Keywords: engineering, physical workload, surface electromyography Highlights

The clip fitting task is a frequently encountered assembly operation in the car industry. It can causeupper limb pain. During task laboratory simulations, upper limb muscular activity and external force were compared for 4 clip fitting methods: with the bare hand, with an unpowered tool commonly used at a company and with unpowered and powered prototype tools. None of the 4 fitting methods studied induced a lower overall workload than the other three. Muscle activity was lower at the dominant limb when using theunpowered tools and at the non-dominant limb with the bare hand or with the powered tool. Fitting clips with the bare hand required a higher external force than fitting with the three tools. Evaluation of physical workload was different depending on whether external force or muscle activity results were considered.Measuring external force only, as recommended in several standards, is insufficient for evaluating physical workload.

INTRODUCTION

The current trend, in manufacturing industries, of seeking productivity gains combined with a high level of quality has resulted in a willingness on the part of designers to ensure an uniformity in the ways in which operators work [START_REF] Gold | Specific and non-specific upper extremity musculoskeletal disorder syndromes in automobile manufacturing workers[END_REF][START_REF] Parent-Thirion | European Foundation for the Improvement of Living Standards[END_REF][START_REF] Neumann | Production system design elements influencing productivity and ergonomics in a case study of parallel and serial flow strategies[END_REF][START_REF] Domkin | Joint angle variability in 3D bimanual pointing: uncontrolled manifold analysis[END_REF][START_REF] Chassaing | Vers une compréhension de la construction de la gestuelle des tôliers d'une entreprise automobile[END_REF][START_REF] References Andersen | Risk factors in the onset of neck/shoulder pain in a prospective study of workers in industrial and service companies[END_REF][START_REF] Neumann | A case study evaluating the ergonomic and productivity impacts of partial automation strategies in the electronics industry[END_REF]. Workstation designers define a single succession of postures and movements to be performed by the operator, without offering any alternative. Assembly lines are no exceptions to this rule. Such lines are made up of series of workstations on which tasks are performed in succession and repeatedly [START_REF] Carnahan | Incorporating physical demand criteria into assembly line balancing[END_REF]. Many of these tasks are performed manually, with the bare hand or using a tool, powered or unpowered [START_REF] Byström | Clinical disorders and pressure-pain threshold of the forearm and hand among automobile assembly line workers[END_REF]. In view of the repetitiveness of the movements, of the level of force requiredto perform an action, of extreme joint amplitudes and/or of activity maintained for long periods, neck and upper limb pain or indeed musculoskeletal disorders occur frequently in the workers performing such tasks [START_REF] Ferguson | Shoulder muscle fatigue during repetitive tasks as measured by electromyography and near-infrared spectroscopy[END_REF][START_REF] Ferguson | Musculoskeletal disorder risk during automotive assembly: current vs. seated[END_REF][START_REF] Jansen | Musculoskeletal discomfort in production assembly workers[END_REF][START_REF] Xu | Design of assembly lines with the concurrent consideration of productivity and upper extremity musculoskeletal disorders using linear models[END_REF][START_REF] Spallek | Work-related musculoskeletal disorders in the automotive industry due to repetitive work -implications for rehabilitation[END_REF][START_REF] Nordander | Risk of musculoskeletal disorders among females and males in repetitive/constrained work[END_REF][START_REF] Landau | Musculoskeletal disorders in assembly jobs in the automotive industry with special reference to age management aspects[END_REF][START_REF] Buckle | The nature of work-related neck and upper limb musculoskeletal disorders[END_REF][START_REF] Silverstein | Use of a prevention index to identify industries at high risk for work-related musculoskeletal disorders of the neck, back, and upper extremity in Washington state, 1990-1998[END_REF][START_REF] Sluiter | Criteria document for evaluating the work-relatedness of upper-extremity musculoskeletal disorders[END_REF][START_REF] Fransson-Hall | Self-reported physical exposure and musculoskeletal symptoms of the forearm-hand among automobile assembly-line workers[END_REF]. In ergonomics, workplace exposure to such physical workload is often evaluated by measuring muscular activity, which has been correlated with pain or musculoskeletal disorder symptoms [START_REF] Ferguson | Musculoskeletal disorder risk during automotive assembly: current vs. seated[END_REF][START_REF] Porter | Analysis of applied forces and electromyography of back and shoulder muscles when performing a simulated hand scaling task[END_REF][START_REF] Bao | Force measurement in field ergonomics research and application[END_REF][START_REF] Ostensvik | Association between numbers of long periods with sustained low-level trapezius muscle activity and neck pain[END_REF][START_REF] Southard | Ergonomic interventions for the reduction of back and shoulder biomechanical loading when weighing calves[END_REF]. Conversely, designers mostly use standards as a basis for evaluating physical workload, such standards recommending assessment of external force or posture (CEN 1005(CEN -4, 2004;;CEN 1005CEN -3, 2002;;CEN 894-3, 2008).

One of the tasks that are frequent in automotive assembly processes is insert fitting. The inserts are small components of different shapes, made of metal, plastic or composite material. They are referred toby various names including clips, staples, nuts, rings or 3 bushings. They are used to secure two parts together, for example a glove compartment and a dashboard. This task can be performed manually or in automated manner. As in other assembly tasks, automation is considered in order to reduce musculoskeletal disorders related to manual fitting. However, investment in automated machinery is costly and requires considerable expertise [START_REF] Andrews | Acceptable peak forces and impulses during manual hose insertions in the automobile industry[END_REF]. Usually, it is not considered to be costeffective in view of the lifespan of such a part and of alterations that are often performed half way through its life. Therefore, insert fitting is generally performed manually, with or without a tool.

An ergonomic investigation conducted at an automotive supplier specialized in designing and producing dashboards preceded this study (Gaudez, 2008a;Gaudez, 2008b). The request from that company involved objectifying physical workload exerted during the insert fitting operation, which was a source of neck and upper limb pain or of musculoskeletal disorders.

In that company, the insert fitting operation was combined with other operations such as deflashing, visual quality inspection, and packaging of the dashboards. The company had developed an unpowered tool. Its aim was to reduce the physical workload during the insert fitting operation.But it was observed that, when fitting the particular variety of clip-type inserts, most of the operators performed the operation with the bare hand despite the fact that the workstation working procedure recommended fitting them with the tool. In that company, the operators suffering from upper limb pain fitted the clips sometimes with their bare hand and sometimes with the tool. Operators changing their working practices depending on their physical conditions, such as depending on whether they feel tired or in pain, has already been observed during work activities [START_REF] Derosier | Studying work practices: a key factor in understanding accidents on the level triggered by a balance disturbance[END_REF]. Those operators explained that alternating the two fitting methods allowed them to vary their movements and reduced the physical workload on different parts of the body. In addition, many operators found that the tool was too heavy and that its handle was too large, cold, hard, and slippery when sweaty. This laboratory study simulated the clip fitting activity. Its aim was to use muscular activity and external force measurements to evaluate the physical workload on the neck and upper limbs. Four different insert fitting methods were analyzed: two used in the company, namely bare hand and unpowered tool,as well as two prototype tools, one unpowered and one powered. The first objective of this study was to determine whether any one of these four methods generated lower physical workload than the other ones, thereby demonstrating its benefit to the musculoskeletal health of workers. The second was to compare the results of muscular activity measurements with the results of external force measurements. This laboratory study supplemented the initial ergonomic investigation. Indeed, this simulation offered the advantage of isolating the insert fitting operation and thus of satisfying the initial request of the automotive supplier. It also allowed the use of prototype tools and techniques that were difficult to apply out in the companysuch as measuring resultant force, which would have required the workstation to be transformed.

METHOD

Subjects

Eleven right-handed male volunteers took part in the experiment. Those subjects did not work in the company in which the ergonomic investigation had been conducted, due to economic and social difficulties present at the time of the laboratory study and to the distance between the company and INRS(National Research and Safety Institute), where the laboratory was located.The volunteers were professionally experienced in performing precision assembly work.

The 11 subjects had not suffered from any musculoskeletal pain during the month preceding the experiment. Their average age was 27 years (ranging from 19 to 60 years), their average height was 178 cm (ranging from 171 to 191 cm), their average weight was 77 kg (ranging from 57 to 111 kg) and their body mass index was 19 (ranging from 19 to 37).The subjects gave their informed consent to the experiments, which were approved by the local ethics committee.

Test bench

An experimental test bench was used to simulate the clip fitting task. The shape, dimensions, and material of the clip supports were identical to those making up a dashboard in the company. Ten clip supports were fixed to a rule (Figure 1). The clips were purchased from the same manufacturer as the one used by the automotive supplier. The supports were inclined such that the subjects inserted the clips forward and downward at a 45° angle in the sagittal plane. This inclination of the supports was frequently to be found on the dashboards.

