Bastien Thomas

Ocan Sankur

PyLTA: A Verification Tool for Parameterized Distributed Algorithms

Keywords: Data: n processes, t < n 4 Byzantine faults, id ∈ {0 . . . n -1}, v ∈ {0, 1}

We present the tool PyLTA, which can model check parameterized distributed algorithms against LTL specifications. The parameters typically include the number of processes and a bound on faulty processes, and the considered algorithms are round-based and either synchronous or asynchronous.

1 Process PhaseKing(n, t, id, v):

Introduction

Distributed algorithms -algorithms that run on multiple communicating processes -are used in many domains including scientific computing, telecommunications and the Blockchain. Standard distributed algorithms typically perform relatively simple tasks such as consensus or leader election [START_REF] Lynch | Distributed Algorithms[END_REF], but complexity arises from the lack of reliability of the network: some processes may crash, communications may be lost, faulty processes may send arbitrary messages (Byzantine faults). . . In this setting, various automated verification techniques have been developped in order to provide guarantees on the executions of such algorithms. Notably, parameterised verification attempts to verify these algorithms for every possible number of processes and faults at once [START_REF] Bloem | Decidability of Parameterized Verification[END_REF].

Threshold automata [START_REF] Konnov | On the completeness of bounded model checking for threshold-based distributed algorithms: Reachability[END_REF] (TA) are a formalism based on counter abstraction [START_REF] Pnueli | Liveness with (0, 1, infty)-counter abstraction[END_REF] that model asynchronous distributed algorithms with parameterised number of processes under crash and Byzantine faults. Verification can be performed using a complete encoding to SMT formulas [START_REF] Konnov | A short counterexample property for safety and liveness verification of fault-tolerant distributed algorithms[END_REF]. The decidabililty of generalisations of these models was studied in [START_REF] Kukovec | Reachability in parameterized systems: All flavors of threshold automata[END_REF] while [START_REF] Balasubramanian | Complexity of verification and synthesis of threshold automata[END_REF] focuses on the complexity of the underlying problems. These algorithms were implemented in the Byzantine model checker ByMC [START_REF] Konnov | Bymc: Byzantine model checker[END_REF]. However, algorithms based on threshold automata require bounding the diameter of the underlying transition system, either in the asynchronous case with bounded protocols (with only finitely many exchanged messages) in [START_REF] Konnov | On the completeness of bounded model checking for threshold-based distributed algorithms: Reachability[END_REF], or with unbounded messages but in the synchronous case, and for reachability properties only [START_REF] Stoilkovska | Verifying safety of synchronous fault-tolerant algorithms by bounded model checking[END_REF]. These techniques are therefore incomplete for threshold automata where such a bound does not exist.

In this article, we introduce PyLTA, a tool for fully verifying parameterised distributed algorithms both in the synchronous and asynchronous cases, without bounding the diameter of the state space or the number of exchanged messages. It is based on layered threshold automata (LTA), a formalism developped in [START_REF] Bertrand | Guard automata for the verification of safety and liveness of distributed algorithms[END_REF] which can be thought of as some form of infinitely repeating threshold automata. These generalise the synchronous TAs used in [START_REF] Stoilkovska | Verifying safety of synchronous fault-tolerant algorithms by bounded model checking[END_REF] and can handle both synchronous and asynchronous communication by exploiting some notions similar to communication closure [START_REF] Damian | Communication-closed asynchronous protocols[END_REF]. This allows us to verify any LTL formula, including liveness properties, even on algorithms where processes may send unboundedly many messages (unlike [START_REF] Konnov | On the completeness of bounded model checking for threshold-based distributed algorithms: Reachability[END_REF] where only finite TAs and a fragment of LTL was considered).

Concretely, PyLTA takes as input the LTA description of a parameterised distributed algorithm as well as an LTL specification. It then verifies the specification under all parameter valuations, or finds a counterexample disproving the specification. The tool is meant to provide support for distributed algorithm designers. In fact, distributed algorithm design is not a single step process. In practice, the implemented versions of an algorithm often contain additional features or optimizations, and PyLTA can be used to automatically check these variants for counterexamples.

Modeling Distributed Algorithms

In order to illustrate the capabilities of PyLTA, we use the Phase King algorithm (Algorithm 1) [START_REF] Berman | Cloture votes: n/4-resilient distributed consensus in t+1 rounds[END_REF]. In general, the algorithms that can be handled by PyLTA exhibit the following characteristics:

1. They are parameterized: in Algorithm 1, n denotes the number of processes and t a bound on the number of Byzantine faults. PyLTA verifies the algorithm for all the valuations of these parameters at once. 2. They can exchange messages in an unbounded domain: the indices 2i and 2i + 1 in Algorithm 1 are not bounded by a constant. 3. They can be synchronous or asynchronous but must ensure communication closure: sent and received messages are tagged with indices (2i and 2i+1 in Algorithm 1) that can only increase with time. As noted in [START_REF] Damian | Communication-closed asynchronous protocols[END_REF], communication closure appears both in synchronous and asynchronous algorithms in the literature. 4. The algorithms should use threshold conditions. This means that the conditions in branches on the algorithms should be arithmetic formulas comparing numbers of received messages and the values of parameters (see line 10).

Under these conditions, algorithms can be encoded in an LTA. The last two conditions can often be worked around. For example, we will show along this article how Algorithm 1 can be verified despite the fact that the condition on line 6 is not ameanable to counter abstraction as it uses the identity of processes which is lost in the abstraction.

Algorithm 1 uses the parameters n, and t with the condition t < n 4 . We introduce an additional paramter f ≤ t which is the actual number of faulty processes: the algorithm does not have access to f , but it is used during verification. Communication closure yields a layered structure of our models: a layer indexed by ∈ N models the portion of the program that deals with messages tagged with . In Algorithm 1, the layer = 2i corresponds to lines 3-5, while layer = 2i + 1 corresponds to lines 6-12. Algorithm 1: The Phase King algorithm [START_REF] Berman | Cloture votes: n/4-resilient distributed consensus in t+1 rounds[END_REF] is a synchronous algorithm that solves binary consensus under t < n 4 Byzantine faults. It executes t+1 rounds, and each round i ∈ {0 . . . t} is further decomposed into two layers (for round i, the layers are named 2i and 2i+1). In layer 2i, the processes broadcast their preferences v, and in layer 2i+1, they update v either to the majority if it is strong enough, or to the preference of the process with id i, which is the king of the round i.

We use counter abstraction to model executions of the algorithm, meaning that we define a counter storing the number of processes at each state of the algorithm. Here, our approach differs from other works on threshold automata because we count the number of processes that have been through the state instead of those that are currently in it. It follows that the number of messages m sent during the execution can be accurately deduced from these counter values as the number of processes at states where messages m have been sent. The downside of counter abstraction is that the identities of the processes are lost. Notably, the condition on line 6 needs to be abstracted with a non deterministic choice.

Parameter values: n ∶ 5, t ∶ 1, f ∶ 1 = 0 = 1 = 2 = 3 = 4 ⋯ ⋯ ⋯ a0 ∶ 2 a1 ∶ 2 k0 ∶ 0 b0 ∶ 0 b ? ∶ 4 b1 ∶ 0 k1 ∶ 0 a0 ∶ 1 a1 ∶ 3 k0 ∶ 0 b0 ∶ 0 b ? ∶ 2 b1 ∶ 1 k1 ∶ 1 a0 ∶ 0 a1 ∶ 2 ×2 ×2 ×3
Fig. 1: A configuration of the Phase King algorithm (Algorithm 1).

Configurations. PyLTA verifies properties on all reachable configurations. A configuration can be interpreted as a record of events that occured during an execution. An example is depicted in Fig. 1 which we now explain.

The configuration contains an instantiation of the parameter values (given on the bottom of the figure). Moreover, for each layer index, it specifies the number of correct (i.e. non-faulty) processes that were at a given state at that layer; as well as the number of correct processes that moved from one state to another between consecutive layers.

In Fig. 1, initially, 2 correct processes are at state a 1 , and 2 are at a 0 , for a parameter valuation n = 5, t = 1, f = 1. Recall that layers 2i and 2i + 1 correspond to round i, and that the meaning of the states are given in Algorithm 1; in particular, a x is the first line of an iteration where variable v has value x. All 4 correct processes go to b ? at layer 1, which means that the Byzantine process was king at round 0. Then three of them go to a 1 at layer 3, and one of them goes to a 0 , etc. This models the situation where the Byzantine process sent a message (2 × 0 + 1, 1) to the latter process but (2 × 0 + 1, 0) to the others. In the next layer, a correct process is king with value 1 (state k 1 ), and one correct process has received a majority of value 1 (state b 1 ), but not all correct processes have arrived to layer 4 yet. This configurations thus represents a finite prefix of an execution. When needed, LTL fairness assumptions can ensure that we only consider infinite configurations.

Input Format and Usage

The input format is based on layered threshold automata (LTA) defined in [START_REF] Bertrand | Guard automata for the verification of safety and liveness of distributed algorithms[END_REF], which we illustrate on the running example. An input file needs to define three elements: parameters, states and guards.

In PyLTA, the set of parameters are declared as follows.

PARAMETERS: n, t, f PARAMETER_RELATION: 4*t < n

The second line declares a constraint on these parameters, here 4t < n, which is a necessary condition for the correctness of Algorithm 1. As in our running example, the input format assumes that the states of the considered systems belong to layers. The following line defines two consecutive layers A, B, and specifies after layer B, we come back to layer A and loop.

LAYERS: A, B, A

In other terms, this results in the sequence of layers A, B, A, B,.... One can also specify lasso-shaped sequences; for instance, LAYERS: A, B, B would yield the sequence A, B, B, B, ....

States can be declared by specifying the name of the layer and the name of the state separated by a period as below. For instance, the first line defines the states a 0 and a 1 in Figure 1, and the second line is the rest of the states.

Transitions are defined by distinguishing cases for each state using guards. In Algorithm 1, a process needs to receive more than n 2 + t messages (2i, 1) in order to move from state a 1 (line 3) to b 1 (line 11). These messages can either come from processes in state a 1 or from Byzantine processes. In PyLTA, this condition is called the guard from a 1 to b 1 and it is expressed with the formula 2(a 1 + f ) > n + 2t. State names correspond to the number of correct processes that have been at that state, so transitions are declared as follows. The formula Afull is used to enforce synchrony: no process can take a transition before every message was received. We present the other transitions for Algorithm 1 in Table 1. Note that Afull or an equivalent Bfull should also be added each time in order to avoid considering asynchronous executions.

