Synthèse et étude de complexes neutres de nickel bisdithiolènes pour application photovoltaïque organique

Ce travail fait partie d'un projet financé par l'ANR dédié à la conception d'un nouveau type de cellule photovoltaïque organique. Le but est de concevoir un nouveau dispositif de type bicouche ou multicouche, et composé de deux matériaux (donneur et accepteur d'électrons) moléculaires cristaux liquides colonnaires. Ce mémoire de thèse décrit la synthèse et la caractérisation de nouveaux matériaux accepteurs combinant plusieurs propriétés : stabilité en température et à l'air, capacité à s'auto-organiser en cristaux liquides colonnaires, absorption forte dans le domaine proche infrarouge et infrarouge. Le choix s'est porté sur des complexes de nickel bisdithiolenes neutres. Plusieurs séries de complexes ont été synthétisées avec des ligands de type dpedt (diphenyl-ethylenedithiolate). Leurs comportements physico-chimiques ont été caractérisés par utilisation de différentes techniques : analyse thermique différentielle et thermogravimétrique, microscopie optique en lumière polarisée, voltammétrie cyclique et voltammétrie à vague carrée, spectrométrie d'absorption. Les résultats montrent qu'ils sont tous très stables à l'air et thermiquement jusqu'à 300°C, qu'ils absorbent fortement entre 750 nm à 1100 nm et qu'ils possèdent une haute affinité électronique. De plus, certains de ces composés présentent en phase condensée une phase cristalline liquide colonnaire autour de 80 à 110°C, métastable à température ambiante. En particulier, il est montré que le gap énergétique entre les niveaux HOMO et LUMO de tels complexes peut être modulé en fonction des groupements fonctionnels portés par les ligands. L'ensemble de ces propriétés rendent ces composés très intéressants pour une application photovoltaïque.This work is part of a project funded by the ANR dedicated to the design of a new type of organic photovoltaic cell. The goal is to design a new device architecture, bilayer or multilayer, composed of two columnar liquid crystalline molecular materials (electron donor and electron acceptor). This thesis describes the synthesis and characterization of new electron acceptor materials combining several properties: thermal stability and stability in air, capability of self-organize into columnar liquid crystals, strong absorption in near infrared and infrared spectral domain. The choice is the neutral nickel bisdithiolene complexes. Several series of complexes have been synthesized with dpedt (diphenyl-ethylenedithiolate) ligands. Their physicochemical behaviors were characterized by using different techniques: differential thermal analysis and thermo-gravimetric, polarized light microscopy, cyclic voltammetry and square wave voltammetry, absorption spectroscopy. The results show that they are all very stable in air and heat until 300 °C, they absorb strongly between 750 nm to 1100 nm and they have high electron affinity. In addition, some of these compounds show columnar liquid crystalline phase around 80 to 110 °C, metastable at room temperature in the condensed state. In particular, it is shown that the HOMO-LUMO energy gap of such complexes can be modulated as a function of functional groups grafted on the dpedt ligands. All these properties make these compounds very interesting for photovoltaic application

Is Nonfarm Diversification a Way Out of Poverty for Rural Households? Evidence from Vietnam in 1993-2006

school. Using the four high quality household living standards surveys available to date this paper reveals that Vietnam’s rural labour force has been markedly diversifying toward nonfarm activities in the doi moi (renovation) reform period. The employment share of the rural nonfarm sector has increased from 23 percent to 58 percent between the years 1993 and 2006. At the individual level, the results indicate that participation in the rural nonfarm sector is determined by a set of individual-, household-, and community-level characteristics. Gender, ethnicity, and education are reported as main individual-level drivers of nonfarm diversification. Lands as most important physical assets of rural households are found to be negative to nonfarm employment. It is also evident that both physical and institutional infrastructure exert important influences on individual participation in the nonfarm sector. At the household level, a combination of parametric and semi-parametric analysis is adopted to examine whether nonfarm diversification is a poverty exit path for rural households. This paper demonstrates a positive effect of nonfarm diversification on household welfare and this effect is robust to different estimation techniques, measures of nonfarm diversification, and the usage of equivalent scales. However, the poor is reported to benefit less than the non-poor from nonfarm activities. Though promoting a buoyant nonfarm sector is crucial for rural development and poverty reduction, it needs to be associated with enhancing access to nonfarm opportunities for the poor.Rural nonfarm sector, nonfarm diversification, household welfare, Vietnam

Correlation between Resilient Modulus MR and Deviator Stress for Subgrade soils of northern provinces in Vietnam

Recently, Resilient Modulus is applied in pavement structural design in Vietnam. The resilient modulus of subgrade soil is an essential input parameter for a flexible pavement design. The resilient modulus depends on soil properties, stress state, and soil type.  However, there is limited research on resilient modulus of soils and models to estimate resilient modulus in Vietnam. Therefore, in this study, soil samples were collected from two provinces in northern Vietnam, namely Bac Giang province and Ninh Binh province, and then physical and mechanical tests were conducted for these samples. In addition, a series of cyclic triaxial tests also conducted according to AASHTO T307 specification to obtain resilient modulus of these soils.  The results showed that the resilient modulus decreased with the increase of deviator stress for Bac Giang samples and increased with the increase of deviator stress in the case of Ninh Binh samples. Simple deviator stress models have developed to estimate a resilient modulus of soils in the area