The rule was fixed to an elevating table simulating the height-adjustable workstations of the company. The table height was adjusted tothe anthropometry of each subject. It was set at 90% of the elbow-to-floor height of the subject, corresponding to working in a standing position requiring average normal vision and precision (CEN ISO 14738, 2008).

Task

Standing and facing the rule, each subject fitted clips to each support using four different methods: with the bare hand, with an unpowered tool commonly used at the company, with an unpowered prototype tool, and with a powered prototype tool (Figure 1). The prototype tools were developed at INRS with the help of the company's methods department that worked with the operators.

The unpowered tool commonly used at the companywas circular in cross-section and cylindrical in longitudinal section. Its length was 120 mm, its diameter was 32 mm and its weight was 200 g. It had a magnetic cavity at its end that was preformed to match the geometrical shape of the clip for subsequent positioning on the support. The clip was held by magnetization in that cavity.An unpowered prototype tool featuring merely a modified handle was therefore developed from that commonly used tool. Various studies bear witness to the importance of the ergonomics of the handle of the hand tool in terms of performance, comfort, and physical stress for the operator (Harih andDolsak, 2014a, 2014b;[START_REF] Ng | A review of shape and size considerations in pinch grips[END_REF][START_REF] Garneau | Optimization of product dimensions for discrete sizing applied to a tool handle[END_REF][START_REF] Eksioglu | Relative optimum grip span as a function of hand anthropometry[END_REF]. Its handle had a shape that was circular in cross-section and conical in longitudinal section. That shape appeared to be optimum for hand tools requiring handling with precision or with force [START_REF] Kong | Evaluation of handle shapes for screwdriving[END_REF][START_REF] Dong | The effect of tool handle shape on hand muscle load and pinch force in a simulated dental scaling task[END_REF]. Its length was 115 mm. Its largest diameter was 36 mm and its smallest diameter was 20 mm. The diameter of the handle splayed to 25 mm in the vicinity of the cavity to form a guard and was made of slightly rough, hard plastic in order to prevent the fingers and hand from slipping, and the handle from feeling cold. This prototype tool weighed 130 g. The cavity located at the tool tip was identical to that on the tool commonly used at the company. The magnetic force of the cavity was identical for both tools.The subjects were told to hold the unpowered tools with a full hand grip in theirdominanthand with the thumb directed towards the cavity to ensure consistency between subjects. That way of holding the tool was the one that was observed most frequently during the ergonomic investigation. The powered prototype tool was developed from a pneumatic stapler, whose nose and loading magazine were modified. Its loading magazine contained 10 clips. Urged by a spring, the clip went into place automatically in the cavity of the tool. The handle extended at right angles and was held in the dominant hand, with the forearm extended in alignment with the hand.

The handle was 140 mm long, oval (40 mm X 30 mm) in cross-section and cylindrical in longitudinal section.A trigger that was 45 mm long, was actuated by the index finger and the middle finger of the dominant hand. It weighed 970 g and was sheathed in slightly rough plastic. The tool tip featured the same cavity as that of both of the unpowered tools and a position markwas added to the cavity so as to make it possible to pre-position the tool tip above the support. The subject pulled the trigger, to discharge a jet of compressed air that initiated percussion on the top of the clip, allowing the clip to be inserted into its vacant support.

The upper limbs were mobilized differently depending on the 4 fitting methods. The clips were placed at the center of the table. When fitting with the bare hand, subjects picked up the clip with their dominant hand and then inserted it in the vacant support. With unpowered tools, subjects picked up the clip with their non-dominant hand and positioned it in the cavity of the tool. The tool was held in a full hand grip with the dominant hand. Thus,subjects inserted it with the tool into the vacant support. Using these tools, each limb was mobilized to perform different actions. The powered tool was held in the dominant hand. Unlike with unpowered tools, the operator did not have to place the insert in the cavity. The subject triggered insertion of the clip by pulling the trigger with the index and middle finger of his dominant hand.

Experimental design

Prior to starting the experiment, each of the 11 subjects practiced fitting clips using the four methods until each of them declared he was fitting the inserts with ease. Then, each of the subjects fitted clips at a regular pace set by a metronome of one every 4 seconds, which was close to the fitting rate at the company. The order in which each subject passed from one of the four fitting methods to another was randomized. For each of the four methods, each subject fitted in succession 10 clips on the rule, starting with the supports at its left-hand end.

Each subject therefore fitted 40 clips in all (4 fitting methods x 10 clips).

Instrumentation

The resultant external force exerted, when fitting clips, was measured using a force platform located between the rule and the elevating table (AMTI BP 600900-1000). The subjects were asked not to touch the table with any part of their body to avoid influencing the measured data.

A portable surface electromyography (sEMG) signal analysis system (Wave wireless EMG, COMETA, Italy) was used to record the subject's myoelectric activity. The sampling rate was 2 Ks/sec -16 bits. The signals were band-pass filtered in the 10-1000 Hz frequency range, sampled at 2000 Hz and amplified 1000 times. All sEMG signals were post-processed. The root mean square values of each signal were calculated over consecutivetime windows (10 ms). Flexor digitorumsuperficialis (FDS),extensor digitorumcommunis (EDC), biceps brachii (BIC), triceps brachii (TRI), deltoideus anterior (DEL) and trapezius pars descendens (TRA) muscular activities in both upper limbs were measured by surface electromyography. Bipolar sEMG electrodes (Ambu® Blue Sensor N-00-S/25, Denmark) were aligned on abraded cleaned skin along the direction of the muscle fibers. The inter-electrode distance was set at 2 cm. The impedance was checked to be below 5 kΩ. The electrodes were placed according to [START_REF] Zipp | Recommendations for the standardization of lead positions in surface electromyography[END_REF]. Two maximum (5 s) reference contractions were performed for each muscle to standardize the EMG signals with respect to their corresponding maximal voluntary electrical (MVE) activity. Each of the contractions was separated by a pause of 3 minutes to avoid any risk of muscular fatigue appearing.The subject was provided with verbal encouragement. For taking measurements on the FDS and the EDC muscles, the subject was seated with his forearm resting horizontally on a table. The subject's upper arm remained in a vertical position and his hand was unsupported. For the FDS and EDC muscles, the back and the palm of the subject's hand faced the floor respectively [START_REF] Delisle | Comparison of three computer office work stations offering forearm support: impact on upper limb posture and muscle activation[END_REF]. A non-elastic strap was placed around his hand at the metacarpal-phalangeal joints. For the FDS muscle, the subject was required to perform a maximum wrist and finger flexion and, for the EDC muscle, he had to perform a maximum wrist and finger extension.

The non-elastic strap enabled the subject to perform maximum movements against a static resistance. For the BIC and TRI muscles, the subject was seated with his forearm horizontal and elbow flexed to 90°, with his wrist in a neutral position and his hand unsupported. A nonelastic strap was placed around his wrist perpendicular to his forearm. For the biceps muscle, the subject was required to perform a maximum elbow flexion and, for the triceps muscle, a maximum elbow extension. For the DELmuscle, the subject sat with his elbow flexed to 90° and his shoulder flexed to 45°. A non-elastic strap attached to the floor behind the subject, passed just over his elbow joint, perpendicular to the arm. The subject was required to perform a maximum shoulder flexion [START_REF] Delisle | Comparison of three computer office work stations offering forearm support: impact on upper limb posture and muscle activation[END_REF]. For the TRA muscle, the subject stood with his arms abducted to 90°. A non-elastic strap attached to the floor was placed around his arm at the elbow joint [START_REF] Mathiassen | Normalization of surface EMG amplitude from the upper trapezius muscle in ergonomic studies -A review[END_REF]. He was required to perform a maximum abduction of both upper limbs. For each muscle, myoelectric activity was expressed as a percentage of the MVE activity.

Statistical analysis

In order to avoid any border effect, the first and the last clip fitting were excluded.

For the resultant external force, the 90 th percentile was analyzed. This was compared with the values recommended by CEN 894-3 (2008). According to that standard, the recommended maximum actuation force for manual control parts is 20 N, when using a finger grip to perform a forward movement along the forearm axis; this movement is similar to that the movement that was performed for fitting theclips with a bare hand. The recommended maximum actuation force for manual control parts is 55 N, when using a full hand grip to perform a forward movement along the forearm axis; this movement is similar to of the movement that was performed for fitting the clips with a tool.

For the muscular activities, the amplitude probability distribution function (APDF: [START_REF] Jonsson | Quantitative electromyographic evaluation of muscular load during work[END_REF]) was used to determine the 10 th , 50 th and 90 th percentiles for the EMG signal. These were compared with thresholds proposed by [START_REF] Jonsson | Quantitative electromyographic evaluation of muscular load during work[END_REF] to prevent muscular fatigue occurring. According to that author, the 10 th percentile for the muscular activity must not exceed 5% and/or the 50 th percentile must not exceed 14% and/or the 90 th percentile must not exceed 70% of the MVE.

