Jean Esterle
email: j.esterle@estia.fr

Smart Interfaces at ESTIA, zer da hori?

Keywords: smart interfaces for engineering, complex systems, microgrids

Smart Interfaces at ESTIA, what is that (zer da hori in the local basque language) ? Smart Interfaces for Engineering is one of the topics of the iaria conference at Venice. This notion emerged as a unifying research theme at the engineering school ESTIA at the end of the year 2014, after several years of common work between researchers in Sciences and Technology and researchers in Management Sciences. There is a good flow of papers on various aspects of smart interfaces, but it is not easy to find in the literature a global approach to this notion. The purpose of this paper is to contribute tio fill this gap. In section 2 we give some historical background, going back to the Macy Conferences and the Palo Alto group, to Levins equation and Action Research, and to Edgar Morins approach to complexity. In section 3 we analyze several recent thesis at ESTIA and show how the notion of smart interfaces for engineering appears on topics as different as, for example, flight critical systems, isolated rural microgrids and the Lean approaches in corporate management. We hope that this survey will contribute to the stucturation of Smart Interfaces for Engineering as a branch of modern research.

I. INTRODUCTION

ESTIA-Recherche started as a research team in 2008, when GRAPHOS (Groupe de Recherches Appliquées Pluridisciplinaire sur l'Hôpital et les Organisations de Santé) and LIPSI (Laboratoire en Ingénierie des Processus et des Services Industriels) decided to merge in order to work together to develop research activities in both Management Sciences and Sciences and Technology, and at the crossroads of these domains.

Research at ESTIA is aimed at: Giving ESTIA engineering students an opportunity to work with established researchers who belong to both national and international scientific networks. Developing a synergy between research works and evolution of academic programs.

Proposing innovative answers to technological, economic and societal questions.

Raising awareness among students and companies about the practice of research.

Contributing to the influence of ESTIA and to the attractivity of the territory.

The research project concerns engineering and technology; hence complex systems, open and self-organizing, in which there are also (and mainly) human beings, users, managers, etc. The dynamics of ESTIA-Recherche follows from the action of constraints, goals and objectives which may appear as contradictory: there is a need to obtain applications while producing theoretical contributions, and to contribute to transfert of technology while insuring academic valorization of research results through publications in internationnally recognized journals; also the researchers at ESTIA need to develop scientific links with Bordeaux University, but they are employed by ESTIA, a private entity linked to the Chamber of Commerce and Industry of Bayonne-Pays Basque and their research is partially supported from answers to calls for projects. They have to combinate in investigations about corporate management individual initiative and top-down approach, and to provide a continuous flow of electricity from intermittent sources, etc. Generally speaking, scientific activity at ESTIA consists in studying interactions inside systems which are often complex.

Hence, researchers at ESTIA try to address simultaneously the need for academic recognition and the need for concrete benefits for firms. This double need lies at the heart of the research strategy of ESTIA. This explains why part of the research, especially the part which involves Creativity, Innovation and Management Sciences is performed through Action-Research, as explained below.

ESTIA-Recherche relies on an interdisciplinary team of researchers working on scientific, technological and societal topics in order to adress transversal projects. Innovation requires common work between specialists in sciences and technologies, but also between specialists in sciences and technologies and researchers in human sciences. Hybridation of ideas, concepts, methods and scientific domains is there a powerful fertilizer.

The prospective discussions within ESTIA-Recherche to prepare the external evaluation performed in January 2015 by ANR (Agence Nationale de la Recherche) led to the elaboration of the concept of Smart Interfaces for Engineering. Before illustrating this concept through examples we will go through a little amount of historical background.

II. SOME HISTORICAL BACKGROUND

A. Interaction: Macy Conferences and the Palo Alto group

The objective of Macy Conferences, organised from 1942 to for the last one, organized at auberge Nassau, Princeton, New-Jersey), was nothing less than building a general science of the way thinking works. These conferences were organized by a pluridisciplinary group of mathematicians, logicians, anthropologists, psychologists and economists. A description of these ten conferences can be found on Wikipedia [30]. There were two main participating groups, the first wished to establish an interaction between mathematics, physics and well-established psychological sciences, and the second, a group of "cyberneticians", including the famous mathematician Norbert Wiener, that wanted to fight well-established psychological sciences on behalf of mathematical and physical sciences. The group also included John Von Neumann, another prominent mathematician who played an important role at the beginning of computer science. This cycle of conferences played a seminal role in the emergence of Information Theory, Cybernetics and Cognitive Science, and led one of the participants, the anthropologist Gregory Bateson, to form a group, known as the Palo Alto group. The object of this group was to study the "paradox of abstraction in communication". We refer to [START_REF] Wittezaele | A la recherche de l'Ecole de Palo-Alto[END_REF] for more information about this group, whose work led to a deep change in the diagnostic of mental illness. Analyzing a "personnality" is impossible without taking into account the complex network of interpersonal relationships. Schizophrenia can be understood as a way for the patient to adapt to the pathological structure of his relations with his family [START_REF] Bateson | Toward a theory of schizophrenia[END_REF]. They also thought that the best moment for a therapist to intervene was during a crisis, when the patient would be ready to do something to find a new equilibrium, unlike the traditional method of waiting for the patient to "cool down". Of course ESTIA Recherche does not intend to perform mental therapy, but the idea of taking into consideration the interactions of a person or a system with external environment plays an important role in the scientific approach developed at ESTIA.

B. B = f (P, E), Lewin's equation and Action-Research

Action-Research did not arise all of a sudden from nowhere. In the XIX-th century, Karl Marx encouraged workers in industry to think about their living conditions by answering questionnaires (used as militant tools). This tradition of "inquiries" about peasant and/or worker situations and movements was followed more recently by Robert Linhart in his study of the struggle of workers in northeastern sugar areas of Brasil [START_REF] Linhart | Le Sucre et la Faim, Enquête dans les régions sucrières du Nord-Est brésilien[END_REF]. Of course ESTIA, which was created by the Chamber of Commerce and Industry of Bayonne-Pays Basque, does not have any revolutionnary goal in its research objectives, but Lewin's equation B = f (P, E) [START_REF] Lewin | Principles of Topological Psychology[END_REF], which states that the behavior B is a function f of the person P and her or his environment E, describes heuristically various aspects of Estia-Recherche investigations. Kurt Lewin was a professor at Berlin University, specialized in Gelstat psychology. At the beginning, he was mostly interested in child psychology, and after moving to the United States he played a crucial role in the development of Action-Research, a research method where the researcher intervenes during the research and in the research, in order to bring positive changes and also to produce knowledge and theory. (He became very influential, and the U.S. government asked him during World War 2 to help dealing with food scarcity by helping customers to learn how to use and cook cheap cuts of cattle, like heart, tongue, tripe and kidneys). These ideas had been introduced by the "Chicago group," which asked sociologists to rely on leaders of communities under consideration (population of poor neighborhoods, ethnic minorities, professional groups) in order to elaborate knowledge which comes from the bottom and goes back to the bottom. Thus, the academic researcher and community leaders become "co-researchers" who produce new knowledge and act together in various domains. We refer to [START_REF] Barbier | La Recherche-Action, collection Anthropos[END_REF] and [START_REF] Dickens | Action research: rethinking Lewin[END_REF] for modern developments of Action-Research. This approach, which sometimes relies on a thorough investigation of a single case, inspired a lot of the research performed at ESTIA on innovation and on change in corporate management and organization.

C. Complex systems and the principle of dialogy

The dialogy principle is a concept introduced by Edgar Morin to understand complex systems. "The dialogy principle means that two or several different "logics" are linked in a single entity, in a complex way (complementary, concurrently and antagonistically) without the duality getting lost in unity. Hence the unity of european culture is not a judeo-christiangreek-roman synthesis, it is the game not only complementary, but also concurrent and antagonistic, between these cultures which have their own logic: this is their dialogy" [START_REF] Morin | Penser l'Europe[END_REF], p. 28. " "The number and depth of interactions increase when one goes to the level of interactions, not only between particles, but between organized systems, atoms, stars, molecules, and over all living being, societies . . . , and the diversity and complexity of effects and transformations produced by these interactions increases as well. Once the organisations that are the atoms and the stars are in place, the rules of the game of interactions may appear as Laws of Nature. Hence interaction is a hub between disorder, order and organization. This means in turn that order, disorder and organization are now tied, via interactions, in a single interdependent loop, where none of them can be conceived without refereeing to the others, and there they have complex (dialogic) relations, that is to say complementary, concurrent and antagonistic [START_REF] Morin | La Méthode: la Nature de la nature[END_REF]. We refer, for example, to [START_REF] Aït | sociologue et théoricien de la complexité[END_REF] for a survey of Edgar Morin's contributions to complexity theory. It is not necessary to perform research at ESTIA to have read the six volumes of La Méthode, or to understand deeply the filiation between the principle of dialogy and the idea of dialectics (Heraclite, de Cruse, Hegel, Marx), but the fact that ESTIA Recherche arose from the union of research groups from Engineering Sciences and Management Sciences which have been working together since 2008 allows all these researchers to have a systemic approach in their various research directions, and one could say that the concept of Smart Interfaces for Industry comes from a sucessful dialogy between these two groups.

