delivery a priority for the country and has done so using a publicly-owned and publicly-operated utility.

Post-revolutionary Tunisia presents STEG with some remarkable new challenges, however, not least of which will be its ability to democratize itself and work out new governance relationships with the state. STEG's status as a 'public' agency may also be in question, as neoliberal actors (internal and external) put pressure on the state to privatize and/or introduce stronger market-based operating principles in the electricity sector.

How these political dynamics will play out in a highly fluid national and regional context remains to be seen. What is clear is that STEG offers fascinating insights not only into the Tunisian revolution, but into the complex nature of corporatization and its ability to adapt (or not) to a more democratized regime.

This chapter provides a brief history of STEG, and reviews the company's main strengths and weaknesses as a public electricity provider over the past four decades. We summarize the current political transition in the country and its effects on STEG to date, followed by a discussion of (possible) future trajectories for corporatized electricity provision in Tunisia. Our analysis draws on our own extensive research on the electricity sector in the region over the past decade, combined with recent interviews with senior STEG managers, union leaders and regular union members since the January 2011 revolution, as well as representatives of the Department of Industry, funders and international organizations with projects linked to STEG, such as the European Union and the French Development Agency (AFD).

History of STEG

On the eve of independence in 1956, the distribution and production of electricity in Tunisia was in the hands of eight private companies. These companies provided electrical power to an estimated 100,000 urban residents. Total installed power was 100 MW, most of which was provided by the thermal plant of La Goulette (Tunis) and three smaller hydraulic units in the north of the country. The major cities of the centre and south of the country were supplied by diesel generators from dealers with their own distribution and production networks as well as their own tariff systems. This arrangement did not allow for any interregional connection. The provision of electricity was limited to a few hours in the day and to the big cities. It situation was similar for gas, which powered 25,000 customers located in the central part of the capital city.

After Independence, the government established a committee called the Tunisian Company of Electricity and Transport (1958) to oversee the operation of these companies. Four years later they were nationalized and the monopoly over production and distribution entrusted to STEG, a public industrial and commercial utility with legal and financial autonomy. It is currently under the supervision of the Department of Industry.

Tunisian political leaders have always considered electricity to be strategic economically, socially and politically, and set themselves the objective of universal access to all groups and geographical areas (STEG 2009, 30). Electricity has been seen as a touchstone of national development and improved living standards. The fact that this objective has garnered political support from across the country is telling in a context where politics has long been rife with regionalism and ethnic cleavages. In other words, STEG has played a major unifying role in Tunisia and helped to give the post-independence state a national presence.

Three major stages can be identified in the development of STEG. The first corresponds to large investments in the transmission network in the 1960s to connect cities and new industries to a national grid, as well as a standardization of voltage. The second stage, starting in the late 1970s, saw an expansion of electricity to rural areas, initially in agglomerated villages and towns of more than 100 households, and later in the 1990s to sparsely populated areas.

The third phase, since 2000, has been characterized by a slowdown in the connection of new users to the electricity grid and a shift toward gas distribution after large natural gas fields were discovered in the country. The extension of the gas network is now part of a strategy to reduce energy dependency on petroleum from neighbouring countries and to promote the use of this cheaper and more efficient energy source. STEG has prioritized gas distribution to cities with energy-intensive companies.

In 2012, on its 50th anniversary, STEG could be commended for having raised the urban rate of electrification from 21% to 99.5 %, and rural electrification from 6% to 99%. Installed power had reached 3,473 MW in 2010(from 100 MW in 1962), and STEG now has 30 times more subscribers (3,150,000) than when it began (STEG 2011).

Although the company still holds a monopoly over the transmission and distribution of electricity, production has long been shared with other actors. Already in the 1960s, 12% of electricity produced came from surpluses that industry generated for its own use and sold to STEG -initially a response to STEG's capacity shortfalls. Today this represents 8% of electricity produced.

Faced with growing energy demand and pressure from foreign actors to privatize, the Tunisian government also conceded a share of production in 1994 to the Carthage Power Company (CPC), which operates as an independent power producer on a 'build, own and operate' basis 3 . CPC provides 25% of the commercial electrical production in the country, on terms that are largely favourable to the private company because STEG commits to providing the gas required for generation and to buy all of the electricity it produces. However, according to the 2011 report of the National Auditor (Cour des Comptes 2011), CPC electricity production has fallen short of what is stipulated by the contract, forcing STEG to operate simple-cycle gas units which are very inefficient, contributing to a loss of over 38 million Tunisian dinar (TND) (approximately 19 million Euros). To make matters worse, the company has not settled for non-compliance with its production commitment, estimated at 14 million TND (Cour des comptes, 2011).

In general, however, STEG has managed to avoid the privatization thrust that affected other parts of the Tunisian economy with the introduction of structural adjustment programmes in the mid-1980s, and the same is true of other large public service companies such as SONEDE (drinking water), ONAS (sanitation) and urban transportation.

Contractualization = Corporatization

During our research for this paper, Tunisian interviewees were generally surprised by the use of the term 'corporatization'; a word which is absent from the vocabulary of reforms in the country. The term that is used is 'contractualization', which refers to a series of contracts signed between a public agency and the state but which nonetheless parallel the definition of corporatization used in this booki.e. the creation of arm's length publicly-owned and -operated agencies that are financially and managerially ringfenced from the state.

According to Ben Letaeif (1998) the introduction of contracts between the state and public enterprises began in the 1970s and picked up rapidly from 1987 onwards. STEG's contractualization is based on internal targets set for different STEG branches, and external contracts with the state. Jointly defined objectives encourage the autonomy of each branch, with control mechanisms in the form of performance indicators geared towards overall development plan targets.

More importantly, Ben Letaief (1998, 393) argues that contractualization has been used as a way of "inserting public companies into the logic of the market, and alignment of their management with private enterprises that are excessively focused on financial and commercial aspects." In the contract between the state and STEG 3 Equity in CPC was initially composed of Public Sector Enterprise Group Global from the USA (35%), Marubeni Corporation from Japan (32.5%) and Sithe Energies (based in New York but dependent on Vivendi in France, 32.5%). Source: http://business.highbeam.com/3882/article-1g1-60822964/tunisia-1st-ipp-rades. Today, its shareholders are BTU ventures and Marubeni (http://www.carthagepower.com.tn/actionnaires.php, accessed 24 April, 2012).

To be quoted as : Bennasr, A. & Verdeil, É., 2014. An 'Arab Spring' for for the period covering 1992-1996, for example, objectives assigned to "serving the public" remain vague, with "the search for financial balance…considered a priority objective" (contract 92-96, art. A VI Financial Strategy). The establishment of a policy of cost recovery "making the customer bear the economic cost incurred to the company" is particularly noteworthy, as is "the progressive elimination of preferential rates whose prices are not justified economically" (art. VII-1.1).

According to Ben Letaief (1998, 413), contractualization represents "the state as shareholder", but it has not been seen as a precursor to privatization, as has been the case with corporatization in other countries. In what follows, we analyze the contractualization of STEG and evaluate its performance as a public service provider. Some indicators point to a neoliberal bias, some reveal the organization's authoritarian roots, while others suggest a deep commitment to a broader public good. This seemingly paradoxical combination of values is not easy to explain, but this is the complex reality of corporatization in Tunisia. Understanding it may help sustain and expand progressive public electricity delivery in the country in the future.

Assessing STEG's performance

Access to Electricity

Access to electricity can be seen as a measure of social equity, particularly in geographical terms. Electricity grids often reflect structural inequalities on a national scale between urban and rural areas, and within cities. From this point of view, STEG has an excellent track record, with close to universal electricity access in cities and a connection rate of 99% in the countryside.

Connection of informal urban settlements has also been a strong focus for STEG. Since the 1970s, a strategy for slums has been part of a focus on restoration of older districts and neighbourhoods undertaken by the Agency of Urban Rehabilitation and Renovation (ARRU). STEG has taken part by rehabilitating old distribution networks to connect these households (e.g. Bab Souika-Halfaouine, the old city of Tunis) or by constructing new networks.

Pricing

Social equity can also be assessed in terms of the price of electricity. It is important here to distinguish between connection costs and electricity pricing. Before 2005, connection was billed to the subscriber at a price depending on installed power and distance to the nearest outlet, which was calculated by the number of poles needed to reach the newly connected building. As such it penalized low-consumption, remote households. To remedy this situation, STEG asked people who applied to split connection costs (although some households would still wait for a better-off neighbour to cover the costs of the initial connection before they subscribed).

To be quoted as : [START_REF] Bennasr | An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG)[END_REF] From 2005, a flat rate pricing was put in place, helping subscribers in peri-urban and dispersed rural areas. However, officials with the STEG union have argued that this system effectively subsidizes developers in urban areas and does not translate into reduced costs for consumers. Indirectly, this new pricing scheme has also encouraged the development of informal settlements near the network, since informal dwellers can share the cost of connections and the state cannot deny them access despite their 'illegal' situation.

The issue of electricity pricing has also been the subject of intense debate in Tunisia.

