D Lorgeoux

R Faure-Catteloin

R Bounaceur

Michels

V Burklé-Vitzthum
email: valerie.vitzthum@univ-lorraine.fr

N C Leguizamon Guerra

C Lorgeoux

D Faure-Catteloin

R Michels

INFLUENCE OF H 2 S ON THE THERMAL CRACKING OF ALKYLBENZENES AT HIGH PRESSURE (70 MPA) AND MODERATE TEMPERATURE (583-623 K)

Keywords: Pyrolysis, organosulfur compounds, high pressure, H 2 S, alkylbenzene, kinetic effect, apparent kinetic parameters Highlights

Introduction

H 2 S can be the dominant gas in hot (>100°C) carbonate petroleum reservoirs [START_REF] Belenitskaya | Distribution pattern of hydrogen sulphide-bearing gas in former Soviet Union[END_REF][2][3] [START_REF] Zhu | Genesis and distribution of hydrogen sulfide in deep heavy oil of the Halahatang area in the Tarim Basin, China[END_REF]. Its abundance in reservoirs is essentially linked to Thermochemical Sulfate Reduction (TSR) which is the reaction of hydrocarbons with sulfate in formation waters within rock strata (e.g. [START_REF] Orr | Changes in sulphur content and isotopic ratios of sulphur during petroleum maturation -Study of Big Horn Basin Paleozoic oils[END_REF][6] [START_REF] Heydari | Burial diagenesis and thermochemical sulfate reduction, Smackover southeastern Mississippi salt basin[END_REF][8] [START_REF] Worden | H 2 S-producing reactions in deep carbonate gas reservoirs, Khuff Formation, Abu Dhabi[END_REF]) at T>100°C. TSR is one of the most important reactions detrimental to oil composition in petroleum reservoirs; it involves a complex reaction network that leads to the reduction of sulfate to H 2 S and to the oxidation of hydrocarbons to CO 2 ([8] [START_REF] Worden | H 2 S in North Sea oil fields: importance of thermochemical sulphate reduction in clastic reservoirs[END_REF]). The deficiency in available iron of carbonate reservoir rocks prevents the precipitation of iron sulfides. Therefore, H 2 S will accumulate in petroleum traps.

Because of its deleterious effect on oil composition, as well as greater production risks and costs due to the toxicity and corrosiveness of H 2 S and CO 2 , TSR has been extensively studied in the literature (e.g. [START_REF] Worden | H 2 S in North Sea oil fields: importance of thermochemical sulphate reduction in clastic reservoirs[END_REF] [START_REF] Manzano | The influence of thermochemical sulphate reduction on hydrocarbon composition in Nisku reservoirs, Brazeau river area, Alberta, Canada[END_REF] [START_REF] Cai | Thermochemical sulphate reduction and the generation of hydrogen sulphide and thiols (mercaptans) in Triassic carbonate reservoirs from the Sichuan Basin, China[END_REF][13] [START_REF] Zhang | Experimental investigation on thermochemical sulfate reduction by H 2 S initiation[END_REF]). In experimental studies, much attention has been paid to the formation of H 2 S and sulfur compounds arising from reaction within the water phase or at the interface with the hydrocarbon phase. Very few studies deal with the consequence of a direct reaction of H 2 S on the hydrocarbons ( [START_REF] Zhang | Experimental investigation on thermochemical sulfate reduction by H 2 S initiation[END_REF] [15] [START_REF] Nguyen | Thermal reactions between alkanes and H 2 S or thiols at high pressure[END_REF] [17] [START_REF] Walters | Proto-solid bitumen in petroleum altered by thermochemical sulfate reduction[END_REF]) within the organic phase or at the oil-gas interface, especially in the absence of TSR conditions. Yet, such information would be of great value since an improved understanding of the fate of H 2 S and organic sulfur compounds would be highly beneficial for petroleum exploration, exploitation of high sulfur petroleum fields, recovery of heavy oil by steam injection, enhanced recovery by gas injection and sequestration of H 2 S in depleted petroleum reservoirs.

Up to now, published studies about the influence of H 2 S on hydrocarbons concern either oils [START_REF] Walters | Proto-solid bitumen in petroleum altered by thermochemical sulfate reduction[END_REF] or pure alkanes (n-octane or n-hexadecane) as model compounds ( [START_REF] Zhang | Experimental investigation on thermochemical sulfate reduction by H 2 S initiation[END_REF][15] [START_REF] Nguyen | Thermal reactions between alkanes and H 2 S or thiols at high pressure[END_REF] [START_REF] Nguyen | Pyrolysis mechanism of the n-octane/H 2 S mixture at 70 MPa and 603-623K[END_REF]). The reaction of H 2 S in the presence of an alkane leads to organosulfur compounds that are mostly thiols, thiacycloalkanes and thiophenes, whereas naphthenoaromatic species with 1-3 S atoms are produced during the pyrolysis of oils in the presence of H 2 S. Moreover, it has been shown that H 2 S slightly inhibits the pyrolysis of n-octane at 70 MPa and 603-623 K and this result enabled the construction of a detailed kinetic model [START_REF] Nguyen | Pyrolysis mechanism of the n-octane/H 2 S mixture at 70 MPa and 603-623K[END_REF]. In the conversion range studied, no sulfur naphthenoaromatic species were produced from n-octane, although they are formed from oils. An assumption is that they may derive from aromatic compounds by pyrolysis in the presence of H 2 S. Indeed petroleum contains about 20 to 60 weight % of aromatic hydrocarbons [START_REF] Tissot | Petroleum Formation and Occurrence[END_REF].

The purpose of this paper is to study the influence of H 2 S on the pyrolysis of aromatic compounds. Nbutylbenzene has been chosen as the model compound of the aromatic fraction as in several previous studies ([20][21] [START_REF] Freund | Detailed chemical kinetic modeling of butylbenzene pyrolysis[END_REF] [START_REF] Yu | Thermal Decomposition of Jet Fuel Model Compounds under Near-Critical and Supercritical Conditions. 1. n-Butylbenzene and n-Butylcyclohexane[END_REF]). The alkyl side chain is long enough to allow the possible production of polycyclic compound. A previous published paper presented the experimental results and the construction of the detailed kinetic model of the pyrolysis of pure n-butylbenzene [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF]. Here the pyrolysis of the n-butylbenzene/H 2 S (80% : 20% mol) mixture is investigated at 70 MPa and in the range 583-623 K. The detailed results, i.e. product distribution, conversion and kinetic influence of H 2 S, are presented, as well as some results for other aromatic compounds with H 2 S as exploratory experiments: toluene, ethylbenzene and n-propylbenzene. This study may help in our understanding of the fate of sulfur species in petroleum reservoirs.

Experimental and analytical procedure

Samples

Toluene, ethylbenzene, n-propylbenzene and n-butylbenzene (purity ≥ 99%), were obtained from Sigma Aldrich and used as received. H 2 S (purity ≥ 99.5%) was provided by Air Liquide.

Loading procedure and pyrolysis device

Confined pyrolysis of alkylbenzene (toluene, ethylbenzene, n-propylbenzene and n-butylbenzene) / H 2 S mixtures with constant molar ratio of 80/20 was carried out in gold tubes (purity 99.99%, 10 cm length, 5 mm i.d. and 0.5 mm thickness). Each gold tube was prepared in two steps: first, 100 µL of liquid n-butylbenzene were loaded in using a syringe; then, following the procedure developed by Jacquemet et al. [START_REF] Jacquemet | A new experimental procedure for simulation of H 2 S+CO 2 geological storage[END_REF], 160 µmol of H 2 S were liquefied into the gold tube plunged in a liquid nitrogen bath. The gold tubes were maintained frozen under a cold nitrogen flow while sealed by pulse arcwelding and then placed in a pressurized autoclave at 70 MPa. Details on the confined pyrolysis procedure can be found in [START_REF] Landais | Pyrolysis of organic matter in cold-seal autoclaves. Experimental approach and application[END_REF] and [START_REF] Michels | Artificial coalification -comparison of confined pyrolysis and hydrous pyrolysis[END_REF]. Suitability of confined pyrolysis for the study of thermal evolution of kerogen and hydrocarbons in petroleum systems and sedimentary basins was discussed elsewhere ( [28][29]). In the case of n-butylbenzene, nine reaction sets, composed of four tubes each, were pyrolyzed at 583 K, 603 K and 623 K (± 1 K) for durations of 3, 7 and 15 days. These experiments were used for quantification and mass balance calculations. An additional experiment was conducted at 623 K for 15 days and used for the identification of reaction products. Pyrolysis was quickly stopped by using a water heat exchanger to cool the autoclaves to room temperature.

For the mixtures of toluene, ethylbenzene or n-propylbenzene / H 2 S, only one experimental condition was studied: 70 MPa, 623 K and 7 days.

Identification of products

Gas products (C 1 -C 4 ) of the pyrolysis of the n-butylbenzene / H 2 S mixture were identified by comparison of chromatographic retention times with those of a certified mixture (Air Products).

Thermodesorption-GC-FID was used for this purpose. Principles of the technique are described in [START_REF] Gerard | Analysis of confined pyrolysis effluents by thermodesorption multidimensional gas chromatography[END_REF]. A gas sample of 10 µL was directly injected by a Valco pneumatic valve into a Zebron ZB 5-MS column (Phenomenex, length: 60 m, 0.25 mm i.d., 0.10 μm film). The chromatographic column was installed in a GC-Shimadzu 2010 Plus (carrier gas H 2 ) equipped with a cryogenic focus temperature controller (Frontierlab MJT 1035E) and a Flame Ionization Detector (FID). The GC-FID temperature program started at 303 K and was kept stable for 4 min, then a heating rate of 6 K/min was applied up to 593 K, and the final temperature was maintained during 10 min. The cryogenic focus froze the top of the column at 78 K during the first 2 minutes of the chromatographic program enhancing the separation of the light hydrocarbons (from C 1 to C 4 ).

The identification of the liquid products was performed by gas chromatography coupled to mass spectrometry (GCMS). A gold tube plunged in a beaker containing 10 mL dichloromethane was carefully opened from both ends. The solution and the gold tube were transferred into a vial and extracted in an ultrasonic bath during 1 hour. After rinsing of the gold tube, the recovered solution volume was normalized to 25 mL with a graduated flask, then 1 µL of solution was analyzed by GC-MS (Shimadzu GCMS-QP 2010 Plus; carrier gas: He) using a Zebron ZB 5-MS column (Phenomenex, length: 60 m, 0.25 mm i.d., 0.10 μm film, 5%-Phenyl, 95%-dimethylpolysiloxane phase). The temperature program was set as follows: the initial temperature was set at 313 K during 3.5 min, then a heating rate of 6 K/min was applied up to 593 K and final temperature was kept 10 min.