Prior to statistical modeling, the measured percentiles of the EMG signal were logtransformed to give approximately symmetrical residual distributions. The data were analyzed based on a 2-way mixed-effects ANOVAincluding main effects for tools and subjects, and tool-subject interaction. Tool was a fixed factor whereas subject and thus toolsubject interaction wererandom factors. Thus, the differences between tools took into account possible differences between subjects, due to age, height or weight. Model assumptions were checked by graphical inspection of the residual distributions. The statistical analysis was performed using the Stata 12 software (College Station Tx).

A difference between two fitting methods was considered interpretable when the 90 th percentiles for the resultant external force or the 10 th , 50 th and 90 th percentiles for the activity of a muscle deviated by more than the model-based estimate of its within-subject residual error. To ensure a higher reproducibility of the results, only the differences apparent in at least 8 out of the 11 subjects taking part in the experiment were interpreted.

RESULTS

Resultant external force

The mean 90 th percentiles for the resultant external forces measured when fitting with the bare hand and with unpowered tools were higher than the thresholds recommended by CEN 894-3 (2008) (with the bare hand: 132 +/-52 N compared with 20 N for a finger grip; with the unpowered tool commonly used at the company: 77 +/-33 N and with the unpowered prototype tool: 65 +/-32 N compared with 55 N for a full hand grip) (Figure 2). The mean 90 th percentile for the resultant external force measured when fitting with the powered prototype tool (53 +/-27 N) was closer to the force recommended by the above standard (55 N). Fitting clips with the bare hand required a higher external force than fitting with the three tools (p<0.001) (Table 1).

Muscular activity

Fitting with the powered tool was the only investigated method where the recommended values given byJonsson (1978) were exceeded. The 10 th percentile values for EDC andTRA activity in the dominant limb exceeded 5% of the MVE (Figure 3).

With regard to the dominant limb muscles, clip fitting methods involving the powered prototype tool and the bare hand generally induced higher muscle activities than fitting with the unpowered prototype tool (Table 1). Compared with the unpowered tool used at the company, and/or the unpowered prototype tool and/or the bare hand, clip fitting with the powered tool produced higher 10 th percentile values for the FDS (p≤0.001), the TRI (p=0.002) and the DEL (p≤0.001) muscles, and 50 th percentile values for the FDS (p≤0.001) and the DEL (p=0.003) muscles. Moreover, fitting with the bare hand generated 90 th percentile values for the EDC (p=0.002), the BIC (p≤0.001), the TRI (p≤0.001) and the DEL (p≤0.001) muscles higher than those generated when fitting with the unpowered tool used at the company and/or with the unpowered prototype tool and/or with the powered tool.

Furthermore, fitting with the tool commonly used at the company generated 10 th percentile (p≤0.001) and 50 th percentile (p≤0.001) values for the BIC muscle higher than those generated when fitting with the powered tool. Regardless of which muscle of the dominant limb was considered, the unpowered prototype tool generated no percentile values higher than those generated when using the other three fitting methods.

With regard to the muscles of the non-dominant limb, fitting with the unpowered tool commonly used at the company, and with the unpowered prototype generated higher muscular activities than fitting with the bare hand or with the powered prototype tool (Table 1). Fitting with the unpowered tool commonly used at the company generated a 50 th percentile value for the DEL muscle (p=0.002) and 90 th percentile values for the EDC (p≤0.001), the BIC (p≤0.001), the TRI (p≤0.001), the DEL (p≤0.001) and the TRA (p=0.016) muscles higher than those generated when fitting with the powered tool. The 90 th percentile value for the FDS muscle (p≤0.001) was higher when fitting with the unpowered tool commonly used at the company than when fitting with the bare hand. The 50 th percentile value for the EDC muscle (p≤0.001) and 90 th percentile values for the FDS (p≤0.001), the EDC (p≤0.001) and the DEL (p≤0.001) muscles were higher when fitting with the unpowered prototype tool than when fitting with the powered prototype tool.

Muscular activities presented no significant difference between both unpowered tools. However, compared with the unpoweredprototypetool, clip fitting with the unpowered toolcommonlyusedat thecompany produced higher mean values for the 90 th percentile of theexternalforce, and the10 th , 50 th et 90 th percentiles of the FDS, the BIC, the TRI and the TRA muscles of the dominantlimb,of theFDS, the EDC, the TRI, the DEL and the TRA muscles of the non-dominant limb, the 50 th and90 th percentiles of the EDC muscle of thedominant limb and of the BIC muscle of thenon-dominantlimband the90 th percentile of the DEL muscle of thedominant limb.

DISCUSSION

None of the four clip fitting methods induced a lower overall physical workload, as estimated from muscular activities and resultant external force, than the other three. Muscle activity of the dominant limb was lower when using unpowered tools in comparison to using the bare hand or the powered tool. However, fitting with the bare handor with the powered tool generated lower muscular activity at the non-dominant limb in comparison to unpowered tools. There was a risk for operator health, whatever the method used. Fitting clips with the bare hand, with the unpowered tool commonly used at the company and with the unpowered prototype tool effectively required resultant external forces that exceeded those recommended by CEN 894-3 (2008). Moreover, fitting clips with the powered prototype tool resulted in a risk of muscular fatigue, according to [START_REF] Jonsson | Quantitative electromyographic evaluation of muscular load during work[END_REF].

Therefore, the improvements in the 2 prototype tools, unpowered and powered, developed by INRS, need to be continued in order to reduce the physical workload on operators. For the unpoweredprototype tool, the ergonomics of the handle and the cavity receiving the insert could be improved. Furthermore, mechanical assistance to gear down the force exerted for the insertion could also be integrated into this tool.When fitting with the powered tool, the 10 th percentile values for the EDC and the TRA muscles of the dominant limb exceeded the thresholds proposed by [START_REF] Jonsson | Quantitative electromyographic evaluation of muscular load during work[END_REF]. The 10 th percentile value represents the static workload [START_REF] Ankrum | Questions to ask When Interpreting Surface Electromyography (SEMG) Research[END_REF] and, when this is high, certain muscular fibers are continuously active, allowing no, or only little, muscular rest and thereby compromising muscular integrity.

Weighing nearly 1 kg, the powered tool was the heaviest of the studied tools. A high and continuous activity of the EDC and TRA muscles of the dominant limb was associated with holding the tool. Moreover, this weight difference between tools explained the significantly higher 10 th percentile values for FDS, EDC and DEL muscles, when using the powered tool, compared with the three other fitting methods. For this reason, the powered tool cannot be used in its current state. A feasible solution would be to optimize its design by trying to reduce its weight or by suspending it.

This study also reveals possible mismatch between the results from resultant external force and surface electromyography. When fitting clips with the powered tool, the resultant external force value was smaller with this tool compared with the other three fitting methods, while the muscular activity measurement results indicated that the method involving the powered tool was the only one to cause a risk of muscular fatigue. Holding the tool requires a cocontraction of agonist-antagonist muscle. This physical load is measured by surface electromyography, and not by resultant external force. Resultant external force is a mechanical measurement recorded in the environment close to the subject, while muscular activity is a physiological measurement recorded directly on the subject. Measuring muscular activity reflects the real loads exerted on the subject to a greater extentthan resultant external force does and it would therefore seem more relevant for evaluating an operator health-related risk. Nevertheless, resultant external force is used often by designers [START_REF] Delleman | International standards on working postures and movements ISO 11226 and EN 1005-4[END_REF]Karger and Bayha, 1987) while muscular activity measurement is used only exceptionally.

Depending on theclip fitting methods, the upper limbs moveddifferently. This led to different physical workload of the upper limbs. Clip fitting with unpowered tools required less muscular activity of the dominant limb than fitting with the bare hand or with the powered tool, while clip fitting with the bare hand or with the powered tool required less muscular activity of the non-dominant limb than fitting with the two unpowered tools. Thus, although the initial objective of the study was to reduce the physical workload by identifying the insert fitting method that was least stressful, these results lead us to consider exploring another way for reducing the physical workload:diversifying the ways in which the task of inserting clips is performed at the same workstation.Out in the company, the operators who were suffering from aches and pains alternated between fitting with the tool and fitting with the bare hand. This proposal involving alternation of different ways of performing the same work activity goes against the current design practices, which tend to promote uniformity and standardization of the ways in which operators work.Multiple studies reveal that existence of variability in muscular activity can have a preventive effect on fatigue development [START_REF] Srinivasan | Motor variability in occupational health and performance[END_REF][START_REF] Bosch | The effect of work pace on workload, motor variability and fatigue during simulated light assembly work[END_REF][START_REF] Van Dieën | Lowlevel activity of the trunk extensor muscles causes electromyographic manifestations of fatigue in absence of decreased oxygenation[END_REF][START_REF] Farina | The change in spatial distribution of upper trapezius muscle activity is correlated to contraction duration[END_REF][START_REF] Andersson | Lumbar disc pressure and myoelectric back muscle activity during sitting. Part I: studies on an experimental chair[END_REF]. Furthermore, this proposal to alternate various different ways of fitting the inserts might bring to mind the technique of changing to different workstations. It is based on the assumption of reducing physical stress of operators by varying the parts of the body that are stressed. However, in practice, it can have the opposite effect and even be harmful to worker health [START_REF] Comper | The effectiveness of job rotation to prevent work-related musculoskeletal disorders: protocol of a cluster randomized clinical trial[END_REF][START_REF] Luger | The influence of task variation on manifestation of fatigue is ambiguousa literature review[END_REF][START_REF] Horton | Effects of rotation frequency and task order on localised muscle fatigue and performance during repetitive static shoulder exertions[END_REF][START_REF] Keir | Task rotation effects on upper extremity and back muscle activity[END_REF]. The protocol put in place in this study does not make it possible to validate this proposal. A future study will need to be performed in order to demonstrate this benefit for worker health.

