperature is variable range hopping (VRH). For this regime the resistivity should follow:

ρ(T) = ρ 0 exp[T 0 /T] p , ( 1
)
where p = 1/4 for Mott (Mott-VRH) [40] and p = 1/2 for Efros and Shklovskii (ES-VRH) [41]. Both mechanisms were observed in ion implanted TiO 2 single crystals [42] and disordered TiO 2 thin films [43,44] in a wide temperature range. To determine which one of the mechanisms is dominant in our sample we used the method proposed by Zabrodskii and Zinoveva [45] to obtain the exponent p, where w(T) = -∂log(R)/∂log(T) and log(w) = log(pT0 p) -p log(T). By plotting log(w) versus log(T) we can find the value of the exponent p from the slope of the curve. As depicted in the insert of Figure 10(b), for T > 235 K the curve is fitted with p = 0.488 ± 0.007, very close to value expected for ES-VRH conduction mechanism. For lower temperatures, the data diverge, indicating a change in the conduction mechanism. Further study is necessary to understand this behavior but is outside the scope of this work.

Optical Characterization

The UV-Vis-NIR light transmission spectra for the studied samples are shown in Figure 11. The transmission spectra for amorphous quartz (used as substrate) and undoped anatase prepared at 400 and 500° are also shown. Interference fringes are observed for the thin films and the maximum transmission is in the range from 500 to 600 nm (green). It is observed that undoped anatase have a transmission maximum very similar to amorphous quartz and that by doping the thin films the transmission falls from about 90% to 85% (with respect to air). Such observed transmission is better than some literature results for doped TiO 2 with similar resistivity, as indicated above. [4,6,34]. The transmission curves were simulated (not shown) using the method described in ref [ 46 ] and the general shape is very well described considering only the thickness and refraction indexes of the film and substrate. Transmission spectra measured further into the IR up to 3000 nm (not shown) are still featureless with only one absorption region near 2720 nm due to the quartz substrate. Absorption spectra can be used to determine the optical band-gap. Taking in account that Anatase has an indirect band-gap and following the procedure indicated in [47], the optical band gap can be obtained by plotting the square-root of the absorption coefficient as function of the energy and extrapolating the absorption edge at high energies [48]. Figure 12 shows the results for two extreme cases: undoped Anatase thin film prepared at 500°C and nitrogen implanted for 60 minutes also prepared at 500°C. Optical band-gap in both cases is about 3.29 eV, in agreement with Anatase value [47,49]. This indicates that the doped region does not affect significantly the overall light absorption edge. Similar results were obtained for all other samples (not shown). Such result is in agreement to literature reports that indicate that gap narrowing is related to substitutional nitrogen, which in our case could be restricted to the surface. Interstitial nitrogen, on the other hand, does not reduce band-gap [12,50,51].

Shelf stability

Finally, the shelf stability was evaluated by measuring the resistivity, mobility and carrier concentration on the interval of some days for the sample implanted for 30 minutes at 500°C (without any surface protection/coating). The results, shown in Figure 13, indicate that the films maintains its resistivity with only a 40% resistivity increase, despite the fact that TiO 2 is thermodynamically favorable with respect to TiN. It is observed that the resistivity increases slightly from (1.8±0.2) to (2.5±0.3) cm, see Figure 13 (a). This change is accompanied by a decrease of carrier density and an increase in mobility, as shown in Figure 13(b) and (c). Such changes could be due to surface oxidation that would displace nitrogen and reduce its concentration. However, oxygen diffusion would be too slow to displace nitrogen deeper in the thin film. The stability of this N:TiO 2 film, even if not subjected to heat or UV light, is interesting with respect to literature [52]. Further study is needed to compare the stability of N:TiO 2 to that of other TCOs [53].

Conclusions

In summary, a comprehensive study showed that, by implanting 150 eV nitrogen and hydrogen ions into Anatase films, it is possible to build ~33% nitrogen surface concentrations which drive nitrogen diffusion into the volume of the film. For the sample prepared at 500°C and implanted for 60 minutes, the films resistivity could be as low as 310 -1 cm while transparency at 550nm is about 85%. In this case, nitrogen diffusion could reach about 25 to 30 nm deep into the thin film. Note that 150eV nitrogen ions are readily available with simple laboratory ion guns.

The proposed two step deposition and doping technique could, as planned, provide Anatase thin films with a nitrogen doped zone near the surface. Moreover, carrier densities and conductivities similar to other established TCOs could be obtained. These results show the effectiveness of nitrogen diffusion into the Anatase film from the surface due to the obtained nitrogen surface concentration and applied temperature. Clearly, it was not possible to dope with nitrogen the whole film or to create homogenously doped sample at 500°C and 60 minutes of implantation. However, by adjusting properly the nitriding implanting time, desired thin film properties could be obtained. Indeed, the presented results indicate that, by doping during longer times until the whole thin film is doped, it could be possible to obtain resistivities lower than 10 -1 cm.

This study supports the interpretations that interstitial nitrogen has higher binding energy in XPS, that it diffuses faster in Anatase (with respect to Nitrogen in substitutional sites) and that it does not affect Anatase optical bandgap.

Finally, low energy ion doping using simple ion guns can be applied to Anatase prepared by other means, even colloidal synthesized nanoparticles. The high reactivity of low energy nitrogen ions associated with hydrogen ions, we speculate, could be also effective in other Anatase samples kinds.

Figure 1 :

 1 Figure 1: In situ x-ray photoemission spectra from sample grown at 500°C and implanted (at the same temperature) for 60 minutes with 150 eV nitrogen ions. The spectra include decomposition into components for different expected chemical bounds in the sample.

Figure 2 :

 2 Figure 2: X-ray photoemission spectra are shown for samples prepared with and without hydrogen in the gas feed to the ion gun. The peak associated to Nitrogen in interstitial sites is observed in both samples.