The following instruction is used to declare an LTL specification to be verified on the configurations: The instructions between WITH and VERIFY define predicates at given layers, which can be used in the subsequent LTL formula. Here, A.one0 holds when at least one process is in state A.0; and B.not_two_kings is used to prevent executions where more than one king is present in a round. These predicates can then be used as propositions of the LTL formula that will be verified.

A layer type name (A or B) inside a formula indicates a predicate that only holds in the corresponding layers. An interpretation of the formula can therefore Table 1: The guards of the transitions for Algorithm 1. The table on the left is for transitions leaving states of layers = 2i, and the table on the right is for those with layer = 2i + 1. Each cell is the guard of the transition from the state of the row to the state of the column.

= 2i k0 b0 b ? b1 k1 a0 2(a0 + f ) 2(a0 + f ) 2a0 ≤ n + 2t 2(a1 + f ) 2(a1 + f ) a1 ≥ n ≥ n + 2t ∧2a1 ≤ n + 2t ≥ n + 2t ≥ n = 2i + 1 a0 a1 k0
true false b0 b ? k1 = 0 k0 = 0 b1 false true k1 be the following: "if there are n processes, and no process in A.0, and there is always at most one non-Byzantine king in layers of type B, then at all layers of type A, there is no process in A.0."

Tool Overview and Usage

PyLTA is written in Python. In addition to counter abstraction and predicate abstraction, PyLTA performs counter-example guided abstraction refinement [START_REF] Clarke | Counterexample-guided abstraction refinement for symbolic model checking[END_REF]. Since we are working in an unbounded domain due to parameters, the tool uses an SMT solver to check the realizability of the traces, and refine the abstraction using interpolants produced by the solver [START_REF] Henzinger | Abstractions from proofs[END_REF]. The current version uses MathSAT [START_REF] Cimatti | The MathSAT5 SMT Solver[END_REF] via PySMT [START_REF] Gario | Pysmt: a solver-agnostic library for fast prototyping of smt-based algorithms[END_REF]. We use Lark [START_REF] Shinan | [END_REF] for parsing.

The LTL specification is first negated, and then converted into a Büchi automaton using Spot [START_REF] Duret-Lutz | Spot 2.0 -a framework for LTL and ω-automata manipulation[END_REF]. The product between this automaton and the predicate abstraction is then built dynamically. We check the language emptiness of the resulting product automaton; if it is empty, then the specification holds. Otherwise, the abstract counterexample is checked for realizability using the SMT solver, and either the counterexample is confirmed, or the abstraction is refined.

We run PyLTA on an input file as follows.

python -m pylta [input_file]

The output on the file corresponding to our running example is the following:

VERIFYING R.initial & ! R.one0 & G (B -> B.not_two_kings) ...

Formula is Valid

More details such as the abstract counter examples encountered and the added predicates can be obtained by adding a -v flag. In this case, a single refinement was necessary, which added the predicate B.k0 + B.0 + B.u <= 0. The verification algorithm does not require user interaction since abstractions are refined automatically. However, any predicate defined in the VERIFY instruction is used in the predicate abstraction, even if it does not appear in the formula. This behaviour provides a way to manually add predicates in order to help with the verification. The tool is distributed under the GNU GPL 3.0 licence and is available at https://gitlab.com/BastienT/pylta.

Conclusion

We have presented PyLTA, a tool for verifying parameterised distributed algorithms. Despite the undecidability barrier even in simple versions of the problem [START_REF] Stoilkovska | Verifying safety of synchronous fault-tolerant algorithms by bounded model checking[END_REF], PyLTA is able to verify complex properties on distributed algorithms, and unlike previous works, makes no assumptions on bounds on the state space or exchanged messages. As future work, one might explore the use of implicit predicate abstraction [START_REF] Tonetta | Abstract model checking without computing the abstraction[END_REF] to speed up the verification process. Another direction would be to integrate well ordered functions providing termination arguments [START_REF] Cook | Termination proofs for systems code[END_REF] as used in [START_REF] Daniel | Infinite-state liveness-to-safety via implicit abstraction and well-founded relations[END_REF] which could extend the usability of PyLTA.

A Tool Demonstration

In this section, we detail how the tool will be demonstrated. We will start by giving an example of a simple distributed algorithm, called the Flood-Min Algorithm, that can be modeled and verified with PyLTA. This algorithm is simpler than Phase King described in the core of the paper; although it does not illustrate all the capabilities of the tool, it is more convenient and easier to understand for an oral presentation.

We will thus focus on the modeling aspects, and the usage of the tool by showing a property that is easy to prove, and another property that requires some interaction, thus showing the strengths but also the limitations of the tool.

The Flood-Min algorithm is from [START_REF] Chaudhuri | Tight bounds for k -set agreement[END_REF] and given in Algorithm 2.

1 Process FloodMin(n, t, v): Data: n processes, t allowed crashes, v ∈ {0, 1}.

2 for i = 0 to t do // t + 1 iterations 3 broadcast v 4 receive values u0, . . . , u l-1 from all 5 v ← min{u0, . . . , u l-1 } 6 end 7 return v;
Algorithm 2: The Flood-Min algorithm [START_REF] Chaudhuri | Tight bounds for k -set agreement[END_REF], is a synchronous algorithm that solves consensus under at most t crashes.

We will directly explain configurations and the semantics of threshold automata without excessively formalizing these. A configuration can be thought of as some records of events that happened up to a point of an execution. A configuration of Algorithm 2 is represented on Figure 2.

Parameter values: n ∶ 5, t ∶ 2 = 0 = 1 = 2 = 3 ⋯ ⋯ ⋯ v0 ∶ 0 c0 ∶ 1 v1 ∶ 4 c1 ∶ 0 v0 ∶ 0 c0 ∶ 1 v1 ∶ 3 c1 ∶ 0 v0 ∶ 1 c0 ∶ 0 v1 ∶ 2 c1 ∶ 0 v0 ∶ 3 c0 ∶ 0 v1 ∶ 0 c1 ∶ 0 ×3 ×2 ×2
Fig. 2: A configuration of the Flood-Min algorithm (Algorithm 2).

Figure 2 specifies the valuation of parameters n and t. Additionally, each column contains the possible states of a process at each iteration of the loop. Such a column is called a layer. The shown configuration contains the number of processes that are at each state of each layer. For example, state v 1 (resp. v 0 ) in layer = 0 has value 4 (resp. 0) meaning that 4 (resp. 0) correct processes had v = 1 (resp. v = 0) at the first iteration of the loop.

The states c 0 (resp. c 1 ) represent processes that had values 0 (resp. 1) but have crashed during the execution of the round. It is important to represent them separately since these processes may not have sent their values to all other processes.

Indeed, in the next layer, we see that a single process updates its value to 0 (by going to state c 0 ), meaning that it received a value 0 while the others only received 1's. This illustrates the correction argument of the algorithm that depends on the existence of a round where no process crashes (guaranteed by executing t + 1 rounds).

Next, we will show how this algorithm is described in PyLTA's input format. The parameters and states of these configurations are defined as follows:

PARAMETERS: n, t LAYERS: L, L STATES: L.c0, L.v0, L.v1, L.c1

The first line defines the two parameters n and t. The second line says that there is only one layer L, and that each layer L is followed by another layer L. The last line defines the four states that appear in layers L.

Next, we show how to specify the transitions between the defined states. In most cases, this depends on the number of processes in other states of the same layer. For example, a process moves from v 1 to v 0 if it receives a message 0 in the current round. This can only happen if another process is in state v 0 or c 0 . This condition is encoded with the linear arithmetic expression v 0 + c 0 > 0 where v 0 and c 0 are interpreted as the number of processes in the corresponding state. Conversely, a process moves from v 1 to v 1 (of the next layer) if it did not receive any message 0. This can be encoded with the condition v 0 = 0, we omit c 0 in this case because it is possible for the process to not receive a message from a crashing process.

In PyLTA, this results in the following code: We do not need to give the successors of c 0 and c 1 , processes in these states will simply not take part in subsequent layers.

Last, we show how to define properties to be verified by PyLTA. First, we will show how to prove the validity property: 'If no process has v = 0, then no process will ever have v = 0'. In order to encode such a property, we need a predicate that states that a process has v = 0, this can be done with one 0 ∶ v 0 + c 0 > 0. Then the property can be stated in linear temporal logic as ¬one 0 → G¬one 0 . In PyLTA, this is written as follow: WITH L.one0: L.v0 + L.c0 > 0 VERIFY: ! L.one0 -> G ! L.one0

By this example, we illustrate how predicates (such as L.one0) can be defined, as used in temporal logic properties.

On this example, PyLTA immediately outputs:

Formula is Valid

Now, let us try to prove the termination of this algorithm. This can only hold under a fairness property. In this case, an appropriate fairness property can be that at every layer there are at least nt non-crashing processes, fair ∶ v 0 + v 1 >= nt. Under this assumption, a termination condition can be decided ∶ v 0 + c 0 = 0 or v 1 + c 1 = 0. We will also add the initial condition ini ∶ v 0 + c 0 + v 1 + c 1 = n. Then, we can attempt to give PyLTA the following input: We see that PyLTA attempted to instantiate an abstract path (i.e. a Boolean valuation of the predicates). It managed to instantiate a finite prefix of the path, but did not manage to concretise the loop. In other terms, it was not able to determine whether for some valuation of the parameters, there exists an infinite execution matching the abstract counterexample lasso.

In this case, every finite prefix of the path is concretisable, meaning that with predicate abstraction alone, PyLTA will not be able to solve this problem. This shows a limitation of the tool which attempts to solve an undecidable problem. Future directions to handle these cases are discussed in the paper and will be shortly mentioned in the demonstration.

We will then show how to bypass this issue in this case. In fact, the reason why the algorithm is iterated t + 1 time is to provide one clean round, meaning a round where no process crashes giving the predicate clean ∶ c 0 + c 1 = 0. Assuming the existence of such a round gives us the following:

  STATES: A.0, A.1 STATES: B.k0, B.0, B.u, B.1, B.k1

FORMULA

  Afull: A.0 + A.1 + f == n CASE A.1: IF Afull & 2*(A.1 + f) >= n THEN B.k1 IF Afull & 2*(A.1 + f) >= n + 2*t THEN B.1 ...