LIMITATIONS AND FUTURE WORK

In this laboratory-based study, the activity was simulated and focused on insert fitting. It differed from the real work activity partly due to the absence of other activities generally associated with insert fitting, such as deflashing, part packaging or quality control, due to the workstation design and to the visual and acoustic conditions. These differences between laboratory and real working conditions may lead to different results [START_REF] Moriguchi | Are posture data from simulated tasks representative of field conditions? Case study for overhead electric utility workers[END_REF].

This study comparing physical workloads for different fitting methods requires validation in relation to real work activity.

This study analyzed only one of the very many types of inserts. Future studies could focus on analyzing physical workload associated with fitting other types of inserts and implementation of other fitting methods. Moreover, the prototype tools used in this study may be further improved, for example to reduce the resultant external force and the muscular activity required for inserting clips.

The study population was exclusively masculine yet, women do perform this activity at manufacturers. A study combining a masculine and feminine population could be envisaged.

The results of the present study lead us to propose alternating between different clip fitting methods. However, these methods have been analyzed separately. Future research could focus on the benefit to operator health based on a protocol comparing clip fitting method alternation with fitting based on each of these methods. It could also attempt to define the best method alternation frequency in relation to employee health.

CONCLUSION

This study shows different results depending on which technique was used to measure the physical workload: muscular activity versus resultant external force. It highlights the risk of erroneous interpretation when only resultant external force is taken into account. That measurement is recommended in several standards for evaluating the physical load on operators.

The results of this study show that none of the four clip fitting methods studied was preferable in relation to benefitting operator health. None induced lower activities on all the recorded muscles than the other three. Each of the 4 clip fitting methods exceeded the recommended thresholds, be they [START_REF] Jonsson | Quantitative electromyographic evaluation of muscular load during work[END_REF] for muscular activity, or the thresholds of CEN 894-3 (2008). Thus, the improvement of the prototype tools needs to be continued.

Alternating different insert fitting methods with a view to varying upper limb muscular activities could have a preventive effect on the risk of occurrence of fatigue or musculoskeletal pain. However this proposal needs to be validated in a future study. Unpowered tool used at company=tuc, Unpowered prototype tool=ut; Powered tool=pt):

Figures and Table

Value of p, difference between two fitting methods greater than fitting method residual error (fitting method X > fitting method Y indicating that method X induces muscular activity or resultant external force at least greater than the fitting method residual error for fitting method Y) and number of subjects affected by this difference Authors

Figure

  Figure 1: The 4 ways of fitting the clips

  Figure 1: The 4 ways of fitting the clips

Figure 3 :

 3 Figure 3: Mean and standard deviation of the 10 th , 50 th and 90 th percentiles for flexor

Table 1 :

 1 ANOVA-based statistical test results on effect of fitting method (Bare hand=h;

Acknowledgements

The authors wish to thank Olivier Morel and Gilles Reno for their technical contribution.


Guillaume Barbier
email: guillaume.barbier@gipsa-lab.grenoble-inp.fr

Louis-Jean Boë

Guillaume Captier

Rafael Laboissière

Human vocal tract growth: A longitudinal study of the development of various anatomical structures

Keywords: human vocal tract, growth, longitudinal study, speech production, acoustics

The growth of the head and neck and its components, including that of the vocal tract, is not homothetic but appears rather as an anamorphosis. The growth of various structures presents a phenomenon of heterochrony. Another important issue in vocal tract growth is sexual dimorphism. It was first claimed that sexual dimorphism appears at puberty, but a recent study has suggested that some prepubertal differences exist. To study these two phenomena, we used longitudinal radiographic data of sixty-eight typical subjects (966 radiographs, taken from 1 month to 25 years) and twelve fetuses (anatomical sections). In this study, we analyzed the growth curves and growth types of the hard and soft palate, the pharyngeal cavity and the estimated length of the whole vocal tract using non-linear mixedeffect models, in order to take advantage of our unique longitudinal dataset. Results indicate that most of the structures follow a neural/somatic growth type, while the pharyngeal cavity follows a more somatic growth type. As concerns sexual dimorphism, no prepubertal differences were found, suggesting that the sexual dimorphism is likely to begin at puberty. These results have implications for the acoustics of speech production during development and should lead to improvements in vocal tract growth modeling.

Introduction

Since the first studies on the growth of human head and neck, it has been shown that this development is not homothetic (linear), but appears rather as a true anamorphosis (complex nonlinear transformation). Furthermore, the growth of different structures does not follow a unique growth type, highlighting a phenomenon called heterochrony. Since 1930 [START_REF] Scammon | The measurement of the body in childhood[END_REF], it has been shown that the structures belonging to the skull follow a rapid growth in the first years of life to achieve the adult size quite early, which was named neural type of growth, while other structures follow a more continuous growth showing two inflections, which was named somatic type of growth.

Few studies have investigated human vocal tract growth [START_REF] Goldstein | An articulatory model for the vocal tracts of growing children[END_REF][START_REF] Lieberman | Ontogeny of postnatal hyoid and larynx descent in humans[END_REF][START_REF] Fitch | Morphology and development of the human vocal tract: a study using magnetic resonance imaging[END_REF][START_REF] Vorperian | Anatomic development of the oral and pharyngeal portions of the vocal tract: an imaging study[END_REF]. These studies have quantified the growth of different vocal tract structures, and have observed that different structures follow different growth rates and types. But none of these studies was done longitudinally nor included pre-natal data.

The first goal of the present study, based on a longitudinal data set and including fetal data, is to quantify the growth of various human vocal tract structures and to define their type of growth, in order to explain their development in relation to the ones of the main structures of the head and the neck.

Another goal of this study is to assess sexual dimorphism (anatomical differences between males and females). Sexual dimorphism is an important issue in vocal tract growth since it could explain the differences in speech production between males and females. The age at which sexual dimorphism emerges is therefore important because it indicates the age from which the observed differences between males' and females' vocal productions could be due to anatomical differences, indicating that before the onset of sexual dimorphism, such differences could only be due to differences in the control of the oro-facial articulators.

Besides these two main issues addressed in this study, detailed knowledge of developmental vocal tract anatomy is a prerequisite in understanding how children learn to produce articulatory gestures with their own oro-facial apparatus and in understanding how the acoustic space for speech production is constrained during ontogeny. The overall growth of the vocal tract has important implications on how the acoustic space for speech production is constrained, since formant frequencies are, roughly, inversely proportional to the vocal tract length [START_REF] Fant | Acoustic Theory of Speech Production[END_REF][START_REF] Mol | Fundamentals of Phonetics II: Acoustical Modes Generating the Formants of the Vowel Phoneme[END_REF]. Since the detailed vocal tract growth is not known, it is not possible to predict the maximal acoustic spaces of infants and children from those of adults with a simple scale factor [START_REF] Fant | A note on vocal tract size factors and non-uniform F-pattern scalings[END_REF]. Thus, it is necessary to have precise anatomical data in order to understand the development of the acoustic space for speech production. An interesting step torwards the understanding of this relationship is the use of vocal tract growth models [START_REF] Goldstein | An articulatory model for the vocal tracts of growing children[END_REF][START_REF] Boë | Modélisation de la croissance du conduit vocal. espace vocalique des nouveau-nés et des adultes. conséquences pour l'ontogenèse et la phylogenèse[END_REF]. We believe that anatomical data, as presented in this paper, should improve the accuracy of such models, leading to a more detailed understanding of the anatomic-acoustic relationship during ontogeny.

Materials and methods

Subjects

Four X-ray images databases were used in the present study: the Denver, Iowa, Michigan and Oregon Growth Studies, which are available from the American Association of Orthodontists Foundation in the AAOF Craniofacial Growth Legacy Collection (http://www.cril.org/ aaof/aaof_home.asp). Measurements obtained from one of these databases (Denver growth study, 28 subjects) were already used for studying the ontogeny of hyoid and larynx de- scent in humans [START_REF] Lieberman | Ontogeny of postnatal hyoid and larynx descent in humans[END_REF].