The module "Transformées" for second year students, which is taught at ESTIA by the author of the present paper, culminates with the celebrated Shannon sampling theorem, which reconstructs all the values of a square integrable function having a compactly supported Fourier transform from the values it takes on the integers, [START_REF] Esterle | Transformées[END_REF] (théorème 9.5.1 p. 131). Claude Shannon was working as an engineer for Bell Telephone company, and attended the 7th, 8th and 10th Macy Conference, where he presented his Information Theory in which signification was deliberately not taken into account. Reading Edgar Morin during the preparation of this paper, I realized that the approach to noise which was presented during some conferences on signal that I attended rather recently were based on Shannon's approach -where noise is a form of disorder which should be eliminated from the signal, while other appoaches could rely on finding some order in the disorder related to the dialogy order/disorder. Of course experts in signal theory are aware of this.

III. WORKING ON SMART INTERFACES FOR ENGINEERING

We now briefly describe the eight theses completed at ESTIA during the years 2015 and 2016. At first glance the topics look different: Augmented Reality applied to conception, gestion and maintenance of urban structures and furnitures; use of model reduction algorithms to optimize placement of robotized fibers, reduced model of scavenging to optimize cylinder for a 2stroke diesel engine; design of an architecture for measurement and diagnosis of physical parameters in critical airborne systems, algorithms and architectures for control and diagnosis of flight critical systems; study of a hybrid fuel cell/turbine system in the context of an isolated rural microgrid; visualization for an informed decision to design space exploration by shopping, accompanying maturation of concepts in ecoinnovation, taking in account human factors to overcome the limitations of the Lean approaches.

But, in all situations the researchers dealt with complex systems, for which a smart approach is proposed: Combining a monocular georeferenced tactile device with a topography laser in order to diminish the edition and interpretation errors of cartography of urban structures; Using model reduction algorithms to reduce the number of parameters in optimization of placement of robotized fibers, and introducing a cognitive dimension in reduced and separated meta-models of the scavenging by ports in 2-stroke Diesel engines;

Relaxing tolerance to the defects of the processing chain of signal obtained from the captor by improving the mathematical model of the processing chain and introducing dynamical models in measurement, diagnosis and control of flight critical systems;

Combining a fuel cell of type SOFC and a microturbine to reach the best electrical performance with a low environment impact for isolated rural microgrids;

Finding efficient graphs for information visualization in design space exploration according to the paradigm design by shopping, supporting the maturation of eco-innovative concepts to overcome the so-called collective fixations during the development of eco-innovations, defining a performance model supporting an actor vision of man at work to overcome the limitations of the Lean approaches. From these eight theses, which we now describe briefly, we see why the notion of Smart Interfaces for Engineering emerged at ESTIA.

Environment of Augmented Reality for conception, gestion and maintenance of urban structures and furnitures is the topic of the University of Bordeaux thesis of Emeric Baldisser in computer science, prepared at ESTIA (2013-2016) under a CIFRE contract [START_REF]Conventions CIFRE cifre[END_REF] with SIG-IMAGE, a company located at Technopole Izarbel at Bidart [START_REF] Baldisser | Environnement de réalité augmentée pour la conception, la gestion et la maintenance d'ouvrages et de mobiliers urbains[END_REF]. This work points out the relevance of Augmented Reality in order to diminish the edition and interpretation errors in cartography of structures. A prototype is proposed, evaluated and discussed. It combines a monocular georeferenced tactile device with a topography laser. It allows to draw and consult technical plans on a 2D representation of the site in real-time. The validity of this approach with respect to french reglementation remains limited. Another approach is proposed, which consists in fitting/matching the clouds of dense points obtained from topography scanners with the orthoscopic 2D representation of the site. The interactions in the augmented environment of the site then depend on its cloud of points. They are geolocalized and follow the paradgim of Picking-Outlining-Annotating. These interactions are described in [START_REF] Baldisser | Apports de la Réalité Augmentée à la Gestion de Réseaux et de Mobiliers Urbains, 8èmes journées de l'Association Franc ¸aise de Réalité Virtuelle[END_REF].

Development of model reduction algorithms to optimize the PFR process is the topic of the UTC (Université Technologique de Compiègne) thesis of Nicolas Bur, prepared at ESTIA (2012-2015) [START_REF] Bur | Développement d'algorithmes de réduction de modèles pour l'optimisation du procédé de Placement de Fibres Robotisé[END_REF]. The realization by robotized processes of composites parts intends to improve productivity. Nevertheless the "Placement de Fibres Robotisées" (PFR) is still at a stage of maturation and requires numerous developments, in particular in the case of composites with thermoplastic matrix or with dry fibers. The thesis proposes different tools in order to determine in advance the best heating power to implement these composites. The difficulty arises from the fact that this power depends on many parameters, arising not only from the components (density, etc.) but also from the process itself (moving speed, number and orientation of the folds). The technique called Proper Generalized Decomposition (PGD) has been used to construct a reduced multiparametric model and thus overcome the complexity of the system. The results were compared to those obtained by more conventional methods and also to experimental data, [START_REF] Bur | On the use of model order reduction for simulating automated fibre placement processes[END_REF].

Reduced and separated meta-models of the scavenging by ports in 2-stroke Diesel engines to use evolutionary algorithms in search space is the topic of the thesis prepared at ESTIA by Stéphanie Cagin [START_REF] Cagin | A new reduced model of scavenging to optimize cylinder design[END_REF], [START_REF] Cagin | Méta-modèles réduits et séparés du comportement de balayage d'un moteur Diesel 2-temps pour l'exploration évolutionnaire des espaces de solutions[END_REF]. The use of numerical methods to design a product became more and more common over the past 30 years. However, numerical models are still specialized and they do not run fast which makes their use problematic. So, some reduced models of scavenging have been developed. These models are analytical and generic; they run quickly and avoid the numerical treatment problems. They are also efficient tools in the search of design solutions. The work carried out has led to a new methodology based on a behavioral meta-model called neuro-separated including a neuronal model of state, a pseudo-dynamic neuronal model and a model with separated variables. Then, exploiting the models previously developed, a process of decision with evolutionary algorithms (genetic algorithms) is used to determine optimal designs and the fast behavioral simulation of the optimal designs solutions is done, thanks to the kriging approach. This design approach is multi-viewpoints, multi-criteria and multiphysics. It also includes a cognitive dimension: both free and controlled evolutionary explorations of solution spaces have been done. To validate the method, some qualification criteria have been evaluated for each model. They allow to understand and to assume the gap between the reduced models and the initial CFD base (where the model are coming from). This approach has led to the development of a tool of model and decision aids using Python and Matlab software programs Study of an hybrid system fuel cell/turbine in the context of an isolated rural microgrid is the topic of the Bordeaux University thesis of Sylvain Baudouin (2012-2015) [START_REF] Sylvain Baudoin | Etude d'un système hybride pile à combustible/microturbine dans un contexte microréseau rural isolé[END_REF]. Rural areas, often located far away from the main electrical network, are particularly suitable for deploying microgrids (MG), which allow to use efficiently a large number of renewable energy sources. Biogaz, obtained from methanation of agricultural waste, is a renewable energy source available in rural areas which is esay to store in large quantities, and more reliable and less dependent from random phenomena than solar or wind turbine energy.

A study of the state of the art leads to the conclusion that an hybrid system combining a fuel cell of type SOFC and a microturbine (MT) allows to reach the best electrical performance with a low environmenral impact. A unique multilevel converter of type SLNPC has been used to integrate the microgrid to the main electrical network. The first objective of the command strategy applied to the SLNPC converter was to regulate the power of the SOFC fuel cell to its nominal value, and the second objective was to fix the tension and the frequency of the microgrid when it is disconnected from the main electrical network. This system has been tested and validated through simulation and then experimentally on the EnerGea platform [21] of ESTIA.

Design of an architecture for measurement and diagnosis of physical parameters in critical airborne systems is the topic of the University of Bordeaux thesis of Romain [START_REF] Martin | Process for Diagnosis Method Selection of Flight Critical Systems[END_REF][START_REF] Martin | Design of an architecture for measurement and diagnosis of physical parameters in critical airborne systems[END_REF] [START_REF] Martin | Design of an architecture for measurement and diagnosis of physical parameters in critical airborne systems[END_REF]. The objective of this work was to propose a new architecture for measurement of physical parameters as temperature, pression and speed in airborne systems in critical situations. The goal for this architecture is to improve the integrity of the measured data while keeping their level of disponibility and fiability in highly critical airborne systems.