In 2005, a block tariff was introduced for low voltage consumers (65% of domestic subscribers) in an effort to subsidize the poorest householdsa model similar to that of the country's water sector. In practice, there are now three levels of pricing based on the amount of electricity used (less than 50kWh, 50-300 kWh, and greater than 300 kWh). Some of these gains are cancelled out by a municipal tax that penalizes small consumers, but an international comparative study based on 2009 rates found STEG's pricing of domestic subscribers to be relatively progressive (General Secretariat UPDEA 2009). It is also interesting to note that electricity pricing appears more equitable than that of water in Tunisia, which is proportionately more expensive in rural areas and for small consumers [START_REF] Sahtout | La recherche de ressources alternatives à l'eau potable urbaine : le cas du Grand Sousse[END_REF][START_REF] Touzi | Le service de l'eau potable en Tunisie[END_REF].

On the other hand, one area that has drawn complaints is tariff increases. STEG's contract with the government requires tariffs to be cost reflexivea policy called "vérité des prix" (truth of the price) in Frenchin an attempt to limit budget deficits.

From 2000 to 2010, price increases took place up to twice a year, averaging 5% annually at the same time as consumption has been growing (2% more per subscriber on average) (STEG 2011). 4 The fact that STEG also invoices consumers for the (unpopular) fees for public television channels does not help matters (Turki 2011, 181).

Trade union delegates say that STEG's pricing policy is not progressive enough, arguing that pricing for the upper block of consumption is insufficient, suggesting that industry should pay more. 5 It is also worth noting that subscribers unable to pay their bills receive tough treatment from STEG. After two unpaid bills, and if the amount is higher than 30 TND, an order of disconnection (coupon de coupure) is issued. To be reconnected customers must pay the full amount of the bill plus a reconnection fee of 17.70 TNDalthough in practice local party representatives can deal with this on a

To be quoted as :

Participation in decision making

Public consultation is not formalized at STEG but it has taken three forms. First, STEG's board of directors 6 includes union representatives who participate in decision making. On two occasions, the union has threatened to go on strike over partial privatization projects and sub-contracting (to collect unpaid bills and to ink a second concession for a thermal power plant), which led the management of the company to abandon those projects. 7

Second, although consumer participation is not formal practice, a sales management representative at STEG claims that his department regularly conducts large consumer satisfaction surveys. In addition, customer offices receive complaints and the company's website offers a forum to voice concerns with the service. There also exists a convention with the Organization of Consumers but it was associated with the ruling party under former-President Ben Ali, and was not in a position to act as an effective electricity watchdog.

STEG has therefore opened various channels for communication with end users but this has been done essentially in the spirit of a commercial relationship. STEG has not provided opportunities for deeper citizen engagement in shaping the utility's longterm objectives. Instead, citizen engagement has been ad hoc and highly dependent on the whims and objectives of the ruling party [START_REF] Chabbi | La réhabilitation des quartiers populaires en Tunisie : de l'intégration à la régulation sociale[END_REF][START_REF] Legros | La « refondation » des quartiers mal lotis de la banlieue de Tunis dans les années 1990[END_REF]. Since the end of Ben Ali's regime, consultation is undergoing transformation but it is too early to assess what the outcomes will be.

Relationships with private companies represent STEG's third mode of interaction, with client companies surveyed to measure satisfaction with the service. Large commercial customers in particular are asked to assess their needs and make suggestions for service improvement. In the post-revolutionary context, media have uncovered privileges of certain companies close to the regime (e.g. cement plants), and investigations are ongoing. 8 STEG has procedural safeguards against 6 Composed of nine representatives from various government departments (energy, agriculture, etc.), a state controller, two staff representatives (often from the union) and two members at large. patronage, but these will also have to be reviewed in light of the political developments of the 'Arab Spring'.

Quality of service

Service quality is a major concern of STEG's and is integrated in its policy of contractualization. Indicators relate to the quality of the electricity service as well as STEG's service to subscribers. The latter is based on customer complaints and comments received via a call centre and website. As for technical performance, data show that the number of incidents per 100 km of network has decreased from 2.55 in 2000 to 1.75 in 2010 (largely caused by exogenous factors such as lightning, birds, etc), although indicators vary significantly from one district to another. Major incidents such as the blackout of 2002which interrupted the broadcasting of the World Cup football finalhave not been repeated.

Another indicator measures time required to deal with troubleshooting. According to STEG data, time needed varies from one to two hours on average in urban districts, with the best troubleshooting times being 38 minutes (although delays of more than five hours have been recorded in more remote districts). STEG also measures the performance of its distribution network and the satisfaction of its customers by looking at the number of complaints per 10,000 subscribers, which has been in sharp decline and stands roughly at 70, in line with international standards.9 STEG estimates that connection delays vary from one week to a month. Data show a degradation of the service between 2002 and 2010 as the connection time increased in some districts: from 17 days up to one month in the north of Tunis; from 10 to 39 days in the north of Sousse; from 12 to 28 days in Kairouan; etc 10 . It appears that this extension of waiting periods is linked to the strong demand in some areas (suburbs of major cities, tourist areas), technical connection problems, and insufficient equipment, some of which has to be imported. In this regard, the National Auditor has criticized STEG on several occasions when it lacked spare parts because of bad planning (Cour des Comptes, 2011).

Financial efficiency STEG's supervisory authorities (Directorate of Energy, Department of Industry and Mining Resources) monitor its financial efficiency closely, as do donors and funding agencies. Two major objectives are assigned to the company (Tunisian Republic 2010, 13):

• Take appropriate measures to enable the company to achieve positive financial results and to self-finance the investment programs of the sector;

To be quoted as : • Take the necessary measures to enable the company to reach the required levels of financial ratios and to attract external funding.

Among the main demands is optimization of fuel consumption, which accounts for roughly 75% of the cost of electricity production for STEG. Thus, the company has been transitioning to technologies of combined cycle power plants, which are more efficient. This change has not come as fast as expected however. The 2011 report of the National Auditors pointed out several problems in this regard. While STEG planned to establish two simple-cycle units in Ghannouch (Gabes) and in Sousse starting in 2005, major delays raised costs significantly and blocked the transition to cleaner energy. At the Ghannouch plant works were delayed until 2011, while deadend negotiations with private partners forced STEG to sign contracts for the establishment of two gas units even though gas consumption would amount to double the energy needed to operate simple cycle units, thereby defeating the optimization purpose. Delays have also been recorded with regard to wind turbine installation due to opposition from expropriated landowners (Cour des Comptes 2011).

More recently, fuel price hikes have prompted STEG to request tariff adjustments from the government. Indeed, under the terms of the contract the state has to compensate for the gap between the cost of production and the selling price by earmarking operating subsidies for the public utility. But despite such subsidies STEG experienced recurring deficits in 2007, 2008, 2010 and 2011. STEG is now forced to look for sources of energy with more stable prices, such as nuclear power, which may be installed by 2023 11 , and renewable energies, which are already being developed. In both cases, production costs would appear to be higher than current costs to STEG, thanks to gas subsidies from the state.

Despite these concerns, STEG is recognized by international donors as rigorous in its management and control of debt. State guarantees for STEG also allow it to access sovereign borrowing rates. Its principal lenders are the European Investment Bank, the Arab Fund for Development, the African Development Bank, and the French Development Agency, often in the form of co-financing.

Despite a generally positive assessment of the financial management of STEG, funders do point to some shortcomings in the internal financial information system that make it difficult to analyze performance by sector (gas and electricity) or by branch.12 Funders are also pushing for greater correspondence between costs and prices, and are concerned with the suspension of the tariff adjustment policy that came with the revolution (more on this below).

Accountability

There are no clear laws in Tunisia defining the type of data that public utilities must provide or the form of public consultation they should offer. The public can access information on STEG's activities (including from its website), and its contract requires the publication of annual reports, including its financial situation (costs, profits and losses), but much of this data is in summary format requiring strong technical and accounting skills to understand, and internet access is not widespread in the country. STEG is no different than other major Tunisian public companies in this regard, however.

Quality of workplace

As of 2010, STEG employed approximately 9,200 employees, which was set to expand to 12,000 by the end of 2012, making it one of the largest Tunisian companies, public or private. Before 2011 there had been a slight decrease in the number of employees, even though production and demand were increasing.

The profile of employees has changed in recent years as well, with more staff having qualifications for the "maîtrise"13 level (currently at about 56%), reflecting the increasing need for qualified personnel. A significant decline in the number of lowerskill employees, on the other hand, reflects a process of outsourcing of certain tasks (e.g. security, cleaning). There are still very few women employed (14.3%, much lower than the national employment average of 25% for 2011) and they mostly occupy administrative positions (STEG 2011).

Employment in STEG promises good pay in comparison to other sectors in Tunisia, and good job security. Remuneration is set by a salary scale and raises are based on seniority and collective agreements. In 2007-2010, the annual salary increases were between 5-7.5% while inflation stood at 3-4% (STEG 2011). There exists a system of performance bonus which represents a maximum of two months' salary. It is unclear when it was introduced and how it is actually assigned.

There are also professional development opportunities in the form of training, benefiting some 4,500 staff in 2010, and STEG offers social benefits such as medical

To be quoted as : [START_REF] Bennasr | An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG)[END_REF] coverage and free electricity (10,000 kWh per year for executives and 5,400 kWh per year for other workers, which is set to be raised14 ).