Quantification of products

The pyrolysis products of the n-butylbenzene/H 2 S mixture were quantified by Thermodesorption-GC-FID using the method described in [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF]. The gold tubes were desorbed at 523 K inside a sealed piercing device under vacuum. An aliquot of remaining reactant and reaction products in the gas phase was directly injected by a Valco pneumatic valve into the Zebron ZB 5-MS column. Gas compounds were calibrated from 0.28 µmol to 59.89 µmol using a certified bottle containing normal alkanes from methane to pentane (Air Products: Ar: 14.9600%; CO 2 : 24.9800%; CH 4 : 30.0300%; C 2 H 6 : 13.0400%; C 3 H 8 : 8.9660%; C 4 H 10 : 7.0240%; C 5 H 12 : 1.0022%). Liquid compounds from C 6 to C 14 (29 compounds) were calibrated in the range 0.05 µmol -14.20 µmol using solutions prepared with commercially available molecules (Fluka, Acros Organic, SigmaAldrich, Techlab). An external calibration curve of 6 concentrations was established for each compound. Every week the calibration mixtures were injected to verify the quality of detector response.

The quantification of the liquid sulfur compounds was performed by gas chromatography using parallel detection by FID and FPD (GC-FID-FPD, Agilent Technologies 7890 A). The calibration of the sulfur compounds detected by the FPD was performed with a solution of 21 compounds (thiols, thiophenes, benzothiophenes and dibenzothiophenes). The concentration range used for the calibrated compounds started at 1.19x10 -2 µmol/mL up to 5.45x10 -1 µmol/mL. Prior to injecting, 1-decanethiol (C 10 H 21 SH) was added to the calibration as well as to the sample solutions to be used as internal standards of FPD quantification. 1-Decanethiol was not produced by pyrolysis and did not co-elute with any of the pyrolysis products. The internal calibration curve with 7 concentration levels was determined for each compound. For the quantification of the sulfur compounds, the pyrolyzed gold tubes were extracted as described in subsection 2.3. After the addition of the internal standard, a 1 µL aliquot was injected in splitless mode and analyzed by GC-FID-FPD. The column and the chromatographic program of the GC-FID-FPD are similar to those used for the identification of liquid products by GC-MS in subsection 2.3.

Unreacted n-butylbenzene, and major pyrolysis products, toluene, 1-methylpropylbenzene, 2methylpropylbenzene and 1-propylbutylbenzene, were present in high concentrations for several pyrolysis conditions making impossible their quantification by Thermodesorption-GC-FID. Therefore these compounds were quantified by FID detection using the Agilent 7890 A GC-FID-FPD and using a known dilution of the extracted solutions. An internal standard (n-C 20 H 22 ) was added before injection. n-C 20 was chosen for this study because it is not a reaction product and nor does it co-elute with any product. An internal calibration curve of 7 concentration levels (from 1.19×10 -5 µmole/µL to 2.11×10 -4 µmole/µL) was constructed for each compound. Calibration reliability of the FID and FPD detectors was tested by injection of control solutions after every 10 samples analyzed. The standard deviation is usually less than 10%, except for the very low concentrations for which it is much higher (Supplementary materials 1 and 2).

For the other mixtures (toluene, ethylbenzene, n-propylbenzene / H 2 S), only the liquid sulfur products were analyzed, not the gas, nor the liquid hydrocarbon products.

Experimental results (pyrolysis of the n-butylbenzene / H 2 S mixture)

The detailed experimental results are given as Supplementary Materials 1 and 2.

Conversion

The conversion of n-butylbenzene has been calculated by carbon balance, according to Eq. ( 1):

(1)
Where N i is the number of carbon atoms in the product i, n i the amount (in moles) of i and n°B B the initial amount (in moles) of n-butylbenzene.

Indeed, the quantification of the remaining n-butylbenzene was not precise enough to allow the calculation of the conversion, especially at low values. That is why the conversion of n-butylbenzene has been based on the products, except at high reaction advancement (623 K and 15 days) for which the conversion has been calculated with remaining n-butylbenzene (Eq. ( 2)).

(

) 2
Where n BB is the amount (in moles) of remaining n-butylbenzene. The conversion (Table 1) is in the range 2.5 % (at 583 K, 3 days) -73.2% (at 623 K, 15 days).

The carbon balance C.B has been calculated according to Eq. ( 3):

(3)

The carbon balance (Table 1) is between 86% and 109% and the mean value is 102%. These results are globally satisfying considering that the quantification procedure combines two sampling methods and two analytical devices. At high conversion, the carbon balance is only 86%, which is probably due to the great number of products in this case. The quantification of all of them is difficult.

The conversion of H 2 S has been estimated by Eq. ( 4). The sulfur balance could not be verified because the remaining H 2 S could not be quantified with the analytical tools used. That is why the conversion of H 2 S can only be estimated and its values should be considered with caution.

(

) 4
Where n°H 2S is the initial amount (in moles) of H 2 S and n jSC the amount (in moles) of the sulfur compound j.

It should be noted that all identified sulfur compounds only contain one sulfur atom. The estimated conversion of H 2 S (Table 2) is in the range 1.9% (at 583 K, 3 days) -17.8% (at 623 K, 7 days). The maximum conversion of H 2 S is about 4 times lower than the conversion of n-butylbenzene. The decrease of the conversion between 7 days and 15 days at 623 K is probably not significant, according the high error-bar at 623 K -15 days.

Product distributions

The hydrocarbons produced by the pyrolysis of n-butylbenzene/H 2 S mixture are globally the same than those obtained by the pyrolysis of pure n-butylbenzene [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF]: short alkylbenzenes (toluene, ethylbenzene), branched alkylbenzenes (iso-butylbenzenes, iso-heptylbenzenes), alkenylbenzenes (styrene, butenylbenzenes), gaseous products (from methane to butane) and methylindane. Typical gas chromatograms obtained for gaseous and liquid products can be seen in [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF].

The relative abundance of sulfur compounds S SC has been defined by Eq. ( 5):

(

Where n iHC is the amount (in moles) of the produced hydrocarbon i, and n jSC the amount (in moles) of the produced sulfur compound j.

Table 3 shows the relative abundance of sulfur compounds. It appears clearly that it decreases as the time and temperature decrease: its value is equal to almost 16% at 583 K and 3 days, but only to 4% at 623 K and 15 days. This means that 84% of the products are purely hydrocarbons at low conversion and 96% at high conversion. days). The FPD does not detect the hydrocarbons, but only the sulfur species.

Kinetic effect of H 2 S on n-butylbenzene thermal cracking

The conversion of n-butylbenzene in mixture with H 2 S is compared to the conversion of pure nbutylbenzene [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF] (Fig. 2). It appears that H 2 S increases n-butylbenzene conversion in every studied operating condition: H 2 S accelerates the pyrolysis of n-butylbenzene at 70 MPa, in the range 583-623 K. In order to quantify this acceleration effect, the ratio of the conversion of n-butylbenzene in mixture to the conversion of pure n-butylbenzene has been calculated (Table 4). No monotonic trend can be highlighted for the acceleration effect of H 2 S on n-butylbenzene pyrolysis.

Nevertheless, it seems that the acceleration effect of H 2 S decreases when duration and temperature increase.

The apparent kinetic parameters for the pyrolysis of n-butylbenzene in mixture with H 2 S were calculated. The assumption of first-order kinetics allows computation of the rate constant by plotting ln (1-butylbenzene conversion) as a function of time (Table 5). The calculation of each rate constant requires the use of the three experimental conversions per temperature that were measured. According to the Arrhenius law, the plot of ln k vs 1/RT (Fig. 3) allows the calculation of the apparent frequency factor A and the apparent activation energy E a . E a was found to be 55.9 kcal/mol and A to be 4.2×10 13 s -1 for the n-butylbenzene/H 2 S mixture, whereas these values were 66.6 kcal/mol and 6.3×10 16 s -1 respectively, for pure n-butylbenzene pyrolysis [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF]. The significantly lower value of E a in comparison to pure n-butylbenzene thus characterizes: 1) the global acceleration effect of H 2 S on nbutylbenzene cracking, despite the lower value of A which decreases the rate constant to a lower extent than the increase due to the relatively low value of E a 2) the higher acceleration effect of H 2 S at 583 K than at 623 K.

The acceleration effect of organic sulfur compounds on hydrocarbon cracking is widely described in the literature ( [31] [32]). Our results are the first to demonstrate the acceleration effect induced by H 2 S which is notable, even at low degrees of advancement of the reaction. At higher degrees of advancement, the formation of organic sulfur compounds may also contribute to the acceleration.

Indeed, labile organic sulfur compounds such as thiols have also been recognized as accelerators The comparison of the pyrolysis product distributions between the n-butylbenzene/H 2 S mixture and pure n-butylbenzene [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF] focuses on hydrocarbons. As highlighted above, the hydrocarbons produced by the pyrolysis of n-butylbenzene/H 2 S mixture are globally the same than those obtained by the pyrolysis of pure n-butylbenzene [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF]. The major differences are the yields X i , which are expressed by Eq. ( 6):

Where n i is the amount of the product i and the initial amount of n-butylbenzene (in moles).

The yields of toluene, ethylbenzene, iso-butylbenzenes, butenylbenzenes and gaseous products are higher in the presence of H 2 S than for the pyrolysis of pure n-butylbenzene, in agreement with the global acceleration of the pyrolysis with H 2 S. On the contrary, the yield of iso-heptylbenzenes decreases in the presence of H 2 S. The yield of methylindane increases with H 2 S at 583 K, but decreases at 603 and 623 K. No clear trend can be highlighted for styrene. In order to quantify the effect of H 2 S, the yield ratios of pyrolysis products obtained in the presence of H 2 S to those obtained with pure n-butylbenzene have been calculated for the most important hydrocarbons. Table 6 shows the results, for the case of experiments at 623 K. The results show that toluene, methane and propane are the most increased by H 2 S. H 2 S also increases the yields of ethylbenzene and iso-butylbenzenes in a significant manner. On the contrary, the formation of iso-heptylbenzene is strongly decreased by H 2 S: the yield decreases by a factor of 3 to 9 and this effect increases with time. Iso-heptylbenzenes are mostly formed by addition of phenylbutyl radicals to propene [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF]. The results obtained indicate that there is a competing reaction pathway in the presence of H 2 S.

n-Butylbenzene/H 2 S mixture vs. other alkylbenzene/H 2 S mixtures

The distribution of the sulfur compounds obtained by pyrolysis of the n-butylbenzene/H 2 S mixture is compared to those observed for other alkylbenzene (toluene, ethylbenzene and n-propylbenzene)/H 2 S mixtures (80% : 20% mol). For these mixtures, only one condition was tested which is 623 K, 70 MPa and 7 days. Note that the gaseous products were not analyzed except for the n-butylbenzene/H 2 S mixture.