These sagittal radiographs, which have been digitized, have been taken between 1931 and 1970 from healthy typically developing Americans. The populations covered by these different databases are uniform and can be grouped together.

A total of 68 people, 35 males and 33 females were followed longitudinally from 1 month of age to 25 years of age, and 15 radiographs were taken per individual, on average, over this period. For each radiograph, the age, sex, a code that anonymously identified the subject, and the resolution (in mm/pixel) are included with the data. Altogether, 966 lateral radiographs of the head and neck (496 for males, 470 for females) were used for the present study.

To ensure a continuity of data around birth, we added to this longitudinal database, 12 anatomical sections of formalin-fixed human fetuses, which were taken from the laboratory collection at the Department of Anatomy, Montpellier University [START_REF] Captier | Anatomy and growth of the fetal soft palate: A cadaveric study to improve its ultrasonographic observation[END_REF]. For each anatomical section, radiographs were performed in order to verify that the landmarks located on anatomical sections and on radiographs were comparable. The measurements are made on digitized images of these heads sectioned along the sagittal median plane. The sexes of these fetuses are unknown and their age is given in terms of amenorrhea weeks.

Landmarks

All measurements were made using CRANIOMAT, a software developed at GIPSA-lab under MATLAB® environment. Each image was calibrated using a scale visible on the radiograph or with the relative pixel/mm factor provided.

Six major landmarks, located manually on each radiograph and on each fetal anatomical section, were used in this study. These are Pr (prosthion, most anterior point of the anterior and inferior septum interalveolar maxillary central incisors), ANS (anterior nasal spine), PNS (posterior nasal spine), Ve (lowest point of the lower end of the soft palate), Ph (pharyngeal point, at the intersection of the occlusal plane and the pharyngeal wall) and Gc (glottis center, midpoint of the orifice of the larynx between the vocal folds along the anterior-posterior axis). The location of these landmarks is illustrated in Fig. 1.

Measurements of interest

In this paper, we present results for 4 main measurements of interest, which are defined as follow: (1) Hard palate length: Euclidean distance between ANS and PNS, (2) Soft palate length: Euclidean distance between PNS and Ve, (3) Pharyngeal cavity length: Euclidean distance between Ph and Gc, (4) Estimated vocal tract length (hereafter VTL). To give an estimation of the VTL in a rest position, we adapted a geometric model of the vocal tract (the VLAM model [START_REF] Boë | Modélisation de la croissance du conduit vocal. espace vocalique des nouveau-nés et des adultes. conséquences pour l'ontogenèse et la phylogenèse[END_REF][START_REF] Maeda | Compensatory articulation during speech: Evidence from the analysis and synthesis of vocal-tract shapes using an articulatory model[END_REF] to the subject-specific anatomy thanks to three main landmarks: Pr, Ph and Gc. The VTL estimation is given as the curvilinear distance from the glottis to the lips measured as the midline of this subject-specific model. The first 3 measurements are illustrated in Fig. 1, the VTL estimation is illustrated in Fig. 2.

Growth curves and statistical analyses

In order to compute growth curves for each variable, we used non-linear mixed-effect models, to take advantage of our unique longitudinal data set (under the R environment [START_REF] Hardcastle | R: A Language and Environment for Statistical Computing[END_REF], using the lme4 package [START_REF] Bates | lme4: Linear mixed-effects models using S4 classes[END_REF]). For each variable, we fitted different functions that describe the growth, so we used various non-linear functions, with increasing complexity: simple logistic function, third degree polynomial function, third degree polynomial function with a logistic function, double logistic function and a fifth order polynomial with logistic function. We performed comparisons among those different models using the Akaike Information Criterion (AIC, [START_REF] Akaike | A new look at the statistical model identification[END_REF]). For each fitted function, we considered the individual deviations of the parameters by introducing subjects random effects. Using a stepwise method, the optimal set of random effects was selected. Growth type is assessed for each variable thanks to the interpretation of the values obtained for the parameters.

As regards sexual dimorphism, its examination was done through to the comparison of the random terms obtained for males and females subjects.

Results

Overall growth of vocal tract structures

This section presents the quantitative results on vocal tract growth structures. In sum, these results indicate that, on average, the hard palate grows 22 mm from birth to adulthood, the soft palate grows only 12 mm from birth to adulthood, the pharyngeal cavity grows 55 mm, and the vocal tract length at birth is 80 mm and reaches the adult size of 175 mm for males and 155 mm for females. The population mean growth curves are shown in Fig. 3. Around those mean values, inter-individual differences exist, as well as differences between males and females. The analysis of sexual dimorphism is presented in section 3.4.

Growth curves

Among all functions that have been tested to explain growth, and for all measurements, the best model is the double logistic model, according to the AIC criterion (see section 2.4). The double logistic equation is:

f (t) = L1 1 + e -a 1 (x-x 1 ) + L2 -L1 1 + e -a 2 (x-x 2 )
in which t is time (loarithm of age), L1 is the value of the first plateau, x1 is the age of the first inflection, and a1 is the slope at this inflection. The meaning of parameters L2 , x2, and a2 are equivalent as thos for the first inflection.

To account for inter-individual variability, parameters L1, x1 , a1, L2, x2, and a2 were set as random parameters of the mixed-effects model. This accounts for the fact that there are inter-individual differences in the ages and slopes for the first and the second inflection, as well as for the two plateaus. One of the major advantages of the double logistic model is that the parameters are directly interpretable in terms of growth. By looking at the values of these parameters, we can induce which type of growth underlies each variable of interest. We can also assess sexual dimorphism by looking at the estimated values for the random parts of these parameters for both males and females. The growth curves of each vocal tract structure are presented in Fig. 3.

Growth types of vocal tract structures

The growth type of each structure was studied by looking at the values of the parameters of the double logistic model. For the hard palate, the growth is typically a somatic growth type, with two inflections, both substantial. For the soft palate, the growth is very rapid around birth and is very slow after 2 years. Its growth type can thus be characterized as being more neural than somatic. For the pharyngeal cavity length, the growth is very protracted and the first inflection is lesser than what has been observed for the other measurements. However, the second inflection is very substantial and happens quite late. Its growth is clearly somatic, with the particular fact that the growth at puberty is substantial. The growth of the VTL is a mixture of neural and somatic growths, because the whole vocal tract length depends on the dimensions of different structures, either having a more neural growth type (like the soft palate, and to a lesser extent, the hard palate) or having a more somatic growth type (like the pharyngeal cavity).

Sexual dimorphism

Sexual dimorphism is assessed by comparing the values of the parameters obtained with the double logistic model for males and for females. This analysis reveals that there is no sexual dimorphism on parameters L1, x1, and a1, for none of the four measurements studied here. In contrast, in all four measurements, there are a statistically significant sexual dimorphisms for the parameters of the second inflection L2, x2, and a2 (ttests, for p < 0.01). This indicates that the sexual dimorphism appears at puberty. No pre-pubertal sexual dimorphism can be put in evidence from the data, according to our analysis. A transversal analysis, in which we grouped data by one-year age groups, confirmed this finding. According to this transversal analysis, sexual dimorphism appears at 12 years of age for the pharyngeal cavity, and at 15 years for the vocal tract length.

Discussion

This study has quantified the growth of various vocal tract structures. Our results were compared to previous anatomical studies on vocal tract growth [START_REF] Goldstein | An articulatory model for the vocal tracts of growing children[END_REF][START_REF] Lieberman | Ontogeny of postnatal hyoid and larynx descent in humans[END_REF][START_REF] Fitch | Morphology and development of the human vocal tract: a study using magnetic resonance imaging[END_REF][START_REF] Vorperian | Anatomic development of the oral and pharyngeal portions of the vocal tract: an imaging study[END_REF], with which they are highly consistent in terms of measurements. However, this study also includes the analysis of inter-individual differences, thanks to the longitudinal data, and adds an analysis of sexual dimorphism that takes into account these differences.

As regards this particular issue, we found no evidence for a pre-pubertal sexual dimorphism. Even though the differences in vowel production between adult males and females are well documented [START_REF] Johnson | Auditory-visual integration of talker gender in vowel perception[END_REF][START_REF] Johnson | Speaker normalization in speech perception[END_REF], our results suggest that the observed gender differences in vocal production of young children [START_REF] Perry | The acoustic bases for gender identification from children's voices[END_REF] are likely to be due to differences in the control of oro-facial articulators. Indeed, it has been shown, for example, that for the production of /s/, girls as young as 4-5 years old have higher mean spectral frequencies than boys at the same age [START_REF] Kinsman | The relationship between genderdifferentiated productions of /s/ and gender role behaviour in young children[END_REF]. This is not the case for /S/, for example. This indicates that this difference in production is due to a difference in the articulatory control: If it would be due to a difference in anatomy, these differences would be reported for a large range of phonemes, which is not the case. These differences are very likely to be due to differences in the control of the tongue positioning, since it has been shown that adult females use a more anterior point of constriction than males while producing /s/ [START_REF] Fuchs | Do differences in male versus female /s/ reflect biological or sociophonetic factors?[END_REF]. This particular gender difference is explainable in terms of sociophonetics, but is really difficult to explain if one tried to explain this phenomenon in terms of anatomical differences between 4-years-old boys and girls.