The solution consits in relaxing tolerance to the defects of the processing chain of signal obtained from the captor. In order to do this more functions are introduced, including the mathematical model of the processing chain, to make the system smarter. The thesis was supported by a CIFRE contract [START_REF]Conventions CIFRE cifre[END_REF] with the Thales company [34].

Algorithms and architectures for control and diagnosis of flight critical system is the topic of the Bordeaux thesis prepared at the same time by Alexandre Bobrinskoy [START_REF] Bobrinskoy | Model-based fault detection and isolation design for flight-critical actuators in a harsh environment[END_REF], [START_REF] Bobrinskoy | Algorithms and architectures for control and diagnosis of flight critical systems[END_REF]. Flight-Critical Systems such as Electromechanical Actuators driven by Engine Control Units (ECU) or Flight Control Units (FCU) are designed and developed regarding drastic safety requirements. In this study, an actuator control and monitoring ECU architecture based on analytic redundancy is proposed. In case of fault occurrences, material redundancies in avionic equipment allow certain critical systems to reconfigure or to switch into a safe mode. However, material redundancies increase aircraft equipment size, weight and power (SWaP). Monitoring based on dynamical models is an interesting way to further enhance safetyand availability without increasing the number of redundant items. Model-base default detection and isolation such as observers and parity space are recalled in this study. The properties of differential flatness for nonlinear systems and endogenous feedback linearisation are used with nonlinear diagnosis models. Linear and nonlinear observers are then compared with an application on hybrid stepper motor (HSM). A testing bench was specially designed to observe in real-time the behaviour of the diagnosis models when faults occur on the stator windings of a HSM. The thesis was also supported by a CIFRE contract with the Thales company.

Information Vizualization for an informed decision to design space exploration by shopping is the topic of the Centrale-Supelec thesis prepared by Audrey Abi Akle at ESTIA (2012-2015) [START_REF] Abi | Visualisation d'information pour une décision informée en exploration d'espace de conception par shopping[END_REF]. In Design space exploration, the resulting data, from simulation of large amount of new design alternatives, can lead to information overload when one good design solution must be chosen. The design space exploration relates to a multi-criteria optimization method in design but in manual mode, for which appropriate tools to support multidimensional data visualization are employed. For the designer, a three-phase process -discovery, optimization, selection -is followed according to a paradigm called Design by Shopping. Exploring the design space helps to gain insight into both feasible and infeasible solutions subspaces, and into solutions presenting good trade-offs. Designers learn during these graphical data manipulations and the selection of an optimal solution is based on a so-called informed decision. The objective of this research is the performance of graphs for design space exploration according to the three phases of the Design by Shopping process.

The results reveal three efficient graphs for the design space exploration: the Scatter Plot Matrix for the discovery phase and for informed decision-making, the Simple Scatter Plot for the optimization phase and the Parallel Coordinate Plot for the selection phase in a multi-attribute as well as multi-objective situation. In consequence, five graphs, identified as potentially efficient, are tested through two experiments. In the first, thirty participants tested three graphs, in three design scenarios where one car must be chosen out of a total of forty, for the selection phase in a multi-attribute situation where preferences are enounced. A response quality index is proposed to compute the choice quality for each of the three given scenarios, the optimal solutions being compared to the ones resulting from the graphical manipulations. In the second experiment, fortytwo novice designers solved two design problems with three graphs. In this case, the performance of graphs is tested for informed decision-making and for the three phases of the process in a multi-objective situation. Part of this work was presented in [START_REF] Abi Akle | Information visualization for selection in Design by Shopping[END_REF].

How to support the maturation of eco-innovative concepts?: proposition of the method MIRAS to overcome collective lock-ins and explore stakeholder networks is the topic of the thesis prepared at ESTIA by Marion Real [START_REF] Real | A cognitive approach to complement support practices for the maturation of eco-innovations[END_REF], [START_REF] Real | Accompagner la maturation des concepts au sein de l'ecoinnovation: proposition de la méthode MIRAS, pour aider à surmonter les fixations collectives et explorer les réseaux de parties prenantes[END_REF], using a Research-Action approach inside the support group APESA. During the development of eco-innovations, companies are looking to implement a new activity that can create ruptures with its existing practices and cause many changes in their business model. In such complex situations, the stakeholders of emerging projects have some difficulties to consciously deviate from existing cognitive frameworks to explore alternatives in line with the initial goals of the project. Thus, they take trajectories that may lead to a dilution of the environmental and social values or cause the abandonment of projects. The work presented in the thesis focuses on the maturation of eco-innovative concepts and seeks to develop tools and methods to avoid and overcome such situations called collective fixations. The methodological approach is structured in two steps:-The analysis of three case-studies of eco-innovative projects allowed to characterize supporting practices and deepen the knowledge on the collective fixation present during the maturation of concepts. This first study has fueled the design process of the MIRAS method, the main contribution of this research. The MIRAS method offers a toolkit designed for eco-innovation intermediaries in order to help them to structure their intervention during the stage of concept maturation. Specifically the tools help to improve the sustainability potential of concepts, to analyze project group behaviors during sessions and to revisit stakeholder networks so as to anticipate future mutations and news ways of incubation.

Taking into account the human factor to overcome the limitations of the Lean approaches: proposal for a performance model and an accompanying methodology is the topic of the thesis prepared by Patrick Badets at ESTIA [START_REF] Badets | Kaizen en contexte Lean : La santé des opérateurs mise à mal[END_REF], [START_REF] Badets | Prise en compte du facteur humain pour pallier les limites d'une démarche Lean: proposition d'un modèle de performance et d'une méthode d'accompagnement[END_REF]. Lean is an approach aiming at eliminating non-value added operations, used by companies to improve the performance of their production activities. Companies applying this approach are observing rapid gains in operational terms but gradually some observe a fall in operating results or a degradation of the health of work force. The objective of the thesis was to overcome these limits and improve the ability of those of the company to anticipate and to take corrective actions. The performance model and the decision adopted by corporate actors to deploy Lean was questioned. It is proposed that corporate actors evaluate the efficiency of production, processed by the Lean approaches, taking into account not only the operational level of performance, but also the human dimension integrating realwork activity. A performance model that supports a kind of actor vision of man at work is defined. To help corporate actors to change their existing model of Lean performance, a support methodology based on a reengineering approach integrating coaching aimed at changing there presentations of the actors by a sociocognitive learning is offered. This methodology is based on modeling tools to represent the impact of this new performance model on the decision and on the sustainability of the lean benefits.

IV. CONCLUSION

We hope that this survey will help the researchers in the field of Smart Interfaces to Industry to have a more global vision of scientific activities in this direction and understand how science and technology and management sciences can help each other. We also hope that this paper will help other scientists to discover this emerging subject, and, more generally, to get interested in a systemic approach to complex systems.

ACKNOWLEDGMENT

The author, who has been the Research Director of ESTIA from november 2007 to July 2015 and is still present at ESTIA, would like to thank all the members of ESTIA-Recherche for the warm and creative pluridisciplinary environment he has been enjoying there during all these years. He also wishes to thank Jean-Roch Guiresse, who was director of ESTIA until March 2016, and the new director Patxi Elissalde, as well as the ESTIA corporate fund for their constant support to research activities. The intervention of Patxi Elissalde at the symposium on Smart Interfaces held at ESTIA on November 18, 2016 gave an interesting synthesis about complex systems and the societal, environnemental and economic, technological and conceptual challenges that need to be adressed by researchers at ESTIA working on Smart Interfaces for Engineering in the following years [START_REF] Elissalde | oral communication[END_REF]. The author also benefited from many conferences given at ESTIA, in particular from the conference given before the opening of the 2012 edition of "24h de l'Innovation" by Jeremy Rifkin, an internationnally recognized expert in scientific and economic prospective [START_REF] Rifkin | The third Industrial Revolution[END_REF], who presented in October 2012 at ESTIA his convictions concerning the challenges of globalisation, the emergency of climate change and the impact of energy revolutions which change the economic paradigm.


Senior Member, IEEE Andrea Cozza
email: andrea.cozza@ieee.org.

Likelihood of Meeting Isotropic Conditions in Reverberation Chambers from Power Transmission

Keywords: Reverberation chamber, modal overlapping, Rayleigh fading, multipath propagation, statistical tests

The ability of a metallic cavity to sustain an isotropic diffusive regime is a necessary condition in order to be used as a reverberation chamber (RC) in narrow-band settings, for which field samples are expected to behave as complex Gaussian random variables. Yet, no reliable method has been introduced so far that accurately predicts the lowest usable frequency (LUF), starting from which field samples are more likely to pass goodness-of-fit (GoF) tests, statistical tools that can measure how well field samples behave as Gaussian variables. This letter presents Monte Carlo simulation results that prove that the likelihood of passing GoF tests can be accurately predicted by measuring power transmission through the RC, without any a priori information about its characteristics. These results allow to identify the LUF from which a cavity is fit to generate rich multipath environments, as ideally expected for RCs, e.g., for over-the-air tests of wireless devices, and EMC tests.