Figure 3 :

 3 Figure 3: Nitrogen, Oxygen and Titanium concentration obtained by in situ XPS for samples prepared at 400° and 500°C for several implantation times. Lines are a guide to the eyes. Nitrogen concentration reaches about 33at.%.

Figure 4 :

 4 Figure 4: Diffractograms from grazing incidence X-ray Diffraction for TiO 2 films prepared at 400 and 500°C and implanted for the time indicated in each curve. Anatase lines are indicated in the bottom according to ICSD 9852.

Figure 5 :

 5 Figure 5: TEM cross-section micrograph from sample prepared at 500°C and implanted for 60 minutes. (a) A modified region at the surface is observed. (b) HR-TEM shows atomic planes from small grains from bottom to the top of the thin film. The insert shows a SAED pattern obtained nearby on a region with larger grains.

Figure 6 :

 6 Figure 6: (a) Nitrogen, Oxygen and Titanium semi-quantitative profile determined by STEM-EELS on a cross-section lamella. A complementary error function fit was added to nitrogen profile. (b) Averaged EEL spectra of titanium 2p and oxygen 1s absorption edges indicating the difference from the upper (nitrogen doped) layer to the bottom (pristine) TiO 2 .

Figure 7 :

 7 Figure 7: AFM images of the surface of samples implanted by 0 minutes (undoped) and 30 minutes, both prepared at 400°C, are shown is (a) and (b), respectively. Ion implantation reveals partially the grains by preferential sputtering. Arrows in (b) indicate grain boundaries.

Figure 8 :

 8 Figure 8: (a) Sheet resistance and (b) Resistivity from all samples measured by 4-probe and van der Pauw, respectively. The results are in close agreement.

Figure 9 :

 9 Figure 9: Hall mobility and carrier concentration measured by van der Pauw method. Carrier density is show in open symbols while solid symbols show carrier mobility.

Figure 10 .

 10 Figure 10. (a) Resistance versus temperature for the film prepared at 500°C and implanted for 60 minutes. A small hysteresis was observed. (b) Logarithm plot of resistance versus T -1/2 showing a linear dependency (blue line) at high temperature. The inset shows the double-log plot of function w(T) and T and the value of exponent "p", as determined from the slope of the curve.

Figure 11 :

 11 Figure 11: Light transmission for samples prepared at 500 and 400°C. Amorphous quartz substrate and undoped anatase thin film are also shown.

Figure 12 :

 12 Figure12: Square-root of the absorption coefficient for undoped and 60 minutes N doped Anatase films prepared at 500°C. In both cases, the gap is about 3.29 eV.

Figure 13 :

 13 Figure 13: Resistivity, carrier concentration and mobility for shelf storage of the sample nitride for 30 minutes and prepared at 500°C.

Acknowledgments

Part of this work was supported by FAPESP, projects 2014/23399-9 and 2012/10127-5. TEM experiments were performed at the Brazilian Nanotechnology National Laboratory (LNNano/CNPEM).


Keywords: process assessment, competencies model, capstone project

The capstone is arguably the most important course in any engineering program because it provides a culminating experience and is often the only course intended to develop non-technical, but essential skills. In a software development, the capstone runs from requirements to qualification testing. Indeed, the project progress is sustained by software processes. This paper yields different settings where students, teachers and third-party assessors performed [self-] assessment and the paper analyses corresponding correlation coefficients. The paper presents also some aspects of the bachelor capstone. A research question aims to seek if an external process assessment can be replaced or completed with students' self-assessment. Our initial findings were presented at the International Workshop on Software Process Education Training and Professionalism (IWSPETP) 2015 in Gothenburg, Sweden and we aimed to improve the assessment using teacher and third-party assessments. Revised findings show that, if they are related to curriculum topics, students and teacher assessments are correlated but that external assessment is not suitable in an academic context.

Introduction

Project experience for graduates of computer science programs has the following characteristic in the ACM Computer Science Curricula [START_REF]Computer Science Curricula -Curriculum Guidelines for Undergraduate Degree Programs in Computer Science[END_REF]: "To ensure that graduates can successfully apply the knowledge they have gained, all graduates of computer science programs should have been involved in at least one substantial project.

[…] Such projects should challenge students by being integrative, requiring evaluation of potential solutions, and requiring work on a larger scale than typical course projects. Students should have opportunities to develop their interpersonal communication skills as part of their project experience."

The capstone is arguably the most important course in any engineering program because it provides a culminating experience and is often the only course used to develop non-technical, but essential skills [START_REF]The glossary of education reform[END_REF]. Many programs run capstone projects in different settings [START_REF] Dascalu | Computer science capstone course senior projects: from project idea to prototype implementation[END_REF][START_REF] Umphress | Software process in the classroom: the Capstone project experience[END_REF][START_REF] Karunasekera | Preparing software engineering graduates for an industry career[END_REF][START_REF] Vasilevskaya | Assessing Large-Project Courses: Model, Activities, and Lessons Learned[END_REF][START_REF] Bloomfield | A service learning practicum capstone[END_REF][START_REF] Goold | Providing process for projects in capstone courses[END_REF]. The capstone project is intended to provide students with a learning by doing approach about software development, from requirements to qualification testing. Indeed, the project progress is sustained by software processes.

Within the ISO/IEC 15504 series and the ISO/IEC 330xx family of standards, process assessment is used for process improvement and/or process capability determination. Process assessment helps students to be conscious about and improve what they are doing. Hence, a capstone teacher's activity is to assist students with appreciation and guidance, a task that relies on the assessment of students' practices and students' products. This paper yields different settings where students, teachers and third-party assessors performed [self-] assessment and analyses correlation coefficients. Incidentally, the paper presents some aspects of the bachelor capstone project at Brest University. Data collection started 3 years ago. Initial findings were presented in [START_REF] Ribaud | Process Assessment Issues in a Bachelor Capstone Project[END_REF].