Therefore no comparison is possible, but in the case of n-butylbenzene, methanethiol, ethanethiol and propanethiol were quantified and represent about 20% of the sulfur compounds at high conversion (623 K and 15 days).

Possible reaction pathways

The aim of this part is to propose possible formation pathways for the sulfur compounds, by considering free-radical reactions.

The key free-radical for the production of organosulfur compounds is probably HS . which may be mostly formed by H-transfers between radicals derived from the pyrolysis of n-butylbenzene and H 2 S (Fig. 5). The H-transfers with H 2 S seem more favorable (higher rate constants) than with hydrocarbons [START_REF] Zeng | Inhibition and Promotion of Pyrolysis by Hydrogen Sulfide (H 2 S) and Sulfanyl Radical (SH)[END_REF] and they probably are predominant among all H-transfers. Except in the case of thiophenol, thiols may be produced by three pathways: additions of HS . to double bonds (Fig. 6) followed by H-transfers; terminations by recombination between HS . and radicals (Fig. 7); ipso-additions of radicals to H 2 S (Fig. 8). Note that all these pathways compete with the additions of phenylbutyl radicals to propene that yield iso-heptylbenzenes. They may explain the decreasing concentration of iso-heptylbenzenes in the experiments conducted with H 2 S in comparison to the pyrolysis of pure n-butylbenzene. Thiophenol might be produced by termination reactions implying recombination between HS . and the phenyl radical as well as ipso-addition of the phenyl radical to H 2 S. Yet, the concentration of the phenyl radical is negligible [START_REF] Leguizamon Guerra | Thermal cracking of nbutylbenzene at high pressure: Experimental study and kinetic modelling[END_REF]. Thiophenol may also be produced by ipso-addition of HS . to alkylbenzene (Fig. 9), in the same way as for H . or CH 3 . [START_REF] Lannuzel | An extended mechanism including high pressure conditions (700 bar) for toluene pyrolysis[END_REF]. to n-butylbenzene.

Phenylthiophenes may derive from phenylbutanethiols. Indeed, they are produced only in the case of the pyrolysis of n-butylbenzene/H 2 S and not for the shorter alkylbenzenes. Moreover phenylbutanethiols are less concentrated than their shorter alkylbenzene homologs, which may indicate a consumption pathway for these compounds. Two pathways can explain the formation of phenylthiophene. For the first pathway, the initial step may be the formation of a radical by H-transfer, then an internal ipso-addition of the single electron to the -SH group yielding a bicyclic molecule, and finally aromatization by successive H-transfers and decompositions by -scission leading to the phenylthiophenes (Fig. 10). For the second pathway, the first step may be the formation of a phenylbutenethiol, followed by the formation of a sulfured radical, an intramolecular addition, and finally aromatization (Fig. 11). Traces of benzothiophenes were detected for the pyrolysis of each alkylbenzene/H 2 S mixture, except for toluene since the length of its alkyl substituent is too short to allow cyclisation. They may be produced by H-transfers from 2-phenylethanethiol, ring-closure reactions and decompositions by scission (Fig. 12).

Figure 12.

Proposed pathways for the formation of benzothiophene.

Kinetic effect of H 2 S on n-butylbenzene thermal crackingcomparison with n-octane

As previously shown, H 2 S has an acceleration effect on the pyrolysis of butylbenzene. However, the experimental study conducted by Nguyen et al. [START_REF] Nguyen | Pyrolysis mechanism of the n-octane/H 2 S mixture at 70 MPa and 603-623K[END_REF] on the n-octane/H 2 S mixture showed an inhibition effect. Thus, the kinetic influence of H 2 S depends on the nature of the hydrocarbon (n-alkane vs alkylaromatic), while the overall kinetics will depend on the competitive contributions of H 2 S vs organo-sulfur compounds. Such dependency of the reaction rate on the initial nature of reactants as well as on composition changes of the system during pyrolysis might explain why the effects of sulfur compounds on the thermal cracking of petroleum lead to variable kinetic factor estimations [START_REF] Waples | The kinetics of in-reservoir oil destruction and gas formation: constraints from experimental and empirical data, and from thermodynamics[END_REF].

Further understanding of the inhibition/acceleration effect induced by H 2 S can be investigated by comparing the results of the n-butylbenzene/H 2 S system to the n-octane/H 2 S system obtained under the same operating conditions [START_REF] Nguyen | Pyrolysis mechanism of the n-octane/H 2 S mixture at 70 MPa and 603-623K[END_REF]. For the n-octane/H 2 S mixture, the inhibition effect of H 2 S increases when the temperature increases. A detailed kinetic model for the pyrolysis of the n-octane-H 2 S mixture was previously constructed and validated at 70 MPa, 603-623 K and for durations ranging from 3 to 15 days (conversion up to 15% [START_REF] Nguyen | Pyrolysis mechanism of the n-octane/H 2 S mixture at 70 MPa and 603-623K[END_REF]). This kinetic model has been extrapolated to lower temperature and simulations have been performed using the software package CHEMKIN II [START_REF] Kee | Chemkin-II: A Fortran chemical kinetics package for the analysis of gas-phase chemical kinetics[END_REF] and more precisely SENKIN at constant pressure and temperature. The ratio of the conversion of n-octane in mixture with H 2 S to the conversion of pure n-octane has been computed at 70 MPa, 10% conversion of pure n-octane and from 523 to 623 K (Fig. 13). The simulation results show that H 2 S would become an accelerator for n-octane pyrolysis at temperatures below 573 K and that the acceleration effect would increase as the temperature decreases.

The experimental ratios of the conversion of n-butylbenzene in mixture with H 2 S to the conversion of pure n-butylbenzene are also shown in Fig. 13. Despite the apparent opposing kinetic effects of H 2 S on n-octane (inhibition) and n-butylbenzene (acceleration) at high temperature, the simulation results indicate that the kinetic effect of H 2 S on n-octane and n-butylbenzene shows similar trends with temperature. Both trends decrease with increasing temperature, but there is a difference in the transition temperature between acceleration and inhibition (intersection with the "no kinetic effect" line in Fig. 13) that is shifted to higher temperature for n-butylbenzene.

In the case of n-octane-H 2 S, the inhibition effect in the temperature range (583-623 K) is interpreted by the detailed kinetic model previously published [START_REF] Nguyen | Pyrolysis mechanism of the n-octane/H 2 S mixture at 70 MPa and 603-623K[END_REF]. It invokes three major reaction pathways with mutually antagonistic effects: 1) new terminations with HS . which decrease the pyrolysis rate; 2) new bimolecular initiations with H 2 S which increase the pyrolysis rate 3) a new parallel propagation loop which increases the pyrolysis rate. The relative importance of each effect depends on temperature.

The case of n-butylbenzene/H 2 S mixture will also require a complete study of reaction mechanism. A further step would be the study of the ternary system (n-butylbenzene/n-octane/H 2 S). Indeed H 2 S seems to accelerate the pyrolysis of n-butylbenzene as well as that of n-octane at geological reservoir temperatures. But it has been previously shown that alkylbenzenes and particularly toluene inhibit the pyrolysis of alkanes under all temperature conditions investigated ( [42][43][44]). A study of these competing effects would be required. Nevertheless, it could be assumed that, if the H-transfers with H 2 S are really predominant in the system, the inhibition effect of alkylbenzenes on alkane pyrolysis would be suppressed in the presence of H 2 S.

Conclusion

The thermal cracking of n-butylbenzene was experimentally studied in the presence of H 2 S (80% :

20% mol) at high pressure (70 MPa), moderate temperature (583, 603 and 623 K) and for durations of 3, 7 and 15 days. The pyrolysis was performed in sealed gold tubes in an isobaric regime. Under these conditions, the conversion of n-butylbenzene varies between 2.5% and 73.2%. H 2 S accelerates the pyrolysis of n-butylbenzene by a factor up to 3.6 depending on the operating conditions in comparison with the pyrolysis of pure n-butylbenzene. This acceleration factor seems to decrease with increasing time and temperature. The apparent activation energy of the pyrolysis of n-butylbenzene decreases from 66.6 kcal/mol (pure n-butylbenzene) to 55.9 kcal/mol (n-butylbenzene in mixture with H 2 S). A previous study has shown that H 2 S has an inhibition effect on n-octane pyrolysis under the same operating conditions. Nevertheless, simulations of the pyrolysis kinetic model of the n-octane-H 2 S mixture reveals that H 2 S becomes an accelerator below 573 K and this acceleration effect increases as the temperature decreases. Thus, despite apparently contradictory behaviors, these results suggest that the kinetic effects of H 2 S on n-octane and n-butylbenzene show a similar temperature dependence but the transition temperature between acceleration and inhibition is shifted to a higher temperature for nbutylbenzene.

The main hydrocarbons produced during the pyrolysis of the n-butylbenzene/H 2 S mixture are alkylbenzenes (mostly toluene and ethylbenzene), branched alkylbenzenes (mostly isomers of isobutylbenzene and iso-heptylbenzene to a lesser extent) and short alkanes (from CH 4 to C 3 ). Several sulfur compounds are also produced and their total relative abundance among the reaction products is in the range 4-16% depending on the operating conditions. These sulfur compounds are mostly short thiols (methanethiol, ethanethiol and propanethiols), phenylbutanethiols, and phenylthiophenes. Some additional experiments were also conducted with alkylbenzenes with a shorter alkyl chain than nbutylbenzene, in order to help elucidate the formation pathways of the sulfur compounds. Thus, formation pathways are proposed for the main sulfur compounds based on free-radical reactions.

