Development of an optical redox chemical sensor for nitrite determination

An optical chemical sensor for the determination of nitrite based on incorporating methyltrioctylammonium chloride as an anionic exchanger on the triacetylcellulose polymer has been reported. The response of the sensor is based on the redox reaction between nitrite in aqueous solution and iodide adsorbed on sensing membrane using anion exchange phenomena. The sensing membrane reversibly responses to nitrite ion over the range of 6.52×10-6 - 8.70×10-5 mol L-1 with a detection limit of 6.05×10-7 mol L-1 (0.03 µg mL-1) and response time of 6 min. The relative standard deviation for eight replicate measurements of 8.70×10-6 and 4.34×10-5 mol L-1 of nitrite was 4.4 and 2.5 %, respectively. The sensor was successfully applied for determination of nitrite in food, saliva and water samples.

Monitoring of praseodymium(III) ions in aqueous solutions, soil and sediment samples by a PVC membrane sensor based on a furan-triazole derivative

A furan-triazole derivative has been explored as an ionophore for preparation of a highly selective Pr(III) membrane sensor. The proposed sensor exhibits a Nernstian response for Pr(III) activity over a wide concentration range with a detection limit of 5.2×10-8 M. Its response is independent of pH of the solution in the range 3.0-8.8 and offers the advantages of fast response time. To investigate the analytical applicability of the sensor, it was applied successfully as an indicator electrode in potentiometric titration of Pr(III) solution and also in the direct and indirect determination of trace Pr(III) ions in some samples.

Potentiometric determination of Nickel (II) ion using 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone as electroactive material

A potentiometric Nickel sensor was prepared using 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone as electro-active material and epoxy resin as a binding material. A membrane composed of 40% Schiff's base and 60% epoxy resin exhibited the best performance. The membrane showed excellent response in the concentration range of 0.15 ppm to 0.1 mol L- 1 Ni+2 ions with non-Nernstian slope of 22.0 mV/decade, had a rapid response time (less than 10 s), and can be used for three months without any considerable loss of potential. The sensor was useful within the pH range of 1.3 to 9.6, and was able to discriminate between Ni2+ and a large number of alkaline earth and transition metal ions. The practical utility of the sensor has been demonstrated by using it successfully as an indicator electrode in the potentiometric titration of Ni2+ with EDTA and oxalic acid.

Luistonestojärjestelmän ja elektronisen tasauspyörästön suunnittelu ja implementointi hybridityökoneympäristöön

Ympäristörasituksen vähentäminen, tiukkenevat päästörajat ja ehtyvät öljyvarat ovat ajaneet kulkuvälineteollisuuden hakemaan uusia vaihtoehtoja ajoneuvojen energiatehokkuuden kehittämiseksi. Hybriditeknologia tarjoaa ratkaisuja kustannustehokkuuden ja ympäristöystävällisyyden parantamiseksi. Hybriditeknologian yleistyessä myös työkoneympäristössä saadaan paitsi kehitettyä energiatehokkaampia ja pienemmillä käyttökustannuksilla olevia työkoneita, niin myös tuotua siviiliajoneuvoista tuttuja turvallisuusominaisuuksia työkoneympäristöön. Perinteisten diesel-moottorien korvaaminen nopeavasteisilla ja tarkasti säädettävillä sähkömoottoreilla tarjoaa mahdollisuuksia toteuttaa tarkempia ja monipuolisempia säätöjärjestelmiä kuin perinteisessä ympäristössä. Tässä diplomityössä suunnitellaan luistonestojärjestelmä ja elektroninen tasauspyörästö hybridityökoneympäristöön. Järjestelmä voi käyttökohteesta riippuen pienentää huomattavasti käyttökustannuksia ja mahdollistaa uusien sovellusten tuomista markkinoille, kuten esimerkiksi kääntymisen avustaminen differentiaalisella ohjauksella.