The paper structure is: section 2 overviews process assessment, section 3 presents different settings we carried process assessments; we finish with a conclusion.

2

Process assessment

Process Reference Models

Most software engineering educators will agree that the main goal of the capstone project is to learn by doing a simplified cycle of software development through a somewhat realistic project. For instance, Dascalu et al. use a "streamlined" version of a traditional software development process [START_REF] Dascalu | Computer science capstone course senior projects: from project idea to prototype implementation[END_REF]. Umphress et al. state that using software processes in the classroom helps in three ways: 1 -processes describe the tasks that students must accomplish to build software; 2 -processes can give the instructor visibility into the project; 3 -processes can provide continuity and corporate memory across academic terms [START_REF] Umphress | Software process in the classroom: the Capstone project experience[END_REF]. Consequently, the exposition to some kind of process assessment is considered as a side-effect goal of the capstone project. It is a conventional assertion that assessment drives learning [START_REF] Dollard | Personality and psychotherapy; an analysis in terms of learning, thinking, and culture[END_REF]; hence process assessment drives processes learning. Conventionally, a process is seen as a set of activities or tasks, converting inputs into outputs [START_REF]Systems and software engineering --Software life cycle processes[END_REF]. This definition is not suited for process assessment. Rout states that "it is of more value to explore the purpose for which the process is employed. Implementing a process results in the achievement of a number of observable outcomes, which together demonstrate achievement of the process purpose [START_REF] Rout | The evolving picture of standardisation and certification for process assessment[END_REF]." This approach is used to specify processes in a Process Reference Model (PRM). We use a small subset of the ISO/IEC 15504-

Ability model

From an individual perspective, the ISO/IEC 15504 Exemplar Process Assessment Model (PAM) is seen as a competencies model related to the knowledge, skills and attitudes involved in a software project. A competencies model defines and organizes the elements of a curriculum (or a professional baseline) and their relationships. During the capstone project, all the students use the model and self-assess their progress.

A hierarchical model is easy to manage and use. We kept the hierarchical decomposition issued from the ISO/IEC 15504 Exemplar PAM: process groupsprocessbase practices and products. A competency model is decomposed into competency areas (mapping to process groups); each area corresponding to one of the main division of the profession or of a curriculum. Each area organizes the competencies into families (mapping to processes). A family corresponds to main activities of the area. Each family is made of a set of knowledge and abilities (mapping to base practices), called competencies; each of these entities is represented by a designation and a description.

The ability model and its associated tool eCompas have been presented in [START_REF] Ribaud | Towards an ability model for SE apprenticeship[END_REF].

Process assessment

The technique of process assessment is essentially a measurement activity. Within ISO/IEC 15504, process assessment has been applied to a characteristic termed process capability, defined as "a characterization of the ability of a process to meet current or projected business goals" [START_REF]Information technology --Process assessment --Part 5: An exemplar software life cycle process assessment model[END_REF]. It is now replaced in the 330xx family of standards by the larger concept of process quality, defined as "ability of a process to satisfy stated and implied stakeholders needs when used in a specific context [START_REF]Information technology --Process assessment --Concepts and terminology[END_REF]. In ISO/IEC 33020:2015, process capability is defined on a six point ordinal scale that enables capability to be assessed from the bottom of the scale, Incomplete, through the top end of the scale, Innovating [START_REF]Information technology --Process assessment --Process measurement framework for assessment of process capability[END_REF]. We see Capability Level 1, Performed, as an achievement: through the performance of necessary actions and the presence of appropriate input and output work products, the process achieves its process purpose and outcomes. Hence, Capability Level 1 will be the goal and the assessment focus.

If students are able to perform a process, it denotes a successful learning of software processes, and teachers' assessments rate this capability. Because we believe that learning is sustained by continuous, self-directed assessment, done by teachers or a third-party, the research question aims to state how students' self-assessment and teacher's assessment are correlated and if self-assessment of BPs and WPs is an alternative to external assessment about ISO/IEC 15504 Capability Level 1. Obviously, the main goal of assessment is students' ability to perform the selected processes set.

3

The Capstone Project

Overview

Schedule

The curriculum is a 3-year Bachelor of Computer Science. The project is performed during two periods. The first period is dispatched all the semester along and homework is required. The second period (2 weeks) happens after the final exams and before students' internship. Students are familiar with the Author-Reader cycle: each deliverable can be reviewed as much as needed by the teacher that provides students with comments and suggestions. It is called Continuous Assessment in [START_REF] Karunasekera | Preparing software engineering graduates for an industry career[END_REF][START_REF] Vasilevskaya | Assessing Large-Project Courses: Model, Activities, and Lessons Learned[END_REF].

System Architecture

The system is made of 2 sub-systems: PocketAgenda (PA) for address books and agenda management and interface with a central directory; WhoIsWho (WIW) for managing the directory and a social network. PocketAgenda is implemented with Java, JSF relying on an Oracle RDBMS. WhoIsWho is implemented in Java using a RDBMS. Both sub-systems communicate with a protocol to establish using UDP. The system is delivered in 3 batches. Batch 0 established and analyzed requirements. Batch 1 performed collaborative architectural design, separate client and server development, integration. Batch 2 is focused on information system development.

Students consent

Students were advised that they can freely participate to the experiment described in this paper. The class contains 29 students, all agreed to participate; 4 did not complete the project and do not take part to the study. Students have to regularly update the competencies model consisting in the ENG process group, the 6 processes above and their Base Practices and main Work Products and self-assess on an achievement scale: Not -Partially -Largely -Full. There will be also teacher and third-party assessments that will be anonymously joined to self-assessments by volunteer students.