The comparison of the results obtained by the pyrolysis of the n-octane/H 2 S and the nbutylbenzene/H 2 S systems highlights the kinetic effects of H 2 S on hydrocarbon cracking. The inhibition/acceleration effects of H 2 S depend on 1) the composition of the co-reactant (alkane vs alkylaromatic), 2) the temperature range, 3) the nature and abundance of the sulfur compounds generated during the reaction, 4) the presence of hydrocarbon species having their own kinetic influence on the mixture (e.g. toluene, long-chain-alkyl-aromatics, hydro-naphthalenics). The complex interdependence of these variables implies that the kinetic behavior of high sulfur oils, the calculation of the concentration of species of interest (like H 2 S) and the understanding of reaction pathways must rely on reaction modelling.

Thus, the next step of this study will be the construction of a detailed kinetic model for the pyrolysis of n-butylbenzene/H 2 S mixtures in order to identify the main reaction pathways and understand the kinetic effect of H 2 S on n-butylbenzene pyrolysis.

List of table captions

List of figure captions

Figure 1 .

 1 Figure 1. GC-FPD obtained after pyrolysis of the n-butylbenzene/H 2 S mixture (70 MPa, 623 K, 15

Figure 2 .

 2 Figure 2. Conversion (%) of n-butylbenzene obtained by pyrolysis at 70 MPa, 523-623 K for 3 to

([ 33 ]

 33 [34][35][36][37][38]).

Figure 3 . 5 . Comparison of product distributions 5 . 1 .

 3551 Figure 3. Plot of ln k as a function of 1/RT for the pyrolysis of n-butylbenzene in mixture with

Figure 4 .

 4 Figure 4. Yields X i of thiols, benzothiophenes (for ethylbenzene and propylbenzene) or phenylthiophenes (for n-butylbenzene), and liquid sulfur compounds in relation to the initial amount

Figure 5 .

 5 Figure 5. Example of H-transfer between the 1-phenylbutyl radical and H 2 S.

Figure 6 .

 6 Figure 6. Examples of addition of HS .to butenylbenzene and propene.

Figure 7 .

 7 Figure 7. Examples of termination by recombination between HS . and 1-phenylbutyl radical, and

Figure 8 .

 8 Figure 8. Examples of ipso-addition of 1-phenylbutyl and propyl radicals to H 2 S.

Figure 9 .

 9 Figure 9. Example of ipso-addition of HS .to n-butylbenzene.

Figure 10 .

 10 Figure 10. First proposed pathway for the formation of 2-phenylthiophene from butanethiol.

Figure 11 .

 11 Figure 11. Second proposed pathway for the formation of 2-phenylthiophene from butenethiol.

Figure 13 .

 13 Figure 13. Comparison between the ratio of the conversion of n-octane in mixture with H 2 S to the conversion of pure n-octane, and the ratio of the conversion of n-butylbenzene in mixture with H 2 S to the conversion of pure n-butylbenzene. For n-octane: simulation results at 70 MPa and 10%

Figure 1 .

 1 Figure 1. GC-FPD obtained after pyrolysis of the n-butylbenzene/H 2 S mixture (70 MPa, 623 K, 15 days). The FPD does not detect the hydrocarbons, but only the sulfur species.

Figure 2 .

 2 Figure 2. Conversion (%) of n-butylbenzene obtained by pyrolysis at 70 MPa, 523-623 K for 3 to 15

Figure 3 .

 3 Figure 3. Plot of ln k as a function of 1/RT for the pyrolysis of n-butylbenzene in mixture with H 2 S.

Figure 4 .

 4 Figure 4. Yields X i of thiols, benzothiophenes (for ethylbenzene and propylbenzene) or phenylthiophenes (for n-butylbenzene), and liquid sulfur compounds in relation to the initial amount

Figure 5 .

 5 Figure 5. Example of H-transfer between the 1-phenylbutyl radical and H 2 S.

Figure 6 .

 6 Figure 6. Examples of addition of HS. to butenylbenzene and propene.

Figure 7 .

 7 Figure 7. Examples of termination by recombination between HS. and 1-phenylbutyl radical, and

Figure 8 .

 8 Figure 8. Examples of ipso-addition of 1-phenylbutyl and propyl radicals to H 2 S.

Figure 9 .

 9 Figure 9. Example of ipso-addition of HS .to n-butylbenzene.

Figure 10 .

 10 Figure 10. First proposed pathway for the formation of 2-phenylthiophene from butanethiol.

Figure 11 .

 11 Figure 11. Second proposed pathway for the formation of 2-phenylthiophene from butenethiol.

Figure 12 .

 12 Figure 12. Proposed pathways for the formation of benzothiophene.

Figure 13 .

 13 Figure 13. Comparison between the ratio of the conversion of n-octane in mixture with H 2 S to the conversion of pure n-octane, and the ratio of the conversion of n-butylbenzene in mixture with H 2 S to the conversion of pure n-butylbenzene. For n-octane: simulation results at 70 MPa and 10%

Table 1 .

 1 Conversion of n-butylbenzene and carbon balance after pyrolysis in the presence of 20 mol% H 2 S at 70 MPa.

	Temperature (K)	Time (days)	Conversion (%)	Carbon balance (%)
		3	2.5 ± 0.2	104 ± 5
	583	7	3.2 ± 0.1	101 ± 5
		15	5.2 ± 0.2	101 ± 5
		3	6.0 ± 0.1	107 ± 6
	603	7	8.3 ± 0.2	101 ± 7
		15	24.6 ± 0.4	109 ± 5
		3	26.9 ± 0.3	99 ± 5
	623	7	47.7 ± 0.1	107 ± 8
		15	73.2 ± 0.3	86 ± 5

Table 2 .

 2 Estimated conversion of H 2 S after pyrolysis of H 2 S-butylbenzene mixture at 70 MPa.

	Temperature (K)	Time (days)	Conversion (%)
		3	1.9 ± 0.1
	583	7	2.2 ± 0.3
		15	2.6 ± 0.1
		3	3.3 ± 0.4
	603	7	4.7 ± 0.4
		15	8.1 ± 4.0
		3	12.3 ± 1.5
	623	7	17.8 ± 1.5
		15	17.0 ± 5.1

Table 3 .

 3 Total relative abundance of sulfur products as a function of time and temperature obtained after pyrolysis of H 2 S-butylbenzene mixture at 70 MPa.

				Temperature (K)
	Relative abundance of sulfur	583	603	623
	products (%)
		3	15.8 ± 1.0	11.0 ± 1.4	7.8 ± 1.6
	Time (days)	7	14.2 ± 2.7	10.6 ± 0.5	6.2 ± 0.3
		15	10.5 ± 0.4	5.9 ± 1.2	4.2 ± 1.0

The distribution of the liquid sulfur products can be seen in Fig.

1

. Several families of sulfur compounds have been identified: short thiols (methanethiol, ethanethiol and propanethiols), branched thiophenes, thiophenol, phenylbutanethiols, phenylthiophenes and some branched isomers, and polycyclic sulfur compounds. At high conversion, the most abundant sulfur compounds are in decreasing order of concentration: 2-phenylthiophene, propanethiols, methanethiol, 3-phenylthiophene and benzylthiophenes.

Table 4 .

 4 Ratio of the conversion of n-butylbenzene in mixture with H 2 S to the conversion of pure n-butylbenzene (70 MPa, 583-623 K, 3-15 days).

	Conversion of butylbenzene in		Temperature (K)
	mixture with H 2 S / Conversion of	583	603	623
	pure butylbenzene
		3	3.6	2.7	2.0
	Duration	7	2.2	1.1	1.5
	(days)	15	2.6	2.3	1.3

Table 5 .

 5 Apparent rate constant (day -1 ) for the pyrolysis of n-butylbenzene in mixture with H 2 S.

	Temperature (K)	Apparent rate constant k	R²
		(day -1 )
	583	0.004	0.72
	603	0.018	0.95
	623	0.089	0.99

Table 6 .

 6

	n-butylbenzene/H 2 S mixture to pure n-butylbenzene yield ratios calculated for major reaction
	products at 623 K and 70 MPa.
	Compound

Table 7

 7 compares the distribution of the sulfur compounds as a function of the length of the alkylbenzene side chain.

Table 7 .

 7 Comparison of the distribution of the sulfur compounds as a function of the length of the alkylbenzene side chain after pyrolysis of the n-alkylbenzene/H 2 S mixture at 623 K and 70 MPa.

	Alkylbenzene	Aromatic thiols	Benzothiophenes	Aromatic thiophenes
	Toluene
	Ethylbenzene		(traces)
	Propylbenzene		(traces)

Table 1 .

 1 Conversion of n-butylbenzene and carbon balance after pyrolysis in the presence of 20 mol% H 2 S at 70 MPa.

Table 2 .

 2 Estimated conversion of H 2 S after pyrolysis of H 2 S-butylbenzene mixture at 70 MPa.

Table 3 .

 3 Total relative abundance of sulfur products as a function of time and temperature obtained after pyrolysis of H 2 S-butylbenzene mixture at 70 MPa.

Table 4 .

 4 Ratio of the conversion of n-butylbenzene in mixture with H 2 S to the conversion of pure nbutylbenzene (70 MPa, 583-623 K, 3-15 days).

Table 5 .

 5 Apparent rate constant (day -1 ) for the pyrolysis of n-butylbenzene in mixture with H 2 S.

Table 6 .

 6 n-butylbenzene/H 2 S mixture to pure n-butylbenzene yield ratios calculated for major reaction products at 623 K and 70 MPa.

Table 7 .

 7 Comparison of the distribution of the sulfur compounds as a function of the length of the alkylbenzene side chain after pyrolysis of the n-alkylbenzene/H 2 S mixture between 583 and 623 K and 70 MPa.

Acknowledgements. This work was supported by ICEEL (Institut Carnot pour l'Energie et l'Environnement en Lorraine). We thank M. Aurelien Randi and M. Gilles Bessaque for their technical support.


Michael Schnell

Sophie Couffignal

Jean Lieber

Nicolas Jay
email: n.jay@chru-nancy.fr

Improving Medical Coding with Case-Based Reasoning -Evaluation for Cancer Registries

Keywords: interpretation of best practices, interpretive case-based reasoning, coding standards, cancer registries, user assistance, decision support

Providing a comparable and consistent description of any entity is a difficult task. Vocabulary, semantics and objectives need to be very clearly defined and followed. The same can be said about cancer registries. They are an essential element in the fight against cancer. Among the main tasks of these registries is the data collection and coding process of cancer cases. To ensure comparable and consistent data, complex international standards and numerous best coding practices have been defined. Unfortunately this complexity can easily overwhelm operators, which are the people in charge of data collection and coding. While coding experts can help operators in their job, this represents a great burden on their precious time. To assist operators in their task and reduce the burden on coding experts, a coding assistant relying on arguments was designed and implemented. This system provides answers and a partial explanation, using arguments in favor and against answers. In this paper, a first evaluation of this system is presented, testing the system on real topography questions asked by operators.