I. INTRODUCTION

Reverberation chambers (RCs) are test facilities that are expected to generate a rich multi-path environment, which can be described by means of a superposition of N plane waves, E(r, ν) = N (ν) n=1 Ẽ( kn (ν)) e -jko kn(ν)•r [START_REF] Morse | Methods of Theoretical Physics[END_REF] where kn (ν) and Ẽ( kn (ν)) are, respectively, the direction of arrival and the complex amplitude of the nth plane wave, both functions of frequency ν; r is the position of the observer and k o = 2π/λ the wavenumber associated to the wavelength λ. Under ideal conditions, N → ∞ and energy injected into the RC is scattered with equal probability among all possible states, i.e., angles of arrival, polarization and amplitude, a propagation regime implying isotropic diffusion [START_REF] Morse | Methods of Theoretical Physics[END_REF], [START_REF] Ishimaru | Wave propagation and scattering in random media[END_REF], which results into a homogeneous spatial distribution of energy. This condition makes up the basis for the ideal ability of RCs to yield position-and orientation-independent test results [START_REF] Hill | Electromagnetic Theory of Reverberation Chambers[END_REF].

It is therefore of practical importance to know the lowest usable frequency (LUF) from which an RC approximates with sufficient accuracy isotropic conditions. RC users may rely on the use of goodness-of-fit (GoF) tests [START_REF] Agostino | Goodness-of-fit techniques[END_REF], to evaluate the likelihood that a population of samples adhere to a reference probability law: in fact, ideal diffusion leads to Gaussiandistributed field samples [START_REF] Hill | Electromagnetic Theory of Reverberation Chambers[END_REF]. This approach necessarily implies an a posteriori decision, since based on measured samples, with no possibility of predicting the LUF [START_REF] Lemoine | Investigation of reverberation chamber measurements through high-power goodness-of-fit tests[END_REF], [START_REF] Adardour | On the low-frequency optimization of reverberation chambers[END_REF].

As opposed to plane-wave models, as in [START_REF] Morse | Methods of Theoretical Physics[END_REF], preferred in communication theory, physical considerations rather lead to a different representation [START_REF] Morse | Methods of Theoretical Physics[END_REF], seeing the field distribution within a metallic cavity as the result of a superposition of independent resonant responses, or modes, i.e.,

E(r, ν) = i∈I γ i e i (r)ψ i (ν), (2)
where e i (r) is the spatial distribution of the standing wave underpinning the ith mode, ψ i (ν) its Lorentzian frequency response and γ i its complex amplitude. When used in a narrow-band setting, only the few modes with a resonance frequency close to the working frequency contribute [START_REF] Cozza | The role of losses in the definition of the overmoded condition for reverberation chambers and their statistics[END_REF]: these modes are collected into the set of indexes I . Based on (2), a number of criteria have been proposed to identify diffusive conditions, all of them requiring a minimum number of degrees of freedom, here modes: either looking for modal density [START_REF] Hill | Electromagnetic Theory of Reverberation Chambers[END_REF], modal overlap [START_REF] Cozza | The role of losses in the definition of the overmoded condition for reverberation chambers and their statistics[END_REF] or, similarly, minimum electrical dimensions, often set with respect to the first RC resonance [START_REF]Reverberation chamber test methods[END_REF]. While most of these criteria are based on rules of thumb, none of them provides any quantitative estimate of how likely GoF tests would be passed.

This paper fills in this gap, by proving that there exists a direct relationship between average power transmission through an RC and probability of rejecting the hypothesis of isotropic diffusion. All predictions are supported by experimental results. This work is expected to help RC users to more easily and confidently predict over what frequency range isotropic diffusion can be obtained with sufficient accuracy, by means of a straightforward measurement procedure.

II. PROBABILITY OF REJECTION FROM MODAL OVERLAP

Eq. ( 2) can be implemented into a Monte Carlo (MC) scheme, in order to generate large populations of random field samples sharing the same average number of overlapping modes. This pool of data can then be used in order to explore the relationship between modal overlap and the degree of diffusion.

Field samples are generated at an arbitrary position r, taking a single scalar component of the electric field along a direction p, as a linearly polarized antenna or probe would do. Hence, (2) reduces to p • E(r, ν) = i γ ′ i (r)ψ i (ν), with γ ′ i now accounting for the randomness of spatial modal distributions and their excitation coefficients. In the MC scheme, the {γ ′ i } were modelled as zero-mean Gaussian random variables, while the frequencies of resonance involved in the {ψ i (ν)} were considered as uniformly distributed around the working frequency. Defining as B m the 3 dB modal bandwidth covered by ψ i (ν), an average modal overlap M W (see sec. III) is enforced by distributing N M = M W B e /B m resonant frequencies over a bandwidth B e . In this paper B e /B m = 50, in order to enable M W < 1 to be simulated, since modes come as integers. This protocol was used in order to generate sets of 10 5 field samples for each value of M W going from 0.1 to 100. From this pool of data, subsets of N s samples were extracted randomly, in order to study the impact of sample population size, namely for 50, 100, 250, 500 and 1000 samples. This choice covers most of the practical cases encountered by RC users. For each population size, 1000 random realizations were created in this way, practically independent because of the shear number of available combinations.

As recalled when introducing (1), isotropic diffusion implies that scalar components of field samples accurately follow a complex Gaussian distribution, or exponential when dealing with quantities proportional to their squared absolute value, as is received power. These expectations are never fully met, as they would require an infinite number of degrees of freedom. But they can still be acceptable in statistical terms, since the underlying distribution of populations of finite size can only be inferred with finite precision. GoF tests take this statistical uncertainty into account, by defining a statistics (i.e., a metric), based on the available samples, whose distribution is known in case field samples follow, e.g., an ideal Gaussian distribution: this is known as the null hypothesis H o .

In this respect, Kolmogorov-Smirnov (KS) test was applied on the MC data subsets, but other tests may also be used without any change in the procedure. KS test is based on the statistics D KS = max x | F (x) -F (x)|, with F (x) the empirical cumulative distribution obtained from the available subset of data and F (x) the reference distribution associated to the null hypothesis H o of isotropic diffusion. D KS is expected to be smaller than a critical value D cr = D α / √ N s with a probability 1 -α, where α represents the probability of rejecting H o even when the samples are distributed according to H o , i.e., a false alarm: typical values of α are chosen around 0.05. According to the measurement of power transmission discussed in sec. III, an exponential distribution is expected for ideal conditions. Then D α = 1.25, 1.06 and 0.96, for α = 0.01, 0.05 and 0.1, respectively. These values are those for a Lilliefors test, taking into account the fact that the exponential distribution requires one parameter (its average) to be empirically estimated [START_REF] Crutcher | A note on the possible misuse of the Kolmogorov-Smirnov test[END_REF].

For ideal conditions the probability P rej of observing D KS > D cr coincides with the significance level α; otherwise, a higher value would be expected, pointing to a measurable departure from H o . P rej can be estimated from the set of D KS obtained for each random realization of samples generated by the MC scheme, by computing the empirical cumulative distribution function of D KS and thus the probability that D KS > D cr .

Figs. 1 and2 show how P rej evolves as N s and M W change, for different values of α. It can be noticed how a transition occurs as M W 1. The transition region changes with N s , since as it increases GoF tests become more selective at detecting ever smaller drifts from H o . These results unambiguously prove that P rej is univocally determined by M W and N s , so that knowledge of M W would allow predicting the likelihood of an RC performance undistinguishable from ideal isotropic diffusion. P rej decreases monotonously as M W increases, converging to P rej = α as M W → ∞. Therefore, there exists a critical M W representing the minimum number of effective degrees of freedom needed in order to ensure that P rej be small enough.

In order to provide for simple decision criteria, the following approximation of the MC results was studied

P rej (M W , α, N s ) ≃ 1 -α 1 + (M W /M c ) 2 + α, (3)
where M c = M α √ N s is a characteristic modal overlap, for which P rej ≃ 0.5. M α was found only to depend on α, and equal to 0.0917, 0.0759 and 0.0569 for α = 0.01, 0.05 and 0.1, respectively. Approximation (3) only holds for P rej 0.4 and covers the region of decision values used in practice. Its accuracy is shown in Figs. 1 and2.

From (3), a decision criterion ensues

M W /M c 1 -(P th -α) P th -α (4)
where P th is the maximum probability of rejection accepted by an RC user. For a significant increase in P rej , e.g., P th -α 0.1, (4) yields M W /M c 3.