Batch 0 : writing and analyzing requirements

Batch 0 is intended to capture, write and manage requirements through use cases. It is a non-technical task not familiar to students. In [START_REF] Bloomfield | A service learning practicum capstone[END_REF], requirements are discussed as one of the four challenges for capstone projects. Students use an iterative process of writing and reviewing by the teacher. Usually, 3 cycles are required to achieve the task. Table 1 presents the correlation coefficient r between student and teacher assessment for the ENG.4 Software requirements analysis. It relies on 3 BPs and 2 WPs. Table 2 presents also the average assessment for each assessed item. The overall correlation coefficient relates 25 * 6 = 150 self-assessment measures with the corresponding teacher assessment measures, its value r = 0.64 indicates a correlation. Thanks to the Author-Reader cycle, specification writing iterates several time during the semester and the final mark given to almost 17-8 Interface requirements and 17-11 Software requirement documents was Fully Achieved. Hence correlation between students and teacher assessments is complete. However, students mistake documents assessment for the BP1: Specify software requirements. Documents were improved through the author-reader cycle, but only reflective students improve their practices accordingly. Also, students did not understand the ENG.4. BP4: Ensure consistency and failed the self-assessment. Most students did not take any interest in traceability and self-assessed at a much higher level that the teacher did.

A special set of values can bias a correlation coefficient; if we remove the BP4: Ensure consistency assessment, we get r = 0.89, indicating an effective correlation. However, a bias still exists because students are mostly self-assessing using the continuous feedback they got from the teacher during the Author-Reader cycle.

Students reported that they wrote use cases from a statement of work for the first time and that they could not have succeeded without the Author-Reader cycle.

Batch 1 : a client-server endeavor

For the batch 1, students have to work closely in pairs, to produce architectural design and interface specification and to integrate the client and server sub-systems, each sub-system being designed, developed and tested by one student. Defining the highlevel architecture, producing the medium and low-level design are typical activities of the design phase [START_REF] Dascalu | Computer science capstone course senior projects: from project idea to prototype implementation[END_REF]. 4 pairs failed to work together and split, consequently lonesome students worked alone and have to develop both sub-systems. We were aware of two biases: 1 -students interpret the teacher's feedback to selfassess accordingly; 2 -relationship issues might prevent teachers to assess students to their effective level. Hence, for ENG.3 System architectural design process and ENG.7 Software integration process, in addition to teachers' assessment, another teacher, experienced in ISO/IEC 15504 assessments, acted as a third-party assessor.

Architectural design

For the ENG.3 System architectural design, table 2 presents the correlation coefficient between student and teacher assessments and the correlation coefficient between student and third-party assessments. Assessment relies on 3 BPs and 2 WPs. Table 2 presents also the average assessment for each assessed item. The correlation coefficient between self-assessment and teacher assessment measures is r1 = 0.28 and the correlation coefficient between self-assessment and third-party assessment measures is r2 = 0.24. There is no real indication for a correlation. poor, except maybe for database design and interface design, but these technical topics are deeply addressed in the curriculum. An half of students perform a very superficial architectural work because they are eager to jump to the code. They believe that the work is fair enough but teachers do not. The BP4. Ensure consistency is a traceability matter that suffers the same problem described above. A similar concern to requirements arose: most students took Work Products (Design Documents) assessment as an indication of their achievement.

Students reported that requirement analysis greatly helped to figure out the system behavior and facilitated the design phase and interface specification. However, students had never really learnt architectural design and interface between sub-systems, indeed it explains the low third-party assessment average for BPS and WPs.

Integration

ENG.7 Software integration is assessed with 6 main Base Practices and 2 Work Products. The correlation coefficient between self and teacher assessments is r1 = -0.03 and the correlation coefficient between self and third-party assessments is r2 = 0.31. However, several BPs or WPs were assessed by the third-party assessor with the same mark for all students (N or P): the standard deviation is zero and the correlation coefficient is biased and was not used. Table 3 presents the assessment average for the third types of assessment. 48 All BPs and WPs related to integration and test are weakly third-party assessed, indicating that students are not really aware of these topics, a common hole in a Bachelor curriculum. Some students were aware of the poor maturity of the integrated product, partly due to the lack of testing. Although the Junit framework has been taught during the first semester, some students did not see the point to use it while some others did not see how to use it for the project. As mentioned by [START_REF] Umphress | Software process in the classroom: the Capstone project experience[END_REF], we came to doubt the veracity of process data we collected. Students reported that they appreciated the high-level discipline that the capstone imposed, but they balked at the details.

Batch 2 : information system development

For the batch 2, students have to work loosely in pairs; each of the two has developed different components of the information system and has been assessed individually. Table 4 presents the correlation coefficient r between student and teacher assessment for the ENG.6 Software construction process. It relies on 4 Base Practices and 2 Work Products. Table 4 presents also the average assessment for each assessed item. The correlation coefficient is r = 0.10 and there is no indication for a correlation.

However, BPs and WPs related to unit testing were assessed by the teacher with almost the same mark for all students (N or P), biasing the correlation coefficient. If we remove BPs and WPs related to unit testing (17-14 Test cases specification; 15-10 Test incidents report; BP1: Develop unit verification procedures), we get r = 0.49, indicating a possible correlation. Our bachelor students have little awareness of the importance of testing, including test specification and bugs reporting. This issue has been raised by professional tutors many times during the internships but no effective solution has been found until yet.

Students reported that the ENG.6 Software construction process raised a certain anxiety because students had doubt about their ability to develop a stand-alone server interoperating with a JDeveloper application and two databases but most students succeeded. For some students, a poor Java literacy compromised the project progress. It is one problem reported by Goold: the lack of technical skills in some teams [START_REF] Karunasekera | Preparing software engineering graduates for an industry career[END_REF].