Introduction and Context

The world is a complex entity. People have ever since tried to quantify it, describing it using carefully selected features and metrics. This gargantuan task presents many challenges, which we also find in medical coding. The latter is needed when it comes to understanding and evaluating the public health of the Supported by the Fondation Cancer (http://www.cancer.lu). The authors wish to thank the anonymous reviewers for their helpful comments.

overall population, but also for health care of individual patients. In order to have comparable and high quality data, international standards have been developed (e.g International Classification of Diseases, 10 th edition or Systematized Nomenclature of Medicine (SNOMED)). These standards define the codes used to describe medical data and how to select the correct coding given a patient's medical data. Despite complex and extensive coding standards, there will always be cases that simply do not fit in the described situations and coding decisions. In those situations, coding experts need to make decisions, based on their knowledge and understanding. This work is done in the context of the Luxembourg National Cancer Registry (NCR). The goal of the NCR is to assess the incidence and the treatment of cancer in Luxembourg. To achieve this objective, data on all cancer cases diagnosed and/or treated in Luxembourg is collected. Among the retrieved information, we find the cancer type, which is mainly defined by a topography and a morphology. The topography of a tumor is the location where the tumor originated, i.e. where the first tumor cells developed. The morphology of a tumor describes the tumor cell type and behavior (e.g. aggressiveness).

As an illustrating example of the topography coding of a tumor, let us consider the following case. An operator is confronted with a tumor that spans between the middle lung lobe and the pulmonary pleura. The pulmonary pleurae are membranes that envelop the lungs. In the patient record, the operator finds one imaging that describes the tumor as originating from the pulmonary pleura and then invading the lung tissue. Later that tumor was surgically removed and the surgery report confirms this finding, i.e. a tumor originating in the pulmonary pleura. The removed tissue was sent to a laboratory for histological analysis. In their report, the pathologist contradicts the presumed origin, stating that given the tumor cell type, this tumor actually originated in the lung tissue and later spread to the pulmonary pleura. For the treatment of this patient, the exact origin of the tumor is not relevant and any later mention of the tumor just references it as a lung cancer, where lung designates the general type of cancer, but not the exact origin. For both origins, we talk about "lung" cancer. The NCR uses the ICD-O 3 rd edition [START_REF]World Health Organisation: International classification of diseases for oncology (ICD-O) -3rd edition[END_REF] to describe tumor topography. For our example, two codes are considered, C34.2 for middle lung lobe and C38.4 for pulmonary pleura. For an operator this is a difficult choice, as it relies on both medical knowledge and coding knowledge to determine which opinion should be preferred. In this situation, coding experts decided to follow the pathologist's point of view, given his very strong argumentation.

In this situation, the information provided was contradictory, but clear. In other situations, the provided information might be more vague or simply missing. In those situations, operators cannot easily decide what to code and have to rely heavily on coding experts. For the NCR, operators can ask questions when faced with difficult cases, but this process takes up a lot of time for the coding experts of the NCR. This project aims at designing a method to reduce the burden on coding experts and to facilitate coding.

In this paper, we summarize and explain the designed question solving method. We then present the evaluation of the coding assistance method, before concluding and highlighting possible future work.

Coding assistant

To tackle the issue of coding, we developed a coding assistant using case-based reasoning [START_REF] Schnell | Case-Based Interpretation of Best Medical Coding Practices -Application to Data Collection for Cancer Registries[END_REF]. This choice was done after carefully analyzing the reasoning process of the coding experts when confronted with coding questions from operators. The designed solving method was implemented in a web portal, intended to centralize communications between operators (asking questions) and coding experts (answering questions). Figure 1 provides an overview of the interactions with our system. Figure 2 shows an example of a case viewed in the implemented system. In the following paragraphs, we will introduce some of the techniques and methods used for our system, before summarizing the argument-based retrieval design for our project.

The Semantic Web [START_REF] Berners-Lee | The semantic web[END_REF] is an extension of the World Wide Web, aiming at facilitating the access and reuse of all available information. The World Wide Web has grown immensely since its creation, yet most of the information is only accessible in unstructured textual form. To make this information machine-usable, a new knowledge representation language was defined, namely Resource Description Framework (RDF) [START_REF] Klyne | RDF 1.1[END_REF]. Data is represented using triples (subject predicate object) that can be seen as a sentence (predicate as the verb). RDF Schema (RDFS) [START_REF] Brickley | RDF Schema 1.1[END_REF] is an extension of RDF for data-modeling. An RDFS base is a set of triples and can be assimilated to a graph, where nodes are subjects or objects and edges are labeled with predicates. The RDFS base shown in figure 3 partially describes the illustrating example from the introduction and expresses that John has an imaging with one finding of a tumoral lesion in the pulmonary pleura.

SPARQL (SPARQL Protocol and RDF Query Language) [START_REF] Group | SPARQL 1.1[END_REF] is a query language used to retrieve and manipulate RDF (or RDFS) data stores. There are several types of queries, some to manage the underlying data (insert, update, delete) and others to retrieve it (select, construct, ask). ASK queries are used to check if a given pattern can be found in the underlying data store. ASK {?person hasExam ?exam} is a valid query, where ?person and ?exam are variables (name starting with a ?), that can match any subject, property or object. Given the RDFS base shown in figure 3, the previous query will evaluate to true, as there is a set of triples (e.g. {(john hasExam imagingExam1)}) that matches the described pattern.

Case based-reasoning is a problem solving method where, for a given domain, previously solved problems are used to solve new problems. A case is defined as a problem-solving episode, typically represented by a pair (pb, sol(pb)), where pb is a problem from the given application domain and sol(pb) is a solution of pb.

The new problem to solve is called target problem, denoted by tgt. Using the description of tgt and domain knowledge, a suitable case from the case base, i.e. the set of all previously solved cases, is identified. This case is called source case, denoted by (srce, sol(srce)). Then sol(srce) together with domain knowledge are used to solve the target problem. This new case (tgt, sol(tgt)) is then revised, e.g. to correct the solution or update the problem description. This revised case (tgt', sol(tgt')) is then added to the case base, enabling the system to potentially solve new problems.

Our method, summarized in figure 4, uses case-based reasoning and a 4-R cycle [START_REF] Aamodt | Case-based reasoning: Foundational issues, methodological variations, and system approaches[END_REF] and two knowledge containers [START_REF] Richter | Case-based reasoning: a textbook[END_REF]. The domain knowledge container consists mainly of medical knowledge (e.g. hierarchical definition of body parts, exam types. etc.). For this project, the application domain is medical coding for a cancer registry. A problem is defined as a question, a patient record and a reference for the applied coding standards. The question consists of a subject, i.e. the variable or information to code (e.g. incidence date, topography), and a general cancer type, e.g. breast cancer, prostate cancer, lung cancer, etc. The patient record consists mainly of a summary description of the medical exams (e.g. date of exam, findings, etc.) and main history of the patient (e.g. cancer antecedents). Figure 5 shows a partial RDFS graph for the illustrating example. The coding standard references are used to track which version was followed for this case (e.g TNM version 7 or TNM version 8). A solution of a problem consists of an answer for the given question and arguments explaining the given answer. An argument is a piece of domain knowledge which is used by a coding expert to support or attack a specific answer. We distinguish between three types of arguments, strong pro, weak pro and weak con. A strong pro is an argument in favor that leaves no doubt for the given answer. A weak pro is also an argument in favor, however by itself it is not sufficient evidence to conclude. Indeed there might be situations where despite this argument, a different answer is chosen. Similarly, a weak con is an argument against, but it is not sufficient to exclude a given answer. Let's reconsider the example described in the introduction. For this problem, the subject is the topography, the cancer type is lung cancer, and the patient record description contains the imaging findings, the surgery report and the histological surgery report. The solution of this problem contains the answer to the topography question, i.e. C34.2 (middle lung lobe), and arguments for this answer. For this problem, there are two weak cons and one strong pro. The latter states The morphology of the tumor is incompatible with a primary origin in the pulmonary pleura and is possible with a lung primary origin. The weak cons state The surgeon concludes that the tumor originated in the pulmonary pleura, and The imaging concludes that the tumor originated in the pulmonary pleura.

To compare cases, we propose a method using arguments. In the retrieve step, we look for the most suited source case among all other cases in the case base which have the same subject as the target problem. These cases are ranked using three criteria. The first two criteria take the applicable arguments into account and the last, default criterion compares the patient records. An argument is considered to be applicable for a given problem if it is considered true for the described patient. Formally, an argument arg is a function that takes a case and returns a boolean. If the argument is applicable, then arg(case) = TRUE. Arguments are formalized using SPARQL ASK queries.

The first comparison criterion, denoted by C strong , takes only strong pros into account. Given two source cases, the source case with the most applicable strong pros for the target problem is preferred. The second criterion, denoted by C weak , uses only weak arguments (both pro and con). Given two source cases, the case with the most applicable weak pros and the least weak cons for the target problem is preferred. The last criterion, denoted by C dist , relies only on the patient records. Given two source cases, the case with the patient record that is closest to the patient record of the target problem is preferred. The distance between the patient records is computed using a graph edit distance [START_REF] Bunke | Similarity measures for structured representations[END_REF].

In order to find the most suitable source case, all the cases forming the case base are compared to each with regards to the target problem using the three criteria mentioned above, in a lexicographical way, that is first C strong , then C weak and finally C dist . Formally, to solve a new problem tgt, the source case will be the case srce such that for all case ∈ CaseBase, srce tgt case, where tgt is a preorder such that, given two source cases srce i and srce j , srce i tgt srce j if ∆ s i,j > 0 or (∆ s i,j = 0 and (∆ w i,j > 0 or (∆ w i,j = 0 and ∆ d i,j ≥ 0))) where ∆ s i,j is defined as ∆ s i,j = N sp (srce i , tgt) -N sp (srce j , tgt) and ∆ w i,j is defined as

∆ w i,j = λ p • (N wp (srce i , tgt) -N wp (srce j , tgt)) -λ c • (N wc (srce i , tgt) -N wc (srce j , tgt))
and λ p and λ c are two non-negative coefficients currently fixed to λ p = 3 and λ c = 2 and ∆ d i,j is defined as ∆ d i,j = dist(srce j , tgt)dist(srce i , tgt) and N args (srce s , tgt) denotes the number of arguments of type args of the source case srce s which are applicable for the problem tgt and is defined as

N a (srce s , t) = |{a ∈ args(srce s ) | a(tgt) = TRUE}|
and args ∈ {sp, wp, wc} is function which returns all arguments of a case of a given type (sp for strong pros, wp for weak pros and wc for weak cons) and dist is a function where dist(x, y) returns the graph edit distance between x and y.