  WITH A.initial: A.0 + A.1 + f == n A.one0: A.0 > 0 B.not_two_kings: B.k0 + B.k1 <= 1 VERIFY: (A.initial & ! A.one0 & G(B -> B.not_two_kings)) -> G(A -> ! A.one0)

  CASE L.v0: IF TRUE THEN L.v0 IF TRUE THEN L.c0 CASE L.v1: IF L.v0 + L.c0 > 0 THEN L.v0 IF L.v0 + L.c0 > 0 THEN L.c0 IF L.v0 == 0 THEN L.v1 IF L.v0 == 0 THEN L.c1

  WITH L.ini: L.v0 + L.c0 + L.v1 + L.c1 == n L.fair: L.v0 + L.v1 >= n -t L.decided: L.v0 + L.c0 == 0 | L.v1 + L.c1 == 0 VERIFY: L.ini & G L.fair -> F L.decidedWe now run PyLTA on this model, but it fails:Cannot verify formulaIn order to understand what happened, we run PyLTA again with the verbose flag:python -m pylta -v .... We obtain the following output:

  WITH L.ini: L.v0 + L.c0 + L.v1 + l.c1 == n L.fair: L.v0 + L.v1 >= n -t L.clean: L.c0 + L.c1 == 0 L.decided: L.v0 + L.c0 == 0 | L.v1 + L.c1 == 0 VERIFY: L.ini & G L.fair & F L.clean -> F L.decided Under this assumption, PyLTA immediately manages to verify the property.


Jean-Baptiste B Vaney

Julie Carreaud

Andrea Piarristeguy

Cédric Morin

Gaëlle Delaizir

Romain Viennois

Maggy Colas

Julie Cornette

Eric Alleno

Judith Monnier

M Bigot

A P Gonçalves

E B Lopes

G J Cuello

V Nassif

C Candolfi

B Lenoir

A Pradel

Stabilization of Metastable Thermoelectric Crystalline Phases by Tuning the Glass Composition in the Cu-As-Te System

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

Introduction

Due to their large optical window extending in the infrared range, chalcogenide glasses can be used as optics for thermal cameras as well as biosensors for medical applications. [1][2][3] Their low melting temperature (< 300 °C) combined with the ability to easily switching between amorphous and crystalline states make chalcogenide glasses candidates of choice for phase change memories. 4,5 Among their remarkable properties, their high linear and non-linear refractive indices enable applications in the photonic domain. 6 Further, chalcogenide glasses have attracted significant attention in the field of energy as electrolyte for solid-state batteries.

In this last application, the crystallization of a Li-based metastable phase ranks glass-ceramic systems among the most competing materials for such applications. [7][8][9] Similarly, chalcogenide glasses and glass-ceramics have recently driven interest as possible thermoelectric materials due to their high thermopower (α > 500 µV K -1 ) and extremely low thermal conductivity (λ < 0.3 W m -1 K -1 ), both properties being two prominent criteria to achieve high thermoelectric performances, evaluated by the dimensionless thermoelectric figure of merit ZT = α²T/ρλ, where T is the absolute temperature and ρ is the electrical resistivity. [10][11][12][13][14][15] The main drawback of these materials remains their high electrical resistivity that presently still prevents them from being competitive with state-of-the-art thermoelectric materials such as Bi2Te3 or PbTe. [16][17][18][19] However, the partial crystallization of the parent glass in the Cu-As-Te ternary system has proved to be an efficient pathway towards reducing the electrical resistivity by several orders of magnitude. 15 This glassy system exhibits a wide vitreous domain leading to a large choice of glass compositions that allows for a fine tuning of its transport properties.

Here, we report on a systematic investigation of the first crystallization of glasses in the Cu-As-Te system. Interestingly, we show that specific binary phases can be selectively crystallized within the glassy matrix upon heating by controlling the initial glass composition. Some of these crystalline compounds are metastable and can only be stabilized through this peculiar soft devitrification process, making this technique a powerful tool to produce such phases. Three compositions in the Cu-As-Te vitreous domain have been carefully chosen to achieve the stabilization of three different crystalline phases, namely α-As2Te3, the metastable binary β-As2Te3 and the as-yet unknown binary AsTe3. The influence of the nature of the crystalline phase on the microstructure and physical properties of the glass-ceramics has been investigated in details by means of powder X-ray diffraction, neutron thermodiffraction, Raman scattering and transport properties measurements. These experimental results are complemented by lattice dynamics calculations. Finally, the physical properties of these glassceramics are compared to both the parent glass and the pure crystalline phases that have been successfully synthesized.

Experimental

Synthesis

Three glassy samples of nominal compositions, Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65 were synthesized in silica tubes sealed under secondary vacuum. Starting elements, As (Goodfellow, 99.99%), Te (5N+, 99.99%) and Cu (Sigma-Aldrich, 99.999%) were first weighed in stoichiometric quantities (for a total batch of  4g) and introduced in a silica tube. The tube was subsequently evacuated, sealed and heated in a furnace with a low heating rate of 9 K.h -1 up to 1123 K, held at this temperature for 2 hours and finally quenched in a salt-ice-water mixture. The resulting ingots were hand-ground into micron-sized powders.

Spark Plasma Sintering (SPS) of the powders was realized in 10 mm diameter graphite dies with the Dr. Sinter 825 Syntex apparatus. This technique allows obtaining both amorphous bulk samples and glass-ceramics, depending on the temperature program. The sintering temperature was checked by a thermocouple placed inside the graphite die at about 6 mm from the sample. The SPS experimental parameters for the different samples (temperature, dwell time and pressure) will be described in details in section 3.1.

Crystalline α-As2Te3, β-As2Te3 and AsTe3 were successfully synthesized in polycrystalline form. β-As2Te3 was synthesized by the melt-quenching technique (melting at 923 K) and densified by cold pressing. 20 α-As2Te3 was obtained by annealing the β-As2Te3 phase at 553 K for 72 hours. The resulting ingot was ground into fine powders and densified by SPS at 618 K for 2 minutes under a pressure of 50 MPa. AsTe3 was synthesized from the full and congruent crystallization of the parent glass obtained by the twin-roller quenching technique. 21 The fine powder was subsequently densified by SPS at 453 K for 30 minutes under a pressure of 50 MPa.

Structural and chemical characterization

To verify the amorphous nature of the samples and to identify the crystalline phases, powder X-ray diffraction (PXRD) measurements on the surface of the SPS bulk samples were carried out at 300 K using a D8 Bruker diffractometer equipped with a Vantec 1D-detector (λCu=1.5406 Å).

The density of the bulk samples was determined through the Archimedean principle using a Kern balance. This balance enables weighing solids in air (mair) as well as in a solvent (in our case, water mwater). When the density of the buoyancy medium is known (δ0), the density of the solid (δ) is calculated as follows:

𝛿 = 𝑚 𝑎𝑖𝑟 𝑚 𝑎𝑖𝑟 -𝑚 𝑤𝑎𝑡𝑒𝑟 𝛿 0 (1)
The microstructure of both the amorphous and glass-ceramic bulk samples synthesized by SPS was investigated on well-polished surface using a Cambridge Scanning Electron Microscope (SEM). Composition of crystalline phases was estimated using Energy Dispersive X-Ray Spectroscopy (EDXS). For the unknown AsTe3 crystalline phase, the composition was also determined using Electron Probe Micro Analysis (EPMA).

The thermal behavior of the as-quenched samples was studied by Differential Scanning Calorimetry (DSC) performed using TA instrument AQ100 equipment from 300 up to 573 K using a heating rate of 10 K.min -1 .

Neutron thermodiffraction

Neutron thermodiffraction experiments were carried out to probe the crystallization process undergone by the glasses upon heating. These measurements were performed using the D1B instrument at the Institut Laue-Langevin (ILL) in Grenoble (France) with a nominal wavelength of 2.52 Å. The three glassy samples (Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65) were placed under vacuum inside unsealed cylindrical vanadium containers (inner diameter of 10 mm). Using a dedicated D1B furnace (vertical top loading furnace), neutron diffraction spectra were continuously collected on the samples subjected to the following heating ramps: from 300 to 363 K at a rate of 5 K.min -1 and from 363 to 473 K at a lower rate of 0.1 K.min -1 . For the cooling process, the furnace was simply switched off to allow the samples to reach room temperature in 'free fall'. Rietveld refinements were performed on the neutron patterns measured at high temperature on the three fully crystallized Cu-As-Te glasses, with the help of the program Fullprof. 22 Prior to these refinements, the crystalline phase identification was carried out with the commercial software EVA (Bruker), after conversion of the ILL data file to the proper format. The nuclear scattering lengths published by Sears were used. 23 The neutron wavelength of the ILL-D1B two-circle diffractometer λ = 2.522 Å was calibrated with the help of a TiO2 standard and the Gaussian broadening of the lines by the instrument was modelled by a Cagliotti function with its parameters fixed to the values U = 1.4066, V=-0.2154 and W = 0.0890. In all three cases, the refined parameters were the phase fractions, the zero-shift, the lattice parameters, the atomic positions and a simple Scherrer size to account for the Lorentzian broadening of the lines by the sample. The thermal displacement parameters were held fixed to B = 1.2, a value large enough to account for the "natural" disorder that is usually seen in these phases crystallized from a glass.

Raman scattering

Raman spectroscopy characterizations of Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65 glass-ceramics and of α-As2Te3, β-As2Te3, AsTe3 crystalline phases were performed using an

In Via Reflex Renishaw Raman spectrophotometer. We used the 2D mapping module in confocal mode, which gives access to high definition maps and high spatial resolution images due to the large number of recorded spectra. The maps (25µm  25µm with a step of 1µm) were recorded using a 50 objective with 785 nm wavelength excitation and low power (0.03 mW)

to avoid any damage of the sample. The use of a 1200 grooves/mm grating permitted to reach a resolution of 2.4 cm -1 .

Lattice dynamics calculation details of α-and β-As2Te3 pure crystalline phases

The theoretical Raman band positions of α-As2Te3 and β-As2Te3 pure crystalline phases were modeled using first-principles calculations performed within the Density Functional Theory (DFT) with the plane-wave VASP package and Projector Augmented Wave (PAW) pseudopotentials. 24,25 Because the crystal structure of AsTe3 is so far unresolved, the investigation was restricted to α-and β-As2Te3. Two types of exchange-correlation functionals were used: the standard Generalized Gradient Approximation (GGA) functional of Perdew, Burke and Erzenhof (PBE) type and the corrected van der Waals functional of PBE-D2 type from Grimme that includes empirically damped atom-pairwise dispersion corrections of the form C6R -6 . 26,27 In all calculations, an energy cut-off of 500 eV was used. The k-mesh used was 15×15×15 and 12×12×12 for the rhombohedral β-As2Te3 and monoclinic α-As2Te3 phases, respectively. The structures and atomic positions were relaxed until the residual forces were smaller than 10 -4 and 10 -5 eV.Å -1 , respectively. Phonon calculations were performed at the  point of the Brillouin zone using the Density Functional Perturbation Theory (DFPT) as implemented in the VASP code and the atoms were displaced by 0.015 Å from their equilibrium positions. 28 With these conditions, the calculations were highly converged.