III. MODAL OVERLAP FROM POWER TRANSMISSION

Recalling that the modal bandwidth B m (ν) = ν/Q(ν), with Q(ν) the average quality factor of the RC, its average modal overlap is M W (ν) = m W (ν) ν/Q(ν), where the average modal density m W (ν) of an electromagnetic cavity of volume V was predicted by H. Weyl to be m W (ν) = 8πV ν 2 /c 3 , with c the speed of light for the medium filling the cavity. Hence,

M W (ν) = 8πV λ (ν)/Q(ν) (5)
with V λ (ν) = V /λ 3 . Several methods have been developed in order to estimate Q(ν), of which the most popular is based on the measurement of power transmission through the RC [START_REF] Hill | Electromagnetic Theory of Reverberation Chambers[END_REF]. The method requires two antennas to be present within the RC and to measure the average power transmission. When done by means of a vector network analyzer (VNA), S ij scattering parameters are measured for each random realization generated by a stirring technique, e.g., a rotating paddle. The internal power transmission, i.e., the fraction of power transmission occurring within the RC, is then estimated

T (ν) = |S 21 | 2 η 1 η 2 (1 -|Γ 1 | 2 )(1 -|Γ 2 | 2 ) ( 6
)
where • is the ensemble average, inevitably substituted by the sample mean during experiments. Γ i is the reflection coefficient of the ith antenna, either measured in free-space conditions or estimated from RC measurements of the S ii scattering parameter, as Γ i ≃ S ii . The radiation efficiency of the antenna, η i , also needs to be taken into account, in order to estimate the actual power transmitted through the RC.

It can then be demonstrated that [START_REF] Hill | Electromagnetic Theory of Reverberation Chambers[END_REF]

T (ν) = Q(ν)/Q a (ν), (7)
with Q a (ν) = 16π 2 V λ the contribution of antenna coupling to power lost by the RC [START_REF] Hill | Electromagnetic Theory of Reverberation Chambers[END_REF]. This definition does not consider non-idealities in the antennas, as they are already taken into account in [START_REF] Adardour | On the low-frequency optimization of reverberation chambers[END_REF]. From ( 5) and [START_REF] Cozza | The role of losses in the definition of the overmoded condition for reverberation chambers and their statistics[END_REF], it is therefore possible to directly express

MW (ν) = 1/2πT (ν), (8)
where the hat identifies an estimator, as opposed to M W enforced during the MC simulations. The above expression makes M W (ν) more tangible, as it now directly appears to be related to power transmission, a quantity that can be estimated and even monitored quite easily, without a priori information about the RC. Alternatively, a similar result can also be derived in case power reflection rather than transmission is measured. Estimating Q(ν) from S ii data has been discussed in [START_REF] Besnier | Antenna efficiency measurement from quality factor estimation in reverberation chamber[END_REF]. In this case, instead of (6), R(ν) should be used, defined as

R(ν) = |S ii | 2 -|Γ i | 2 η 2 i (1 -|Γ i | 2 ) 2 , (9)
which was shown to be related to (6) as R(ν) = 2T (ν) [START_REF] Junqua | On the power dissipated by an antenna in transmit mode or in receive mode in a reverberation chamber[END_REF], thus yielding MW (ν) = 1/πR(ν).

IV. EXPERIMENTAL VALIDATION

The accuracy of these results and predictions were tested in a cuboid RC, with dimensions 5.95 × 2.46 × 3.24 m 3 in CentraleSupelec. Two sphere-capped monocone antennas were placed within the RC, oriented in such a way as to have their axis orthogonal, thus minimizing any direct coupling. Weakly-directive antennas allow to excite the largest number of directions of arrival in the RC. These antennas are made of copper and not electrically small, being about λ/5 high at 300 MHz; their radiation efficiency can therefore be assumed to be close to one. The antennas were connected to a VNA outside the RC, with cables whose losses were fully calibrated and compensated. A Z-folded stirrer was oriented along 50 uniformly spaced positions, in order to introduce randomness in the transmission process. 6000 samples of the three main scattering parameters were measured over the frequency range 0.3 to 3 GHz, for each stirrer position, and translated into an estimate of T (ν), as defined in [START_REF] Adardour | On the low-frequency optimization of reverberation chambers[END_REF]. The background lag-1 auto-correlation between the samples was found to be lower than 5 % over the entire frequency range.

T (ν) was then smoothed using a local regression (LOESS) processing, in order to reduce the impact of outliers at low frequency and the uncertainty due to the limited number of available samples. Results are in Fig. 3. From the same data KS statistics were computed for each frequency, yielding one D KS (ν) value for each population. In order to estimate the probability of rejection P rej (ν), the distribution function of KS was estimated by clustering 50 neighboring frequencies on a receding-horizon basis, finally computing the probability that D KS (ν) > D cr , as discussed in sec. II. In order to test the impact of increasing the population size N s , raw measured data were clustered over 2 or 5 adjacent frequencies, yielding 100-and 250-sample populations; the processing for the computation of P rej (ν) is the same, apart for D cr , which changes according to N s . The results of this operation are shown in Fig. 4.

These empirical results are expressed as functions of T (ν) in Fig. 5, where they are compared to MC results using [START_REF]Reverberation chamber test methods[END_REF] and LOESS results in Fig. 3, in order to map M W (ν) → T (ν). In particular, ( 3) and ( 8) can be used for predicting the maximum T (ν) such that P rej (ν) P th . E.g., for P th -α < 0.1 and α = 0.05, (4) and (8) require T (ν) 1/1.43 √ N s , hence T (ν) 0.099, 0.069 and 0.044, corresponding to M W (ν) 1.6, 2.3 and 3.6, for N s = 50, 100 and 250, respectively. From Fig. 3, the LUFs are therefore expected to be found around 447, 539 and 683 MHz, which are within less than 10 % of the frequencies at which data in Fig. 4 cross P th = 0.15.

In practice, using GoF on empirical data does not allow a clean-cut decision criterion, because of the inevitable statistical uncertainty with which P rej (ν) is evaluated, clearly observable in Fig. 4. Fig. 5 shows that the fluctuations in P rej (ν) are indeed well explained by using a binomial law applied to MCpredicted values of P rej , modeling the uncertainty inherent in empirical frequencies of occurrence. Another advantage of results in Figs. 1 and2, together with their approximation (3), is that they do not suffer from significant statistical uncertainty.

V. CONCLUSIONS

MC simulations have demonstrated the univocal relationship existing between power transmission T (ν) and the likelihood of measuring field samples closely approximating the behavior of a perfectly isotropic diffusion within an RC. Given the maximum acceptable risk of finding an RC not performing as expected, the results presented in this paper accurately predict the LUF from which an RC can be safely operated. Thanks to its intrinsically smooth and regular nature [START_REF] Hill | Electromagnetic Theory of Reverberation Chambers[END_REF], T (ν) can be estimated even from relatively small sets of samples, using smoothing techniques, as LOESS, applied across frequency.

The fact that the proposed models, when applied to empirical estimates of the modal overlap MW , accurately predict the probability of rejection, is an important result in its own right, since it provides unequivocal evidence that modal overlap estimators accurately represent the number of effective degrees of freedom underpinning the behavior of an RC. Moreover, M W (ν) is more readily accessible than the number of plane waves N (ν), thus making it a natural candidate for predicting the stochastic performance of an RC.

Fig. 1 :

 1 Fig. 1: Monte Carlo estimated probability of rejection from KS tests of 100-sample data sets, as a function of the average modal overlap M W and significance level α (marked values) for the null hypothesis of isotropic diffusion. Solid lines represent approximation (3).

Fig. 2 :

 2 Fig. 2: Monte Carlo estimated probability of rejection from KS tests for a significance level α = 0.05, as a function of the average modal overlap M W and the size of the data sets (marked values). Solid lines represent approximation (3).

Fig. 3 :

 3 Fig. 3: Internal power transmission estimated from measured data and their LOESS-smoothed version obtained over 300 (N s = 50) and 60 (N s = 250) adjacent frequency samples (thick solid line). The modal overlap expected from (8) is shown on the right-hand vertical axis.

Fig. 4 :Fig. 5

 45 Fig. 4: Probability of rejecting H o (ideal isotropic conditions) estimated from experimental data, for three sample population sizes.

Fig. 5 :

 5 Fig. 5: Probability of rejecting H o expressed as a function of power transmission T (ν) (top axis) and estimated modal overlap MW (ν) (bottom axis), for N s equal to: (a) 50 and (b) 250. The solid thick lines correspond to the MC-based results results in Fig. 2, with the shaded area marking the 95 % confidence interval of estimators of P rej (binomial process).


The CISG Advisory Council : a model to improve uniform application of the CMR ?