Helicopter emergency medical rescue for the traumatized: experience in the metropolitan region of Campinas, Brazil

OBJECTIVE: To analyze the profile of patients served by the air medical rescue system in the Metropolitan Region of Campinas, evaluating: triage and mobilization criteria; response time; on-site care and transport time; invasive procedures performed in the Pre-Hospital Care (PHC); severity of patients; morbidity and mortality.METHODS: We conducted a prospective, descriptive study in which we analyzed medical records of patients rescued between July 2010 and December 2012. During this period, 242 victims were taken to the HC-Unicamp. Of the 242 patients, 22 were excluded from the study.RESULTS: of the 220 cases evaluated, 173 (78.6%) were male, with a mean age of 32 years. Blunt trauma was the most prevalent (207 cases - 94.1%), motorcycle accidents being the most common mechanisms of injury (66 cases - 30%), followed by motor vehicle collisions (51 cases - 23.2%). The average response time was 10 ± 4 minutes and the averaged total pre-hospital time was 42 ± 11 minutes. The mean values of the trauma indices were: RTS = 6.2 ± 2.2; ISS = 19.2 ± 12.6; and TRISS = 0.78 ± 0.3. Tracheal intubation in the pre-hospital environment was performed in 77 cases (35%); 43 patients (19.5%) had RTS of 7.84 and ISSd"9, being classified as over-triaged. Of all patients admitted, the mortality was 15.9% (35 cases).CONCLUSION: studies of air medical rescue in Brazil are required due to the investments made in the pre-hospital care in a country without an organized trauma system. The high rate of over-triage found highlights the need to improve the triage and mobilization criteria.

Clinical and blood gasometric parameters during Vaquejada competition

ABSTRACT: Clinical and complementary analysis are good alternatives to evaluate physiological demand in performance horses. The aim of this study was to assess whether the physical effort variation of the three-day Vaquejada competition (a Brazilian form of bullfighting) reflected in clinical and blood gasometric changes. During the competition eight sprints have been performed on the first day (D1), eight on the second (D2) and three on the last one (D3). Ten horses were evaluated by checking heart and respiratory rates and collecting blood samples for use in portable chemistry analyzer. Through that, it was assessed potential of hydrogen ion (pH), carbon dioxide pressure (pCO2), bicarbonate (HCO3-) and titratable base concentration (cBase). Evaluations were carried with resting of at least twenty hours, before physical activity (D0), as control parameter, and up to thirty minutes after each sprint. Clinical parameters have increased on D1, D2 and D3, when compared to D0, which demonstrated the increased demand for substrate and oxygen to the cells.. Blood gasometric trial showed reductions of all variables, most marked between D1 and D2. It was verified less alteration of all clinical and blood gasometric parameters in D3 against D0. We concluded that the change effort between days of competition influenced the clinical and blood gas parameters, demonstrating appropriate physiological response. The data were presented as mean and standard error of the mean (mean ± SEM) obtained in different days. Normality was confirmed by the Kolmogorov-Sminov test and data were compared by one-way ANOVA, followed by post-test Holm-Sidak (GraphPad Prism 2.6 for Windows, GraphPad Software, San Diego, CA, USA). P≤0.05 was considered as statistically significant.

Combined effects of diethylpropion and alcohol on locomotor activity of mice: participation of the dopaminergic and opioid systems