Transport properties measurements

Electrical resistivity and thermopower measurements were carried out simultaneously with a ZEM-3 (ULVAC-RIKO) system between 300 and 375 K. Bar-shaped samples of typical dimensions 1  1.5  8 mm 3 were cut with a diamond wire-saw. Uncertainty for electrical resistivity and thermopower was ±6% and ±5%, respectively. The thermal conductivity was determined via thermal diffusivity measurements carried out with a LFA 427 (Netzsch) equipment. Cylinder-shaped samples were used for these experiments that were performed under argon atmosphere between 300 and 375 K. The uncertainty on the measurements was ±11%. Thermal conductivity 𝜅 and thermal diffusivity 𝑎 are related by the formula 𝜅 = 𝑎𝐶 𝑝 𝛿

where 𝐶 𝑝 is the specific heat and 𝛿 is the density measured by the Archimedean principle.

Specific heat measurements were performed by the continuous scanning method under an argon atmosphere using a DSC 403 F3 apparatus (Netzsch). In the present case, the temperature dependence of 𝛿 was neglected. The dimensionless thermoelectric figure of merit ZT was calculated from the relationship ZT = α²T/ρλ with an experimental uncertainty estimated to be ±17%.

Results and discussion

Thermal properties of parent glasses: SPS experimental conditions for glassceramics elaboration

The glassy domain in the Cu-As-Te system obtained by melt-quenching is shown in A decrease in Tg when increasing the Te content is observed, consistent with a weaker structural rigidity. For all compositions, the Dietzel criterion is low, indicating that these glasses are rather unstable towards crystallization. The increase in the specific surface of the Cu15As20Te65 sample from bulk to powder causes a shift of the crystallization peaks towards lower temperatures (from Tx = 455 K for bulk sample to Tx = 423 K for powder sample). Such a trend is a clear signature of preferential surface crystallization. [START_REF]From glass to crystal: Nucleation, growth and phase separation: from research to applications[END_REF] The sintering of amorphous powders by SPS through viscous flow mechanisms is thus well adapted to obtain glass-ceramics with a significant volume fraction of crystalline phases. 31 Based on the crystallization behavior determined by DSC data, we carried out a series of SPS experiments on the three compositions. The temperature and dwell time were the adjustable parameters while the pressure was maintained constant at 50 MPa. Our aim was to obtain either a glassy bulk material or a glass-ceramic with a controlled crystalline fraction. As a rough estimation, the relative part of amorphous and crystalline domains was determined from EDXS-SEM images using an image-analysis software.

In order to be able to compare the transport properties in the three types of composite materials, glass-ceramics with similar crystalline fraction were elaborated for the three compositions. A crystalline fraction of 30% in volume was chosen to ensure that the electrical percolation threshold is reached. 32 The SPS conditions to obtain glass-ceramics with a crystalline fraction of ~ 30 % in volume were found to be:

• 488 K, 5 minutes dwell time, 50 MPa for the Cu20As35Te45 composition ;

• 413 K, 20 minutes dwell time, 50 MPa for the Cu15As30Te55 composition ;

• 413 K, 5 minutes dwell time, 50 MPa for the Cu15As20Te65 composition.

Bulk glasses were obtained by consolidating amorphous powders by SPS through a viscous flow mechanism using temperatures and pressures similar to those used for glassceramics of similar compositions but with no dwell time applied.

Characterization of glass-ceramics

The amorphous nature of the samples after synthesis by melt-quenching was verified by PXRD measurements (Figure 3). The nature and chemical compositions of the phases crystallizing in the glassy matrix after the SPS treatment were determined by PXRD measurements combined with EDX (Figure 3). EPMA analysis revealed that the Cu15As20Te65 based glass-ceramic contains crystals with the As25Te75 composition (see Supplementary Information, Figure S1). The well-defined peaks that show up in the Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65 glassy matrices after SPS treatment correspond to the signature of α-As2Te3, β-As2Te3 and AsTe3 phases, respectively. The symbols correspond to the crystalline phases:  AsTe3, ♦ β-As2Te3 and  α-As2Te3.

While α-As2Te3, precipitated within the Cu20As35Te45 glassy matrix, is a stable phase in ambient conditions, the β-As2Te3 polymorph is metastable and could be so far only synthesized under high-pressure or by rapid quenching. [33][34][35][36][37] The fact that the metastable high-pressure β-As2Te3 phase is favored in the Cu15As30Te55 glass may be due either to the applied pressure during the SPS process or to the local stress-induced pressure due to the abrupt change in density. The stabilization of β-As2Te3 in the glassy matrix has already proven to be an effective way to improve the thermoelectric performances of the glass thanks to the induced large decrease in electrical resistivity combined with only a moderate increase in thermal conductivity. 15 Most interesting is the fact that an unreported and metastable phase, AsTe3 precipitates in the Cu15As20Te65 glass matrix upon crystallization. Such finding led us to investigate the direct synthesis of the AsTe3 phase, never reported earlier. All attempts failed except that described in section 2.1, that is, the full and congruent crystallization of the parent AsTe3 glass, which itself can only be obtained by the twin-roller quenching technique. An approximate crystal structure based on the neutron thermodiffraction data is reported in the present article. A full resolution of the crystal structure is currently in progress and will be reported in a forthcoming paper. [START_REF] Vaney | Thermoelectric properties of new AsTe3 crystalline compound[END_REF] Figure 4 shows backscattered electron mode-SEM images of the three glass-ceramics evidencing different microstructures. While the α-As2Te3 and β-As2Te3 crystalline phases exhibit needle-like shape (Figures 4a and4c), AsTe3 crystals form an assemblage of plate-like shape structure (Figure 4e). As previously shown by thermal analysis of both bulk samples and powders, surface crystallization plays a major role upon heating Cu-As-Te glasses. In the present samples, crystals are found to be disseminated within the whole volume of the glassceramics prepared by SPS from amorphous powders. It is noteworthy that the crystals form an infinite network of connected paths through the glassy matrix (Figures 4b, 4d and4f). A clear chemical contrast is observed at the particle boundaries, which is a characteristic of surface devitrification phenomenon leading to the so-called "coast-and-island" microstructure. Such phenomenon is confirmed by high-resolution Raman scattering maps, which unambiguously demonstrate the localization of the crystals at the grain boundaries surrounded by amorphous grains.

Neutron thermodiffraction

Neutron thermodiffraction experiments were carried out in order to get insights into the crystallization process occurring in the glassy matrices upon heating, e.g. the first phase that precipitates and its evolution with increasing temperature. For Cu20As35Te45, the first reflections at ~ 457 K correspond to the stable α-As2Te3 phase (Figure 5a). Indeed, the four main peaks of this phase appear at 2θ = 49.3°, 51.9°, 75.3° and 77.3° (Figures 6a and6b). The crystallization of the sample is complete at 477K. Rietveld analysis of the diffractogram collected at this temperature reveals that the main phase present in the compound is the monoclinic α-As2Te3 phase (57%) with Cu1.4Te (31%), As (9%) and AsTe (3%) as secondary phases (see Supplementary Information, Figure S2).

The sample Cu15As30Te55 remains amorphous up to 405 K (Figure 5b). Beyond this limit, three peaks appear at 48.1°, 65.5° and 75.5° (Figures 6c and6d) which correspond to the three main reflections of the metastable β-As2Te3 phase. A further increase of ~ 2 K leads to the phase transition β→α and finally to the full crystallization of the sample. The Rietveld refinement of the diffractogram collected at 409K reveals that the phases present in the crystallized compound are the monoclinic α-As2Te3 phase (55%), CuTe (32%) and Te (13%) (see Supplementary

Information, Figure S3). For both Cu20As35Te45 and Cu15As30Te55, no evident change is observed beyond ~ 477 K and ~ 409 K, respectively.

The crystallization process for the glass Cu15As20Te65 is more complex and involves several steps (Figure 5c). At about 394 K, a first crystalline phase corresponding to AsTe3 appears, the existence of which has never been reported in the binary As -Te phase diagram.

The three main peaks at 2θ = 48.0°, 65.4° and 75.1° have relative intensities of 100%, 35% and 34%, respectively (Figure 6e). The peak intensity first increases when the temperature increases up to about 445 K, then decreases with further increasing temperature, up to the end of the thermal treatment at  465 K (see Fig. 5c). The AsTe3 phase is the unique crystalline phase observed between 394K and 430K. As seen in Figures 5c and6e, an intermediate phase appears at ~ 430 K. Its diffraction peaks correspond to the signature of Cu1.4Te (see Fig. 6f). The intermediate phase starts disappearing (as shown by the decrease in the diffraction peak intensity) at about 460K when a new series of crystallization peaks, signature of one or several new crystalline phases appear (see Figure 5c). The Rietveld refinement of the neutron pattern collected at 433K is shown in Fig. 7. Phase identification was easier at this temperature due to the well-established intensity of the secondary crystalline phases: α-As2Te3, Cu1.4Te and AsTe. [START_REF] Morin | [END_REF]40,41 The AsTe3 pattern could be approximated by a modification of the β-As2Te3 The thermodiffraction data shows that the three first-phases to crystallize in the three glasses are the ones that were stabilized in the corresponding glass-ceramics, that is, α-As2Te3, β-As2Te3 and AsTe3 in the Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65 glass compositions, respectively. Therefore, SPS appears as the process of choice to stabilize a crystalline phase in a glass-ceramics. It is particularly remarkable for β-As2Te3 in the sample Cu15As30Te55 owing to its very narrow domain of existence (~2 K). The applied pressure during the SPS process and/or internal stresses probably play an important role in the stabilization of this phase.