To finish, these data could be used to improve vocal tract growth models, in order to better understand the articulatoryacoustic relationships during ontogeny. Some work has already been done in this direction [START_REF] Ménard | Articulatoryacoustic relationships during vocal tract growth for french vowels: Analysis of real data and simulations with an articulatory model[END_REF], and we believe that a more detailed model in terms of anatomy could lead to a better understanding of the constraints applied to the vowel acoustic space during ontogeny. It is also a necessary step in understanding how children learn to organize speech gestures in their own vocal tracts.

Conclusion

In sum, this study, the first using longitudinal data and fetal data, has quantified and qualified the anatomical changes of various vocal tract structures during ontogeny. It has been shown that different structures showed different growth rates and growth types, due to their belonging to different anatomical structures (skull, neck, mandible or face). The emergence of sexual dimorphism has been studied, for which it was shown that no prepubertal sexual dimorphism emerges from these data. According to these results, we believe that the differences observed in the vocal productions of young children would be due to differences in the control of oro-facial articulators, such that these differences cannot be explained by anatomical differences.

Figure 1 :

 1 Figure 1: Landmarks and measurements used in the study. The landmarks are shown in dots and the three measurements of interest (1: hard palate, 2: soft palate, and 3: pharyngeal cavity) are shown with lines, superimposed on an exemple of radiographic image.

Figure 2 :

 2 Figure 2: Vocal tract length estimation method. The contour of the articulatory model is superimposed to an exemple of radiographic image, adjusted to the landmark points Pr, Ph, and Gc. The VTL measurement of interested is indicated by the midline labelled 4.

Figure 3 :

 3 Figure 3: Raw data and fitted growth curves, four each of the four measurements of interest: (A) hard palate, (B) soft palate, (C) pharyngeal cavity, and (D) vocal tract length. The measurements for all subjects at all ages are shown as gray dots. The blue lines represent the population average growth curves. Measurements for individual subjects are shown with yellow dots, with their estimated growth curves shown with red lines. The vertical gray line represents birth.

Acknowledgements

The authors are grateful to the American Association of Orthodontists and Daniel Lieberman for providing access to the radiographic archives. This research was partly supportend by the French ANR project SkullSpeech.


Stephan Baumann
email: stephan.baumann@dfki.de

Melanie Dulong De Rosnay
email: melanie.dulong-de-rosnay@cersa.fr

Music Life Cycle Support through Ontologies

The focus of this paper is the exploration of ontologies as a means for knowledge sharing in music information retrieval scenarios. Our approach is intended to support the complete "life cycle of digital music" and focuses on the implications of a digital world for all the actors involved in the process of creation, consumption and modification of such entities. As a novelty we take care about legal aspects, digital rights management being heavily tangled in such scenarios. MPEG-7 and MPEG-21 vocabularies are considered as basic ingredients for our ontology which ensures in this way interoperability within the multimedia delivery and music research communities.

1.Introduction

"In the morning the alarm of Peters PDA gets off. He crawls out of the bed but he is still very tired since he had to burn the midnight oil to finish his project. The only thing that can help is the right music to get going. He grabs his PDA and says: "I need some fast Hard Rock music right now". Seconds later he listens to Ace of Spades from Motorhead. This motivating music helps him a lot to leave his house in time to drive to work. However after a couple of kilometres he finds himself in a traffic jam, which starts making him nervous. To calm down he grabs again his PDA. "I need some music to calm down" he says and listens immediately to songs from Sade, Phil Collins and Celine Dion. After a long days work he starts to prepare for an after work party in his favourite club. In order to prepare for the nice evening, again he grabs his PDA and says "Something funky". Only a wink later, he listens to music from Chaka Khan and Kool & the Gang. Tomorrow, Peter will try to compare his personal library with his friends' collection in order to discover new titles and build an original play-list for his girlfriend birthday party.

usual consumption. Moreover, he was able to lend some tracks to his brother who is a music teacher and reused them easily in educational material." Digital media access in a post-Napster world with respect of copyright and fair use may look like this [START_REF] Mulligan | Implementing Copyright Limitations in Rights Expression Languages[END_REF]. Since we have to foresee a multitude of different users in such scenarios providing the pure contents and a variety of different services, knowledge sharing among all actors of the value chain becomes a major issue. In this paper we describe our joint work about the combination of an MPEG-7 related ontology -which has been used in various music information retrieval scenarios -with an MPEG-21 oriented approach for online sharing and transactions of copyrighted work. In section 2 we will introduce the digital life cycle of a piece of musical work, section 3 describes the basic ontology supporting human actors and machines, section 4 is about our prototypical application and section 5 gives a conclusion and an outlook on future work.

Life Cycle of Digital Music

The life cycle of digital music begins during the creation period. The author needs to exchange work-in-progress samples within his creative community (other artists, potential producers) in a way enabling to date and attribute versions, collaborative contributions and protect the unreleased work. Once the work has been edited, authors and producers expect it to be disseminated, retrieved and distributed according to legal and contractual conditions, including derivative works conditions, copyright royalties sharing processing between rights holders and their local mandates (collective societies, intermediate service providers…) and event reporting on effective uses in respect of the end-user privacy. Music titles, albums, compilations, sound track for motion pictures and other derivative works may involve numerous contracts, making tracks use and re-use more complicated.

The task to retrieve exhaustively all different copyright owners and follow eventual rights transfer in order to ask for relevant entities authorisation, and share the royalties according to corresponding national laws and collective management, is time-consuming and burdensome. End-users expect to find a user-friendly access to the music they like. Convenient retrieval, sharing and modification of musical entities is directly related to the existence of meaningful metadata. The state-of-the-art approaches aim either at automatically extracting metadata from the audio material [START_REF] Allamanche | Content-based Identification of Audio Material Using MPEG-7 Low Level Description[END_REF] or using manually attached metadata from expert databases (www.allmusic.com) or voluntary work of user communities (www.freedb.org, www.gracenote.com ). Musical concepts and features may be described in standards such as MPEG-7 which simplifies worldwide exchange (e.g. for web services or autonomous agents). Cross-domain upper ontologies could be used to support extensions to music-related areas [START_REF] Hunter | Enhancing the Semantic Interoperability of Multimedia through a Core Ontology[END_REF]. For the future MPEG-7 enabled creativity tools (e.g. audio or MIDI sequencing software and compositional tools) could allow the author to add the intended metadata on-the-fly during the creative process. Coming MPEG-21 applications may also enable right holders to express, update and enforce rights conditions, and all users and terminals to interact with them.

Ontology to support Music Information Retrieval and Automated Rights Management in the Life Cycle of Digital Music

"An ontology defines the basic terms and relations comprising the vocabulary of a topic area as well as the rules for combining terms and relations to define extensions to the vocabulary" [START_REF] Neches | Enabling technology for knowledge sharing[END_REF]. In our application scenario we noted as terms the concepts of required knowhow in the music domain. The relations consist of several types, namely is-a and part-of relations are used quite often. Is-a-relations are used to indicate specializations of concepts (e.g. audio is-a media type, lyrics is-a text, remix is-a derivative work, author is-a rights owner) while partof-relations denote required parts (e.g. lyrics part-of song, member part-of band).

Legal requirements

The legal part of the ontology was elaborated in the context of MPEG-21 standardisation [START_REF]MPEG-21 Overview v5[END_REF] with respect to Rights Expression Language [START_REF]ISO/IEC FDIS 21000-5, MPEG-21 Rights Expression Language (REL)[END_REF] and associated Rights Data Dictionary [START_REF]ISO/IEC FDIS 21000-6, MPEG-21 Rights Data Dictionary (RDD)[END_REF] aiming at copyright domain knowledge representation and computed exploitation in further MIR applications associating DRM. As it would have been possible to build several ontologies, the composition of ours was deduced from the task it is designed for [START_REF] Bench-Capon | Task Neutral Ontologies, Common Sense Ontologies and Legal Information Systems[END_REF], i.e. expression of questions and decisions about copyright for Music Information Retrieval: licensing, infringement, and exception. Derivating requirements are:

use context description and self-categorization by all users, with a special target on non-lawyer users, and user-friendly update of Rights Expressions and use situations attached to a context and a work, allowing retrieval according to each use situation enforceability and validity in most national legal systems, including fair use respect [START_REF] Dussolier | Fair use by design in the European Directive of 2001: an empty promise[END_REF][START_REF] Dulong De Rosnay | Digital Right Management systems toward European law[END_REF] [START_REF] Borges | Conception of cognitive Interfaces for legal knowledge -Evolution of the JURISQUE project on the risks of avalanches[END_REF] as their understanding is related to external conditions such as the context. This diversity generates difficulties for the implementation of DRM systems. Indeed, it is important to express the conditions attached to a work's use with accuracy and flexibility.