Correlation between Resilient Modulus MR and Deviator Stress for Subgrade soils of northern provinces in Vietnam

Recently, Resilient Modulus is applied in pavement structural design in Vietnam. The resilient modulus of subgrade soil is an essential input parameter for a flexible pavement design. The resilient modulus depends on soil properties, stress state, and soil type.  However, there is limited research on resilient modulus of soils and models to estimate resilient modulus in Vietnam. Therefore, in this study, soil samples were collected from two provinces in northern Vietnam, namely Bac Giang province and Ninh Binh province, and then physical and mechanical tests were conducted for these samples. In addition, a series of cyclic triaxial tests also conducted according to AASHTO T307 specification to obtain resilient modulus of these soils.  The results showed that the resilient modulus decreased with the increase of deviator stress for Bac Giang samples and increased with the increase of deviator stress in the case of Ninh Binh samples. Simple deviator stress models have developed to estimate a resilient modulus of soils in the area

Tuning Electronic Transport Properties of Zigzag Graphene Nanoribbons with Stone-Wales Defect

Influences of the symmetric Stone-Wales (SW) defect on the electronic transport properties of the zigzag graphene nanoribbons (ZGNRs) has been studied using $\it{ab}$ $\it{ initio}$ simulation based on density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) technique. The calculated transmission spectra T(E) at various bias windows, device densities of states (DDOS), current characteristics as well as local density of states (LDOS) of the defective asymmetric and symmetric ZGNRs are presented in comparison of those for the pristine ZGNRs. It has been established the metallic character of the electronic transport in asymmetric ZGNRs, and in symmetric ones, the current has a semiconductor behavior, with negative differential resistance (NDR) effect. Symmetric SW defect, as a most unfavorable SW defect type for electric conductance, remarkably decreases the current values, but does not change the character of conductivity in both the asymmetric and symmetric ZGNRs. NDR has been explained by the altering by SW defect the number of frontier molecular orbitals entering bias windows

Multiobjective Logistics Optimization for Automated ATM Cash Replenishment Process

In the digital transformation era, integrating digital technology into every aspect of banking operations improves process automation, cost efficiency, and service level improvement. Although logistics for ATM cash is a crucial task that impacts operating costs and consumer satisfaction, there has been little effort to enhance it. Specifically, in Vietnam, with a market of more than 20,000 ATMs nationally, research and technological solutions that can resolve this issue remain scarce. In this paper, we generalized the vehicle routing problem for ATM cash replenishment, suggested a mathematical model and then offered a tool to evaluate various situations. When being evaluated on the simulated dataset, our proposed model and method produced encouraging results with the benefits of cutting ATM cash operating costs

Measurement of the Upper Tropospheric Density and Temperature Profiles in Hanoi Using a Raman Lidar

The nitrogen molecular density and temperature profiles of the upper troposphere are measured by a Raman lidar system in Hanoi over the range from 3 km to 19 km. The spatial and temporal resolutions of profiles are 60 m and 1h, respectively. The nitrogen molecular density profiles are directly calculated from the range-corrected lidar signal. The temperature profiles are derived from the molecular density profile based on the assumptions of the hydrostatic equilibrium, the ideal-gas law and a fixed nitrogen molecule ratio in the atmosphere. The results of our lidar measurements show good agreement with the MSISE-90 atmospheric model. The maximum errors of density and temperature measurements are 6% and 7%, respectively. We estimated the height of tropopause in Hanoi about 16 km from the derived temperature profile. The measured density and temperature profiles from this Raman lidar can be used for studying the trends and characteristics of the upper troposphere in Hanoi

Study of Using Cassava Pulp to Produce Livestock Feed Pellet

In Vietnam, the cassava production capacity is about 10 million tons annually. Indeed, it eliminates approximate 4 million tons of cassava pulp from the cassava starch factories. This amount of cassava is usually dried to feed cattle or fertilizer. However, drying of cassava pulp has its disadvantages such as air pollution, difficult storage and transportation. This study has proposed and successfully tested a line of equipment used to produce pellets from the utilization of fresh cassava pulp bringing from cassava starch processing plants. The processing includes a mixing of fresh cassava pulp with dried cassava starch, pressing and drying of pellets. The experiment results show that when the mixing ratio between cassava starch and cassava residue is 1:10 – 1:5, the cassava pulp pellets after drying achieved the required technical specifications. Hence, it has high volume density, the dried specific weight of the pellets is about 700 kg / m3, the breaking strength of the pellets is greater than 2 kG, the tanning time of the pellets is greater than 116 minutes in water, the moisture content of the pellets is remained in 13% after drying in 5-5.5 hours

Liquid pumping and mixing by PZT synthetic jet

In this paper, a PZT synthetic jet that can function as both an efficient pumping and mixing device is developed. Compare with the conventional design where the practice of controlling the internal flow is undertaken by microvalves structure, this approach promotes the durability and allows the device to work with different liquids at high Reynold number without losing of backflow from the diffuser, therefore provides efficient mixing. The pumping performance is applicable for commercialized counterparts while the homogeneous medium was obtained at downstream in the experiments, which was further confirmed by simulation. Notably, the chaotic mixing feature of the device is also applicable for immiscible liquids with the micro-droplet formation result at the outlet