3.4

Comparative study of the three types of materials: glasses, glass-ceramics and pure crystalline phases

Raman experiments and lattice dynamics calculations

Figure 8 illustrates the reduced Raman spectra of both the crystals and the residual glassy matrix for the three different glass-ceramics. The broadening of the Raman peaks of the residual glassy matrix with respect to the embedded crystals evidences a higher degree of disorder in the glassy part. The three spectra collected on glasses are rather similar, each spectrum exhibiting three main bands in the frequency range 70-300 cm -1 with approximate wavenumber positions at 150 cm -1 , 190 cm -1 and 220 cm -1 attributed to Te-Te, As-Te and As-As stretching modes, respectively. 42 The main difference in the three Raman spectra lies in the change in intensity of these three bands. The Raman spectra of the crystals in the glass-ceramics exhibit three distinct shapes (Figure 8d). The detailed attributions of the bands will be discussed in detail below. We chose this method because reference spectra were available in both glassy matrix and crystalline part. The DCLS algorithm approximates the spectrum at each point in the map by summing together scaled copies of each reference spectrum. The scaling factors are chosen to get the best possible fit to the original map spectrum and then used to create a map showing the distribution (correlation values) of reference spectrum (color contrasts). In the three samples, we obtained no lack of fit by using only two reference spectra, which is a signature of the crystallization of pure phases. Herein, we present only the maps reconstructed on the crystalline part (the black color is then linked to the glassy matrix). The maps clearly evidenced the crystallization of only one kind of phase in each glassy matrix: α-As2Te3 (green color) in Cu20As35Te45, β-As2Te3 (red color) in Cu15As30Te55, AsTe3 (blue color) in Cu15As20Te65.

Figures 9a and9b show the Raman spectra of α-As2Te3 and β-As2Te3 bulk materials under ambient conditions together with the theoretically predicted frequencies (marked by vertical ticks). In order to interpret the Raman spectra of the α-and β-As2Te3 compounds, lattice dynamics calculations have been performed using DFT.

From structure relaxation calculations with both PBE and PBE-D2 exchange-correlation functionals, we found that the calculated crystal lattice parameters are in better agreement with the experimental ones when van der Waals interaction is taken into account as with the PBE-D2 exchange-correlation functional. [START_REF] Morin | [END_REF]43 This is especially evident concerning the rhombohedral angle R for β-As2Te3 and the lattice parameter a for monoclinic α-As2Te3 (see Tables 1 and2). As these compounds are layered compounds, this is related to the nature of chemical bonding between the layers which are of van der Waals type and to the much larger van der Waals interspace between the layers in -As2Te3 than in Sb2Te3 or Bi2Te3. 39 [START_REF] Morin | [END_REF]43 Of note, a better agreement with experiments was obtained for α-As2Te3 using the D2-PBE exchange-correlation functional without spin-orbit. These results thus contrast with the calculations performed by Cuenca-Gotor et al. who used PBE exchange-correlation functional including spin-orbit interaction. 43 This discrepancy suggests that the van der Waals interactions affect more significantly these calculations than the spin-orbit coupling does in these layered compounds. In good agreement with the experimental findings, we find that the monoclinic phase is more stable than the rhombohedral phase at 0 K by about -0.58 kJ/mole.at and -0.8 kJ/mole.at for the PBE-D2 and the PBE exchange-correlation functionals, respectively. The last value compares well with that calculated by Morin et al. (-0.96 kJ/mole.at) using similar PBE exchange-correlation functional. [START_REF] Morin | [END_REF] Hereafter, because the PBE-D2 exchange-correlation functional better describes the structure of both As2Te3 phases, we will consider only the lattice dynamics calculations performed with this functional.

According to group theory, the decompositions of the lattice vibration modes in irreducible representation are the following:

- As seen in Figure 9, the agreement of our calculations with experiments is quite reasonable for the full phonon spectra of both As2Te3 crystalline phases. More specifically, above 150 cm -1 , we found a slightly larger Raman shift for the higher energy Raman active mode at about 200 cm -1 in the case of the -As2Te3 phase compared to the -As2Te3 phase, as experimentally observed (Figure 9). These modes correspond to As-Te stretching-like modes with Ag and A1g symmetry for the and -As2Te3 phases, respectively. In the case of -As2Te3, the Te1 atoms located in the center of the layers remain motionless. The twofold degenerated Eg modes and the A1g modes correspond to motions within the layers (intra-layer vibrations) and along the c direction i.e. perpendicular to the layers (inter-layer vibrations), respectively.

The two highest-energy A1g and Eg modes involve large motions of the lighter As atoms while this trend is reversed for the two lowest energy and Eg modes. In the case of -As2Te3, the nature of the modes are more complex and the motions of atoms are along the monoclinic b direction and within the ac plane for the Bg modes and Ag modes, respectively.

Below 150 cm -1 , the presence of modes at about 122 and 140 cm -1 due to elemental tellurium in some of the spectra can make difficult the assignments of the modes. 43,44 This is especially true for the -As2Te3 phase since our calculations show that one Eg mode is present slightly below 140 cm -1 . One can tentatively assign the shoulder at about 150 cm -1 to this mode but further experiments are necessary before drawing a definitive conclusion. Concerning the monoclinic phase, the agreement between the Raman spectra obtained in the present work and in the work of Cuenca-Gotor et al. is rather good, the main difference coming from different amounts of elemental tellurium in the samples. 43 However, our calculations are not in agreement with some of the phonon mode assignments made by Cuenca-Gotor et al. for the monoclinic phase using lattice dynamics calculations performed with PBE functional that describes the structure less accurately. For example, the mode at 99 cm -1 should have Ag symmetry contrary to the assignment made by Cuenca-Gotor et al. Finally, in the case of AsTe3, one can assign the modes at 122 and 140 cm -1 to elemental Te and the mode at about 170 cm -1 x<to -As2Te3. 43,44 The presence of these elements might be due to partial decomposition of metastable AsTe3 induced by laser heating during data collection. However, we assign the rather broad peak at about 93 cm -1 to AsTe3 because none of the above phases has intense Raman mode in this spectral range.

Transport properties

Figures 10a-e show the temperature dependence of the electrical resistivity ρ, thermopower α, power factor α 2 /ρ, total thermal conductivity λ and dimensionless thermoelectric figure of merit ZT of the Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65 glasses and glass-ceramics. Similar information for the pure α-As2Te3, β-As2Te3 and AsTe3 crystalline phases is shown in Figure 11. Because of their layered crystalline structure, the measurements on the polymorphic As2Te3 compounds were carried out both parallel and perpendicular to the pressing direction of the dense pellets. Data derived from measurements at 375 K for all samples (glasses, glass-ceramics and crystalline phases) are listed in Table 3 for comparison.

For all compositions, crystallization of glasses leads to a drastic decrease in the electrical resistivity by at least two orders of magnitude. This phenomenon points to the presence of a percolation network achieved for each glass-ceramics, as suggested by the particle surface crystallization observed on SEM images. For Cu20As35Te45, the measured ρ values are even lower than those obtained for the pure α-As2Te3 crystalline phase. In contrast to the α-As2Te3 and AsTe3 crystalline phases that behave as semiconductors, the electrical properties of both the β-As2Te3 crystalline compound and glass-ceramics (Cu20As35Te45 and Cu15As30Te55) are characteristic of metallic systems with relatively low  and  values. According to the effective medium theory, the transport properties of a composite are bound by the properties of each of the constitutive phase of the composite. 32,[45][46][47] Thus, this theory rules out any significant effects of the phase distribution on the overall thermoelectric efficiency. Partial crystallization of the glasses systematically results in a decrease in the  values, which can be attributed to a higher thermopower of the precipitated crystalline phases. In addition, effective medium theory applied to thermopower demonstrated that above the percolation threshold of the most conductive phase (which is likely achieved in the present samples), the  values of two-phase materials tend rapidly to that of the most conducting phase. 32,49 Assuming that this applies in the present case, a rough estimate of the thermopower of the crystallites for each glass-ceramic can be inferred. The Cu20As35Te45 and Cu15As30Te55 glass-ceramics that stabilize α-As2Te3 and β-As2Te3 crystalline phases respectively, exhibit  values of 70 and 80 μV K -1 at 300 K. These results are in fair agreement with the average values of 100 and 150 μV K -1 measured on pure polycrystalline samples. For the Cu15As20Te65 glassceramic that stabilizes AsTe3, the  value of 200 μV K -1 at 300 K compares well with that measured on the polycrystalline sample. Considering the synthesis method of polycrystalline AsTe3 from congruent crystallization of amorphous AsTe3, it is no surprise that roughly the same properties are obtained. The discrepancy observed for the binaries As2Te3 further underlines the difference in nature between the α-As2Te3 and β-As2Te3 crystallites found in the glass-ceramics and those directly synthesized. The power factor of each glass-ceramic is increased by only one order of magnitude compared to that of the corresponding glass. Indeed, the overall significant decrease in electrical resistivity is counterbalanced by the decrease in α values. The maximum power factors achieved for the glass-ceramics fall in the range 50 -100 μW m -1 K -2 , that is, still one order of magnitude lower than in efficient thermoelectric materials.

The evolution of the thermal conductivity λ with the nature of the crystalline phase is also intriguing (Figure 10d). Regardless of the nature of the crystallized phase, the λ values remain very low (0.5 W m -1 K -1 ). For both Cu15As30Te55 and Cu15As25Te65, the λ values are within the range of those typically measured in chalcogenide glasses (0.3 W m -1 K -1 ). Due to the high electrical resistivity values that yield a negligible electronic contribution, the measured λ values solely reflect the lattice contribution. The slight increase in λ in Cu15As30Te55 and Cu15As25Te65 is therefore remarkable and emphasizes the role of the "coast-and-island" microstructure with the percolated conducting phase and the complex dendritic local microstructure of the As2Te3 phases both of which likely acting as efficient phonon scatterers.

Finally, despite an enhancement of the ZT values in all glass-ceramics compared to their respective parent glasses, the electrical resistivity values remain too high to yield interesting thermoelectric properties. Nevertheless, an almost sevenfold increase in ZT is achieved in Cu15As30Te55 glass-ceramic with a value of 0.07 at 375 K. This value is similar to that observed for this particular composition in our prior study. 15 A similar maximum ZT value of 0.08 is reached at 375 K in the Cu15As25Te65 glass-ceramic.

Conclusion

The Glass-ceramics with nearly comparable crystalline fractions (30% in volume) were successfully prepared, which enabled an objective comparison of the influence of the nature of the crystalline phase on the glass-ceramic physical properties. Raman spectroscopy mapping coupled to SEM unambiguously show the localization of the crystallites within the glassy matrix revealing a "coast-and-island" microstructure. This microstructure, ideal to ensure an electrical percolation of the highly-conducting ordered phase, results in a drastic decrease in electrical resistivity accompanied by a very moderate increase in the thermal conductivity. This study may pave the way to the fabrication of either known or yet-to-be discovered novel compounds by glass recrystallization.