The preliminary phase of our work was to study the state of the art of AI and law [START_REF] Valente | Legal Knowledge Engineering[END_REF][START_REF] Breuker | Legal Ontologies: A Functional View[END_REF][START_REF] Sartor | Judicial Applications of Artificial Intelligence[END_REF][START_REF] Visser | A Comparison of Four Ontologies for the Design of Legal Knowledge Systems[END_REF] for existing core legal ontologies (FOLaw, LRI) and legal ontology hooks within foundational or upper level ontologies [START_REF] Dolce | A Descriptive Ontology for Linguistic and Cognitive Engineering[END_REF].

Other domain ontologies with the same applicative scope were also used, i.e. Rights Expression Languages (RELs) and dictionaries as indecs [17], ODRL [START_REF]ODRL[END_REF], XrML [START_REF]XrML[END_REF] and IPROnto [START_REF] Ipronto | [END_REF]. Except the latter one, all projects start from use cases rather than from legal texts. The added value of the proposed methodology is to start from an expertise of the legal knowledge domain, defined as the intersection between copyright law, law for Information Technology and media law. This expertise aims at avoiding texts partial understanding or misinterpretations, as legal doctrine and case law knowledge enable to throw light on texts interpretation. Our reasoning process aims at modeling most music titles uses core with a special focus on re-use cases, the latter aspect being outside other projects' scope.

The ontology concepts and relations are being extracted manually in order to avoid misinterpretations, after legislative corpus automatic retrieval with syntactic parsers. Corpus semantic relations (hypernyms, hyponyms, meronyms, causality…) help to build relations between ontological concepts. Concepts are being linked to corresponding terminological database terms with extensive definitions based on national legislations and case law. Definitions update may be delegated to some trusted third party authority in order to respect balance between stakeholders. The third expression level being the user interface, selected terms and classes have to reflect simple applicative use cases (i.e. play, send, modify).

Music retrieval requirements

The starting point for the part of the ontology related to music retrieval was to model MPEG-7 ontology from scratch with an ontology editor and to add some few concepts, e.g. the lyrics. The connecting concept between the two main parts (legal, music retrieval) is the digital item. The main audio features which are used by our example application are the MPEG-7 descriptors for loudness, tempo and spectral features. Especially the options to import other know-how domains via importing RDF(S) files are important with respect to the ongoing developments of ontologies at different sites for different applications and in different formats. This problem has been described in the musical domain thoroughly in a recent publication of Pachet [START_REF] Pachet | A Classification of Musical Genre[END_REF].

A further difficult question is how to handle the acquisition of instances which represent the actual state of the "musical world". This will be an ongoing and dynamic process since "music never stops": new artists, new releases, the latest trends in genres, etc. pop up at different corners of the world and have to be assembled. The same issue is affecting Rights Expressions at two levels. Rights conditions might be updated by their authors or cancelled by a Court if inappropriate. Besides, legal concepts definitions are not internationally harmonized but depend on states competences. Similar works will receive different legal qualification and induce different remunerations according to the national jurisdiction they depend, requiring Rights Expressions local adaptation.

Prototypical Application for Mobile Music Information Retrieval

Several prototypical systems combining different external web services and internal music processing agents have been realized in our previous work [START_REF] Baumann | Using Natural Language Input and Audio Analysis for a Human-oriented MIR System[END_REF][START_REF] Baumann | Increasing consumer value in virtual music environments[END_REF].

Figure 3: Mobile MIR application

The actual mobile version follows again the multi-agent framework paradigm containing the described ontology as a means for intra agent communication as well as interfacing with external web services. In addition to the previous systems we intended to offer:

mobile access and interactive feedback to the recommendation agent

The mobility aspect was covered by a dense design of the website which can be displayed on a small-sized PDA screen. For the interactive feedback we decided to include a virtual joystick which can be easily accessed using the pen of the PDA. The recommendation agent uses a trimodal global similarity measure which is realized as a weigthed linear combination of three different local similarity metrics S = wso* Sso+ wly* Sly+ wst* Sst with -Sso : sounds-alike similarity -Sly : similarity of lyrics -Sst : similarity by style/cultural aspects

The position of the joystick has a direct influence on the individual weights, e.g.

center position: wso=0.33, wly=0.33, wst=0.33 -sound position: wso=1, wly=0, wst=0 -lyrics position: wso=0, wly=1, wst=0 -style position: wso=0, wly=0, wst=1

In the following three subsections some details about the computation of the local similarity measures will be given. For each of them the input are two entities representing an MP3-encoded audio file of a song with the lyrics attached as a plain ASCII text file and metadata information about the name of the song, album and artist. The output of each local similarity measure is within the range [0..1].

Sounds-alike similarity Sso

The automatic audio analysis recognizes song properties about loudness, tempo and timbral features. These features can be used for the determination of music similarity. For the extraction of basic features such as loudness and psychoacoustic features, we used mel frequency cepstral coefficients and a clustering approach to generate audio profiles [START_REF] Baumann | Music Similarity Analysis in a P2P Environment[END_REF][START_REF] Baumann | A comparison of music similarity measures for a p2p application[END_REF]. In order to perform a similarity computation based on the audio profiles we use both the Earth Moving Distance, as suggested in [START_REF] Logan | Mel Frequency Cepstral Coefficients for Music Modeling[END_REF] as well as a Gaussian Mixture Model as proposed in [START_REF] Aucouturier | Music Similarity Measures: What's the Use?[END_REF]. Even working with a standard Nearest Neighbor (NN) classifier delivered interesting results for cross-genre recommendations of music "sounding" similar.

Similarity of lyrics Sly

Here we use state-of-the-art document retrieval approaches. The top-level concept lyrics is broken down into a taxonomy of typical topics covered by mainstream music. In the future such handcrafted topic ontology may be supported by semi-automatic ontology learning through document clustering approaches. For the current experiments we focused first on the subsymbolic level of lyrics. In a Vector Space model, lyrics are represented as vectors. The dimension of the vectors indicate specific terms, the value of a vectors component indicates the number of times the respective term occurs in the lyrics to be represented. The similarity measure is the cosinemeasure, which computes the angle between two vectors. Roughly spoken, those lyrics, which share many relevant words, will have a high similarity. Typical results deliver similar songs from concept albums of the same artist (intra-album similarity, example 1) or cross artist similarity by topic (example 2).

Cultural similarity Sst

In order to compute cultural similarity we perform a Google search for reviews of the musical work of the artist under investigation. The first 50 pages are downloaded and preprocessed with a filtering stage to remove HTML formatting instructions and find the main textual part of each document. On these textual parts standard techniques from the field of Information Retrieval and Computational Linguistics are subsequently applied. As a result we achieve a cultural representation of the artist which is a vector representation containing the most relevant and discriminating terms and their weightings. On top of this vector representation the cosine measure is used to compute similarity between two entities. More details can be found in [START_REF] Baumann | Using Cultural Metadata for Artist Recommendation[END_REF].

Conclusion and Future Work

In this paper we have presented a framework supporting the life cycle of digital music using an ontology as a knowledge sharing and communication platform for human actors and agents. In our future work we will elaborate the applied automated rights management part of our proposition developing the concept of cognitive interface "taking into account a meta-knowledge implied in a situation of dialog with a view to adapting it to types of specific requests in a domain" [START_REF] Borges | Conception of cognitive Interfaces for legal knowledge -Evolution of the JURISQUE project on the risks of avalanches[END_REF], merging genre requests and legal requirements.

Figure 1 :

 1 Figure 1: Excerpt of the MPEG-21 related ontology supporting music retrieval and rights management aspects

Figure 2 :

 2 Figure 2: Excerpt of the MPEG-7 related ontology supporting music retrieval and rights management aspectsIn this way we were able to set up an initial ontology for further refinement and alignment with other existing

Acknowledgements

We wish to thank DFKI, CERSA, Medialive and Prof. Rousseau for supporting this work.


A second order Ordinary Differential Equation for the frequency domain Green function.

by Alain H. Clément alain.clement@ec-nantes.fr LUNAM Université, Ecole Centrale de Nantes, LHEEA CNRS UMR6598, 1, Rue de la Noë, 44300 Nantes, FRANCE The present work is developped under the usual assumptions of linear potential flow theory. We consider a source point Q (x , y , z ), and a field point Q(x, y, z) both lying in the lower half-plane (z < 0, z < 0). r is the relative horizontal distance, Z = z + z the vertical distance between the field point and Q 1 the image of the source point relative to the free surface (fig. 1). R is the distance

|QQ | and R 1 = √ r 2 + Z 2 the distance |QQ 1 |.
G ∞ (r, Z, iω) = 1 R - 1 R 1 + 2PV ∞ 0 k k -k 0 e kZ J 0 (kr)dk -2iπsgn(ω)k 0 e k 0 Z J 0 (k 0 r) (1) or G ∞ (r, Z, iω) = G 0 (Q, Q ) + G(r, Z, iω)
where k 0 = ω 2 , and PV means principal value of the integral.