The widespread consumption of anorectics and combined anorectic + alcohol misuse are problems in Brazil. In order to better understand the interactive effects of ethanol (EtOH) and diethylpropion (DEP) we examined the locomotion-activating effects of these drugs given alone or in combination in mice. We also determined whether this response was affected by dopamine (DA) or opioid receptor antagonists. A total of 160 male Swiss mice weighing approximately 30 g were divided into groups of 8 animals per group. The animals were treated daily for 7 consecutive days with combined EtOH + DEP (1.2 g/kg and 5.0 mg/kg, ip), EtOH (1.2 g/kg, ip), DEP (5.0 mg/kg, ip) or the control solution coadministered with the DA antagonist haloperidol (HAL, 0.075 mg/kg, ip), the opioid antagonist naloxone (NAL, 1.0 mg/kg, ip), or vehicle. On days 1, 7 and 10 after the injections, mice were assessed in activity cages at different times (15, 30, 45 and 60 min) for 5 min. The acute combination of EtOH plus DEP induced a significantly higher increase in locomotor activity (day 1: 369.5 ± 34.41) when compared to either drug alone (day 1: EtOH = 232.5 ± 23.79 and DEP = 276.0 ± 12.85) and to control solution (day 1: 153.12 ± 7.64). However, the repeated administration of EtOH (day 7: 314.63 ± 26.79 and day 10: 257.62 ± 29.91) or DEP (day 7: 309.5 ± 31.65 and day 10: 321.12 ± 39.24) alone or in combination (day 7: 459.75 ± 41.28 and day 10: 427.87 ± 33.0) failed to induce a progressive increase in the locomotor response. These data demonstrate greater locomotion-activating effects of the EtOH + DEP combination, probably involving DA and/or opioid receptor stimulation, since the daily pretreatment with HAL (day 1: EtOH + DEP = 395.62 ± 11.92 and EtOH + DEP + HAL = 371.5 ± 6.76; day 7: EtOH + DEP = 502.5 ± 42.27 and EtOH + DEP + HAL = 281.12 ± 16.08; day 10: EtOH + DEP = 445.75 ± 16.64 and EtOH + DEP + HAL = 376.75 ± 16.4) and NAL (day 1: EtOH + DEP = 553.62 ± 38.15 and EtOH + DEP + NAL = 445.12 ± 55.67; day 7: EtOH + DEP = 617.5 ± 38.89 and EtOH + DEP + NAL = 418.25 ± 61.18; day 10: EtOH + DEP = 541.37 ± 32.86 and EtOH + DEP + NAL = 427.12 ± 51.6) reduced the locomotor response induced by combined administration of EtOH + DEP. These findings also suggest that a major determinant of combined anorectic-alcohol misuse may be the increased stimulating effects produced by the combination.

Solid-state reference and ion-selective electrodes : towards portable potentiometric sensing

Potentiometric sensors are very attractive tools for chemical analysis because of their simplicity, low power consumption and low cost. They are extensively used in clinical diagnostics and in environmental monitoring. Modern applications of both fields require improvements in the conventional construction and in the performance of the potentiometric sensors, as the trends are towards portable, on-site diagnostics and autonomous sensing in remote locations. The aim of this PhD work was to improve some of the sensor properties that currently hamper the implementation of the potentiometric sensors in modern applications. The first part of the work was concentrated on the development of a solid-state reference electrode (RE) compatible with already existing solid-contact ion-selective electrodes (ISE), both of which are needed for all-solid-state potentiometric sensing systems. A poly(vinyl chloride) membrane doped with a moderately lipophilic salt, tetrabutylammonium-tetrabutylborate (TBA-TBB), was found to show a satisfactory stability of potential in sample solutions with different concentrations. Its response time was nevertheless slow, as it required several minutes to reach the equilibrium. The TBA-TBB membrane RE worked well together with solid-state ISEs in several different situations and on different substrates enabling a miniature design. Solid contacts (SC) that mediate the ion-to-electron transduction are crucial components of well-functioning potentiometric sensors. This transduction process converting the ionic conduction of an ion-selective membrane to the electronic conduction in the circuit was studied with the help of electrochemical impedance spectroscopy (EIS). The solid contacts studied were (i) the conducting polymer (CP) poly(3,4-ethylienedioxythiophene) (PEDOT) and (ii) a carbon cloth having a high surface area. The PEDOT films were doped with a large immobile anion poly(styrene sulfonate) (PSS-) or with a small mobile anion Cl-. As could be expected, the studied PEDOT solid-contact mediated the ion-toelectron transduction more efficiently than the bare glassy carbon substrate, onto which they were electropolymerized, while the impedance of the PEDOT films depended on the mobility of the doping ion and on the ions in the electrolyte. The carbon cloth was found to be an even more effective ion-to-electron transducer than the PEDOT films and it also proved to work as a combined electrical conductor and solid contact when covered with an ion-selective membrane or with a TBA-TBB-based reference membrane. The last part of the work was focused on improving the reproducibility and the potential stability of the SC-ISEs, a problem that culminates to the stability of the standard potential E°. It was proven that the E° of a SC-ISE with a conducting polymer as a solid contact could be adjusted by reducing or oxidizing the CP solid contact by applying current pulses or a potential to it, as the redox state of the CP solid-contact influences the overall potential of the ISE. The slope and thus the analytical performance of the SC-ISEs were retained despite the adjustment of the E°. The shortcircuiting of the SC-ISE with a conventional large-capacitance RE was found to be a feasible instrument-free method to control the E°. With this method, the driving force for the oxidation/reduction of the CP was the potential difference between the RE and the SC-ISE, and the position of the adjusted potential could be controlled by choosing a suitable concentration for the short-circuiting electrolyte. The piece-to-piece reproducibility of the adjusted potential was promising, and the day-today reproducibility for a specific sensor was excellent. The instrumentfree approach to control the E° is very attractive considering practical applications.