Figure 1 . 29

 129 Figure1.[START_REF] Borisova | Glassy Semiconductors[END_REF]

Figure 1 .

 1 Figure 1. Vitreous domain and compositions of interest in the Cu-As-Te ternary system. The

Figure 2 .

 2 Figure 2. DSC curves of the glass compositions Cu15As30Te55 (powder), Cu15As20Te65 (bulk

Figure 3 .

 3 Figure 3. PXRD patterns of the Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65 glasses (G) and

Figure 4 .

 4 Figure 4. SEM images in backscattered electron mode of the microstructure of the different

Figures

  Figures 5a, 5b and 5c show the 2D thermodiffractograms collected between 460 and 488

Figure 5 .

 5 Figure 5. 2D plots of the neutron powder thermodiffraction data (nominal wavelength λ = 2.52

structure 39 ,

 39 for which the main changes are the expansion of the hexagonal lattice parameters to the values a = 4.134 Å and c = 30.728 Å as well as a random replacement of 37.5% of the As atoms in their 6c site by Te atoms, to fulfill the 1:3 stoichiometry requirement. Because of the use of this approximant, weak lines remained unindexed and the reliability factors kept moderately large values (Rp = 16.9 %, RWP= 21 %, and χ² = 12.2). This Rietveld analysis thus strongly suggests that the crystalline phase AsTe3 is the main component at this temperature (~ 67%, a = 4.134 Å and c = 30.728 Å), before α-As2Te3 (~ 14%, a = 14.126 Å, b = 4.027 Å, c = 10.041 Å,  = 96.66°), Cu1.4Te (~ 16%, a = 3.981 Å, b = 4.033 Å, c = 6.119 Å) and AsTe (~ 3%, a = 5.767 Å).

Figure 6 .

 6 Figure 6. Magnification of the 2D maps of the neutron diffraction data of the (a) Cu20As35Te45,

Figure 7 .

 7 Figure 7. Rietveld refined neutron powder diffraction pattern recorded at 432K in

First, we

  recorded 2D Raman maps on each glass-ceramic (Figures8a, 8b, 8c). The maps have been reconstructed by multivariate data analysis method (Direct Classical Least Squares component analysis, DCLS).

Figure 8 .

 8 Figure 8. Raman scattering maps of the (a) Cu20As35Te45 (b) Cu15As30Te55 and (c) Cu15As20Te65

Figure 9 .

 9 Figure 9. (a) Raman spectrum of the monoclinic α-As2Te3 phase together with the position of

Table 1 . 39 Table 2 .

 1392 Crystal parameters (in Å) of the β-As2Te3 rhombohedral phase calculated by DFT with PBE and PBE-D2 exchange-correlation functionals compared to experiment results from Morin et al. Lattice parameters (in Å) of the α-As2Te3 monoclinic phase calculated by DFT with PBE and PBE-D2 exchange-correlation functionals compared to calculations with PBE exchange-correlation functional including spin-orbit and with experiment results from Cuenca-Gotor et al. and Morin et al.

   = 10 Ag  5 Bg  5 Au  10 Bu (including the acoustic modes of Au  2 Bu symmetry) for α-As2Te3; - = 2 A1g  2 Eg  3 A2u  3 Eu (including the acoustic modes of A2u  Eu symmetry) for β-As2Te3. For α-As2Te3, 15 Raman-active modes of Ag and Bg symmetry and 12 Raman-active modes of Au and Bu symmetry exist while for β-As2Te3, only 4 Raman-active modes of A1g and Eg symmetry and 4 Raman-active modes of A2u and Eu symmetry are present.

Figure 10 . 3 .

 103 Figure 10. (a) Electrical resistivity ρ, (b) thermopower α, (c) power factor, (d) total thermal

  influence of partial crystallization of Cu-As-Te glasses on their microstructural and physical properties was studied for three different Cu20As30Te45, Cu15As30Te55 and Cu15As25Te65 compositions. The differences in the chemical composition along with the versatility of the SPS technique allow for fine tuning of the phases crystallizing in the glassy matrices. The results evidenced the possibility to crystallize α-As2Te3, β-As2Te3 or the as-yet unknown binary AsTe3 phases among which the latter two are metastable under ambient conditions. The thermodiffraction data confirms that these crystalline phases are the first to precipitate in the corresponding glasses, that is, α-As2Te3, β-As2Te3 and AsTe3 in Cu20As35Te45, Cu15As30Te55 and Cu15As20Te65 glass compositions, respectively. A complementary study by Raman spectroscopy coupled with DFT calculations taking into account van der Waals interactions provides an accurate description of the lattice dynamics in both As2Te3 phases.

  Cu15As30Te55 and Cu15As20Te65 glass compositions, their corresponding glass-ceramics and the pure α-As2Te3, β-As2Te3 and AsTe3 crystalline phases at 375 K. (Some thermoelectric properties were measured in the perpendicular ⊥ and parallel // direction of the pressing direction).

Figure captions Figure 1 .

 captions1 Figure captions

Figure 2 .

 2 Figure 2. DSC curves of the glass compositions Cu15As30Te55 (powder), Cu15As20Te65 (bulk

Figure 3 .

 3 Figure 3. XRD patterns (nominal wavelength λCu = 1.54 Å) of the Cu20As35Te45, Cu15As30Te55

Figure 4 .

 4 Figure 4. SEM images in backscattered electron mode of the microstructure of the different

Figure 5 .

 5 Figure 5. 2D plots of the neutron powder thermodiffraction data (nominal wavelength λ = 2.52

Figure 6 .

 6 Figure 6. Magnification of the 2D maps of the neutron diffraction data of the (a) Cu20As35Te45,

Figure 7 .

 7 Figure 7. Rietveld refined neutron powder diffraction pattern recorded at 432K in

Figure 8 .

 8 Figure 8. Raman scattering maps of the (a) Cu20As35Te45 (b) Cu15As30Te55 and (c) Cu15As20Te65

Figure 9 .

 9 Figure 9. (a) Raman spectrum of the monoclinic α-As2Te3 phase together with the position of

Figure 10 .

 10 Figure 10. (a) Electrical resistivity ρ, (b) thermopower α, (c) power factor, (d) total thermal

Figure 11 .

 11 Figure 11. (a) Electrical resistivity ρ, (b) thermopower α, (c) total thermal conductivity λ and

Table captions Table 1 .

 captions1 Crystal parameters (in Å) of the β-As2Te3 rhombohedral phase calculated by DFT with PBE and PBE-D2 exchange-correlation functionals compared to experiment results from Morin et al.[Morin].

Table 2 .

 2 Lattice parameters (in Å) of the α-As2Te3 monoclinic phase calculated by DFT with PBE and PBE-D2 exchange-correlation functionals compared to calculations with PBE exchange-correlation functional including spin-orbit and with experiment results from Cuenca-Gotor et al. [Cuenca-Gotor] and Morin et al [Morin].

Table 3 .

 3 Density, crystalline fraction and thermoelectric properties of the Cu20As35Te45,

Acknowledgements

The authors would like to thank financial support from the French National Agency (ANR) in the frame of its program "PROGELEC" (Verre Thermo-Générateur "VTG").

in both α-As2Te3 and β-As2Te3 are present and strongly affect the thermoelectric properties through variations in the carrier concentration. 20,35,48


Nicolas Boffo
email: nicolas_boffo@yahoo.com

Philippe Lambert
email: philippe.lambert@univ-lorraine.fr

Linguistics, applied research and NLP: using NooJ in a technico-operational context. Case-study, analysis and perspectives

Keywords: NLP, NOOJ, functional, operational, technico-operational, technico-functional, reactivity, adaptability, interoperability, dataviz, spatio-temporal visualization of events, QGIS, poorly endowed language, Vietnamese language

NooJ is especially used to formalize languages and linguistic usages for research and didactic purposes, but also to be integrated into information processing technologies such as monitoring systems, semantic search engines, etc. Futhermore, NooJ can also be considered as a major system component in a very functional way or operational context. Nowadays, most of the information systems connected to economic intelligence must technically respond to the three important dimensions: reactivity, adaptability and interoperability. These constraints set up the background of our operational approach. The main purpose of our paper is to demonstrate the potential of NooJ not only for fundamental research in linguistics but also for operational objectives. Our paper will firstly present the linguistic work carried out on a poorly endowed language like Vietnamese for which we build up specific linguistics resources. Then, our study will present the first results of a visual representation of the information extracted by NooJ within a technico-functional uses: dataviz, spatial visualization of events with free and open source Geographic Information System QGIS and timeline visualization. Finally, we will analyze the uses of NOOJ in a technico-operational context by pointing out its weaknesses and strengths suggest innovative ways to improve NooJ tool.

Introduction

In "How the DEM and LVF can serve Digital Humanities" [20] ", the limits of certain statistical analysis tools such as Sketch Engine 1 are pointed out. Indeed, the lexical-semantic fields calculated by this type of software "are not reliable" and "one should absolutely avoid selecting them when one wants to analyze the 1 Cf. Kilgariff (2004) P r e p r i n t 2 archives of a daily newspaper to estimate the evolution of the morale of the French or to find indices of depression in psychological interviews, at the risk of obtaining totally random results". [20] Moreover, Max Silberztein concluded : "We hope that social scientists who need to explore and analyze their corpus will appreciate the qualitative gain obtained when one analyzes a text from its linguistic units (concepts, entities, predicates and relations) rather than from its simple graphic forms." [20] Our approach will be less dichotomous : Expert Systems vs Stochastic Systems.

Indeed, this opposition between the expert system and stochastic system is even stronger nowadays by the fact that Artificial Intelligence (AI) with Deep Learning models is becoming is gaining momentum.

By the way, in this regard, there was a turning point in 2018 in the field of NLP with the arrival of the BERT model (Bidirectional Encoder Representations from Transformers) from Google, and more recently with the ERNIE 2 model from the Chinese tech giant Baidu which dethroned the two American giants Google and Microsoft in the ranking [START_REF] Boffo | Approche technico-fonctionnelle avec NOOJ : Le cas du traitement spatiotemporel de la presse vietnamienne[END_REF] of General Language Understanding Evaluation, otherwise known as GLUE [START_REF] Charolles | L'encadrement du discours : Univers, champs, domaines et espaces[END_REF] .

Despite these advances, is this the end of expert systems and symbolic AI?