The CMR convention celebrates its 60th Anniversary this year. On this occasion, a first colloquium was organized in Rouen -France last May. The subject of this colloquium was to identify the discrepancies in the application of the convention by the domestic courts of the State parties. A few remedies were also explored. Indeed, the CMR convention belongs to the category of uniform law conventions whose aim is to set a certain number of rules, which should be applied identically in the State Parties in order to avoid differences in treatment of the operators involved in international situations. Uniform law is also supposed to promote the development of international trading. But such goal may be compromised by discrepancies in the application of the convention by domestic courts, especially when a provision of the convention is subject to interpretation. The very weakness of international uniform law is the lack of international court in charge of dealing with such cases or at least in charge of uniform interpretation. And even if some conventions, as the CMR in its article 47, provides for an interpretation by the ICJ, we must note that this provision has never been used and seems inefficient. In the introduction of the Rouen colloquium, I raised certain possible remedies which could rather easily be implemented to improve the uniform application of the CMR. I called these remedies 'informal processes' as my idea was to consider remedies that could be developed concretely, avoiding the recourse to Amending Protocols of the convention, as we all know that it is not likely to happen. I would like here to explore some of these 'informal mechanisms'. First, I will expose two original mechanisms existing for other international conventions, and second I will discuss whether one of these mechanisms could be transposed to the CMR.

I -Informal existing mechanisms to improve uniform application of international conventions

The issue of uniform application of international conventions is shared by all institutions governing these conventions. Among several mechanisms identified, I have been working recently, along with one of my Ph.D. students, particularly on two remedies that have in common to allocate the power of interpretation of a convention to a panel of experts, more or less officially appointed. Hague conference. One of these solutions arises from certain Hague conventions on the grounds of Article 8 paragraph 2 of the Status of the Hague conference. This article provides for 'special committees' whose purpose is the practical study of the functioning of the conventions. In practice, such committees have issued opinions that are sometimes used by courts in cases related to these conventions 1 .

However I will not develop this mechanism as it does not seem to be transposable to the CMR convention. This convention has indeed no 'mother' international organization that could be used as a basis for the creation of such committees and therefore no legal ground exists. CISG. The second mechanism we have been studying relates to the CISG. Every scholar interested in international trade law knows that exists a very wide system of databases coordinated by UNCITRAL providing domestic case law on the convention (CLOUT). But what is less known is the existence of the CISG Advisory council 2 .

According to its website 3 , the 'Scope and Aims' of the CISG--AC is the following : "The CISG--AC is a private initiative which aims at promoting a uniform interpretation of the CISG".

It is a private initiative in the sense that "its members do not represent countries or legal cultures, but they are scholars who look beyond the cooking pot for ideas and for a more profound understanding of issues relating to CISG". As declared Professor Jan Ramberg, member of this council, in an interview in 2005, the Council is : " Offering Worldwide Authoritative Opinions For the Uniform Application and Interpretation of the CISG ".

The legal ground which guides the Council is article 7 of the CISG Convention : "as far its interpretation and application are concerned: the paramount regard to international character of the Convention and the need to promote uniformity". The Council also takes into account the multinational and multi--lingual character of the CISG. Professor Franco Ferrari declared, about the uniform interpretation of the Vienna Convention 4 : "It results that uniformity can only be reached if the interpret while analising takes into account practice in other countries. The interpret must consider "what the others already achieved", referring to decisions issued in other coutries on the same issue. He added " these decisions can have a precedent value, or a persuasive value " 5 .

How does it work in practice ?

The panel of experts meets twice a year and establishes a list of issues to be studied, related to identified difficulties in interpretation. After a thorough study of the issues, the CISG--AC issues opinions relating to the interpretation and application of the Convention on request or on its own initiative. Requests may be submitted to the CISG--AC, in particular, by international organizations, professional associations and adjudication bodies 6 . For each topic, a rapporteur is appointed. Every two year, a legal opinion is issued giving the interpretation of the working group on this issue.

2 I would like to thank here greatfully Professor Claude Witz who is the French expert on CISG and who kindly accepted to expose to us the main lines of the CISG--AC philosophy and mechanism. See website. 3 http://www.cisgac.com/about--us/. 4 Free translation from the author. 5 F. FERRARI, "Interprétation uniforme de la Convention de Vienne de 1980 sur la vente internationale", Vol. 48 N°4, Octobre--décembre 1996Octobre--décembre . pp. 813--852, spéc. p. 813. doi : 10.3406/ridc. 1996.5312 http://www.persee.fr/web/revues/home/prescript/article/ridc_0035--3337_1996_num_48_4_5312 6 In practice, these requests are very rare. The question arising from this initiative is : What is the effect of such opinions ? We all have noticed that this Council is a private initiative of about ten scholars. The experts come from different countries parties to the CISG Convention and the panel represents different legal cultures, all beeing experts in international sales' law. Such initiative was not however totally non official as the group has been funded by the UNCITRAL and works closely with this organization, even if the organization does not recognize legally the opinions issued. Every one may wonder how these opinions could influence uniform law. What is original and interesting in this initiative is that the worldwide reputation of theses experts in the field of international sales' law has granted the opinions an informal, but nevertheless practical, authority. Such, authority can be measured in practice by the reference to certain opinions in court cases. Professor Claude Witz, who is the French expert in international sales' law, publishes yearly abstracts of relevant court decisions applying the convention. The German and Dutch Courts sometimes refers to these opinions. For example, the German federal Court of Justice (BGH, 28 May 2014) 7 applied the opinion n°13 " Inclusion of Standard Terms under the CISG " 8 in a case related to a provision included in a standardized leasing contract stipulating the settlement of the obligation of the seller to buy back the equipment. Even if the effects of such opinions on domestic case law remain modest, I believe this initiative is worth studying. In my speech in Rouen, I suggested to develop the use of international case law databases 9 . But I must confess that such tools only allow Courts or abitrators to be aware of the solutions in several countries implementing an international convention. But these databases do not say what should be the adequate solution according to uniform law criteria. On the contrary, the information provided by databases, completed with legal opinions from reputed scholars as the CISG--AC, could provide a better guidance for domestic courts.

II -How can we create a "CMR Advisory Council" ?

Based on the assumption that the CISG AC could serve as a model for the CMR, it is then necessary to identify the conditions to be met to create such a CMR council. I have identified at least 3 necessary conditions:

1. The initiative 2. The panel's composition 3. The material conditions a. travel and accommodation expenses b. webmaster c. collection and dissemination of information 1. The initiative The CISG AC was created upon a private initiative of scholars and more particularly from late Professor Albert Kritzer from the Pace University and the Centre for Commercial Law Studies at the Queen Mary University in London. Professor Kritzer then solicited worldwide experts in international sales of goods to constitute the council. Among the European scholars or Research centers specialized in international carriage of goods by road, it is then necessary to find a reputed Professor, or a group of scholars, who would be interested in such an adventure.

The panel's composition

As a purely private initiative, the constitution of such a panel is necessarily subjective and based upon personal links between scholars. Of course, it cannot be denied that the opinion on the degree of expertise and reputation of the chosen academics is necessarily subjective. However, if the leader wants his initiative to be successful and efficient, he has to be as objective and open minded as possible in choosing his partners. The choice of members issued from different countries and various legal cultures is also fundamental. Among the panel of international experts on one topic, the choice of scholars rather than lawyers or sollicitors, or even judges, is justified by the necessary intellectual and material independence of the council. Thus, should be required from these participants the same conditions that bears on arbitrators : independence and impartiality. As declared on the CISG AC website : " It is a private initiative in the sense that its members do not represent countries or legal cultures …". They should not represent trade interest either. The idea is that the opinions should reflect the 'best' solution as regards uniform interpretation of the concerned convention. Coming back to the CMR, I believe it would not be so difficult to identify, among the State Parties, a dozen of reputed experts on the CMR. Of course the success of the enterprise is subject to approval of these experts to be part of such initiative. Which supposes that these scholars are convinced that such an advisory council is worthwhile.

3. The material conditions A condition of the independence of the members of a council should be the absence of remuneration. If the panel is constituted by scholars, this condition could be rather easily met, provided that their expenses are covered. As a consequence, such panel would need a special funding for travel and accommodation expenses related to the meetings of the council but also to promotional operations.

The success of the enterprise is also subject to efficient collection and dissemination of information on the opinions issued. In particular, an efficient website and may be a webmaster should be funded. Which raises the following question : how could these expenses could be funded? The CISG AC has been funded in its early stages by the UNCITRAL, but it is not the case anymore. Comparatively, the CMR does not have a "mother" international organization. Unifortunately, UNIDROIT transferred the management of the CMR database to the IDIT10 , which is a non profitable private association, as it was no longer capable of dedicating staff to feed this database. Having recourse to the IRU does not appear to be appropriate as this international organization defends the interests of road carriers and thus would not guarantee the independance of the council. One possibility would be to obtain EU funding, as the major State Parties to this convention are EU Member States. Even if finding a permanent source of funding of such a council remains a serious issue, the cost of functionning should not be so high (setting aside possible wages) and could possibly be borne, at least during a reasonable launching period, by the research centers of the scholars.