Comparison of anaerobic threshold determined by visual and mathematical methods in healthy women

Several methods are used to estimate anaerobic threshold (AT) during exercise. The aim of the present study was to compare AT obtained by a graphic visual method for the estimate of ventilatory and metabolic variables (gold standard), to a bi-segmental linear regression mathematical model of Hinkley's algorithm applied to heart rate (HR) and carbon dioxide output (VCO2) data. Thirteen young (24 ± 2.63 years old) and 16 postmenopausal (57 ± 4.79 years old) healthy and sedentary women were submitted to a continuous ergospirometric incremental test on an electromagnetic braking cycloergometer with 10 to 20 W/min increases until physical exhaustion. The ventilatory variables were recorded breath-to-breath and HR was obtained beat-to-beat over real time. Data were analyzed by the nonparametric Friedman test and Spearman correlation test with the level of significance set at 5%. Power output (W), HR (bpm), oxygen uptake (VO2; mL kg-1 min-1), VO2 (mL/min), VCO2 (mL/min), and minute ventilation (VE; L/min) data observed at the AT level were similar for both methods and groups studied (P > 0.05). The VO2 (mL kg-1 min-1) data showed significant correlation (P < 0.05) between the gold standard method and the mathematical model when applied to HR (r s = 0.75) and VCO2 (r s = 0.78) data for the subjects as a whole (N = 29). The proposed mathematical method for the detection of changes in response patterns of VCO2 and HR was adequate and promising for AT detection in young and middle-aged women, representing a semi-automatic, non-invasive and objective AT measurement.

Acute exercise performed close to the anaerobic threshold improves cognitive performance in elderly females

The objective of the present study was to compare the effect of acute exercise performed at different intensities in relation to the anaerobic threshold (AT) on abilities requiring control of executive functions or alertness in physically active elderly females. Forty-eight physically active elderly females (63.8 ± 4.6 years old) were assigned to one of four groups by drawing lots: control group without exercise or trial groups with exercise performed at 60, 90, or 110% of AT (watts) and submitted to 5 cognitive tests before and after exercise. Following cognitive pretesting, an incremental cycle ergometer test was conducted to determine AT using a fixed blood lactate concentration of 3.5 mmol/L as cutoff. Acute exercise executed at 90% of AT resulted in significant (P < 0.05, ANOVA) improvement in the performance of executive functions when compared to control in 3 of 5 tests (verbal fluency, Tower of Hanoi test (number of movements), and Trail Making test B). Exercising at 60% of AT did not improve results of any tests for executive functions, whereas exercise executed at 110% of AT only improved the performance in one of these tests (verbal fluency) compared to control. Women from all trial groups exhibited a remarkable reduction in the Simple Response Time (alertness) test (P = 0.001). Thus, physical exercise performed close to AT is more effective to improve cognitive processing of older women even if conducted acutely, and using a customized exercise prescription based on the anaerobic threshold should optimize the beneficial effects.

Relationship between work rate and oxygen uptake in mitochondrial myopathy during ramp-incremental exercise

We determined the response characteristics and functional correlates of the dynamic relationship between the rate (Δ) of oxygen consumption ( O2) and the applied power output (work rate = WR) during ramp-incremental exercise in patients with mitochondrial myopathy (MM). Fourteen patients (7 males, age 35.4 ± 10.8 years) with biopsy-proven MM and 10 sedentary controls (6 males, age 29.0 ± 7.8 years) took a ramp-incremental cycle ergometer test for the determination of the O2 on-exercise mean response time (MRT) and the gas exchange threshold (GET). The ΔO2/ΔWR slope was calculated up to GET (S1), above GET (S2) and over the entire linear portion of the response (S T). Knee muscle endurance was measured by isokinetic dynamometry. As expected, peak O2 and muscle performance were lower in patients than controls (P < 0.05). Patients had significantly lower ΔO2/ΔWR than controls, especially the S2 component (6.8 ± 1.5 vs 10.3 ± 0.6 mL·min-1·W-1, respectively; P < 0.001). There were significant relationships between ΔO2/ΔWR (S T) and muscle endurance, MRT-O2, GET and peak O2 in MM patients (P < 0.05). In fact, all patients with ΔO2/ΔWR below 8 mL·min-1·W-1 had severely reduced peak O2 values (<60% predicted). Moreover, patients with higher cardiopulmonary stresses during exercise (e.g., higher Δ ventilation/carbon dioxide output and Δ heart rate/ΔO2) had lower ΔO2/ΔWR (P < 0.05). In conclusion, a readily available, effort-independent index of aerobic dysfunction during dynamic exercise (ΔO2/ΔWR) is typically reduced in patients with MM, being related to increased functional impairment and higher cardiopulmonary stress.