No, far from it.

We are going to show that expert systems such as NOOJ have their place, especially in an area that is not economically profitable for NLP companies and that annoys the IT System Department of organizations because it does not meet the strict rules of IT project management.

We will call this zone : the techno-operational and/or functional zone. This area includes the following activities: discourses analysis, KMS, prospecting, investigation,..., all important activities for an organization where the NOOJ engine will have a real added value.

We will then ask the question to know if NOOJ is accessible for users working on language data with a need for dataviz and mapping in technico-operational context. Therefore, our article will be structured as follows: 2 https://github.com/PaddlePaddle/ERNIE 3 https://gluebenchmark.com/leaderboard 4 https://gluebenchmark.com/ P r e p r i n t

2

Define and conceptualize the technico-operational/functional approach Initially, we find the expression technico-operational within the armies which have the vocation to carry out operational missions.

The first approach is : Technico-operational in the context of experimentation/simulation : Indeed, we find first of all the "Technico-operational foresight studies (PTO), which provide elements of appreciation for the expression of future needs..., technico-operational studies (ETO), which are used to optimize, for future systems or within the framework of evolutions of existing systems, the operational characteristics, technical specifications as well as the associated costs." [START_REF] Charolles | Les cadres de discours et leurs frontières[END_REF] Here, we are more upstream by the fact that it concerns the studies and not the operations and the functional mission itself. We will see more that the technico-operational (or functional) approach that we will define is at the bottom of the pyramid.

Staff profiles :

1. The technico-operational experts 6 of a domain working for example in a Technical Department whose mission is: a. to capture the operational need and translate it into Technico-Operational requirements, 5 https://www.ixarm.com/fr/Presentation%2C88413 6 https://fr.linkedin.com/jobs/view/expert-technico-operationnel-cyber-securit%C3%A9-h-f-at-thales- 1621909449 P r e p r i n t b. to ensure the relevance of the technical content with respect to the technico-operational need 2. the specialists of the means of simulations 7 a. Ensure the implementation and the technico-operational follow-up of simulation means.

This category of staff will then be found in organizations such as the CATOD (Centre d'Analyses Technico-Opérationnelle de Défense = Center for Technico-Operational Analysis of Defense) which is the establishment that provides the organizations of the Ministry of the Armed Forces with decision-making assistance in the areas of forecasting, analysis, expression of need, realization and employment of weapon systems, in the form of studies or experiments." [START_REF] Foucard | La bôite à outils du Pilote des Systèmes d'information[END_REF] Nowadays, we must not forget the digital transformation within the organizations, and for that it is essential to "bring the IT department closer to the business" and "the new digital leaders have largely overcome the mutual distrust between business and IT." Indeed, "recruiting dual profiles" such as "technico-functional expert...will also be a good way to create bridges between departments with often incompatible training, languages and practices." [7] The developer Benjamin Delespierre in the website www.medium.com presents the cleavage that exists between technical and operational staff and, in certain cases, this can lead to the formation of clans within the company.

Clans whose members hate each other on principle: «« in any case, they understand nothing of what we do. It's not worth talking to them ». When you get to that point, there's no point in talking about collaboration and synergy within the company. I've seen it many times, there is little mixing of technical and non-technical people.

You don't have to be a management expert to understand that the project, and by extension the entire company, will suffer in the end. » [START_REF] Phuong | Ngu phap tieng viet nhung van de thoi, the[END_REF] But some people choose to combine the technical with the operational and/or functional in a submarine mode or in full visibility depending on the organization to which they belong. 7 REM defense : https://www.defense.gouv.fr/fre/content/download/538408/9248195/REM 2019 final.pdf 8 https://www.defense.gouv.fr/dga/recrutement2/paris/paris-ingenierie 9 https://medium.com/france/les-d%C3%A9veloppeurs-sont-devenus-des-cols-bleus-457bd6287631 P r e p r i n t

Those people are considered as Shadows IT [START_REF] Lambert | Modules NOOJ de traitement de la langue vietnamienne[END_REF] and hackers because they do not respect the standards. Nevertheless, they are useful.

With their corporate hacker [START_REF] Lambert | VIET4Nooj A Vietnamese module for Nooj[END_REF] spirit, they show that there is often no ready-made tool to meet the need. This includes both technical missions in an operational environment, known as "technico-operational", as well as the staff performing them.

Therefore, the second approach (the one we are interested in) is :

Technico-operational (functional) approach:

By staff we mean 2 categories:

• The first one being thestaffs with a high level of expertise : specialists, technicians, engineers, operationals evolving in a technico-operational context and working very often in a business direction for which they have to carry out specialized missions requiring a particular technicality and expertise on the ground in operational situations (e.g.: analysis, data processing, …).

• The second is the junior staff with a strong affinity for technology, information, languages,…,who work in fast thinking and action mode and who then adopt what is called the system D.

Our observation of business needs allowed us to draw a first picture defining the technico-operational approach and a schema of reasoning and process of technico-operationnal (functionnal) approach (see Table 1).

The following table gives a first definition of our approach : P r e p r i n t

TECHNICO-OPERATIONAL (FUNCTIONAL) APPROACH IN NLP Description of the approach Business applications of the approach

• Missions • People • Technical • Functional • NLP • Linguistic • Generally new themes
• Context requires a strong reactivity and adaptability

• Quick execution of tasks • One-shot task • Limited time • Limited cost • Prospecting • Investigations • Geopolitical analysis • Discourse analysis • Text analysis
• Analysis of poorly endowed languages

• Knowledge Management • OSINT Fig. 1.
Reasonning and process of technico-operationnal (functionnal) approach.

Regarding the technico-operational approach, it is important to accept to break silos even if some say that IT shodows can create data silos, in order to achieve a certain technical + operational/functional transversality without harming the specialists' fields as described in Fig. 1.

P r e p r i n t

Case-study : NOOJ in a technico-operational context

A recent experiment in press analysis on "Qualitative Study of Dalian Wanda-AMC" presented in Sisi Zhao's Master's thesis [25], provides feedback on the use of NOOJ in a technical-functional context (press analysis) very close to our work which states that : "Overall, this researcher's experience with NOOJ was mixed: good for suggesting paths of inquiry and possibly seeing things not seen before, but not necessarily useful when doing a qualitative analysis, which still requires deep thinking about the text". [25] We agree that NOOJ is a good tool for suggesting lines of inquiry and possibly seeing things not seen before. This is one of the reasons why we chose NOOJ technology.

However, regarding the point of Sisi Zhao that NOOJ is not necessarily useful to do a qualitative analysis, which always requires a deep reflection on the text. This is normal because NOOJ is a tool to formalize the language. In any case NOOJ requires an entry cost in the analysis of the language corpus on which we are working.

With the objective of testing NOOJ in a technical/operational/functional context, we decided to work on the Vietnamese language which is a poorly endowed language: P r e p r i n t

• very few annotated corpora.

• Vietnamese is a tonal and monosyllabic language.

• no verbal tenses.

• tense, aspect and modality markers.

• Compatible with Temporal Frames according to Michel Charolles' definition [4].

Our corpora will be from the Vietnamese online press.

Spatio-temporal treatment in a technical-operational/functional approach : the case of the Vietnamese press

The Vietnamese language has :

Tenses : Aspect Past Present Futur Neutral Accompli (đã) Progression (đang) Iterative (V+lại) Terminative (xong, hết, thôi, etc.) Imminente (sắp)
Some illustrations :

Thẻ đã mua, xin miễn đổi lại. (Once bought, this card is not exchangeable.) đã = action is accomplished/finished.

Hôm qua khi tôi đang xem TV thì điện thoại reo. (Yesterday, when I was washing TV, the phone rang.)

Tense : Past and aspect : đang = action is "during".

Nếu bạn vượt đèn đỏ thì bạn sẽ bị phạt. (Si vous brûlez le feu rouge, vous êtes pénalisé.) sẽ = action is after.

(From Cao Xuan Hao (1998) & Danh Thanh Do-Hurinville (2009)) [6][14].

In our process we will use the spatio-temporal Frames according and discourse frames and their boundaries from Michel Charolles [4] [5].

His conceptualization can be easily implemented in the linguistic development environment NOOJ as the following syntactic grammar of aspectuo-temporal frames and markers (see Fig. 3.) : P r e p r i n t After some pre-and post-processing of a corpus of 450 press articles, by using Python scripts, we obtain the following table (see Fig. 5) of the events announced by the chairmen and vice-chairmen of the people's committees of different localities in Vietnam.

P r e p r i n t And then, we process this information in the free software QGIS [START_REF] Lambert | A new model of Time Expressions Detection and Annotation in Vietnamese : The hôm case[END_REF] in order to have a mapping of the events as in following Fig. 6.

12 https://www.qgis.org/en/site/ P r e p r i n t P r e p r i n t

Knowledge Management System (KMS)

Knowledge Management and Personal Knowledge Management : definitions and applications

Definitions

When we refer to Knowledge Management, the first problem we face is the definition of the concept. Since the 1960s, management sciences have been trying to define theoretical frameworks for valuing the processes of moving from data to knowledge. Let's give some of them here in order to show what they can overlap:

For Dudezert, "The company's knowledge in all areas of expertise (research and development, production, purchasing, marketing, accounting, finance, etc.) is becoming a resource to be managed in the same way as a fleet of machines or the skills of employees. In order to face this challenge, companies have to set up specific management approaches called Knowledge Management (KM).

One of the most authoritative definitions comes from Jean-Yves Prax who breaks down Knowledge Management into four functional definitions:

1. Utilitarian definition: It defines Knowledge Management as a solution to the overabundance of information characteristic of the Web. It allows to provide a personalized and relevant answer in due time, without the request having been clearly explained (answer to a tacit request).

2. Operational definition: It is about combining knowledge and know-how in processes, products, and organizations to create value. In other words, the improvement of a company's performance requires the combination of knowledge (explicit and diffusible) and know-how (tacit and non diffusible).

3. Functional definition: This is the most widespread definition, which consists of describing Knowledge Management through the knowledge life cycle (formalization, validation, dissemination, etc.) and the devices necessary for its implementation (collaborative work, project management, EDM, etc.). According to Jean-Yves PRAX [START_REF] Lambert | Using NooJ in a Process of Economic Intelligence: Producing Knowledge for Information Monitoring and Re-indexing Content[END_REF] , this definition is limited because it specifies how to do Knowledge Management and not what it is and why to do it.