This expression can be shown to be equivalent to Wehausen [START_REF] Wehausen | Surface waves[END_REF] formulation:

G ∞ (r, Z, iω) = 1 R + PV ∞ 0 k + k 0 k -k 0 e kZ J 0 (kr)dk -2iπsgn(ω)k 0 e k 0 Z J 0 (k 0 r) (2)
by using the identity :(R 1 )

-1 = r 2 + Z 2 -1 2 =
∞ 0 e kZ J 0 (kr)dk [START_REF] Abramowitz | Handbook of Mathematical Functions with Formulas, Graphs and Mathematical Tables[END_REF]. Eq (1) gives the velocity potential at point Q generated by a pulsating source of unit strenght located at point Q . The G ∞ function [START_REF] Clément | An Ordinary Differential Equation for the Green Function of Time-Domain Free-Surface Hydrodynamics[END_REF] is the basic mathematical tool used to solve diffraction-radiation problems in regular waves of frequency ω, and period T = 2π/ω. Time-domain -when the source strength is no longer a cosine function of time but a simple impulse, namely q(t) = δ(t) a Dirac function, then the Green function is given by

F ∞ (r, Z, t) = 1 R - 1 R 1 δ(t) + 2H(t) ∞ 0 √ ke kZ J 0 (kr) sin(t √ k)dk (3) or F ∞ (r, Z, t) = G 0 (Q, Q )δ(t) + H(t)F (r, Z, t)
with H(t) the Heaviside step function. Considering the velocity potential as the output of the fluid system with source strength as the input, it is established that the Green function of frequency domain eq.( 1) can be derived as the Fourier transform of the time-domain Green function eq.( 3), with the following convention and notations:

G ∞ (r, Z, iω) = F∞ (r, Z, iω) = F {F ∞ (r, Z, t)} = ∞ -∞ F ∞ (r, Z, t)e -iωt dt (4)
In [START_REF] Clément | A shortcut to compute time-domain free-surface potentials avoiding Green function evaluation[END_REF] [1], we have shown the integral part F (r, Z, t) of the above time-domain Green function to be the solution of an exact fourth order linear ordinary differential equation with polynomial coefficient,

r 2 + Z 2 F (4) -ZtF (3) + 1 4 t 2 -4Z F (2) + 7 4 tF (1) + 9 4 F = 0 (5)
where the notation F (n) holds for the n th derivative of F with respect to the time variable t. Among other applications, this ODE has been shown [START_REF] Clément | Using differential properties of the Green function in seakeeping computational codes[END_REF] to provide a good mean to speed up the inline computations of the Green function in time-domain BEM computational codes.

In this paper, we will show how to derive from eq.5 a similar ODE, but in the frequency variable, for the frequency domain Green function G(r, Z, iω).

Fourier transform of the time-domain ODE

Let us first introduce the auxiliary function S(r, Z, t) = H(t)F (r, Z, t) with H the Heaviside step function.

Taking into account the differential relation between the Heaviside and Dirac functions, i.e δ(t) = dH(t)/dt = H (1) (t), we establish the following relations by successive differentiation S = HF S (1) = δF + HF (1) S (2) = δ (1) F + 2δF (1) + HF (2) S (3) = δ (2) F + 3δ (1) F (1) + 3δF (2) + HF (3) S (4) = δ (3) F + 4δ (2) F (1) + 6δ (1) F (2) + 4δF (3) + HF (4) The time domain homogeneous ODE (5) obviously still holds when both sides are multiplied by H(t), leading to:

r 2 + Z 2 S (4) -ZtS (3) + 1 4 t 2 -4Z S (2) + 7 4 tS (1) + 9 4 S = (6) +δ r 2 + Z 2 F (3) -3ZtF (2) + 2 1 4 t 2 -4Z F (1) + 7 4 tF +δ (1) 6 r 2 + Z 2 F (2) -3ZtF (1) + 1 4 t 2 -4Z F +δ (2) 4 r 2 + Z 2 F -ZtF +δ (3) r 2 + Z 2 F

Left-hand side

As expected, the left hanfd side of ( 6) is the same as eq.5. Let's now take its Fourier transform

L = F r 2 + Z 2 S (4) -ZtS (3) + 1 4 t 2 -4Z S (2) + 7 4 tS (1) + 9 4 S (7)
By using the basic rules of Fourier transform for a derivative F f (n) (t) = (iω) n f(iω) , and for the product by a polynomial F {t m f(t)} = i m d m dω m f (iω) [START_REF] Debnath | Integral transforms and their applications[END_REF], and after re-ordering we get:

L = ω 2 4 Ŝ(2) -ω ω 2 Z + 3 4 Ŝ(1) + ω 4 r 2 + Z 2 + ω 2 Z + 1 Ŝ (8)

Right-hand side

For developping the Fourier transform of the right hand side of ( 6), we then apply the following relations derived from the fundamental property of the Dirac delta function, and integration by parts:

F {δ(t)f (t)} = +∞ -∞ δ(t)f(t)e -iωt = f(0) (9) F δ (1) (t)f (t) = +∞ -∞ δ (1) (t)f (t)e -iωt = -f (1) (0) + iωf(0) F δ (2) (t)f (t) = +∞ -∞ δ (2) (t)f (t)e -iωt = f (2) (0) -2iωf (1) (0) -ω 2 f(0) F δ (3) (t)f (t) = +∞ -∞ δ (3) (t)f (t)e -iωt = -f (3) (0) + 3iωf (2) (0) + 3ω 2 f (1) (0) -iω 3 f(0)
Then, after simple calculations and simplifications, the Fourier transform of the right-hand side R, is found to be expressed simply as:

R = 2 1 + Zω 2 (r 2 + Z 2 ) (10)

The complete frequency-domain ODE

From (1) and ( 3) is is clear that Ŝ(r, Z, iω) is nothing but the frequency dependent part G of G ∞ (r, Z, iω).

The ODE for G(r, Z, iω) can thus be formed now from its left hand and right hand sides, derived above, giving:

ω 2 4 G (2) -ω ω 2 Z + 3 4 G (1) + ω 4 r 2 + Z 2 + ω 2 Z + 1 G = 2(1+Zω 2 ) √ (r 2 +Z 2 ) (11)
So, for the frequency domain complex Green function G(r, Z, iω), the ODE is of order 2, logically, due to the maximum order 2 of the polynomial coefficients of the time domain ODE [START_REF] Debnath | Integral transforms and their applications[END_REF]. Similar 2nd order ODE can be derived for the gradient ∂G ∂r and ∂G ∂Z by applying straightforwardly the same method to the time domain ODE derived in [START_REF] Clément | An Ordinary Differential Equation for the Green Function of Time-Domain Free-Surface Hydrodynamics[END_REF] respectively for the gradient ∂F ∂r and ∂F ∂Z of the time domain Green function.

The initial conditions for the ODE eq.11 can be easily deduced from the developped expression of G in (1), leading to:

   G(r, Z, 0) = 2 √ (r 2 +Z 2 ) -i(0) lim ω→0 ∂ ∂ω G(r, Z, iω) = 0 + i(0) (12)
The results of a numerical check of this ODE (11) are shown on fig: 2 and fig: 3 were we have integrated it by a standard Runge-Kutta algorithm from ω = 0 to 4. (test case parmeters: r=2, Z=-1). Here all 3 terms of the differential equation are plotted independently, together with their sum, real part on the left, imaginary part on the right. The isolated dots show the same quantities (real and imaginary parts of the LHS of eq:11) calculated from the usual Green function routines of the BEM code AQUAPLUS [START_REF] Delhommeau | Amélioration des performances des codes de calcul de diffraction-radiation au premier ordre[END_REF] based on the classical series and asymptotic expansions for this function [START_REF] Newman | Algorithms for the free-surface Green function[END_REF]. An excellent agreement is observed for both real and imaginary parts.

conclusion

The Green functions of free surface hydrodynamics were shown to be solution of exact linear ordinary differential equations. This result, uncovered at the IWWWFB in Marseille (1997) for the time-domain Green function, is extended here for it's sister function in the frequency-domain. In both cases, theses results can be exploited to speed-up the computations of BEM based seakeeping codes. A lot of other applications will probably be discovered in further research works. The extension of these results to the case of finite water depth is still an open challenge.

Figure 1 :

 1 Figure 1: source and field point -layout and notations

Figure 2 :Figure 3 :

 23 Figure 2: components of the ODE -Real part