After the Revolution

The 2011 Tunisian revolution has forced radical changes on STEG. The new government and the Tunisian population are demanding more transparency, challenging the company's technocratic model of operation. In some cases, mistrust has led to refusals of payment. More broadly, in a context of requests for greater social justice and redistribution, Tunisian public companies, including STEG, are being asked by the state to contribute more to progressive change, breaking with the rigours of the past. These changes raise questions about the sustainability of the autocratic and heavily subsidized growth model that has characterized STEG until now.

Financial turmoil and new charges

Even before the revolution, STEG was facing increasing non-payment of bills, but this has risen dramatically since January 2011. In the first month following the revolution, an estimated 25% of users were refusing to pay. 15 Despite a gradual regularization of the situation, unpaid sums amounted to 304 million TND in 2011 (compared to 160 million TND in 2010) accounting for 12% of revenues [START_REF] Kapitalis | Tunisie. Les impayés de la Steg s'élèvent à 213 millions de dinars[END_REF]STEG 2012).

According to one STEG official, 44% of unpaid sums are from households [START_REF] Kapitalis | Tunisie. Les impayés de la Steg s'élèvent à 213 millions de dinars[END_REF]). STEG's trade union, however, blames other state actors for losses, arguing that unpaid bills from municipalities account for 63% of lost revenue, against just 15% for households. 16 It has also become evident in the post-revolutionary era that favours were granted to the members of the ruling clan, including the Presidency 17 . This informationpartly true and partly exaggeratedhas fed into public mistrust of STEG. Conversely, there is also a fear from some commentators that warn of a possible deterioration in the performance of the company, in a scenario "à la Libanaise" where power would no longer be available at all times (Moalla-Fetini 2011).

Whatever the reasons, unpaid bills have weakened the company's financial position, particularly in light of rising production costs due to global fuel price hikes. There has also been no tariff increase since July 2010. 18 Government has granted STEG heavy subsidies to compensate for both unpaid sums and rising production costs but these do not completely cover the deficit nor guarantee future sustainability.

Regardless, the general public continues to ask for lower electricity rates. In this context, both the electricity union and management have indicated that they would like to eliminate the invoice's flat taxes to help consumers better understand the actual real price of electricity. A general price rise appears excluded for the moment.

The revolution has also introduced significant changes in human resource management policy at STEG. In an effort to fight unemployment, the new government has tasked all public companies with hiring new graduates. According to figures from September 2011, 700 new recruitments had been completed at STEG after the change in government, especially in executive positions. In addition, employees previously involved in sub-contracting are being reinstated as STEG employees. This process is on-going and aims to create 1200 administrative jobs for young graduates at middle and senior levels, and some 2000 lower-skilled positions such as cleaners and security guards. It is anticipated that total staff levels will reach some 15,000 people by the end of 2013, but it is unclear how the new payroll and parallel reduction in subcontracting will affect the budget.

Evolution of political attitudes toward STEG

A second major question raised by the new political context is that of a possible change in the government's position with regard to the public status of STEG. According to some analysts this is not a concern, with the Tunisian revolution seen as a reaction against neoliberal policies imposed by international institutions [START_REF] Hibou | Le moment révolutionnaire tunisien en question : vers l'oubli du mouvement social ? Dossiers du CERI[END_REF]. Most company executives19 seem opposed to privatization, with one senior official noting that, in the short term at least, "government will not let the bird go before knowing how to control it because after that you cannot catch it". 20 The STEG union reaffirmed its opposition to privatization in its union assembly in March 2012, and an anti-privatization stance has also been taken up by the General Union of Tunisian Workers (UGTT), which emerged as a major political force in the social struggles of 2011.

To be quoted as : [START_REF] Bennasr | An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG)[END_REF] However, some observers argue that if the current government does not develop an explicit position on public versus private ownership of public utilities, there is a chance that Islamists and reformist parties might not be hostile to liberalization policies. In August 2012, following power cuts which disrupted water supply in several regions and indirectly caused one casualty in a hospital lacking alternative power, the Prime Minister made harsh comments about the management of STEG. It fuelled a controversy the union and the government about its alleged will to privatize the utility (Colonna Waleski 2012; Espace Manager 2012; Tunisie Numérique 2012). Furthermore, aid conditionality could force a change in management style for public companies, particularly if the deficit continues to grow.

One area where privatization is de facto on the agenda is with renewables. STEG had to accept the decision of the Ministry of Industry and Commerce to create a renewable energy subsidiary (STEG-ER) in May 2010, of which it only owns a 35% share, while the other shareholders are private industrial companies, consulting firms and banks. STEG-ER can study, build and operate wind farms or solar plants and is responsible for the implementation of the Tunisian solar plan, beginning with the planned construction, with the assistance of the Japanese government, of a concentrated solar plant in the Tunisian south (El Borma). Furthermore, a 2009 law on energy management authorizes and encourages the self-production of electricity from renewable energy by industrials, and requires STEG to buy back their surplus21 . However, no such project has been implemented to date, due to flaws in the regulation's design and lack of financial incentives according to representatives of the National Agency for Energy Management and from the GIZ. 22 In 2012, new measures were under study to ease the implementation of renewable project, including small Independent Power Producers.

As a result, energy diversification has involved the liberalization of the electricity sector and the emergence of private actors competing with STEG. On-going projects such as the Desertec Project and the Mediterranean Solar Plan reinforce pressures in this direction [START_REF] Moisseron | Le plan solaire méditerranéen : un projet de l'Union pour la Méditerranée[END_REF]. The upcoming construction of new power plants (thermal or wind turbines) and a high-voltage power line from Cap Bon to Italy, to supply the Italian market, will require STEG to adjust over the longer term as welleven if negotiations are currently at a standstill.

Toward more decentralized and participatory governance? STEG, as with all public Tunisian companies, is characterized by centralized technocratic management. As mentioned previously, users have no role in decisions on major developments in the company. But with the revolution came renewed pressure for transparency, and investigations into a number of scandals and cases of bad management. The public debate around the new constitution also featured arguments in favour of greater decentralization, particularly regarding policy planning regional development. But to date these requests have not been addressed by the members of the Constituent Assembly. In sum, no concrete proposals addressing the sectorial management of public utilities have been issued and are not set to be on the agenda for some time.

Reflections and Lessons Learned

Since its creation, STEG has operated as an autonomous public company. Since the early 1990s, the relations between STEG and the state were defined by a contractual agreement that incorporated some measures associated with corporatization, particularly by emphasizing demands of cost reduction and financial efficiency. This policy has been accompanied by the privatization of certain activities, most importantly electricity generation.

Overall, STEG's performance is satisfactory, particular in a regional context. STEG has managed to meet set objectives, most notably the near universalization of access, including poor urban neighbourhoods and rural areas. STEG has also managed to meet growing energy demand of households and industry, and was able to secure international funding at an affordable rate thanks to its solid financial management and state backing. Electricity tariffs have remained relatively cheap, responding to social development needs and making the country more attractive for industry. Finally, lacking local fossil fuels and with rising global fuel prices, Tunisia has put in place a policy to control energy consumption and to diversify toward renewable energies. The fact that the Tunisian revolution has not generated widespread demands for improved access to infrastructure, and in particular to electricity and gas, points to STEG's overall good performance.

Three main factors may explain the utility's success. First, there exists a relatively strong public ethos in Tunisian service utilities, despite the fact that companies such as STEG have been pursuing efficiency through new management techniques such as greater flexibility and financial autonomy of branches. A culture of technological innovation has enabled them to cope with the challenges of extending the network across the territory and improving energy efficiency. Importantly, these management changes have been made without just blindly replicating logics from the private sector (individualization of remuneration, performance incentives for executives, etc). The contractualization policy has helped STEG meet its financial objectives and allowed the identification of performance indicators that it can use to justify subsidies for the development of certain technologies or unprofitable investments (such as the electrification of rural areas).

Second, contractractualization has preserved the economic and social development objectives of the company. Staff are proud to belong to a company dedicated to social progress. To be sure, STEG has not been immune to vested interest groups close to the former regime (some corrupt, some more noble, such as implementing presidential programs in poor urban or rural areas thereby contributing to legitimizing the dictatorial regime of Ben Ali) but at least the company seems to have offered resistance to privatization projects and sub-contracting that would have directly benefitted Ben Ali's clan, as happened in other economic sectors in the country (Hibou 2006).

Third, STEG's overarching objective was initially to foster national integration and social cohesion in the name of development. The state gave STEG the means of achieving its objectives, particularly for network development programs in the informal rural and urban areas, as well as through very substantial subsidies on the price of gas and on tariffs. By making the electricity tariff a major political issue, the state shielded STEG from criticism on that front.

The strict financial management policy followed by STEG until 2011 had, however, resulted in a significant casualization of employment for groups of less qualified workers that are now sub-contracted. This situation has led to a sharp polarization within the workforce. But the situation has now changed, with STEG having agreed to regularize the situation of contractual workers and sub-contractors by integrating them within the company at the request of the post-revolutionary government. It is yet to be seen how this process will unfold and whether it will impact on the efficiency of the company.