Development and characterization of thin printed films for gas sensing applications

The monitoring and control of hydrogen sulfide (H2S) level is of great interest for a wide range of application areas including food quality control, defense and antiterrorist applications and air quality monitoring e.g. in mines. H2S is a very poisonous and flammable gas. Exposure to low concentrations of H2S can result in eye irritation, a sore throat and cough, shortness of breath, and fluid retention in the lungs. These symptoms usually disappear in a few weeks. Long-term, low-level exposure may result in fatigue, loss of appetite, headache, irritability, poor memory, and dizziness. Higher concentrations of 700 - 800 ppm tend to be fatal. H2S has a characteristic smell of rotten egg. However, because of temporary paralysis of olfactory nerves, the smelling capability at concentrations higher than 100 ppm is severely compromised. In addition, volatile H2S is one of the main products during the spoilage of poultry meat in anaerobic conditions. Currently, no commercial H2S sensor is available which can operate under anaerobic conditions and can be easily integrated in the food packaging. This thesis presents a step-wise progress in the development of printed H2S gas sensors. Efforts were made in the formulation, characterization and optimization of functional printable inks and coating pastes based on composites of a polymer and a metal salt as well as a composite of a metal salt and an organic acid. Different processing techniques including inkjet printing, flexographic printing, screen printing and spray coating were utilized in the fabrication of H2S sensors. The dispersions were characterized by measuring turbidity, surface tension, viscosity and particle size. The sensing films were characterized using X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and an electrical multimeter. Thin and thick printed or coated films were developed for gas sensing applications with the aim of monitoring the H2S concentrations in real life applications. Initially, a H2S gas sensor based on a composite of polyaniline and metal salt was developed. Both aqueous and solvent-based dispersions were developed and characterized. These dispersions were then utilized in the fabrication of roll-to-roll printed H2S gas sensors. However, the humidity background, long term instability and comparatively lower detection limit made these sensors less favourable for real practical applications. To overcome these problems, copper acetate based sensors were developed for H2S gas sensing. Stable inks with excellent printability were developed by tuning the surface tension, viscosity and particle size. This enabled the formation of inkjet-printed high quality copper acetate films with excellent sensitivity towards H2S. Furthermore, these sensors showed negligible humidity effects and improved selectivity, response time, lower limit of detection and coefficient of variation. The lower limit of detection of copper acetate based sensors was further improved to sub-ppm level by incorporation of catalytic gold nano-particles and subsequent plasma treatment of the sensing film. These sensors were further integrated in an inexpensive wirelessly readable RLC-circuit (where R is resistor, L is inductor and C is capacitor). The performance of these sensors towards biogenic H2S produced during the spoilage of poultry meat in the modified atmosphere package was also demonstrated in this thesis. This serves as a proof of concept that these sensors can be utilized in real life applications.

Design and implementation of machine vision system for the mobile assembly robot

The review of intelligent machines shows that the demand for new ways of helping people in perception of the real world is becoming higher and higher every year. This thesis provides information about design and implementation of machine vision for mobile assembly robot. The work has been done as a part of LUT project in Laboratory of Intelligent Machines. The aim of this work is to create a working vision system. The qualitative and quantitative research were done to complete this task. In the first part, the author presents the theoretical background of such things as digital camera work principles, wireless transmission basics, creation of live stream, methods used for pattern recognition. Formulas, dependencies and previous research related to the topic are shown. In the second part, the equipment used for the project is described. There is information about the brands, models, capabilities and also requirements needed for implementation. Although, the author gives a description of LabVIEW software, its add-ons and OpenCV which are used in the project. Furthermore, one can find results in further section of considered thesis. They mainly represented by screenshots from cameras, working station and photos of the system. The key result of this thesis is vision system created for the needs of mobile assembly robot. Therefore, it is possible to see graphically what was done on examples. Future research in this field includes optimization of the pattern recognition algorithm. This will give less response time for recognizing objects. Presented by author system can be used also for further activities which include artificial intelligence usage.