Conclusion

The research question aims to see how students' self-assessment and external assessment [by a teacher or a third-party] are correlated. This is not true for topics not addressed in the curriculum or unknown by students. For well-known topics, assessments are correlated roughly for the half of the study population. It might indicate that in a professional setting, where employees are skilled for the required tasks, selfassessment might be a good replacement to external assessment. Using a third-party assessment instead of coaches' assessment was not convincing. Third-party assessment is too harsh and tends to assess almost all students with the same mark. Self-knowledge or teacher's understanding tempers this rough assessment towards a finer appreciation.

The interest of a competencies model (process/BPs/WPs) is to supply a reference framework for doing the job. Software professionals may benefit from selfassessment using a competencies model in order to record abilities gained through different projects, to store annotations related to new skills, to establish snapshots in order to evaluate and recognize knowledge, skills and experience gained over long periods and in diverse contexts, including in non-formal and informal settings.

Table 1

 1

	: ENG.4 assessment (self and teacher)
		Stud. avg Tch. avg	r
	BP1: Specify software requirements	2.12	1.84	0.31
	BP3: Develop criteria for software testing	1.76	1.76	1.00
	BP4: Ensure consistency	1.92	0.88	0.29
	17-8 Interface requirements	1.88	1.88	1.00
	17-11 Software requirements	2.08	2.08	1.00

Table 2 :

 2 ENG.3 (self, teacher and third-party)

	Stud.	Tch.	3-party	r Std-	r Std-
	avg	avg	avg.	Tch	3party

Table 3 :

 3 ENG.7 indicators

	Stud.	Tch.	3-party
	avg	avg	avg.

Table 4 :

 4 ENG.6 assessment (self and teacher)

	Stud. avg Tch. avg	r

Acknowledgements

We thank all the students of the 2016-2017 final year of Bachelor in Computer Science for their agreement to participate to this study, and especially Maxens Manach and Killian Monot who collected and anonymized the assessments. We thank Laurence Duval, a teacher that coached and assessed half of the students during batch 1.


Cassandra Balland

Néné Satorou Cissé

Louise Hergoualc'h,

Gwendoline Kervot

Audrey Lidec

Alix Machard

Lisa Ribaud-Le Cann

Constance Rio

Louise Hergoualc'h

Maelle Sinilo

Valérie Dantec

Catherine Dezan

Cyrielle Feron

Claire François

Chabha Hireche

Arwa Khannoussi

Vincent Ribaud

Do Scratch a First Round with the Essence Kernel

Keywords: Scratch, gender equality, elementary school

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Girls Who . . .

I. INTRODUCTION

"Girls who…" is a facility intended to disseminate Scratch in elementary schools. It takes part of a French national plan accompanying schools in science and technology (ASTEP -Accompagnement en Sciences et Technologie à l'École Primaire). "Girls who…" is also a girl collective that develops and maintains a practicum of sciences, called the factory. "Girls who…" have a double goal: to set an example of sciences by women and to support the practice of sciences for elementary school pupils.

Scratch is an open-source environment for multi-media creation (https://scratch.mit.edu) young people 8 to 16 years old. The Scratch language is made of blocks, arranged in categories. Series of connected blocks form scripts. Categories Motion and Pen allow the displacement of sprites in a scene (a Cartesian coordinate system) and the layout of geometrical and artistic figures. Categories Data, Control and Operators provide typical primitives of imperative programming languages. Sensing category handles inputs/outputs and manages the usual peripherals: mouse, keyboard, webcam, and clock. Events category allows event-driven programming and a parallel way of thinking. Categories Looks and Sound provide the user with multi-media blocks.

The Essence kernel [START_REF]Object Management Group, Essence -Kernel and Language for Software Engineering Methods, Version 1.1[END_REF] issued from SEMAT initiative [START_REF] Jacobson | The essence of software engineering: the SEMAT kernel[END_REF] helps to assess projects progress and health. Essence yields an actionable and extensible kernel of universal elements, called alphas. Each alpha has a specific set of states that codify points along a progress dimension addressed by the alpha [START_REF] Jacobson | A new software engineering[END_REF].

The first round of "girls who…" produced introductory courses for Scratch, some courses based on the history of Charlie and the chocolate factory [START_REF] Dahl | Charlie et la chocolaterie[END_REF]. Exemplary lessons have been tested in five elementary schools around Brest, France. The development and the delivery of the course were performed in five sprints using Trello boards. After sprints, we performed an Essence assessment, presented in this paper, which revealed several weaknesses of the project and helped to improve the facility. Essence was chosen because we share the SEMAT concerns: to refund software engineering based on a solid theory, proven principles and best practices.

Section II describes the project according to alphas of Customer and Solution areas of concern: opportunities, stakeholders, requirements and software system. After having discussed time, space, actions and matter of "girls who…" section III presents the Endeavor area of concern: work, team and way-of-working. Finally, section IV concludes.

II. ASSESSMENT OF A PROJECT PROGRESS AND HEALTH

A unique feature of the Essence kernel is the way that it handles "things we always work with" through alphas. An alpha is an essential element of the software engineering endeavor -one that is relevant to an assessment of its progress and health. Alphas move through a set of states. Each state has a checklist that specifies the criteria needed to reach the state.

A. Opportunity

In France, the 2016 reform for elementary and secondary schools defined a common grounding of knowledge, skills and culture, structured in five areas [START_REF]Le socle commun de connaissances, de compétences et de culture[END_REF]. The common grounding acts as a reference for the school curriculum from 6 to 16 years. Learning Scratch programming and algorithmic thinking was introduced into the "languages to think and communicate" area. According to its authors [START_REF] Resnick | Scratch: programming for all[END_REF], Scratch is a creative design environment that appeals to people who hadn't imagined themselves as programmers. As a technological tool, it supports the learning of many skills of the common ground.