In the reuse step, we compute the solution for the target problem. The answer is copied from the solution of the found source case. For arguments, only those from the source case which are applicable for the target problem are copied.

In the revise step, a coding expert can review the target problem tgt and the proposed solution sol(tgt). If necessary, they will update the problem description, e.g. to remove unnecessary information, and/or correct the provided answer and/or arguments. In the retain step, coding experts decide if the new case (tgt', sol(tgt')) is interesting for future use and thus should be inserted into the case base. Both revise and retain steps are currently manual and required for each new problem for the initial system use, but could be partially automated in the future.

Evaluation

The described method was developed to assist operators in the coding process. This first evaluation was designed to assess the strength of this approach on real cases. In a first step, it will only focus on comparing provided solutions with expected ones, to give us insights into the effectiveness of our approach and the quality of our evaluation set.

Dataset

The dataset consists of questions asked in the context of the NCR. We only considered questions about topography, as this subject is one of the recurring subjects and the amount of possible answers is reasonable, with only about three hundred possible values against over a thousand for morphology values. A topography code defines a location in the human body. It is composed of three digits, the first two define a global category and the third digit specifies a subcategory. For example, the code C34.2 represents the middle long lube, from the category of bronchus and lung locations (C34). The subcategories 8 and 9 have a special meaning. Subcategory 8 means that multiple subcategories are concerned and that none can be specifically chosen. Subcategory 9 indicates that no information is available to use a more precise subcategory. Thus C34.8 represents an overlapping region of bronchus and lung and C34.9 represents the overall region, without more details.

The dataset consists of 37 cases and their solution. The cases were collected with the invaluable help of the coding experts of the NCR, which provided the necessary explanations. Out of the 333 existing topography codes, 27 were present in our dataset and 6 were used in at least two solutions. Out of the 70 provided arguments, 61 have been formalized into matching SPARQL ASK requests. Table 1 highlights how arguments were used in our dataset.

Strong Weak Weak pro pro con All

Total number 8 55 11 76 Average per case 0.2 1.5 0.3 2.0 Range per case 0-1 0-4 0-3 0-5

Table 1: Argument use in the evaluation set by argument type.

Experiments and Indicators

In our evaluation, both answer quality and explanation (i.e. argument) quality were evaluated using two experiments. Firstly, we attempted to solve each case using the whole dataset (without removing the case to solve from the case base). This test was meant to evaluate if an identical new problem could be solved correctly. For this experiment, we had a dataset consisting of 37 cases.

Secondly, we used a leave-one-out cross-validation, i.e. we tried to solve each case from our dataset using all other cases. For this experiment, we only kept cases for which there was another case with the same answer (topography code), resulting in an evaluation set of 16 cases. This exclusion is linked to the copy reuse method, where a new target problem is given the same answer as the selected source case. Thus if there is no source case with the expected answer, the target problem cannot be correctly answered.

To determine answer quality, we counted the number of correct solutions, for each experiment. For cases which failed to be resolved, we assessed if a source case leading to a correct solution was present in the top five of closest cases. To assess argument quality, we compared the suggested arguments to the expected ones. For additional arguments, coding experts were consulted to evaluate if those were relevant in these situations.

Results and Interpretation

For our first experiment, 35 out of 37 cases were correctly identified and solved. For the 2 remaining ones, the case was present in the top five of closest cases, but failed to reach the top due to missing formal arguments. There were other arguments which could be applied and thus these source cases were preferred.

In our second experiment, 10 out of 16 cases were correctly answered. There was 1 additional case for which a source case with the expected answer was in the top five closest answers. For the 5 remaining cases, the main cause for failure was the limited amount of arguments, with on average only 2 arguments per case. Some of the arguments might also have been too specific to solve these cases.

We also evaluated the provided arguments for each solved case. Only 3 out of 16 cases had exactly the same arguments in their new solution. For the other cases, there were always fewer arguments in the new solution compared to the one provided by coding experts. This difference is partially due to missing formalization of more complex arguments and partially to the sparse reuse of arguments in the cases of the evaluation set. Indeed, most arguments were only used in one case.

There are several possibilities to improve the performance of our approach. Adding more cases and arguments is the most straightforward at this stage.

To increase the range of possible answers, a more complex reuse method and more sophisticated arguments could be used. Take for example two cases, srce 1 with answer C34.2 (middle lung lobe) and a weak pro stating An imaging concludes that there is a tumoral lesion in the middle lung lobe., and srce 2 with answer C18.1 (appendix) and a weak pro stating A CT scan concludes that there is a tumoral lesion in the appendix.. Both arguments could be generalized into a single argument stating An ?imaging concludes that there is a tumoral lesion in the ?location., where ?imaging would match any imaging exam types (CT scans, PET scan, etc.) and ?location would match a location which is known to be coded with the topography code used in the case solution. While solving a new problem, when applicable, this argument could be used to provide new topography codes which have not yet previously been used in a source case. The mapping between the location and the topography codes is an example of domain knowledge needed to improve the system. For example, given a new problem with an exam indicating a tumoral lesion in the liver and knowing that the liver is coded with the topography code C22.0, we could answer this case even if no source case exists in our case base with this answer.

Most other applications in medical coding focus on automatic coding, with little effort into explaining the generated codes [START_REF] Kavuluru | Automatic Extraction of ICD-O-3 Primary Sites from Cancer Pathology Reports[END_REF]. There are other works in the area of argumentation, though they use cases as precedents [START_REF] Aleven | Teaching case-based argumentation through a model and examples empirical evaluation of an intelligent learning environment[END_REF] or focus on the interaction between arguments (arguments defeating each other).

Conclusion

This paper presented a first evaluation for the developed medical coding assistant. More cases and more subjects should allow for a more comprehensive evaluation. This evaluation focused mainly on the answering method, but in a second phase user acceptability for the coding assistant should also be assessed. The implemented tool has been launched in a pilot phase in the context of the NCR. A user survey to understand if users understand the solutions and explanations provided could provide insights into acceptability and trust. It would also be of interest to test this method in a different domain, to assess the generality of this approach.

Fig. 1 :

 1 Fig. 1: Application overview and interactions.

Fig. 2 :

 2 Fig. 2: Summary of the described problem and the proposed solution. The most appropriate source cases are shown similarly to the target problem (partially visible on this screenshot).

Fig. 3 :

 3 Fig. 3: RDFS base example (left) and matching graph (right) describing the imaging found in the illustrating example in the introduction.

Fig. 4 :

 4 Fig. 4: Adapted 4-R cycle and knowledge containers of our approach.

Fig. 5 :

 5 Fig. 5: Partial RDFS graph for the illustrating example, describing the imaging findings. snmifre:T-29000 describes the pulmonary pleura in SNOMED.


Rasha Alokaily
email: rashaokaily@gmail.com

The Role of Audiovisual Translation in Mediating Foreign Language Learning Activity Theory Perspective

Keywords: Audiovisual translation, dubbing, activity theory, language learning

This is a case study of a specific learning environment in the Intensive English Language Program, characterised by technical, spatial, temporal, and motivational restrictions that impede students' progress. Activity Theory was used to describe the situation, and to design an intervention in the form of a new activity system. A dubbing project was designed and implemented in the Listening and Speaking Course. It utilised students' mobile devices in an anywhere, anytime type of learning, and their native language and cultural background as a starting point to engage them in a collaborative effort that led to the production of eight dubbed videos. The resulting videos were entered in an internally-organised video competition which added a further motivational element to the project. To evaluate the project's effect on students' perceptions and motivation, data were collected using 5 focus group interviews. Results show high levels of motivation, increased learning, increased confidence and sense of achievement and pride in the resulting work.

Introduction and context

The dubbing project is a mobile learning project that was carefully designed to fit a specific learning context characterised by a number of restrictions. This paper reports a case study that took place over one academic semester where the learning context was first analysed using Activity Systems Analysis and tensions were identified as temporal, motivational, spatial, and technical. An intervention in the form of a new activity system was designed and implemented by the researcher.

This study was conducted in the Intensive English Language Program (IEP) in a semi-private university in the United Arab Emirates where students are required to demonstrate their English language proficiency by sitting a standardised English language proficiency test (IELTS). Students who do not obtain the required score enrol in the IEP to improve their language proficiency. The programme is in 4 levels, starting from level 1 for false beginners, i.e. students who studied English language before but have little command of the language, up to level 4 for intermediate students. Each level is taught over a period of one academic semester. Students are placed in each level, based on the results of a placement test. Those who miss the placement test prior to programme entry are placed in level 1 regardless of their actual level. All students are allowed to drop out of the IEP as soon as they achieve the required score; therefore, students make multiple attempts to take the standardised test during the semester.

The dubbing project was implemented in two sections at level 1, taught by the researcher. One section had 18 female students and the other had 16 female students. Eight short videos were dubbed to English and were entered in an internally-organised competition to choose the winning video. The winners were chosen by a panel of judges who were four IEP instructors.

This study asked the following questions: 1. How did the video dubbing project remediate English language learning for false beginners and mixed ability classes? 2. What was the impact of this remediation on students' perceptions and motivation?

These questions are significant in that they test dubbing projects in a context different to contexts documented in previous studies (see section 2.2).

Literature review

This section provides a short review of Activity Theory (AT), which is used to problematise the context, followed by a review of relevant literature on practices and concepts that form the theoretical framework for this study. Dubbing as a language learning activity is reviewed, followed by mobile learning. Both of these constitute the basis for the proposed activity system that was designed to overcome the abovementioned constraints.

Activity Theory

AT provides a suitable lens for conceptualising learning environments [1 -3]. It offers the language for description and addresses the situation using a manageable unit of analysis: the activity [START_REF] Yamagata-Lynch | Activity Systems Analysis Methods[END_REF][START_REF] Nardi | Some reflections on the application of activity theory[END_REF]. It is a cultural historical theory where context is integral to the activity itself and is seen to influence the mind and action of people [START_REF] Edwards | Cultural Historical Activity Theory[END_REF]. An activity is an action directed towards an object and is motivated by the need to change the object into an outcome [START_REF] Issroff | Using technology in higher education: An activity theory perspective[END_REF], which means reaching this object is purposeful and leads to achieving an outcome.