What is more problematic is the continuing heavy reliance on direct and indirect subsidies from the state, which has increased further due to spiking fuel prices and problems with non-payment of bills since the revolution. To date, the state's plan to alter its policy of subsidizing electricity is to push towards more renewable energies. Pressures from international financial institutions could radicalize that trend via private sector participation. Debates also continue regarding the best ways to target social pricing, with the risk of fuelling tensions among socio-economic groups, as has been the case with pricing policies in the water sector [START_REF] Touzi | Le service de l'eau potable en Tunisie[END_REF].

Tunisian citizens tend to overlook the technical performance behind STEG's historical success, and are quick to point to its mistakes. One challenge therefore is to raise public awareness of the conditions that make possible fair and equal electricity services. In a context where these conditions are rapidly changing, STEG will have to involve citizens in redefining these objectives.

  Bennasr, A. & Verdeil, É., 2014. An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.case by case basis. It is unclear whether the contractualization policy has made enforcement of such rules stricter. Since the revolution, non-payment has grown so sharply (see below) that the government temporarily issued more flexible rules to recover payments without disconnecting.

  To be quoted as :Bennasr, A. & Verdeil, É., 2014. An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.

7 Interviews with representatives of the union of STEG in December 2011. 8 Source : interview with the union's delegates, December 2011. Several stories about embezzlement involving relatives of former President Ben Ali in STEG projects have been leaked in the press (African Manager 2012; Tiwinoo 2011).

  [START_REF] Bennasr | An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG)[END_REF]. An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.

  [START_REF] Bennasr | An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG)[END_REF]. An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.

	11 The nuclear project is still being assessed, despite the recent Japan nuclear disaster. Since the revolution, a
	debate has been underway in the press: see for instance Sghaïer, Malak. 2011 march 26, « Le nucléaire est il

encore une alternative attrayante pour la Tunisie? » La Presse de Tunisie,. http://www.lapresse.tn/25032011/25464/le-nucleaire-est-il-encore-une-alternative-attrayante-pour-latunisie.html. And « La question énergétique en Tunisie », Blog de l'association Cahiers de la Liberté, 28/8/2011, < http://cahiersdelaliberte.org/blog/?p=293 > (consultation le 21 décembre 2011)

To be quoted as :

  . An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.

  To be quoted as :Bennasr, A. & Verdeil, É., 2014. An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.

  . An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.

  To be quoted as :Bennasr, A. & Verdeil, É., 2014. An 'Arab Spring' for Corporatization? Tunisia's National Electricity Company (STEG). In D. MacDonald, ed. Rethinking Corporatization: Public Utilities in the Global South. London/New York: Zed Books Ltd, p. 88-106.

Our own calculation according to data from STEG 2011. The rise in consumption comes from the fact that more than 95% of Tunisian households now own a television, against 87% in 1984; 92% own refrigerators (against 49.6%),

57.5% own a washing machine (against 10%) and 14.6% now own an air conditioner (against 0.9%) (STEG household survey, 2009, summary tables provided by STEG for our survey).5 Interview with STEG's union officials, December 2011.

STEG, Department of Audit (Contrôle de gestion), data nicely computed at our request, march 2012.

Interviews with several funders representatives, Tunis, September 2011. The National Auditor also recognizes such shortcomings (Cour des Comptes 2011).

The workforce is divided in three categories : workers, "maîtrise" (supervisory staff) and executives.

Interview with several STEG's representatives, September 23, 2011. Such quantities oversize by large the average consumption.

Interviews with STEG's high ranking executives, April and September 2011.

Interview with the delegates of the union of the company, 22/12/2011.

A 2% increase for residential consumers and 8% for commercial and industrial ones has been implemented in September 2012 (Business News, 2012).

Out of 10 senior executives we met for interviews, none seemed to back the idea of privatization. Only a high ranking executive at the General Directorate of Energy mentioned the usefulness of privatization although he noted that the current experience with CPP in Rades was not fully convincing.

Abdelmoumen Ferchichi, Director of Electricity, Gas and Energy Efficiency, General Directorate of Energy, Ministry of Industry and Technology (formerly Industry and Commerce), interview, 22/12/2011.

Bylaw 2009Bylaw -2273 on the 28th of September 2009 on the tariff of transporting and buying electricity.


Filippo Rebecchi

Marcelo Dias De Amorim

Vania Conan

Adaptive Mobile Traffic Offloading

Keywords: Mobile data offloading, delay-tolerant networks, re-injection strategies

Cellular operators count on the potential of offloading techniques to relieve their overloaded radio access networks. In this paper, we propose, design, and evaluate a re-injection strategy to finely control the opportunistic distribution of popular contents throughout a hybrid mobile network. The idea is to use the infrastructure resources as seldom as possible. Unlike existing techniques that bind re-injection to statically defined objective functions, our proposal adapts to the current network topology. This turns out to be particularly effective in highly dynamic scenario, where clustering prevent contents to diffuse properly. We assess the performance of our strategy by re-running a realistic large-scale (more than 10,000 nodes) vehicular dataset to disseminate contents under different tolerances to delay. The results show significant savings in the infrastructure load between 55% and 63%.

Introduction

The recent boom in the smart devices market calls for efficient offloading strategies, as the global mobile traffic is expected to increase significantly in the near future [START_REF]Cisco Visual Networking Index. Global mobile data traffic forecast update[END_REF]. When many co-located users are interested in the same contents, it is possible to benefit from their mobility to shift a portion of the traffic from the primary (cellular) channel onto an alternative (terminal-to-terminal) channel, so to alleviate the load on the operator's cellular infrastructure by reducing redundant traffic.

We propose an adaptive re-injection based offloading scheme to efficiently distribute popular contents to a multitude of mobile users. The strategy adapts to the heterogeneous individual mobility pattern of nodes and to the current evolution of the dissemination process. The motivation behind this work is that this heterogeneity in mobility is responsible for a stepwise evolution of content dissemination, alternating between flat zones (plateaux) and steep periods of diffusion, as we will show in Section 2. The proposed algorithm detects the formation of plateaux in the content diffusion evolution, and, if needed, adaptively re-injects additional copies in the system to finely control the pace at which contents are disseminated. To this extent, the concept of a persistent feedback channel, connecting mobile users with a central offloading coordinator, becomes instrumental, allowing at each instant the infrastructure operator to track the content dissemination status and to anticipate appropriate re-injections.

We investigate the efficiency of the proposed scheme by mimicking a service in which a content, supposed of general interest, must be distributed to a multitude of users within a given maximum reception delay. In our evaluation, we employ a realistic large-scale vehicular trace derived from multiple fine-grained traffic measurements in the city of Bologna [iTE]. We compare our solution with an oracle (unrealistic, but considered only as a benchmark), as well as other offloading strategies based on static objective functions. The results display that the proposed algorithm substantially outperforms existing objective function-based offloading strategies for any considered delay tolerance, reducing by more than half the infrastructure load. Even more importantly, we also show that our approach performs very close to the oracle.

Stepwise epidemic diffusion in real datasets

We plot in Fig. 1 the evolution of the epidemic diffusion for two different datasets : the small-scale Rollernet dataset, composed of 62 nodes [TLB + 11] and the already mentioned large-scale Bologna dataset, composed of more than 10, 000 nodes [iTE]. To trigger the diffusion, the infrastructure injects a small number of initial copies to random nodes at t 0 , monitoring how the diffusion of the message progresses through subsequent direct contacts. A node that has received the message is considered infected, while a node that has not yet received the content is sane. The instantaneous ratio of nodes infected I(t) ∈ [0, 1] follows a stepwise pattern, alternating between plateaux (flat areas) and periods of heavy infection (steep areas). Plateaux correspond to periods during which the dissemination does not progress, as no sane node comes into range of the already infected nodes. This phenomenon is intrinsically related to the heterogeneity of contact patterns. If the contact process of nodes were Poisson homogeneous and stationary, the epidemic diffusion in the network would follow the logistics equation shown by Zhang et al. [START_REF] Zhang | Performance modeling of epidemic routing[END_REF] -the resulting curve would not exhibit any plateau, which is in contrast with our observation.

To catch the heterogeneity of patterns, we adopt a Marked Poisson Process model, in which the meeting times of any two nodes (i, j) is Poisson with rate λ i j = λ • p i j [START_REF] Carreras | A framework for opportunistic forwarding in disconnected networks[END_REF]. The inter-contact times T i j are thus independent exponentials with parameter λ i j , while matrix C = (p i j ) captures the patterns of contacts between nodes. In the homogeneous case, C is the identity matrix, i.e., all nodes can see each other with the same probability. Let S be the set of nodes infected at any given instant of the dissemination process. We are interested in the random plateau duration T p S during which the dissemination does not progress (nodes in S do not meet any other node from S). Looking at the set of links between nodes in S and its complement, one can see that T p S = inf i∈S , j∈S T i j . By Poisson calculus, and noting the cut value ∂S = ∑ i∈S , j∈S p i j , we find that T p S is an exponential random variable with parameter λ • ∂S . The expected plateauing duration, once set S has been reached, is thus (λ • ∂S ) -1 . This argument shows that T p S is directly related to the structural properties of the contact matrix C, providing a natural connection between the community structure of the contact graph and the progression (or lack of progression) of the opportunistic dissemination process. This motivates our further investigation of adaptive offloading that re-injects copies whenever the diffusion evolution runs into a plateau.