Since 1996, within the framework of the ASTEP, scientific students accompany primary school teachers during science and technology lessons. This accompaniment associates the teacher, the scientific student and pupils around the scientific and technological practice, for a mutual enrichment and natural division of competences.

In Brest University, each second year student of any Bachelor of Science degree attends a course about her/his "Preparation to professional life" with an internship. Students' objectives have two points, regarding her/his professional integration: 1 -the student must carry out a task or a set of specific tasks inside the internship organization or company; 2 -the student must be able to show her/his understanding of a professional environment. For students considering a teacher or an academic career, the ASTEP is a unique opportunity to experiment the teaching situation and area of concern.

In Western countries, there is girl disaffection for STEM area (Science, Technology, Engineering, and Mathematics). However, new generations of students are easily investing in communication and information technologies and appreciate the ludic and creative aspects of Scratch. The "girls who…" facility allows elementary schools to be technologically accompanied in Scratch by second year Bachelor girls. Students are demonstrating an example of sciences by women to the elementary school pupils.

Combination of a) Scratch introduction in the elementary school, b) existence of the French ASTEP program and c) commitment of second year students in the "Preparation to professional life" course establishes an identified opportunity. It corresponds to the first progress level of alpha Opportunity [1, Table 8.3 -Checklist for Opportunity]: the idea is clear and the stakeholders (detailed in the following section) are identified and interested.

The second level for the alpha Opportunity is to have a solution needed. In our facility, "girls who…" participation is made of three distinct activities: design and realization of science or technology learning sessions (based on Scratch); deliver learning sessions in the elementary schools; participate to a scientific project with primary schools class under the responsibility of a PhD female student. The whole facility is called the factory, and constitutes the solution. All items of the checklist Solution Needed of alpha Opportunity [1, Table 8.3 -Checklist for Opportunity] are not achieved yet: although the need for a solution is confirmed and that a first solution is identified and suggested, the needs for the stakeholders are not entirely established and all problems and their root causes are not completely identified.

B. Stakeholders

As mentioned in the previous section, second year students have to perform a practical experience through an internship and gain the associated course credits. Parallel to their research work, PhD students have also to gain credits. With primary education pupils, three groups are part of an example chain towards scientific professions. Each group has a role in the factory:

• Apprentices: elementary school pupils (girls and boys) who are learning Scratch and performing projects.

• Workers: second year female students of any Bachelor of Science program who like to prepare Scratch exercises and examples, deliver learning sessions to apprentices and accompany teachers.

• Tutors: PhD female students who animate science project for apprentices with workers' help and who might assist workers on their disciplinary learning.

Several categories of Ministry of National Education employees are also stakeholders. Educational institution employees, called resource persons, provide the factory with various services. Elementary school teachers engage their class in Scratch learning and science projects. School district inspectors (inspecteurs de circonscription, in French) are teachers' supervisor; they agree students' participation in schools and represent the institutional guarantee. Inside the university, heads of bachelors of science degree and PhD advisors facilitate students' participation as "girls who…" Stakeholders groups are identified, key stakeholders are represented and responsibilities are defined; one reached the first alpha level: stakeholders are recognized [1, Table 8.2 -Checklist for Stakeholders]. The second level is to have stakeholders represented. In the "girls who…" facility, the stakeholders' representatives are authorized and responsibilities are agreed. As detailed in section III.C, the collaborative approach is largely agreed. Consequently, to achieve the second level, the remaining task is to ensure that way-of-working is supported and respected.

C. Requirements

"Use cases have been around for almost 30 years as a requirements approach and have been part of the inspiration for more recent techniques such as user stories [START_REF] Jacobson | Use-case 2.0[END_REF]." Some stories are presented below.

A resource person creates, on a Trello board, a schedule list for a school, then a card for each learning sequence where s/he seizes sequence description, fills the expiry date and allocates the workers.

A worker consults a Trello board related to daily tasks, decides to take again the realization of a sequence and consults the task card. She downloads the Moodle resources associated with the card, works on the instructions and the project, and updates the Moodle resources.

A worker arrives in a school to animate a learning sequence. She connects herself to Moodle and set up resources for the sequence on each work station. She starts the presentation of the sequence. Once apprentices are working, she explains the work to be carried out using the presentation and supervises the apprentices' activities.

An apprentice starts working. S/he chooses one activity on her/his current sequence. Then, s/he loads the related Scratch project and get on the task.

All stakeholders are not familiar with requirements engineering. The choice of "user stories" for sketching the requirements makes it possible to communicate them and to effectively share them between the stakeholders. User stories are represented using cards, called story cards, which constitute the smallest grain of requirements. As noted by [START_REF] Sharp | The Role of Story Cards and the Wall in XP teams: a distributed cognition perspective[END_REF], story cards and tasks to be implemented together with the wall where they are displayed are two tangible artefacts of the distributed knowledge of the team.

The need for a facility such as the factory has been agreed by stakeholders. Users (pupils) are identified. Funding and opportunity are clear. The first level for alpha Requirements is reached [1, Table 8.4 -Checklist for Requirements]: requirements are conceived.

The second level aims to have requirements bounded. Workers and tutors are main stakeholders involved in factory development. All stakeholders agree on the factory purpose -Scratch learning -and the factory will be successful if apprentices learn effectively. The stakeholders have a shared understanding of the ASTEP program. Requirements are managed using a Trello board, with a list for each user stories made of pieces materialized by story cards. Assumptions about the system changed (see next section) but are now clearly stated. We are struggling with two items of the Requirements bounded checklist: is the prioritization scheme clear; are constraints identified and considered? In the short history of "girls who…" each new school joining the factory brought new circumstances and new needs, and workers adapted consequently requirements. In order to move to the third level -Requirements coherent -one needs to find a way to manage new constraints and prioritize requirements.