Conclusion : let's do it !

  Normandie Univ, UNIROUEN, CUREJ, 76000 Rouen, France DRAFT Rotterdam CMR Colloquim -October 2016

	7 CISG--online, n° 2513; Claude Witz, Droit uniforme de la vente internationale de marchandises : juillet 2013 --
	décembre 2014, Recueil Dalloz 2015 p.881.

8

CISG--AC Opinion No. 13 Inclusion of Standard Terms under the CISG, Rapporteur: Professor Sieg Eiselen, College of Law, University of South Africa, Pretoria, South Africa. Adopted by the CISG Advisory Council following its 17th meeting, in Villanova, Pennsylvania, USA, on 20 January 2013. 9 C. LEGROS, "Modalités de l'interprétation uniforme de la CMR : Quelles difficultés ? Quels remèdes ?", Unif. L.

Rev. / Rev. dr. Unif. (2016), to be published. © Pr. Cécile

Legros, Ph. D.,

As for the CMR : CMR UNIDROIT--IDIT DataBase : http://www.idit.asso.fr.


Keywords: Image processing, Image segmentation, Counting particles, Cell morphology, Medical Imaging

Measuring the blood cells by means of an image segmentation

Amelia Carolina Sparavigna

Several works had and have as their subject the study of automatic methods for the analysis and counting of the cells in the blood. Some references are given in [START_REF] Richar | Evaluation of an electronic particle counter for the counting of white blood cells[END_REF][START_REF] Mazalan | Automated red blood cells counting in peripheral blood smear image using circular Hough transform[END_REF][START_REF] Poomcokrak | Red blood cells extraction and counting[END_REF][START_REF] Theera-Umpon | System-level training of neural networks for counting white blood cells[END_REF][START_REF] Nasution | Comparison of red blood cells counting using two algorithms: Connected component labeling and backprojection of artificial neural network[END_REF][START_REF] Maitra | Detection and counting of red blood cells in blood cell images using hough transform[END_REF][START_REF] De Keijzer | Automated counting of nucleated red blood cells in blood samples of newborns[END_REF][START_REF] Nazlibilek | Automatic segmentation, counting, size determination and classification of white blood cells[END_REF][START_REF] Aune | Automated counting of white and red blood cells in the cerebrospinal fluid[END_REF][START_REF] Holmes | Single cell impedance cytometry for identification and counting of CD4 T-cells in human blood using impedance labels[END_REF][START_REF] De Smet | Use of the Cell-Dyn Sapphire hematology analyzer for automated counting of blood cells in body fluids[END_REF][START_REF] Tulsani | Segmentation using morphological watershed transformation for counting blood cells[END_REF][START_REF] Fornas | Flow cytometry counting of CD34+ cells in whole blood[END_REF][START_REF] Briggs | Quality counts: new parameters in blood cell counting[END_REF][START_REF] Venkatalakshmi | Automatic red blood cell counting using hough transform[END_REF][START_REF] Pipitone | Evaluation of automated nucleated red blood cells counting on Sysmex XE5000 and Siemens ADVIA 2120[END_REF][START_REF] Theera-Umpon | Training neural networks to count white blood cells via a minimum counting error objective function[END_REF][START_REF] Swolin | Differential counting of blood leukocytes using automated microscopy and a decision support system based on artificial neural networks-evaluation of DiffMasterTM Octavia[END_REF][START_REF] Saunders | A rapid automated system for differentiating and counting white blood cells[END_REF][START_REF] Bins | Texture of white blood cells expressed by the counting densitogram[END_REF]. The reason for the large interest on this subject is quite clear: in medical field, for humans and animals, the analysis of the blood cells is used as an indicator for evidencing several diseases. Usually, the analysis is performed manually by means of an optical microscope. As we can easily see from the titles of the given references, several automatic methods exist for extract information from the specimens, methods which are not only based on microscopic images. However, the large part of the works are concerning automatic approaches based on the image processing. Besides the counting of particles, from the micrographs that we can obtain by microscopes, some measurements concerning the shape of on cells are possible. Here we discuss an approach based on an image segmentation. In fact, the measurement of the size and size distribution of blood cells is the proper task for the method that we have recently developed and applied [START_REF] Sparavigna | Image Segmentation Applied to the Study of Micrographs of Cellular Solids[END_REF][START_REF] Sparavigna | A method for the segmentation of images based on thresholding and applied to vesicular textures[END_REF][START_REF] Sparavigna | Measuring the particles in fly ash by means of an image segmentation[END_REF][START_REF] Sparavigna | Analysis of a natural honeycomb by means of an image segmentation[END_REF][START_REF] Sparavigna | Image segmentation applied to micrographs of microcellular plastics[END_REF][START_REF] Sparavigna | Measuring the size of tubules in phloem and xylem of plants[END_REF][START_REF] Sparavigna | Image Segmentation Applied to the Analysis of Fabric Textures[END_REF][START_REF] Sparavigna | An image segmentation for the measurement of microstructures in ductile cast iron[END_REF]. To the counting of particles we can add some measurements concerning the cell morphology, measurements that we can obtain by means of a rose of directions. One of the measures is the perimeter of the cell, but it is possible to give several other parameters. In image processing, a segmentation is a method of partitioning an image into multiple sets of pixels, defined as super-pixels, in order to have a representation which can be simpler than the original one or more useful to the following desired analyses [START_REF] Vv | Wikipedia[END_REF]. Specifically, the segmentation is a process of assigning a label to every pixel in an image, such that the pixels having the same label share certain characteristics [START_REF] Vv | Wikipedia[END_REF]. As a consequence, the result of a segmentation is a set of "segments", or "super-pixels", or "domains", that are covering the background of the whole image. The segmentation can also give a set of contours, that is of "edges", extracted from the image. In this case, the segmentation gives an "edge detection". Several methods exist for the image segmentation, as we can appreciate from [START_REF] Vv | Wikipedia[END_REF]. Here we use a method based on a thresholding of grey-scale images [START_REF] Sparavigna | Image Segmentation Applied to the Study of Micrographs of Cellular Solids[END_REF]. By selecting a suitable threshold, the image is converted into a binary (black and white) image. In several cases, this is enough for evidencing the domains among the black or the white pixels. Details of the method of segmentation are given in [START_REF] Sparavigna | Image Segmentation Applied to the Study of Micrographs of Cellular Solids[END_REF]. Therefore, here we start immediately to show the results of the segmentation of an image of blood cells. We show that we can measure their apparent areas and perimeters.

GIMP software. GIMP is also giving us the histogram corresponding to the grey tones. As we can see from the Figure 2, the histogram has two large peaks. The grey-scale image is converted into a binary (black and white) image, selecting the threshold between these two peaks. The result of thresholding is shown in the same Figure 2. From the Figure 2, we can see that several cells are attached each others. Therefore, we need to separate them. We can obtain the separation using ImageJ software and its Watershed Separation tool which works on binary images. The result is given in the left panel of the Figure 3. On the right, we can see the segmentation, as obtained by means of the approach proposed in [START_REF] Sparavigna | Image Segmentation Applied to the Study of Micrographs of Cellular Solids[END_REF], for the analysis of the cellular solids.

Figure 3: On the left, the binary image after the separation of the cells. On the right, the segmentation obtained as explained in [START_REF] Sparavigna | Image Segmentation Applied to the Study of Micrographs of Cellular Solids[END_REF].