3 Re-injecting copies under rare encounters Overall operation. We consider a publish-subscribe information system, where users subscribe (unsubscribe) to the service upon entering (exiting) the interest area. A small subset of users receives the content through the cellular channel at t 0 . The content is disseminated opportunistically to encountered nodes via direct ad hoc communications. Whenever a node receives content from a neighbor, it acknowledges its reception using the infrastructure network, forming a feedback loop in the system. This simple mechanism allows monitoring the evolution of the content dissemination process, consuming at the same time very limited resources as acknowledgments are relatively lightweights compared to the expected size of content messages. The coordinator continually estimates the infection ratio, and may decide to re-inject additional copies of the content in order to boost the diffusion. When the maximum delivery delay D approaches, and the time left is equal to the time P required to send the message through the infrastructure, the system enters into a panic zone and pushes the content to all uninfected nodes in order to guarantee total dissemination.

When to re-inject copies ? Re-injection decisions are driven by a derivative-based algorithm. The algorithm needs to keep in memory a short snippet of past infection ratio values. Each content has an associated tracker that stores the evolution of the infection ratio for a temporal sliding window of size W (i.e., at time t the values that will be considered are the ones between [t -W,t]). The size of the sliding window trades off how far in time the algorithm looks back and dictates the reactivity to sudden changes in the infection ratio. At evaluation time, the offloading coordinator performs a forward difference quotient on the instantaneous infection ratio I(t) that approximates to a discrete derivative :

∆ I (t) = I(t)-I(t-W ) W , t -t 0 ≥ W, I(t) t-t 0 , t -t 0 < W. (1)
Note that I(t) is not monotonically increasing, since nodes may exit the simulation area at any time. ∆ I (•) approximates the slope of the infection ratio and is one of the parameters that influence the re-injection decision. Re-injection of additional copies of the content occurs whenever the discrete derivative ∆ I (•) is below a ∆ lim threshold computed, on the fly, as the ratio between the fraction of sane nodes and the time remaining before entering the panic zone. This is the reason why a steeper slope is needed when time gets closer to panic zone or the infection ratio lags (different from when we are at the beginning of the infection process).

Formally speaking, we have ∆ lim (t) =

1-I(t)

(D-P)-(t-t 0 ) . As a final step, the injection rate r inj (t) is computed as a piecewise function, depending on the ratio of the current ∆ I (t) value and the ∆ lim threshold :

r inj (t) =      c, ∆ I (t) ≤ 0, c 1 -∆ I (t) ∆ lim (t) , 0 < ∆ I (t) ≤ ∆ lim (t), 0, ∆ I (t) > ∆ lim (t), (2)
where c ∈ [0, 1] is a clipping value used to limit the overall amount of re-injected copies in the case of negative values of ∆ I . Finally, r inj (t), which represents the percentage of uninfected nodes that need to be targeted, is multiplied to the number of uninfected nodes to find the number R (t) of copies to re-inject at t :

R (t) = ⌈(1 -I(t)) × |N(t)| × r inj (t)⌉, (3)
where |N(t)| is the instantaneous number of nodes subscribed to the content update.

Evaluation and results

Evaluation scenario. We consider a traffic information service, where a central entity periodically issues a new content to be delivered within a maximum delay D. A single content is active in the system at a time.

Possible contents of interest include popular geo-relevant data, such as traffic and roadworks alerts, public utility information, geographic advertising or the distribution of software updates. To evaluate our strategy, we use a large-scale vehicular mobility trace, representing the city of Bologna (Italy), and consisting of 10, 333 nodes [iTE]. In the simulator, we employ a simple contact-based ad hoc MAC model, where a node may transmit only to a single neighbor at a time. Transmission intervals are deterministic, and depend only on the message size and the link data rate. We set cellular downlink and uplink bit rates to 100 KB/s and 10 KB/s, respectively. The bit rate for the ad hoc link is set to 1 MB/s. The size of each content update is set to 100 KB. The size of ack messages is 256 bytes, as they carry very little information (content and node identifiers). We heuristically tune the parameters of the algorithm, using c = 0.05, and W = 5 s in our evaluation. Finally, the panic time duration P is set at 1 s.

Alternative strategies. We compare our algorithm with two baseline strategies : "infrastructure only" (Infra) and "connected-component oracle" (Oracle). In the Infra strategy, there is no offloading at all, and the infrastructure represents the only means of distributing content. In the Oracle strategy, the offloading coordinator has a non-causal picture of the ad hoc connectivity of the entire network (unrealistic but useful to provide an upper bound on performance). We also compare our strategy with Push-and-Track, which relies Results. The derivative re-injection strategy performs very well in terms of reduced infrastructure load, saving between 55% and 63% of traffic for different message delays against Infra, as plotted in Fig. 2. In addition, our strategy pays only a small penalty compared to Oracle. It also always obtains better performance than static objective function-based strategies from [WLL + 12], thanks to its adaptive behavior. Although Derivative and Oracle show more or less the same trend, this result is achieved through two completely different strategies. On the one hand, Oracle exploits the perfect knowledge of the connectivity status in the network, pushing the content to very specific nodes. On the other hand, Derivative has a much less complete, and slightly out of sync, view of the system, and employs its smart re-injection algorithm to guess when additional copies of the content are required. Note also that Oracle presents always larger confidence interval. This is linked to the mobility and turnover of nodes : the resulting connectivity changes in time influencing the Oracle prediction performance.

• • • • • • • • • • • • • • • • • • • • • • • Derivative Static Linear Static Slow Start Oracle
A mobility and connectivity agnostic framework such as ours is less sensitive to this issue.

Conclusion

In this paper † we first described the stepwise behavior of the epidemic diffusion in real-life opportunistic networks. To obtain efficient offloading in such a context, we proposed a strategy that adapts to the varying opportunistic dissemination evolution by re-injecting additional copies only when needed. By analyzing this proposal on a large-scale vehicular dataset, we confirmed that it consistently does better than static objective-based offloading strategies, performing very close to an oracle. Future work includes evaluating our strategy on other (synthetic and real) scenarios and implementing the system in a real testbed.

FIGURE 2 :

 2 FIGURE 2: Offloading efficiency for the considered scenario. Different maximum reception delays for messages are considered. 95% confidence intervals are plotted.

  on static objective functions [WLL + 12]. To be as fair as possible, we consider Push-and-Track's objective function that gives the best result for the considered scenario (namely linear and slow start).

		0.65
	Offloading Efficiency	0.55 0.6
		0.5
		30	60	90	120	150	180
					Delay (s)


François Henry
email: francois.henry@ineris.fr

Philippe Marchal

Jacques Bouillard

Alexis Vignes

Olivier Dufaud

Laurent Perrin

The Effect of Agglomeration on the Emission of Particles from Nanopowders Flow

This paper suggests an original method to evaluate the possible emission of particles from a nanopowder submitted to a shear stress in dense phase and the resulting degree of agglomeration of the particles released. The method is based upon the monitoring of the rheological signature of the nanopowders, thanks to a powder rheometer. As a function of the increasing shear rate, the powder flow will evolve from the newtonian state (dense powder) to the coulombian state (dense rheofluidified phase). If the shear rate is high enough, the powder will be set in suspension and the kinetic state (a leaner dense phase submitted to particles collisions) will be reached. The shear stress in this state is dependent on the particle or the agglomerate diameter for cohesive powders, which can be then calculated from rheograms. Carbon black and silica nanopowders have been tested and compared to other experiments carried out on non cohesive glass beads microparticles, chosen as reference. For the different glass beads powders, the average value of their "agglomerate" diameter is 12% different of the primary diameter, indicating agglomeration of less than two particles. Nanometric agglomerates were found to be of hundred micrometers diameter. That is in line with the high tendency of the nanoparticles to agglomerate. This work can be used to evaluate the current safety tests, such as Hartmann's tube or 20 L sphere apparatuses, to verify whether the standard equipment for microparticles is suitable for the use of nanoparticles. This is linked to research projects like NanoSafe 2.

Introduction

The increase of the use of nanotechnology in research and in industry has led to evaluate the risks related to the nanomaterials. As specified in the Recommendation of the European Directive in 2011, a nanomaterial is a material, which has been formed accidentally or has been manufactured […], whose at least 50 % of the particles have one or more dimensions between 1 and 100 nm. The risk assessment of nanopowders implies the evaluation of the risks linked to powder materials at the nanometric size. Indeed, the toxicity and the inflammation and explosion risks are directly affected by the reactivity of the powder and its dispersion in a carrier fluid (air, water...). But nanoparticles tend to easily agglomerate [START_REF] Mishra | Palladium nanoparticles decorated graphite nanoplatelets for room temperature carbon dioxide adsorption[END_REF], leading to modification of reactivity, dispersion and toxicity of the powder by the modification of the surface properties. This study will focus on the effect of agglomeration on the emission of particles from nanopowders flows. Due to agglomeration, the nanopowder will be composed of agglomerates, whose size depends on the material and on the interaction forces involved. When submitted to a shear, the nanopowder will then be able to emit agglomerates and the monitoring of the rheological signature of the powder is a way to characterize their size and the solicitation necessary to emit them.