Effects of Cerebral Blood Flow and PETCO2 on Cognitive Function During Passive Heat Stress

This thesis tested whether cognitive performance during passive heat stress may be affected by changes in cerebrovascular variables as opposed to strictly thermally-induced changes. A pharmacological reduction in cerebral blood flow (CBF) using indomethacin along with a hypocapnia-induced CBF reduction during passive heat stress (Tre ~1.5°C above baseline) were used to investigate any cerebrovascular-mediated changes in cognitive performance. Repeated measures analysis of variance indicated that One-Touch Stockings of Cambridge (OTS) performance was not affected by a significant reduction in CBF during passive heat stress. More specifically, OTS accuracy measures did not change as a result of either a reduction in CBF or increasing passive heat stress. However, it was found that OTS response time indices improved with increasing passive heat stress independent of CBF changes. In conclusion, a significant reduction in CBF does not cause additional changes in performance of an executive functioning task during severe passive heat stress.

Modelling software quality : a multidimensional approach

Les sociétés modernes dépendent de plus en plus sur les systèmes informatiques et ainsi, il y a de plus en plus de pression sur les équipes de développement pour produire des logiciels de bonne qualité. Plusieurs compagnies utilisent des modèles de qualité, des suites de programmes qui analysent et évaluent la qualité d'autres programmes, mais la construction de modèles de qualité est difficile parce qu'il existe plusieurs questions qui n'ont pas été répondues dans la littérature. Nous avons étudié les pratiques de modélisation de la qualité auprès d'une grande entreprise et avons identifié les trois dimensions où une recherche additionnelle est désirable : Le support de la subjectivité de la qualité, les techniques pour faire le suivi de la qualité lors de l'évolution des logiciels, et la composition de la qualité entre différents niveaux d'abstraction. Concernant la subjectivité, nous avons proposé l'utilisation de modèles bayésiens parce qu'ils sont capables de traiter des données ambiguës. Nous avons appliqué nos modèles au problème de la détection des défauts de conception. Dans une étude de deux logiciels libres, nous avons trouvé que notre approche est supérieure aux techniques décrites dans l'état de l'art, qui sont basées sur des règles. Pour supporter l'évolution des logiciels, nous avons considéré que les scores produits par un modèle de qualité sont des signaux qui peuvent être analysés en utilisant des techniques d'exploration de données pour identifier des patrons d'évolution de la qualité. Nous avons étudié comment les défauts de conception apparaissent et disparaissent des logiciels. Un logiciel est typiquement conçu comme une hiérarchie de composants, mais les modèles de qualité ne tiennent pas compte de cette organisation. Dans la dernière partie de la dissertation, nous présentons un modèle de qualité à deux niveaux. Ces modèles ont trois parties: un modèle au niveau du composant, un modèle qui évalue l'importance de chacun des composants, et un autre qui évalue la qualité d'un composé en combinant la qualité de ses composants. L'approche a été testée sur la prédiction de classes à fort changement à partir de la qualité des méthodes. Nous avons trouvé que nos modèles à deux niveaux permettent une meilleure identification des classes à fort changement. Pour terminer, nous avons appliqué nos modèles à deux niveaux pour l'évaluation de la navigabilité des sites web à partir de la qualité des pages. Nos modèles étaient capables de distinguer entre des sites de très bonne qualité et des sites choisis aléatoirement. Au cours de la dissertation, nous présentons non seulement des problèmes théoriques et leurs solutions, mais nous avons également mené des expériences pour démontrer les avantages et les limitations de nos solutions. Nos résultats indiquent qu'on peut espérer améliorer l'état de l'art dans les trois dimensions présentées. En particulier, notre travail sur la composition de la qualité et la modélisation de l'importance est le premier à cibler ce problème. Nous croyons que nos modèles à deux niveaux sont un point de départ intéressant pour des travaux de recherche plus approfondis.