D. System

The initial idea behind the system was to build an online training of Scratch. The first source of inspiration was the web site code.org. It offers many well-organized activities from simple to complex in terms of teaching programming. Kalelioglu studied the effects of learning programming with code.org regarding reflexive thought, problem resolution, and gender issues. She stated: "Students developed a positive attitude towards programming, and female students showed that they were as successful as their male counterparts, and that programming could be part of their future plans [START_REF] Kalelioğlu | A new way of teaching programming skills to K-12 students: code.org[END_REF]."

During preliminary discussions with elementary school teachers and inspectors, the need moved from a remote on-line course to classroom training sessions. The first round of "girls who…" established the proof of concept thanks to five elementary schools. We kept the code.org principle of learning sequences divided into increasingly complex activities. Strength of code.org is an integrated environment, providing the user with learning instructions, a workspace where you can do programming, on-line help and feedback with learning. This integration remains a requirement of the system, but in a future version. Moreover, some learning sequences use small robots called mbot. Robotics programming is performed in the mblock environment, an open-source Scratch extension.

The architecture of the system is thus made up of:

• Several Trello boards (https://trello.com).

• Prezi presentations (https://prezi.com).

• A Moodle server from Brest University, dedicated to online courses and accessible by external users (https://moodlespoc.univ-brest.fr).

• School computers or tablets with Scratch and mblock.

The architecture selection criteria have been agreed on, hardware platforms identified and technologies selected. System boundary is known and key technical risks agreed to. Significant decisions about the system have been made: opensource software and free contents. All criteria of the first level for alpha System are fulfilled [1, Table 8.5 -Checklist for System Software] and the architecture is selected.

The second level is to have a demonstrable system. According to the checklist associated with this level, one needs to demonstrate architectural characteristics, critical hardware, critical interfaces and integration with other existing systems. One needs to exercise the system and measure its performance. Then the relevant stakeholders will agree that the demonstrated architecture is appropriate. All verifications and measurements will be realized in the next round where "girls who…" will run courses in many schools; the goal is to demonstrate that the architecture of the system is fit for purpose and supports testing.

III. THE ENDEAVOUR AREA OF CONCERN

The Endeavour area of concern contains everything to do with the team, and the way that they approach their work. Endeavour contains three alphas: Team, Work and Way-ofworking. Key aspects of the facility are presented: time, space, actions and matter then alphas' assessment is drafted.

A. Time of girls who…

Each year, "girls who…" will welcome new workers (second-year students) and new tutors (starting PhD students).

"Girls who…" go in schools and have three kinds of contributions: Scratch discovery sessions (in May/June), Scratch learning sequences (from October to February), and science project accompaniments (from March to June). A Trello board equivalent to the product backlog, called the service backlog, contains a list by school. Each school visit is materialized by a card and its attributes: date, members, checklist, and resources.

During her first period in the factory (1-4 weeks, see sections II.A and III.D), each worker produces contents that will be integrated in one of the factory courses. Workers work in pair and the time unit is the week: the product backlog (a Trello board) contains a list per week. The list keeps cards (tasks or sequences in schools) organized in their various stages of progress.

B. Spaces of girls who…

The factory managed by "girls who…" is a common property (like Wikipedia or an open-source software) under a double license, GNU GPL and CC BY-SA.

Digital spaces of the project are numerous: Moodle courses and Prezi presentations, product and service backlogs. The entry point is a public Trello board, in French (https://trello.com/b/83omDwmt/les-filles-qui).

The integration of new workers in the factory occurs during the first internship (1-4 weeks) in the facility. Thanks to a partnership with an engineer school, École Nationale Supérieure de Techniques Avancées -ENSTA Bretagne, new workers are accommodated in a dedicated room at ENSTA Bretagne. Thereafter, "girls who…" will not be always on the same space-time: girls telework, go in schools by pairs, exchange synchronously and asynchronously. However, this integration space-time where "girls who…" meet presentially is a key element of network dynamics. It makes it possible to acquire tools and methods usage which will be then used remotely. A distributed common facility such as our factory has to schedule gathering space-time events throughout the year to keep girls trained, to strengthen network membership and to ensure continuity between presence and distance.

C. Actions of girls who…

"Girls who…" work is ruled by two key principles: setting an example of science and gender equality. "Girls who…" act and are models for other girls who act and so on.

A worker achieves various tasks. She contributes to the facility organization and digital spaces management. She designs and realizes learning sequences for Scratch, Scratch junior, mbot programming and carry out assessments. She accompanies elementary school classes within the national program ASTEP (see section II.A), either delivering learning sequence or participating to science projects. She contributes to a research action endeavor related to the introduction of programming and algorithmic thinking in elementary schools. A tutor achieves targeted action. Upon teachers' request, she leads science projects for elementary school pupils. She might assist workers during their Bachelor studies. At the end of the first round, three courses has been developed and partly tested: a 6-sequence course of Scratch programming for 10-12 years, a 6-sequence course (sharing a few sequences with the previous course) of mbot robots programming for 10-12 years, a 3-sequence introductory course of Scratch junior for 6-8 years. Scratch courses use characters inspired of the book "Charlie and the chocolate factory" of Roald Dahl [START_REF] Dahl | Charlie et la chocolaterie[END_REF].