The agglomeration effect

Two particles, whether micro or nanometric are submitted to attractive and repulsive forces. Agglomeration occurs when the attractive forces are predominant and the smaller the particle size is, the higher these forces are. This explains why agglomeration plays an important role for nanoparticles. According to ISO TS27687 2008 an agglomerateagglomerate is a collection of loosely bound particles or aggregates or mixtures of the two where the resulting external surface area is similar to the sum of the surface areas of the individual components. The standard adds that the forces holding agglomerate together are weak forces, for example Van der Waals forces, as well as simple physical entanglement. The terms agglomerate and aggregate are often assimilated, but as also explained in ISO TS27687 2008, an aggregate is made of particle comprising strongly bonded of fused particles. As a consequence, aggregation is often considered as a non-reversible phenomenon. Agglomerates are brittle structures, which can be broken down and rebuilt depending on the strength of the external solicitations. They can be described by the number and the arrangement of the particles, which they contained.

Physical characteristics of an agglomerate

The number of particles within an agglomerate, nagg, is linked [START_REF] Gmachowski | Calculation of the fractal dimension of aggregates[END_REF] by Equation 1to the diameter of gyration d g of the agglomerate. d g is a mathematic concept equal to the root mean square distance between each particle of the agglomerate and the centre of gravity of this one.

(1) d p is the diameter of each particles. [START_REF] Hess | On the hydrodynamic behaviour of colloidal aggregates[END_REF] proposed, as explained in Equation 2, a relation between the diameter of gyration and the diameter of the sphere circumscribed on the agglomerate, d agg .

/

(2) D f , the fractal dimension, and k f , the structure factor, are two parameters describing the sphericity of the agglomerates, and as a consequence are an information about the arrangement between the particles within the agglomerate. k f is a coefficient between 0 and 1 and D f between 1 and 3. The closer to 3 the fractal dimension will be, the more spherical the agglomerate will be. The structure factor is given by Equation 3 [START_REF] Gmachowski | Calculation of the fractal dimension of aggregates[END_REF].

1.56 1.728 / 0.228 (3)
The inner porosity of an agglomerate can then be linked to d agg and n agg according to Equation 4.

(4)

The agglomeration stress

As explained in ISO TS27687 2008, the particles within an agglomerate are linked with weak forces: Van der Waals, electrostatic, capillary and magnetic forces. For dry suspension and particles without dipole moment, the interaction forces can be limited to the first two ones. Van der Waals forces are inversely proportional to d p ², although electrostatic forces are inversely proportional to d p . As a consequence, Van der Waals forces will be predominant for short distance and will ensure cohesion within the agglomerate. [START_REF] Debrincat | Charaterisation of inter-particle forces within agglomerated metallurgical powders[END_REF] proposed an agglomeration stress, defined by Rumpf, depending on Van der Waals forces and on the agglomerate porosity, as explained in Equation 5.

²

(5)

Figure 1: Measurement cell [START_REF] Madariaga | Characterization of impregnated particles via powder Rheology[END_REF] 3. Nanopowder rheology

Description of the powder rheometer

The experiments have been led with a powder rheometer, which applies shear within a measurement cell.

An induction motors supplies a torque and an optical sensor measures the angular rate. Both parameters are respectively proportional to the shear stress and the shear rate. In this paper, the evolution of shear stress versus shear rate has been monitored. The powder-powder shear is applied with a four blades vane device and baffles within the cell avoid a powder-tank shear on the inner surface of the cell.

The cell, described in figure 1, is submitted to mechanical vibration, with variable frequencies and amplitudes. The vibrating device has two objectives in the case of this study. On first, it allows to induce a Brownian motion within the powder, in order to access to all the spatial configurations of the particles. Indeed, the rheological properties are dependent on the way the powder is loaded and the assurance of the ergodicity of the system is necessary to have an average of these rheological properties. Secondly, in the case of nanoparticles, the strength of the powder within the cell can be high enough to avoid flowing at low shear rates and shear stress is then too high to be measured. The vibrations allow the powder to flow at low shear rates.

The three states of flow

A powder submitted to an external solicitation, as a shear rate, can be described by different states. Silica powder flows like a liquid if it is slightly poured, whereas the powder will behave as a gas if it is highly agitated.

The rheological approach is a good way to follow these behaviours. As shown in figure 2, the state of flow of the powder will then change with the increasing shear rate. The newtonian state describes a state of a dense powder (similar to a pseudo solid). The coulombian state corresponds to a dense rheofluidified phase (similar to a viscous liquid) and the kinetic state to a less and less dense phase submitted to particles collisions. The newtonian state corresponds to a state in which the viscosity tends to a constant value. This is the case when the shear rate is much lower than the critical shear rate . In the same way, when the shear rate is higher than , the shear stress tends to a constant value . This is in accordance with the inverse proportionality of the viscosity in frictional (or coulombian) state. This evolution of the viscosity in newtonian and coulombian states is figured by Equation 6 [START_REF] Marchal | Elements of Statistical Physics applied to the Rheology of non-cohesive Granular Media : The Quicksand Castle Model (QCM)[END_REF]:

η η (6)
At kinetic state, the shear stress increases again and is dependent on the square of the shear rate and on the agglomerate diameter. A first evaluation [START_REF] Andreotti | Granular medium; between fluid and solid[END_REF] is Equation ( 7) :

⁄ ² (7)
e 0 and e app are the porosity of the compact powder and the apparent porosity. The principle of d agg calculation from rheological data lays on the use of the transition regime between coulombian and kinetic states. In Equation 7, in order to calculate d agg , it is necessary to evaluate the apparent porosity, the agglomerate density and the shear rate and stress. Before the kinetic state, the apparent porosity does not change, whereas it is decreasing when the powder is setting on suspension. This value is linked to the inner porosity of the agglomerates and to the total porosity e b (porosity inter-and intra-agglomerates), following Equation 8. The compact powder porosity has been evaluated to the random close packing, 0.36 [START_REF] Lochmann | Statistical analysis of random sphere packings with variable radius distribution[END_REF].

1 (8)
Moreover, knowing that the agglomerate porosity and density are linked, the agglomerate diameter d agg can be expressed in Equation 9.

⁄ 1 ⁄ 1 (9)

Experimental results

Experimental protocol

The experiments have been conducted with nanometric and micrometric powders, whose properties are presented in table 1. Four nanopowders are presented in this paper: three carbon black powders, with particle diameters of 25, 30 and 330 nm (Corax N115, Printex XE2 and Thermal Black, DEGUSSA) and a hydrophilic silica powder, made up of 12 nm particles (Aerosil A200, DEGUSSA). The powder is charged in the rheometer cell and the volume of shear powder V b is 54.4 cm 3 . During each test, the evolution of the shear stress versus the shear rate is monitored. The values of shear rate and stress at the limit between coulombian and kinetic states are then taken down.

In order to compare the values for the nanopowders, other rheological tests have been conducted with micrometric glass powders with diameters of 0.33, 0.5, 0.8 and 1 mm, which are not agglomerated.

Rheological behaviour of the tested powders

Equation 10 can be used on first for glass beads. In this case, the agglomerate density will be null and the agglomerate diameter must be equal to the particle diameter. Table 2 presents the values of agglomerate porosity and of the shear stress and rate at the limit between coulombian and kinetic state.

The values of the "agglomerate" diameter are on average 12 % lower than the primary diameter, confirming that the particles do not agglomerate and considering that these values are strongly dependent on e 0 , which is generally given with experimental errors.

For the tested nanopowders, e agg must be calculated in order to access to the value of d agg . In regard of Equation 8, the agglomerate porosity is linked to the apparent porosity. A hypothesis has then been made: knowing that each powder is vibrated before the shear test in order to avoid the effect of the load in the cell, it is estimated that the apparent porosity of the nanopowder is equal to the apparent porosity (and the total porosity) of the glass beads powder. As a consequence, an average of e app for the nanopowders is 0.425.The agglomerate porosity and diameter can then been calculated. An observation with an optical microscope of 25 nm carbon black, as shown in figure 4, presents agglomerates from 416 to 850 μm. In table 2, the value of d agg is 704 μm. Knowing that this value, in comparison with glass beads, can vary with a small fluctuation of the initial porosity, it can be concluded that the microscopic observation is in the same order of magnitude as the theoretical calculation. It is all the more difficult to compare with microscopic observations since these tests tend to apply a stress on the powder, which can change the size distribution. Finally, assuming that Van der Waals forces decrease when the particle diameter increases [START_REF] Fortes | Particle aggregation and the van der Waals forces in gas-solids fluidization[END_REF], the agglomeration stress for the different nanopowders has been calculated. It appears that 30 nm carbon black and silica agglomerates are the more brittle. It must not be interpreted as an agglomerate diameter inverse dependence of the agglomeration stress. Indeed, for two agglomerates with the same inner porosity, the highest one will be the more brittle one. In the case of this study, 30 nm carbon black and silica agglomerates are the more brittle, due to the high porosity of these agglomerates.