AT studies the activity in its natural context, taking into consideration all variables within the environment of the activity. These variables are the subject or actor, the object or objective which the subject needs and is motivated to achieve, and the tools and artefacts that mediate the activity. All these are governed by rules, and exist within a community where there is a division of labour among community members to ensure the achievement of the objective. These elements are depicted in a triangular form (in Figure 1).

Figure 1.

The structure of a human activity system [START_REF] Engeström | Learning by Expanding: An Activity-Theoretical Approach to Developmental Research[END_REF] Including the community in the system of interaction came as a later development by Engeström [START_REF] Engeström | Learning by Expanding: An Activity-Theoretical Approach to Developmental Research[END_REF], who extended Vygotsky's and Leontiev's understanding of the social mediation of activity to include social mediators within a community. Engeström explains that the tool mediates the relationship between the subject and the object, the rules mediate the relationship between the subject and the community and the division of labour mediates the relationship between the object and the community.

The variables are seen to interact either in an enabling manner, or in a manner that causes tensions and contradictions, also referred to as obstacles [START_REF] Yamagata-Lynch | Activity Systems Analysis Methods[END_REF]. There are four levels of tensions within AT: primary, secondary, tertiary, and quaternary [START_REF] Engeström | Learning by Expanding: An Activity-Theoretical Approach to Developmental Research[END_REF] (see section 3). By identifying these relationships and the tensions, improved activity systems can be designed to enhance the activity by overcoming them.

According to Engeström, Bateson's Learning 3 is relevant here. He refers to it as expansive learning and defines it as learning by constructing a new activity and expanding the context. He explains:

'Learning by expanding or learning 3 is very much going beyond the information given to construct a new set of criteria, a broader picture, a broader object for your activity which liberates you from the constraints of the particular setting in which you are functioning and enables you to create new settings.' [START_REF] Engeström | University of Lancaster interview[END_REF] (minute 8.18 of interview) This came after Engeström's revision of AT when he suggested the possibility of expansive transformations, stating that 'an expansive transformation is accomplished when the object and motive of the activity are re-conceptualised to embrace a radically wider horizon of possibilities than in the previous mode of activity ' [9, p. 137].

Dubbing and audio-visual translation

There are three main types of audio-visual translation: dubbing (or lip-sync); subtitling; and voice-over [START_REF] Díaz-Cintas | Audiovisual Translation, Subtitling[END_REF]. All three types involve a recount of both image and sound of the original video, either in the form of written text at the bottom of the screen, as in subtitling, or in the form of audio voice-over.

The empirical studies that are available show that all three types have been experimented with in the field of language learning. Danan (2010) explains how dubbing from L1 (native language) to L2 (target language) has many benefits which he attributes to the combined use of translation and technology. He asserts that the return of the pedagogical role of translation along with the ubiquity and growing versatility of technological tools have opened up an array of possibilities for language learning, one of which is dubbing activities [START_REF] Danan | Dubbing projects for the language learner: a framework for integrating audiovisual translation into task-based instruction[END_REF]. His approach of implementing the L1 to L2 dubbing activity is interesting, and his findings are promising; therefore, they influenced the design of the new activity system in this study.

Other studies suggest different dubbing activities ranging from intralingual (L2 -L2) to interlingual (L1 -L2/L2 -L1). First, there is the repeat/verbatim activity (intralingual) where learners simply repeat the original speech of the characters [12 -17]. Such studies report improvement in learners' pronunciation, intonation, speed and fluency. Another type involves free translation, i.e. to paraphrase for gist [START_REF] Danan | Dubbing projects for the language learner: a framework for integrating audiovisual translation into task-based instruction[END_REF][START_REF] Sokoli | Audiovisual translation for foreign language learning[END_REF], or translation but with concision since literal, faithful translation may not be possible due to register difference or time constraints or learners' slower speeds of speaking [START_REF] Danan | Dubbing projects for the language learner: a framework for integrating audiovisual translation into task-based instruction[END_REF]. This point proved to be particularly significant in this study because it highlighted areas of difference between L1 and L2 in terms of register, and encouraged students to attempt more fluent speech. Reported benefits of these studies are similar to those of the intralingual activities with additional benefits ranging from the improved overall language skills, grammar, awareness of register, language variation, intercultural awareness, paralinguistic elements (such as expression of emotions through voice and facial expression). Other important behavioural benefits were reported such as motivation, autonomy, collaboration, enjoyment, ownership and pride of finished product. In general, all mentioned studies report high levels of student enjoyment of the projects and a desire to do similar projects in the future.

Researchers have reported that within the available body of literature, little has been done on the use of audio-visual translation in relation to productive skills and autonomous learning [START_REF] Danan | Dubbing projects for the language learner: a framework for integrating audiovisual translation into task-based instruction[END_REF]. There is also a call for empirical evaluation of the effect of dubbing in the foreign language learning context [START_REF] Chiu | Can film dubbing projects facilitate EFL learners' acquisition of English pronunciation[END_REF]. Avila and Talavan (2013) report on dubbing projects used with advanced learners and speculate about the suitability of these projects with beginners [START_REF] Avila | The role of dubbing in foreign language learning[END_REF]. None of the available studies have linked dubbing projects with mixed-ability classes or with class management, nor has it been implemented with beginners/false beginners. This study is an attempt to fill these gaps by providing an empirical study to evaluate the use of dubbing projects for language learning with false beginners and mixed-ability classes.

Mobile learning and Bring Your Own Device (BYOD) policy

The UNESCO report on 'Mobile Learning and Policies' identifies a popular definition of mobile learning to be 'education that involves the use of mobile devices to enable learning anytime and anywhere' [START_REF] Vosloo | Mobile Learning and Policies: Key Issues to Consider[END_REF]. This anytime and anywhere feature relates to the physical and temporal spaces making mobile learning possible for people who face restrictions in terms of time and space as in the context of this study. Palalas identifies five essential spaces -temporal, physical, transactional, technological, and pedagogical -explaining that it is the blending of these spaces that:

'can produce a combination of resources (information and actors), contexts, processes and supports that promote learning. […] Hence, with facilitation and guidance of experts, mobile tools can effectively mediate the interplay of these elements toward successful learning outcomes' [19, p. 87]. This is an important part of the theoretical framework that underlies this study.

The problem statement -constraints

Level 1 of the IEP programme is best explained using AT. By examining how variables relate to each other, contradictions were identified. The information below stems from the researcher's insider knowledge of the programme as a faculty member and as the instructor of level 1 classes. These contradictions are categorised into three types of restrictions or systemic tensions (see Figure 2) and are explained below.

Primary tensions:

Motivational and temporal restrictions. [START_REF] Engeström | Learning by Expanding: An Activity-Theoretical Approach to Developmental Research[END_REF] explains primary contradictions to be relevant to the values 'within each corner of the triangle of the activity [7, p.102]. In this case, the contradiction is within the students' value system. Although they value the outcome of the activity, they do not value the time they need to spend to achieve that outcome. Therefore, students tend to not comply with the timeframe of the original activity system by engaging in several attempts of the standardised test. When they do not achieve the required score, they experience feelings of frustration. This has a noticeable negative effect on students' motivation and engagement, which threatens the activity system since the subject needs to be motivated to reach the object (a motivational constraint).

Secondary tensions: Institutional constraints. '

The secondary contradictions are those appearing between the corners' [7, p.102], i.e. 'between the constituents of the central activity' [START_REF] Weibell | Expansive Learning and Activity Theory (Engeström -1987)[END_REF]. The rules within the IEP stipulate that the curriculum is designed for a community of false beginners when in fact the same rules allow students to enter level 1 without a placement test which causes the community of the level to be more mixed ability, hence, causing a contradiction between rules and community. This also affects the division of labour, which mediates the relationship between community and objective. Because some students are of a higher level, they tend to dominate group work activities or simply disrupt them. In other words, the rules cause inconsistency in the community and cause tension in the division of labour, which reduces its ability to mediate the relationship between community and object.

Tertiary tensions:

Technology related restrictions and spatial restrictions. [START_REF] Engeström | Learning by Expanding: An Activity-Theoretical Approach to Developmental Research[END_REF] clarifies that the tertiary contradiction appears when teachers who represent culture introduce a new, more advanced activity system with a new objective and motive [START_REF] Engeström | Learning by Expanding: An Activity-Theoretical Approach to Developmental Research[END_REF]. The new activity system, the dubbing project, designed by the researcher/instructor had a new object (dubbing a video), a new motive (the dubbing competition), and new tools (a short video, dubbing software, etc.), i.e. technology. This new activity system faced tensions caused by the rules of the previous activity system. All classes of level 1 were located relatively far from the computer laboratory which made it difficult to arrange for computer laboratory classes where students can have access to required software tools, causing spatial and technological restrictions.

Theoretical framework

The theoretical framework for the intervention is based on AT, dubbing as a language learning activity, mobile learning and BYOD. AT was used to identify tensions in the learning environment. An intervention was designed to overcome these tensions. The new activity system is the activity of translating and dubbing an Arabic video clip into English using personal mobile devices as mediators and an internally-organised competition as motivator. As indicated earlier, dubbing activities have been used previously for language learners and studies report positive results. In addition, mobile learning studies show that mobile learning is capable of blending spaces to overcome the temporal, spatial, technological and motivational restrictions of the old activity system and BYOD helps overcome lack of classroom technology.

The change in object, motive, tools, rules and division of labour can lead to collective transformation. Engeström explains that:

'expansive learning theory is concerned with collective transformation, rather than individual learning. Although changes in the collective are initiated by individuals within the community, the transformation itself is a change in the collective system. The object of expansive learning activity is the entire activity system in which the learners are engaged. Expansive learning activity produces culturally new patterns of activity. Expansive learning at work produces new forms of work activity.' [START_REF] Engeström | Expansive learning at work: Toward an activity theoretical reconceptualisation[END_REF]

The new activity system

In the 'Listening and Speaking' class, a multi-stage project was designed. The main outcome for it, other than language learning, being to re-enforce students' selfconfidence to communicate in English, an act they had been resisting. The rules of this new activity system were the set of instructions given to the students. The division of labour enabled the more advanced students to do the more advanced linguistic tasks (translation) and helped weaker students with new vocabulary and pronunciation. Initially, students were instructed to choose any short Arabic video they particularly liked. This stage was designed to engage students through something they were familiar with and enjoyed, while at the same time alleviating the pressure of the foreign language by starting from L1. Students used their own mobile devices to view, save, and share these videos with group members. Then, they collaborated to translate the script into English and handed it in for evaluation. Translations needed to be reworked more than once until it finally reached an acceptable state. The next stage was the division of roles, and practicing performing the parts.