Economic definition:

It is a question of developing the intellectual capital of the company, i.e. all the knowledge and know-how, and of exploiting the skills already present, in order to improve its productivity.

13 Prax, Manuel du knowledge management.

P r e p r i n t 13

A definition that would correspond more to our approach comes from Jean Michel 14 who distinguishes four distinct processes feeding the KM logic:

1. a process of collecting data, information, knowledge rules, feedback and other reports, 2. a process of modeling and extracting meaning, reformulation, elaboration of synthesis, creation of knowledge trees; it is a matter of moving from I (Information) to C (Knowledge) and 3. a process of collection, capitalization, and conservation of information 4. a process of redistribution and sharing with responses in either "push" or "pull" mode 5. finally, a process of dynamization-regulation of all the previous processes with a concern for evaluation".

Personal Knowledge Management

With Personal Knowledge Management, we move to another scale, one where the human being is truly put back at the heart of the knowledge equation.

Like Knowledge Management, there are a plethora of definitions, the two main characteristics of which are: 1/ a conceptual framework that organizes and integrates the information that we consider important and that should be part of our knowledge base and 2/ a strategy for transforming what can be considered as pieces of information that extend our personal knowledge base. David Pauleen 15 from the University of New Zealand explains very well in an article dedicated to this theme that the basis of PKM is the notion of knowledge worker developed in 1998 by Davenport and Prusak [START_REF] Qgis | Système d'Information Géographique Libre et Open Source[END_REF] . On this basis, Jefferson will explain in 2006 that the technological revolution, with its uninterrupted flow of information, has made Personal information management systems (PIM) pivot towards PKM systems. First in a learning logic, since it is at the university that these issues became more pressing, then, more globally, in a managerial logic affecting all fields.

One of the important theoretical bases of KM is given by Nonaka and Takeuchi [START_REF] Schwer | Toward Time Universals Identification in NooJ : A New Model of Time Recognition in Vietnamese[END_REF] , with two key dimensions: tacit or subjective knowledge and explicit or objective knowledge. In the technical-operational approach we present, our effort has been 14 Michel, « Le knowledge management, entre effet de mode et (ré)invention de la roue... » 15 Pauleen, « Personal Knowledge Management ». 16 Davenport et Prusak, Information ecology: Mastering the information and knowledge environment. 17 Nonaka et Takeuchi, The knowledge-creating company: How japanese companies create the dynamics of innovation.

P r e p r i n t focused on transforming tacit knowledge into actionable explicit knowledge for intelligence analysis.

The PKM system we used is based on two software bricks: a first brick for information capitalization and another brick for automatic language processing. Since 2018, several PKM software have emerged with specific information processing functionalities, the main ones being search, categorization, structuring and integration. We can mention solutions such as Roam, Obsidian Bear or Notion that have met their public among the dozens of others available on the market.

Applying NooJ Linguistics Analysis throughout PKM frameworks

The framework

The main logic behind the implementation of this case study is the possibility for analysts to have a tool for capitalizing on information for their operations. The implementation of this tool had to meet three main constraints that we set ourselves in order to reproduce as accurately as possible the professional environment of the analyst:

1. An easy handling of the system via a turnkey system, intuitive and can be set up quickly.

2. Minimizing the risk of being hacked by offering the analyst the possibility to host the solution on his own server with controlled data flows. SAAS type software was therefore not privileged for our case study.

3.

A system with functionalities that facilitate the exploitation of information, in this case through the use of a pivotal format for processing data (markdown) and specific software functionalities (visual representation of information for a Social Network Analysis)

Data processing for exploitation purposes

The corpus

The test is based on a continuous exploitation of articles from the Vietnamese general press. The RSS feeds of three major newspapers of the National Press (Tuoi Tre, Thanh Nien, Nguoi Lao dong) were browsed daily over a week in order to extract the most recent articles. Each news feed had between ten and forty articles for a total of +1.5K documents.

P r e p r i n t

The corpus obtained is a generalist corpus, including the information that the Vietnamese propaganda authorities wanted to highlight throughout the week. One of the objectives of the processing described below is to be able to quickly detect the major current affairs themes of the Vietnamese society.

Preparation of the corpus and processing of the corpus

The corpus used is composed of +1.5K raw text coming from the extraction of the RSS feeds of the three above-mentioned sites to extract three variables: the date, the author, the content of the article. These variables are reintegrated into XML files, which allows NooJ to process specific nodes. In parallel, with the Pandas library, a DataFrame is created gathering the documentary source and its variables. It will then be completed with the results of NooJ extractions (see below).

For this case study, we have created two types of linguistic resources: a specific dictionary with more than 15K entries, each of which is made up of the lexeme, its grammatical nature and a series of labels linking the term to its theme. For example, for proper nouns, we have two resources: the first is a dictionary with the first and last names of political figures as entries, followed by their functions and then the state organization to which they belong. The second resource is a grammar that extracts proper names (see Fig. 8.) The linguistic resources we have developed allow us to extract three types of named entities: proper nouns, dates, and places (see Fig. 9). Concerning the information capitalization and visualization software layer, we chose Obsidian which is a new cross-platform PKM software allowing a complete management and visualization of relational links between several notes. The main advantage of this fast growing software is that it has a very active community of developers and that the texts produced can be placed on a local machine or a synchronized server, which considerably reduces the risk of data piracy.

The results of the NooJ extractions are added to the python dataFrame which then allows the production of markdown files integrating these results. A markdown file consists of a YAML header (data serialization format) including the file creation date and the keywords (see Fig. 10). Using NooJ with Obsidian allows the analyst to structure the information he collects, to link the notes with the backlinks from the wiki logic and to produce knowledge based on the visualization of the information. There are specific Obisidan plugins that allow the processing of the named entities we extracted with NooJ: a timeline production plugin and a geolocation plugin that allows to integrate geographical maps from the GPS points of the named entities of places. Linked to the textual graph, the system offers a dynamic representation of the knowledge produced.

P r e p r i n t

The other interesting point of the system is that the analyst is at the heart of the process of structuring the information he collects to produce intelligence.

Conclusion

To conclude, we were able to lay the first stones of the definition and conceptualization of the technical-operational/functional approach in NLP. This allows us to open the bibliographic field on this approach.

Following our experimentation, we note that NOOJ is compatible with a technical/operational/functional use in the context of discourse analysis and knowledge management.

However, NOOJ requires some expertise, for example when implementing models like Michel Charolles's discourse frameworks.

Nevertheless, a normal user can extract named entities without being an expert. But we would recommend him to follow the NOOJ course.

We can deal with poorly endowed languages vs AI and statistical model.

We should note that it was not possible for us to evaluate our grammars due to the lack of annotated corpora.

P r e p r i n t

In a context that requires reactivity and strong adaptation, should we stop a system that has not yet been calibrated and evaluated? Or should we evaluate it in Agile mode, iteration by iteration or even a posteriori, especially if it has already fulfilled its mission of finding relevant information for which the user would have had difficulty finding it without tools such as NOOJ?

Perspectives

Since mid 2021, on the GITLAB repository, a new open source version of NOOJ written in SWIFT https://gitlab.com/Silberz/RA is being created. Indeed, the university professor Max SILBERZTEIN has taken the option to put a mutli-OS compatible version to the NLP community.

We are convinced that this new version of NOOJ named RA will allow to integrate into a real TOOLKIT that will help people working in an operational/functional context.

To overcome the level of expertise that would be required to use such a However, RA will need to interface with several open source technologies in order to be able to do fully automated end-to-end processing, and then provide some modularity to RA.

To overcome the level of expertise that would be required to use such a toolkit, it will be necessary to foresee reflex cards based on logigrams but also to conceive and conceptualize the construction of NOOJ grammars by using, for example, blocks like in Pythons for Kids [START_REF] Serrano | Vers une capitalisation des connaissances orientée utilisateur : extraction et structuration automatiques de l'information issue de sources ouvertes[END_REF] or Scratch [START_REF] Silberztein | La formalisation des langues, L'approche de NooJ[END_REF] .

Finally, we could use the Analysis of Competing Hypotheses (ACH) [START_REF] Silberzteinm | Les dictionnaires DEM et LVF au service des humanités numériques[END_REF] whose challenge would be to see if we can filter the ACH results with NooJ grammars to corroborate the hypotheses. 18 http://jasonrbriggs.com/python-for-kids/ 19 https://scratch.mit.edu/ 20 ACH : « Analysis of competing hypotheses, sometimes abbreviated ACH, is a tool to aid judgment on important issues requiring careful weighing of alternative explanations or conclusions. It helps an analyst overcome, or at least minimize, some of the cognitive limitations that make prescient intelligence analysis so difcult to achieve. », Chapter 8 Analysis of Competing Hypotheses, Psychology of Intelligence Analysis by Richards J. Heueur, Jr. Center for the Study of Intelligence, CIA, 1999.

P r e p r i n t 1

3 2 .

 2 Define and conceptualize the technico-operational (or functional) approach.

  10 https://www.lemagit.fr/definition/Shadow-IT 11 Understanding corporate culture hacking a new-found source of pleasure and efficiency in the work- place, 2018, WAVESTONE.

Figure 2 .

 2 Figure 2. Scope of our « technico-operational approach » concept.

Fig. 3 .Fig. 4 .

 34 Fig. 3. Syntactic grammar of aspectuo-temporal frames and markers in vietnamese (Boffo 2010, 2012, 2013, 2014, 2021) [2] [3] [9] [10] [12] [17]Then the processing of the spatial information is done in part via the extraction of the functions of the people linked to a locality as described in the grammar below (see Fig.4):

Fig. 5 .

 5 Fig. 5. -Table of events geolocated announced by the chairmen and vice-chairmen of the people's committees of different localities in Vietnam.

Fig. 6 .

 6 Fig. 6. -Map of events of the chairmen and vice-chairmen of the people's committees in Vietnam by using QGIS.For your information, we used to do the chronological visualization with the open source solution SIMILE TimeLine (see Fig.7.) which accepted XML and JSON files. Unfortunately, although it still works, the library is no longer maintained.

Fig. 7 .

 7 Fig. 7. https://www.simile-widgets.org/timeline/ Finally, this use case demonstrates the operationality of NOOJ in a context of operational analysis of the Vietnamese press combined with geographic information processing.

Fig. 8 .Fig. 9 .

 89 Fig. 8. Extraction graph for Proper Nouns

Fig. 10 .

 10 Fig. 10. : Example of a typical file consisting of a YAML header including the tags extracted from NooJ

Table 1 :

 1 Definition

table for the technico-operational (functional) approach.