Conclusions

The effect of agglomeration on the emission of particles from nanopowders flow has then been studied with the use of a powder rheometer. Depending on the mechanical solicitation, the powder follows three different flow states. The first two states, newtonian and coulombian, depend on the cohesion of the particles and the third state, the kinetic state, is dependent on the size of the agglomerates, which are emitted. This size is defined as the diameter of the sphere circumscribed on the agglomerate. The agglomerate diameter and porosity are two characteristics, which allow defining the strength of an agglomerate. The agglomerate stress decreases with the increasing diameter and porosity. The values of the shear rate and stress at the limit between coulombian and kinetic states allow calculating the agglomerate diameter. The method has been used on first for micrometric glass beads powders, which cannot be agglomerated. This diameter must then be equal to the particle diameter of the glass beads. The results give a difference of 12 % between the calculated and particle diameters, which is in accordance with the hypothesis made on the initial porosity of the compact powder. Assuming that the porosity intra-agglomerates for nanopowders is the same as the apparent porosity of the tested glass beads, the agglomerate diameter for carbon black and hydrophilic silica nanopowders have been calculated. The physical characteristics of the agglomerates, which are emitted by the mechanical solicitation of the rheometer, are then defined and their agglomeration stress can be calculated. This stress is highly dependent on the inner porosity and the agglomerates are all the more brittle that they are porous. This work is then a method to assess the state of agglomeration for suspensions of nanoparticles submitted to a rheological shear stress. The safety tests with apparatuses such as Hartmann's tube and 20 L sphere use nozzles to suspend the powder, which is then submitted to shear. It is essential to estimate the effect of these nozzles to the particle-size distribution in order to confirm or not the values of the explosion characteristics actually displayed in literature for nanoparticles.

Figure 2 :

 2 Figure 2: The three flow states

Figure 3 :

 3 Figure 3: Shear stress versus shear rate for glass beads powders and nanometric powders

Table 1 :

 1 Material and bulk properties of the tested powders

				c.b.	c.b.	c.b.	silica	glass	glass	glass	glass
				25 nm	30 nm	330 nm	12 nm	0.33 mm	0.50 mm	0.80 mm	1 mm
	material density (kg.m	-3 ) 2,050 2,350 1,830	2,200	2,700	2,700	2,700	2,700
	sheared mass (g)		21.6	7.32	42.3	2.61	84.0	84.2	87.4	91.2
	bulk density (kg.m	-3 )	397.1 134.6 777.6	47.98	1544.1	1,547.8	1606.6 1,676.5
	total porosity			0.81	0.64	0.57	0.98	0.43	0.43	0.40	0.38

Table 2 :

 2 Material and bulk properties of the tested powders

		c.b.	c.b.	c.b.	silica	glass	glass	glass	glass
		25 nm	30 nm	330 nm	12 nm	0.33 mm	0.50 mm	0.80 mm	1 mm
	σ f (Pa)	154	35.6	178	5.04	168	203	206	204
	γ (s -1 )	160	287	100	193	198	170	90	60
	e agg	0.66	0.90	0.26	0.96	0	0	0	0
	d agg (µm)	704	361	668	234	323	414	720	813
	n agg (*10 9 )	14, 768 1, 575	2.12	7, 168	-	-	-	-
	agglomeration stress (Pa) 3, 536 636.8 1, 532	575.6	-	-	-	-
	Figure 4: Optical microscopy observation of 25 nm carbon black


Guy Marlair
email: guy.marlair@ineris.fr

Alpha-O Diallo

Wassila Benaïssa

Alexis Vignes

Lysiane Blanc

Christophe Len

Developing Dedicated Methods and Tools for Safe Use and Processing of Key Chemicals in Biorefining

The emergence of biorefining, as the key concept of the future biobased economy is announced as the ultimate concept in many concerned industrial R&D roadmaps. Therefore, this paper proposes an insight of some safety related issues, as often underscored part of sustainability evaluation. From recent and still on-going research performed by the authors focusing on the appraisal of materials and process hazards in the context of biorefining, a brief review of recent achievements obtained by the authors in terms of the development of appropriate methods and tools aiming at promoting safety management in the related facilities are given. Both material and process driven safety issues are dealt with in the examples reported. Perspective on future related work in relation with the topic is brought in conclusion.

Introduction

As soon as in 2006 and soon after the emergence of the biofuel industry of first generation (bioethanol, biodiesel), the importance of biorefining as a versatile concept was revealed wordwide. Signs of such a major evolution of the agro-industries are the publication in 2006 of the first edition of a book dedicated to biorefineries edited by B. Kamm (2006) and published by Wiley, or the establishment of the task force 42 inside the International Energy Agency. Since that time significant EU-funded as well as private R&D activities have been performed, as the collaboration initiative on biorefineries called Star-Colibry that ended to two major deliverables clearing visions and R&D roadmap for a fully mature model in 2030 (Lugel, 2011). Whereas lack of sustainability has often been recognized, for various reasons like competition with food and feed, land use change issue, lack of energy efficiency, or poor carbon footprint, the relationship with sustainability and industrial safety remains unclear and in many cases, safety criteria being often considered as implicitly met through simple fulfilment of legal requirements from existing regulations or by recording level of incidents or worker injuries years after years. Such a practice does not allow anticipating the identification of emerging safety issues at early stages of development of more and more complex biorefineries (see Fig. 1) nor facilitate better introduction of inherently safer principles. In reality, errors in safety management may compromise the three pillars of sustainable development as major incidents would clearly impact the environment, may lead to business disruption and temporary and permanent unemployment. In addition, the integration of green chemistry is showing great expectancy in the biorefineries of the future [START_REF] Clark | The integration of green chemistry into future biorefineries[END_REF], also to serve better sustainability. When remembering that at least four of the 12 green chemistry principles claim for safety targets, one cannot ignore the importance of safety goals and thus must be proactive in promoting safety management. These are reasons why authors of this paper are working on the development of dedicated tools and risk assessment methods that aim at promoting sustainable development of biorefining towards better consideration of safe handling and use of chemicals and safer innovating processes. The paper focuses on some of the initiatives recently taken by the authors in that direction, consolidating the idea that biorefinery-dedicated tools are indeed highly desirable to promote a biobased economy [START_REF] Hass | Towards the development of a Training Simulator for Biorefineries[END_REF]. [START_REF] Marlair | Booming development of biofuels for transport, is fire safety of concern[END_REF] and some other rare contributors have illustrated the reality of hazards in the entire value chain of biofuel production of first generation. There is now doubt that the development of biofuel driven advanced biorefineries will require a detailed look of safety issues for multiple reasons. These may come from the development of new biofuel components or as a result of the promotion of more efficient processing of biofuels integrated in biorefineries for terrestrial applications. The climate change issue is also leading to fast development of potential other use of biosourced fuels, such as in the aviation industry. With regard to this latter aspect, INERIS recently contributed to 1st order evaluation of bio-jet fuel component candidates moking up just agreed jet A1 alternatives in the framework of the Alfa-bird. EU-funded project, either processed after biomass gasification by Fisher-Tropsch conversion and post processing, or though hydro-treatment of vegetable oils or fats. Whereas no highly challenging issue was found regarding safety on the supply chain of those new fuels, process safety was not actually examined (see Figure 1) due to competitiveness aspects, however collaboration with one late partner of the project underlined some unexplained results deserving more in depth analysis (Le [START_REF] Nevé | Alternative jet fuels: effect of a fuel change on aircraft fire safety[END_REF]. Some advanced fuels potential was also examined briefly during early phase of this project, like the one of 2.5 DMF (see Figure 2). As also confirmed by [START_REF] Salzano | Emerging risks in the biodiesel production by transesterification of virgin and renewable oils[END_REF] previously, recent joint research effort by INERIS (F) and CERL (Canada) also recently confirmed that emerging risks may still emerge from the conventional production of 1G biofuels by catalytic transesterification of oils (Janès et al, 2012). Recent move in the regulation regarding the use of maritime fuels might also trigger new perspective of use of biofuels in this other sector, and that would also deserve some focus on safety issues.

Qualifying new biofuels components and related value chain safety

Collecting and organising appropriate safety data on key biorefinery products in a user-friendly mode

Considering the full value chains relying on biorefining, chemicals and feedstock materials in modern biorefineries are quite diverse and numerous. They encompass various agro-resources like algae, green biomass materials like switchgrass, many oil containing plants, lignocellulosic rich crops like miscanthus, not to forget all types of biobased residues. In addition, other chemicals of interest are solvents, reactants, catalysts, including biocatalysts, fertilising and crop curing agents, cleaning agents, as well as numerous processed materials like commodities, building block chemicals and high value added chemicals and biomaterials, not neglecting feed and food ingredients. Significant efforts have been done in the past by public agencies like ADEME (F), DOE (USA) and IEA task force 42 (Intl) (Ed Dejong, 2012) to screen potential of commodity platforms and high value added molecules of the future that are likely to drive the market development. Top 50 to top ten lists of those chemicals have been established comprising many organic acids, precursors of biopolymers, furanic derivatives like furfural or 2.5 DMF, chlorinated intermediates, and so on. We currently anticipate according to our current review on conventional and emerging safety issues to consider that no less than 200-300 chemicals would deserve scientific-sound collection and organisation of safety data to serve basic hazard identification in the context of modern biorefining, although many of those chemical and materials are not brand new ones. The need to develop additional more specific databases may also arise from the need of predictive tools like QSPR models, that require consistent database for their pertinent development, see next section of this paper. This is for instance the case at least for two families of chemicals that are considered with increasing interest, namely furanic compounds (as precursors for biopolymers capable of replacing PET or as biofuel components or ionic liquids (ILs), that are experimented as solvent serving biomass fragmentation or biofuel recovery. Experimental work recently performed to check basic information like flash points of less than 10 chemicals show us that direct use of safety data sheet may in some cases be misleading, due to errors, or generalisation of existing data in the literature that does not correspond to technical grades of the chemicals in actual use.