D. Matter of girls who…

E. A first endeavor

During the first five-weeks round, nine workers realized the programming courses described above and are co-authors of this paper. Whereas the initial idea was to prepare courses for next year, it has been quite clear that "girls who…" need to test courses in schools. Generally speaking, the design, the realization and courses delivery occurred in short cycles (one week) and built incrementally, the next week incorporating the current week feedback. A regular health evaluation of alphas Work and Team guided the project progress. The alpha Wayof-Working was barely assessed.

1) Work.

A Trello board was used for definition, planning and assignment of tasks: a list per week and a card per workday with workers present this day. Card descriptions were informal, but for recurring tasks, helped to feed various to-do lists. The lists, as indicated in the section III.A, control tasks and schools' accompaniments and constitute the product backlog and the service backlog of the project.

Required results, constraints, funding sources and priorities are clear; stakeholders are known; initiators are identified. All criteria of the first level of alpha Work [1, Table 8.7 -Checklist for Work] are met and work is initiated.

The second level is to have the work prepared. Commitment of faculty is made; a credible plan and funding is in place and renewable each year. Resource availability (mainly workers) is understood; cost and effort of the work are roughly estimated. Work is broken down sufficiently in learning sequences for productive work to start; tasks are identified and prioritized; at least one of members (the Science Faculty) is ready. Exposure to the risks is minimal thus one will admit that it is understood. There are two points to fulfill to have the work prepared. Criteria of acceptance have to be established, for instance to constitute pupils cohorts and to perform measurements. Integration points have to be defined, in contents terms -how to enrich the poll of courses, and in schools terms -how to insert a new school in the facility.

2) Team.

Seven workers of the first round came from Bachelor of Mathematics and Bachelor of Informatics. They know each other, some students committed immediately to the project and this was the key to decide the others. The project evolved from an online course to face-to-face courses; however the team mission and composition are now defined; constraints are known; required competences in programming and teaching are identified. Student themselves outlined their responsibilities and the need for a clear level of commitment.

"Girls who…" initiators received a training intended to animate collaborative projects (http://animacoop.net). Training was carried out part-time over three months. Training facilitated the selection of a distributed and co-operative leadership model. Training helped to set rules of governance which is shared between workers, tutors, heads of Bachelor studies and network animators.

The greatest difficulty arose from the two latter items of the checklist: definition of mechanisms to grow the team and determination of team size. An identified risk is that schools demand increases too fast; during the first round, we selected five pilot schools; for the 2017-2018 academic year, 18 elementary classes are already part of the program. Due to introduction of Scratch into the elementary school curriculum, it can lead to a demand exceeding supply. In French Faculties of Science, biology studies are largely invested by girls, and there is no need for exemplary models for Biology. However "girls who…" make biology can be interested by Scratch technology and by going in the schools as well. We have to evolve in a way that "girls who…" make biology can bring forces to the facility and find an interest for their scientific discipline. This is the goal of science project accompaniments, thus all criteria of the first level of alpha Team are met [1, Table 8.6 -Checklist for Team] and team is seeded.

The second level is to have a formed team. Workers know their role and their place in the team; individual and team responsibilities are accepted and aligned with competencies. As volunteers, members accept work and it was underlined in the previous section that members must commit to the work and the team. Team communication mechanisms have been defined: Trello for backlog, planning and tasks and Moodle as a Learning Management System. "Girls who…" use Slack as instant messaging and Loomio for collective decision making. The unknown factor relates to the growth: will be enough workers available and did we fail to identify external collaborators? The points will be addressed at the next round.

3) Way-of-working

The first level of alpha Way-of-Working is to have principles established [1, Table 8.8 -Checklist for Way-Of-Working]. The criteria are: the team actively supports the principles, the stakeholders agree with principles, the needs for tool are agreed, the approach is recommended, the operational context is understood and the constraints of practice and tool are understood.

The first round of "girls who…" did not have established principles before its start, but workers defined their way-ofworking and made the following decisions. A pair of workers is assigned to a school; design and realization of learning sequences of training is assigned individually; Prezi presentations are used to present learning instructions and exercises interactively with pupils; Slack, Trello and Loomio usage rules are defined; tools and resources required to be available in schools are identified; a back-up solution is needed and implemented, for content availability as well as for software tools. Foundations are laid and at the next round, we will see if the new "girls who…" will follow these principles. We will check if the first level is reached and principles established.

IV. CONCLUSION

The first round of "girls who…" shaped a facility with a double goal: to set the example of "girls who…" do sciences and technology and to support the introduction of Scratch and algorithmic thinking in the elementary schools. "Girls who…" prepared Scratch lessons, delivered courses in five pilot schools and organized the system for next rounds. Kids loved when "girls who…" came in schools and learned Scratch and robots programming with enthusiasm. For 2017-2018 year, 18 elementary classes are already part of the program.

The facility evolved considerably since we wrote initial specifications nine months ago. The facility was led with a double help: training intended to animate collaborative projects and use of the Essence kernel to assess the state of different areas of concern and to define next steps to complete.

Essence provides an understanding of the progress and health of development efforts and how practices can be combined into an effective way of working. The use of Essence can help teams, among others, to detect systemic problems early and take appropriate action; evaluate the completeness of the set of practices selected, and understand the strengths and weaknesses of the way of working; keep an up-to-date record of the team's way of working, and share information and experiences with other teams [START_REF] Jacobson | Agile and SEMAT: perfect partners[END_REF]. Essence assessment gave us a clear vision of the project state and raised critical weaknesses of the facility. Indeed, we are using Essence to assess our research projects health and progress.

Fig. 1 .

 1 Fig. 1. Illustrations by Lisa, inspired by "Charlie and the chocolate factory" the novel by Roald Dahl and the eponym movie by Tim Burton.

Acknowledgments

Many persons facilitated the birth of "girls who…" including Pascale Huret-Cloastre, Hélène Klucik, Isabelle Queré, Corinne Tarits, Yann Ti-Coz.