In the Figure 3, we can see that each of the cells has a different colour. It means that each cell, that is, each super-pixel in the image is labelled by a different label. Of course, we can determine the area of each cell, simply counting the pixels having the same label. Once we have obtained the areas of all the cells, we can give the size distribution of the sample, as we did in the previous articles [START_REF] Sparavigna | Image Segmentation Applied to the Study of Micrographs of Cellular Solids[END_REF][START_REF] Sparavigna | A method for the segmentation of images based on thresholding and applied to vesicular textures[END_REF][START_REF] Sparavigna | Measuring the particles in fly ash by means of an image segmentation[END_REF][START_REF] Sparavigna | Analysis of a natural honeycomb by means of an image segmentation[END_REF][START_REF] Sparavigna | Image segmentation applied to micrographs of microcellular plastics[END_REF][START_REF] Sparavigna | Measuring the size of tubules in phloem and xylem of plants[END_REF][START_REF] Sparavigna | Image Segmentation Applied to the Analysis of Fabric Textures[END_REF][START_REF] Sparavigna | An image segmentation for the measurement of microstructures in ductile cast iron[END_REF]. The size-distribution is proposed in the Figure 4, where we see the number of super-pixels having areas (in pixels), included in intervals of 200 pixels. After, we can determine the position (in pixels) of the "centre of mass" of each cell. From this centre, we can determine the distance to the cell contour. Here we use a star of 16 directions -in the same approach proposed in [START_REF] Sparavigna | An image-processing analysis of skin textures[END_REF][START_REF] Sparavigna | Mapping images with the coherence length diagrams[END_REF][START_REF] Sparavigna | Texture transitions in the liquid crystalline alkyloxybenzoic acid 6OBAC[END_REF] -to determine 16 distances of the cell edge from the centre of mass. Using the distances given according to this rose of directions, the perimeter of the cell can be easily calculated applying the Carnot theorem. In the Figure 5, we see the upper/left corner of the segmented image, with the black dots which are showing the positions of the centres of mass. On the right, we see the corresponding output of a file giving for each cell the position of the centre of mass, the area (in pixels) of the cell and the 16 distances (in pixels) from the centre of mass to the edge of the cell. The insert in the figure is showing in detail one of the three domains and the rose of directions. As previously told, once we have the rose of the 16 distances, it is possible to calculate the perimeter of the cell. It is enough to use the Carnot theorem for each of the triangles having two distances as sides and the angle of 22 and 1/2 degrees between them. For instance, for the cell with centre (78,20) and area 1178, the perimeter is of 118 pixels. For the cell at (38,32), it is of 132 pixels and for the cell at (59,73), of 125 pixels. Of course, several other parameters can be calculated from the measures obtained by means of the rose of directions.

Human blood

Let us consider the image of human blood cells, courtesy Bobjgalindo, available at https://commons.wikimedia.org/wiki/ File:Monocyte_40x.JPG and here reproduced in the Figure 6 (left panel). Again, the colour image is converted into a grey-scale image and then the binary image obtained manually by means of GIMP (Figure 6, central panel). As we can see, the white cell is not well defined in the binary image. For this reason, in this preliminary work, we modified manually the image to be used for segmentation. The modified image is given in the right panel of the Figure 6 (we have also applied the ImageJ Watershed tool to separate the cells). In the Figure 7, the result of the segmentation is proposed. In this preliminary work, in the case of the human blood, we needed to act manually to adjust the shape of the white cell. Further work is necessary to determine an automatic manner of improving the visibility of the white cells. A possible approach could be based on the use of the image entropy, in particular of the generalized entropies of Kaniadakis and Tsallis, and the related bi-level and three-level segmentations [START_REF] Sparavigna | Tsallis Entropy In Bi-level And Multi-level Image Thresholding[END_REF][START_REF] Sparavigna | Gray-Level Image Transitions Driven by Tsallis Entropic Index[END_REF][START_REF] Sparavigna | Shannon, Tsallis And Kaniadakis Entropies In Bi-level Image Thresholding[END_REF]. These entropies contain an entropic index, which can be used to enhance the different cell morphologies. An example of thresholding using generalized entropies is given in the Figure 8. As in the Ref. [START_REF] Sparavigna | Shannon, Tsallis And Kaniadakis Entropies In Bi-level Image Thresholding[END_REF], the best entropic index is chosen in order to have the largest number of edge pixels, that is, of pixels defining the edges of the cells. The result is quite interesting, because it is evidencing the white cells.

Figure 8: Microscopic image of blood cells (courtesy Wikipedia) on the left. If we assume the "best" bi-level image being that giving the largest number of edge pixels, we have the image on the right (threshold is at the value 102). The result is obtained by using Kaniadakis or Tsallis entropies, and is quite different from that obtained by using the Shannon entropy.

By the segmentation of the Figure 8, right panel, we can measure the morphology of the white cells. Let us conclude showing another interesting result, that we obtained in [START_REF] Sparavigna | Gray-Level Image Transitions Driven by Tsallis Entropic Index[END_REF], using a three-level image made of white, black and grey pixels. The results is reproduced in the Figure 9. Using only the black pixels, we have a map as given in the Figure 10 on the left. Using only the grey pixels, we have the map, on the right, in the same figure. On these two maps, the approach for having the cell morphology can be applied, after an ImageJ Watershed separation. A problem still exists for the red cells and it consists in the fact that some domains can have an empty core (see Figures 9 and10). A method of processing the shape of the cells having an empty core is under development.

Figure 10: These two maps have been obtained from the three-level image in the Figure 9. On the left, we see the black pixels and, on the right, the grey pixels. To these two maps we can apply the approach previously discussed for the determination of the cell morphology.

Figure 1 :

 1 Figure 1: Chicken red blood cells magnified 1000 times, courtesy John Alan Elson.

Figure 2 :

 2 Figure 2: Thresholding of the image in the Figure 1, obtained by selecting the threshold between the two large peaks in the histogram of the corresponding grey-tones.

Figure 4 :

 4 Figure 4: Distribution of the areas of the cells.

Figure 5 .

 5 Figure 5.

Figure 6 :

 6 Figure 6: Human blood cells magnified 40 times, courtesy Bobjgalindo.

Figure 7 .

 7 Figure 7. Segmentation and size distribution. Note that the white cell has a quite different size. In a case, ImageJ Watershed was not able to separate the cells. Of course we can measure the size and the perimeter of the cells too.

Figure 9 :

 9 Figure 9: Original (on the left) and three-level (on the right) images. The three-level image is obtained as described in [34].


Amelia Carolina Sparavigna

published or not. The documents may come

3D Faces reconstruction applied to some paintings of Leonardo da Vinci

As we have discussed in a previous article [START_REF] Sparavigna | 3D Faces from 2D Pictures[END_REF], the reconstruction of a 3D surface from a 2D map is a problem that can be of general interest for several applications. One of these applications is the 3D reconstruction of a face from a single 2D image. A remarkable software exists for this complex task [START_REF] Jackson | Large pose 3D face reconstruction from a single image via direct volumetric CNN regression[END_REF]. This software has been developed by Aaron S. Jackson, Adrian Bulat, Vasileios Argyriou and Georgios Tzimiropoulos, at the University of Nottingham and Kingston University. The researchers are also providing a site for experiments, at the address http://www.cs.nott.ac.uk/~psxasj/3dme/index.php . Let us call here this software as "3DME". For experiments, a frontal image is required. After the image is uploaded, the site brings us to the corresponding 3D model, which is easy to move by means of the mouse. An OBJ file of the 3D model is also given.

In [START_REF] Sparavigna | 3D Faces from 2D Pictures[END_REF], we have experimented 3DME on a painted portray to have a 3D face; Benjamin Franklin portraited by Joseph Duplessis ca. 1785 had been used. We have also experimented on a picture of a marble bust. It was the bust found in the Rhone River near Arles. Some scholars consider it a portrait of Julius Caesar [START_REF] Corazzi | The Rhone Caesar. Archeocommons[END_REF]. Thanks to two images of this bust, a cortesy of Butko for Wikipedia, we concluded that the result of the method proposed in [START_REF] Jackson | Large pose 3D face reconstruction from a single image via direct volumetric CNN regression[END_REF] is excellent.

Here we apply 3DME to a 3D reconstruction of some faces obtained from some paintings of Leonardo da Vinci (La Gioconda, John the Baptiste, Bacchus and the Salvator Mundi). The reconstruction is very interesting in the case of the Salvator Mundi, because gives us the possibility to compare this face to a self-portrait of Leonardo.

In the Figures 1, 2 and3, we see the results of the software applied to the Gioconda, John the Baptist and Bacchus. Let us consider also the Salvator Mundi (Figure 4). The image is a frontal image and therefore is a perfect one for applying 3DME. The result is given in the Figure 5. One of the results given in the Figure 5 is quite interesting. We can compare it to a self-portrait of young Leonardo. The comparison is given in the Figure 6. The self-portrait was obtained from a page of Leonardo da Vinci's Codex on the Flight of Birds, as discussed in [START_REF] Sparavigna | The Digital Restoration of Da Vinci's Sketches[END_REF][START_REF] Sparavigna | A self-portrait of young Leonardo[END_REF]. We can see a remarkable similarity between the two faces. Let me conclude with a question. Is the Salvator Mundi a self-portrait of Leonardo? Figure 6: One of the 3DME reconstruction compared to a self-portrait of young Leonardo [START_REF] Sparavigna | The Digital Restoration of Da Vinci's Sketches[END_REF][START_REF] Sparavigna | A self-portrait of young Leonardo[END_REF].

Figure 1 :

 1 Figure 1: The Gioconda, in her 2D image and in two 3D faces.

Figure 2 :

 2 Figure 2: John the Baptist.

Figure 3 :

 3 Figure 3: Bacchus.

Figure 4 :

 4 Figure 4: The Salvator Mundi.

Figure 5 :

 5 Figure 5: 3DME results on Salvator Mundi.