For those reasons, INERIS is currently promoting an interactive and user-friendly database, entirely dedicated to collecting, storing and documenting safety related data on key materials in modern biorefineries, with the main objective of supporting the health and safety engineer with adequate information, brought in the appropriate context. The current version of the database include safety related data about 150 materials distributing among the following categories: a) agro-resources, b) building block chemicals or commodities, c) high value added chemicals or materials issuing secondary biorefining operations, d) biofuel components, e) solvents and catalysts. Some 30 properties are focused in the database including physical properties, thermodynamic data, data regarding flammability, explosivity, reaction to fire data, reactivity/thermal stability. In addition, the link with the included materials within the existing biorefinery value chain is documented as far as possible (e.g. designation of the process making use of the material as a solvent...). Level of reliability is also addressed, distinguishing home measured data from 4 codified levels of reported information: 1) data picked up in usual handbooks, 2) MSDS, 3) non evaluated web sources, 4) predicted values obtained by use of commercial softwares (e.g. Component Plus). Instruction for use in the database for its use and further development is also implemented.

Developing adequate predictive tools of properties and selecting the right testing

The pertinent development of high added value chemicals often requires screening processes to consider optimised choice of processed materials. This must be done considering regulatory needs, functional objectives of target chemicals (this is true for e.g. derivatives of furan, ionic liquids (ILs), oil crop derived fatty acids...). In such a case, accessing safety data for the whole family considered is unrealistic, either because to being too much time-consuming or even because this is simply not feasible due to unavailability of test samples. Based on early pre-examination of existing correlation aiming at assessing complete heats of combustion of combustible materials like the Boie formula [START_REF] Marlair | An analysis of some practical methods for estimating heats of combustion in fire safety studies[END_REF] and pioneering experience developed for a while by INERIS to develop QSPR models for predicting phys-chem hazard related data [START_REF] Fayet | Predicting explosibility properties of chemicals from quantitative structure property relationships[END_REF], INERIS has started to address the phys-chem safety issues pertaining to ILs, substances that have the remarkable property to be intrinsic ionic media in the liquid phase below 100°C (like imidazolium, phosphonium based ones). Phys-chem hazards for ILs have been a long time denied (Diallo et al, 2011[START_REF] Marlair | An introduction of safety issues in the field of biorefining[END_REF] or underscored. The first output of this specific research effort is the qualification of 5 out of the 18 identified empirical correlations allowing quite reasonable predictions of theoretical heats of combustion of ILs, working as a first order indicator of combustibility issues that may pertain to those chemicals depending on the context of use. Thanks to the on-purpose development of a database of some 50 ILs belonging to 5 main subcategories [START_REF] Diallo | Revisiting physico-chemical hazards of ionic liquids[END_REF], a specific QSPR model developed according to OECD principles for the prediction of the complete heat of combustion has also been set, anticipating the potential need to adjust the model versus time according to the promotion of new subcategories of ILs in the context of biorefineries.

Figure 3: Methodology targeting the appraisal of the full spectrum of physico-chemical hazards of ILs

The design of this tool is part of the development of a more comprehensive and fully dedicated methodology targeting the appraisal of the full spectrum of phys-chem hazards of ILs, encompassing not only combustibility and flammability issues, but also thermal stability, incompatibility issues, corrosivity to metals or polymers, see Figure 3. This work is largely justified, not only because this family of chemicals is nearly infinite [START_REF] Binnemans | How to select the best ionic liquid for a given application?[END_REF] but chiefly by the fact that the behaviour of ILs reveal in many cases to depart significantly to conventional liquid solvents in the manner they may trigger a hazard of phys-chem nature. Inadequate testing is also sometimes observed and also need to be identified. As an example, by no case close or open cup flash point apparatus is the appropriate testing equipment for appraising flammability of ILs since they, although liquid by nature during use mostly behave like solid polymers under the action of heat, leading to the release of condensable and non condensable potentially flammable degradation products. Moreover, the use of Manilla paper test to compare flammability of ILs or other hardy combustible materials as compared to flammable solvents (classified as such due to flash point values) is also greatly misleading (see e.g. Yonxin An et al, 2011), as this only reflect behaviour difference issuing a very small thermal stress initiating event that may be far from the actual context of potential incidents during use (as additive in a lithium based battery of as a catalyst in a biorefinery). Much more pertinent combustibility and flammability testing may be achieved by use of the so-called Fire Propagation Apparatus (ISO 12136:2011) as illustrated in Figures 3a and3b.

Assessing emerging and often intensified processes without too restricted viewpoint

There also the development of a dedicated database was considered as the best way to capitalize appropriate information serving process safety concept integration and risk assessment at early stage of development, in consistency with the development of the database of materials and chemicals (see section 3), facing the reality of modern biorefining, leading in particular to a variety and fast moving technical process options.

The importance of intensified processes

For few years now, process intensification has opened new perspectives to chemical industry to reinvent itself: technological innovations and methods have been developed in order to produce more and better in using less and to sustainably produce molecules responding to environmental and economic challenges The modern Biorefineries have benefited of these new opportunities and some applications have already demonstrated their efficiency in the field of biomass transformation or/and biodiesel production: static mixers, microwave reactors, reactive distillation, membrane reactors, nanosized catalysts, pulse electric fields, ultrasound assisted extraction. Process intensification is perceived in that sector as the best option to render those systems cost-effective [START_REF] Sanders | Process intensification in the future production of base chemicals from biomass[END_REF]. Regarding safety, another important point is that process Intensification is considered as a concept that allows to prevent or reduce risks related to major accidents: it is even commonly admitted that an intensified process is, by default, inherently safer. However emerging studies have demonstrated that the link between process intensification and the concept of ISD (Inherently Safer Design) was not always obvious. As shown by [START_REF] Ebrahimi | Safety analysis of intensified processes[END_REF], the general claim that safety is always improved by process intensification is clearly questioned.

Developing the BIOSAFE_PROCESS toolkit

Process safety relies on early detection of potential hazards and their elimination so far as possible to achieve inherent safety, completed by the implementation of modern protective measures as far as needed. An essential starting point for managing process risks in the context of biorefining is the collection of essential data on all types of processes that may be used, that detail operating conditions, materials used in the facility and the hazards related to the use of (bio)chemicals and (bio)materials used or processed. To make the consultancy of such data user-friendly, a tool designated as the BIOSAFE_PROCESS toolkit as been developed in the form of an Excel folder The user will be able to search for information regarding the production of any bio-based chemical that has a promising future in the bio-based economy, no matter what level of knowledge he has of the process. This tool has been built based on most recent inventories (eg.: de Jong, 2012), reports from development laboratories and literature citing similar processes or provided by the industry. This database is a first step in a more straightforward and comprehensive methodology dedicated for appraising process risks in the context of highly innovating and fast moving biorefinery taking account of main characteristics of such facilities, like high demand in flexibility in material feedstock and portfolio of processed materials, high level of energy integration, no residue target and so on. Configuration of the tool under construction is shown in Figure 5.

Conclusions

The paper has recalled that industrial safety is a prerequisite for the sustainable development of biobased value chains in the context of modern biorefining. Modern biorefining is fast moving, leading to integration of more and more innovating concepts, confirming the fast development of biotechnologies and intensified processes, as well as the emergence of lots of key new chemicals of interest. This in turn needs a special outlook in terms of risk assessment and sometimes justifies fully dedicated new tools, as advocated by [START_REF] Marlair | An introduction of safety issues in the field of biorefining[END_REF] at the occasion of the first summer school on biorefining principles that took place in Paris end of August 2011. Examples of new tools and methodologies under development by the authors have been given. No doubt that a specific R&D safety roadmap is desirable to take account of technical or organizational bottlenecks for adequate safety management. As innovation sometimes drive emerging risks in addition to conventional risks, the authors maintain their research efforts to accompany safe development of biorefineries of the future.

Figure 1 :

 1 Figure1: Current and future production pathways in jet A1 alternative fuel driven biorefineries (adapted from[START_REF] Miller | Guidelines for Integrating Alternative Jet Fuel into the Airport Setting[END_REF]

Figure 5 :

 5 Figure 5: Current structure of the BIOSAFE PROCESS toolkit being developed by INERIS for addressing process safety at early stage of biorefining design

Table 1 :

 1 Illustration of measured and literature safety data values for well known key chemicals in biorefining

	Test	Reported	Measured	Comments
	Compound	flash point	flash point
	HMF	79°C	168°C	Reported flashpoint as indicated in the MSDS from supplier
	Levulic acid 98°C	152°C	Reported flashpoint as indicated in the MSDS from supplier
	Sorbitol	292°C	150°C	Reported data in non peer-reviewed web source

During the process of the database implementation, some testing has shown the usefulness of double checking important information regarding key safety parameters. Table

1

illustrates this comparison measured flash points versus reported data in the literature (in some cases given in the relevant MSDS) for same chemicals.