In the recording stage, the instructor/researcher functioned as a tool along with iMovie App and a personal mobile telephone. This was to monitor students and ensure that pronunciation, intonation, fluency, etc. were all correct. Each recording session turned into a personalised lesson on pronunciation, intonation, grammar and register. This was a valuable stage of the project because it ensured paying attention to each student individually by giving personalised guidance along with mini-lessons on language register and paralinguistic elements.

The result was 8 dubbed videos that were entered in an internally-organised competition for the two sections. All IEP students and staff were invited to the auditorium where the dubbed videos were shown on the big screen. This competition heightened students' motivation, increased their self-confidence and gave them a sense of achievement.

Methodology

This study adopted a constructivist research paradigm since AT is a constructivist-based learning theory. Constructivism aligns with AT because 'Both Cultural Historical Activity Theory (CHAT) and Dewey's idea-based social constructivism bridge the gap between the dualism of mind and world' [21, p.38]. Moreover, it provides an understanding of 'the world of human experience' [22, p.36] through the 'participants' views of the situation being studied' [23, p.8]. Contrary to post-positivists, the study does not start with a theory, but inductively develops patterns of meaning [START_REF] Creswell | Research Design: Qualitative, Quantitative, and Mixed Methods Approaches[END_REF].

The methodology followed was a case study approach to provide a holistic description [START_REF] Cohen | Research Methods in Education[END_REF] and explore students' perceptions of the dubbing activity as an alternative to the prevailing activity system. It was a study of a 'bound system' through detailed data collection using multiple sources within a rich context [START_REF] Creswell | Part 4: Qualitative research, the case study[END_REF].

Case studies benefit from a variety of data collection methods to arrive at a more detailed description of the case [START_REF] Cousin | Researching Learning in Higher Education: An Introduction to Contemporary Methods and Approaches[END_REF]. Data were collected through focus group interviews, a questionnaire to collect demographic data and my personal observations as an insider researcher (who is part of the educational institute, the instructor of the participants and the designer of the new activity system). This required some measures to reduce researcher bias and influence, mainly by delaying data collection until the participants completed the course and moved on.

Participants and procedure

The dubbing project was assigned to two sections of level 1 in the 'Listening and Speaking' class. There was a total of 34 female students aged 18 to 21 years, mostly fresh graduates of Arabic public secondary schools. Around half of the students were placed in level 1 because they missed the placement test.

Data were collected through 5 Focus Group (FG) interviews where students were required to reflect on their experience of the dubbing project, describe, and evaluate it. Twenty students responded to the FG invitation and 5 groups were formed in two different ways. Two groups constituted students who worked together on the same video and three groups contained students who worked on different videos. Although [START_REF] Cohen | Research Methods in Education[END_REF], among others, advise that FGs should be rather heterogeneous so that discussion can be enriched [START_REF] Cohen | Research Methods in Education[END_REF], [START_REF] Cousin | Researching Learning in Higher Education: An Introduction to Contemporary Methods and Approaches[END_REF] tends to disagree, stressing that group members should have something in common to gain a certain sense of cohesion [START_REF] Cousin | Researching Learning in Higher Education: An Introduction to Contemporary Methods and Approaches[END_REF].

Each group interview went through three stages and lasted around one hour. Initially, the dubbed video(s) of the group members were played to remind students and stimulate detailed discussion. The second stage was answering a questionnaire to gather some demographic data, including their IELTS examination results before and after the project. This served as a good reminder of the project, particularly because the interview took place three months after the end of the project. Finally, the interview stage was introduced with an explanation of the purpose of the research.

Data analysis

The group interviews were transcribed, translated and thematically analysed using open coded analysis [START_REF] Flick | An Introduction to Qualitative Research[END_REF]. Apart from the unanimous expression of how much fun and enjoyable the project was, six main themes emerged and are here discussed in order of the emphasis given to them by students.

Group work and collaboration.

This emerged as a strong theme. Students expressed in different ways how group work enriched them and helped them learn. Two groups mentioned how they got together after class to work and how tasks were divided and redistributed if one student faced difficulty. A student remarked that she could not have understood much on her own without the help of her group. The following comments show this meaning: "If one of us did not understand something, other group members would explain it to her" and "When in a group, everyone participates with ideas. When I did not notice something, someone else in the group drew my attention to it." Group 4 mentioned that they did not need the dictionary much because they had a classmate who knew English well enough and asked her for meanings. One student, however, expressed how she did not like to work with a group and that she would have rather worked on her own or used the help of people from outside. This was a point of disagreement in one of the mixed focus groups and generated discussion among group members. Eventually, the student who disagreed acknowledged the need for others in this kind of project, but expressed her preference to work with outsiders for a more enriching experience. These findings show how the community of the new activity system became more harmonious, and division of labour was more effective in reaching the outcome.

8.2

The competition as a motivating factor. This was a prominent theme that emerged strongly without prompting. It was mentioned when asking for general impressions. Words such as 'enthusiastic', 'motivated', 'encouraged', 'competitive', and 'want to win' were quite recurrent. One student said that for her, it was only after announcing the competition that the interest started. "This is when the interest and drive for hard work kicked-in. This is when ideas started to come" she said. Another expressed that the competition made them more serious about the work, especially after knowing that the dubbed videos would be shown to an audience and a panel of judges. "We started to work hard when we knew that other instructors will be on the panel of judges to choose the winner." Two groups remarked that when you work hard on something, you want people to see it. Others said that they finally dared to speak in English after being very reluctant to do so. They said that now they do not mind speaking in English and feel more confident and motivated. They also indicated that they felt honoured to be called on stage and presented with achievement certificates and awards. One student said that she immediately shared her certificate with her family. It is quite clear here that the new activity system was effective in changing students' perceptions and motivating them, which answers the second research question.

Achievement, pride, and sense of ownership.

A general sense of pride and achievement was prevalent. Students repeatedly asserted that doing this project was a big achievement for them since it was their first semester in the university, especially for being able to speak as fluently as they did in the videos. Having it on video was a proof of their improvement. Most students said that they shared the videos with family and friends, except one student who said she did not share it because she felt that she could have done better. This was the same student who did not prefer group work, giving the impression that she could have produced a better video on her own. Many students expressed repeatedly that they never thought they could speak like that. "I don't know how, but I dared to speak! I don't speak much, not even in Arabic! Now I'm more confident and I don't mind speaking as I used to before" one student commented. They also mentioned that they showed it to their other instructors: "they were impressed, told us how well we did and encouraged us to keep it up." One student mentioned a significant remark from one of their instructors. She said that this instructor turned around while the video was playing and said to her: "So you do speak English!" This remark from the instructor is an indicator of how resistant students were to communicating in English, even in their English classes.

8.4 Difficulties. One common difficulty mentioned around 8 times was the fact that they had to speak in English and how they struggled with accepting the idea. They said that seeing others speaking and making mistakes made them feel that it was fine to make mistakes and gave them some confidence. Other remarks varied about the difficulties they faced and different students pointed to different aspects of the project. Students mentioned difficulties such as:

• dealing with Arabic words that do not have English equivalents: "Some words were hard to translate and had no equivalent, so we had to describe them instead"; • lip synching, speaking speed, editing and re-recording: "the duration of our pronunciation was different from the character's lip movement, so we had to rerecord and change some of the dialogue as we were recording"; • acting and changing the voice according to the role: "Sometimes we had to practice a lot just to get the right voice for the character. Acting with your voice is not easy"; • pronunciation of new words.

One student said: "the more difficulties there are, the more you would want to overcome them and it drives you to do more". Finding a suitable, quiet place to do the recording was noted as a challenge, but because the recording was done with a mobile telephone, the location shifted according to availability. 8.5 Learning. Although this might be a difficult aspect to measure, students indicated that they learned a number of new vocabulary words. As students were watching the video at the beginning of the interview, they were prompted to jot down any word they learned in this project. They produced lists of words that ranged from 4 to 11 words per video. There was a correlation between the number of words and the length of dubbed video. The longer the video was, the more words were learned. Moreover, in the interviews they mentioned learning pronunciation and register: "Some Arabic expressions do not fit in the same context in English". This was linked to the difficulty of translating some expressions. Repeating the recording for the sake of proper lipsynching was pointed out as the main reason they improved their pronunciation and fluency. One group specifically said: "this project was good to learn language, vocabulary, pronunciation, how to say things [intonation]… When you translate, you also learn grammar." This relates to the first research question showing that the dubbing project remediated learning for false beginners and mixed ability classes.

8.6 Suggestions. When asked if they recommended this project for other classes and what suggestions they had, they all recommended it. Most said that the project was good as it was, a few suggested dubbing whole episodes or plays. One student suggested individual productions but others in the group did not agree, saying that if they had to act or perform on their own, they would not have done it.

Discussion and conclusion

Students' comments and reflections were overwhelmingly positive and indicated a high level of engagement within the activity of dubbing. This is seen as a significant change to the disengagement, disruption, and frustration that were prevailing in the old activity system. As for motivation, a positive change in students' attitudes towards learning was noted. The activity catered for different levels of language learners. On the one hand, it encouraged collaboration between students. On the other hand, by breaking away from the set curriculum, each student found a task suitable to her level. Stronger students helped weaker ones, while all of them were motivated to do everything they could to win the competition.

Part of the demographic information students provided in the questionnaire was their score in the speaking component in the IELTS examination before and after level 1. Ten students indicated taking the IELTS both before and after level 1. The speaking component score improved for seven of them. Although this cannot be attributed to the dubbing project alone, it can still be suggestive of improvement. These results answer the first research question and provide evidence that this new activity system remediated language learning for false beginners in mixed-ability classes. It also answers the second question by showing students' increased motivation and confidence. Although the dubbing activity proved to be successful and enjoyable, results of the study need further verification in other contexts. For example, in the recording stage, students could be guided to do their own recording, video editing and publishing with less interference from the instructor.

Figure 2 .

 2 Figure 2. Systemic tensions in level 1 activity system