Sol–gel synthesis and characterization of the delafossite CuAlO2

Nanocrystalline CuAlO2 is synthesized by sol–gel method using ethylene glycol as solvent. The stages of formation are followed by thermal analysis. The X-ray diffraction pattern of the powder heat-treated at 1100 °C shows a single phase, indexed in a rhombohedral symmetry (R 3¯¯¯ m). The apparent crystallite size (57 ± 8 nm) is determined from the Williamson–Hall plot. The direct optical transition (=3.69 eV), evaluated from the diffuse reflectance spectrum, is attributed to the charge transfer (O2−: 2p → Cu+: 4s). The oxide is p-type semiconductor, and the conduction occurs predominantly by small polaron hopping between mixed valences Cu2+/+, due to oxygen insertion in the layered crystal. The photoelectrochemical characterization gives a flat band of 0.20 VSCE and a hole density of 1.13 × 1018 cm−3. The semicircle centered on the real axis, in the electrochemical impedance spectroscopy (EIS), is due to the absence of constant phase element with a pure capacitive behavior. The straight line at 35° at low frequencies is attributed to the diffusion in the layered structure

Preparation and characterization of the semiconductor CuMnO2 by sol-gel route

Nano crystallites of the crednerite CuMnO2 are prepared by sol–gel method with two-step annealing process. The powder heated at 450°C under air flow shows a mixture of CuO, Mn2O3 and CuxMn3−xO4. However, when calcined at 900°C under N2 atmosphere, the crednerite CuMnO2 with a monoclinic structure (space group: C2/m) is obtained. The Raman spectrum shows a single peak at 679cm−1 assigned to A1g mode whereas the infrared analysis confirms the linearity of CuO23− units. The optical transition at 1.70eV, determined from the diffuse reflectance is attributed to the inter-band d-d transition of Cu+ ion. The oxide exhibits semiconducting properties with an activation energy of 0.21eV. The photo-electrochemical measurement shows p-type conduction due to O2− insertion in the two dimensional lattice. The flat band potential (+0.12 VSCE), indicates a cationic character of both valence and conduction bands deriving from Cu+: 3d orbital

A Consistency Rule for Graph Isomorphism Problem

International audienceThis paper describes an algorithm for graph isomorphism problem. A consistency rule is proposed to detect as soon as possible the isomorphism permutation. The algorithm, called CRGI, tries to find an isomorphism between two in- put graphs through a backtracking exploration that uses a proposed consistency rule to prune the tree-search. This rule is based on changing cases positions of one adjacency matrix to obtain exactly the second adjacency matrix, according to a permutation that must be defined. If such permutation exists, an isomorphism is detected. The proposed rule is able to prune as early as possible unfruitful branches of the tree-search which leads to reduce the practical time com- plexity. Experimental results comparing CRGI with other popular algorithms show the effectiveness of CRGI especially for random graphs and trees

A Consistency Rule for Graph Isomorphism Problem

International audienceThis paper describes an algorithm for graph isomorphism problem. A consistency rule is proposed to detect as soon as possible the isomorphism permutation. The algorithm, called CRGI, tries to find an isomorphism between two in- put graphs through a backtracking exploration that uses a proposed consistency rule to prune the tree-search. This rule is based on changing cases positions of one adjacency matrix to obtain exactly the second adjacency matrix, according to a permutation that must be defined. If such permutation exists, an isomorphism is detected. The proposed rule is able to prune as early as possible unfruitful branches of the tree-search which leads to reduce the practical time com- plexity. Experimental results comparing CRGI with other popular algorithms show the effectiveness of CRGI especially for random graphs and trees

Tracking COVID-19 by Tracking Infectious Trajectories

Nowadays, the coronavirus pandemic has and is still causing large numbers of deaths and infected people. Although governments all over the world have taken severe measurements to slow down the virus spreading (e.g., travel restrictions, suspending all sportive, social, and economic activities, quarantines, social distancing, etc.), a lot of persons have died and a lot more are still in danger. Indeed, a recently conducted study [1] has reported that 79% of the confirmed infections in China were caused by undocumented patients who had no symptoms. In the same context, in numerous other countries, since coronavirus takes several days before the emergence of symptoms, it has also been reported that the known number of infections is not representative of the real number of infected people (the actual number is expected to be much higher). That is to say, asymptomatic patients are the main factor behind the large quick spreading of coronavirus and are also the major reason that caused governments to lose control over this critical situation. To contribute to remedying this global pandemic, in this article, we propose an IoTa investigation system that was specifically designed to spot both undocumented patients and infectious places. The goal is to help the authorities to disinfect high-contamination sites and confine persons even if they have no apparent symptoms. The proposed system also allows determining all persons who had close contact with infected or suspected patients. Consequently, rapid isolation of suspicious cases and more efficient control over any pandemic propagation can be achieved

New Techniques for Limiting Misinformation Propagation

This paper focuses on limiting misinformation propagation in networks. Its first contribution is introducing the notion of vaccinated observers, which is a node enriched with additional power. Vaccination is adding, locally, a plugin or asking for the help of a trusted third party, called a trusted authority. The plugin or the authority is able to detect if the received information is misinformation or not. Vaccinated Observers must stop forwarding detected misinformation. Based on this notion, two algorithms for limiting misinformation are proposed. The second contribution of the paper is an algorithm based on Moving Observers for locating a strong adversary diffusion source. This algorithm selects a random subset of nodes as observers for a random period $\Delta$ . This means that the observer subset may change over time in a randomized manner. Consequently, the strong adversary diffusion source can’t have global knowledge about observers positions. Having these positions by the diffusion source will make its localization by the observers more complicated, even impossible. The third contribution is proposing an algorithm for stopping misinformation propagation based on a punishment strategy. This algorithm has a very simple principle design and it assumes that an authority or a mechanism $A$ is available. The authority $A$ has the ability to detect if the received information is misinformation or not. If a node $n_{i}$ receives information $m$ from its neighbor $n_{j}$ and $m$ is detected, by $n_{i}$ via the authority $A$ , as misinformation then $n_{j}$ is punished for a period $pp$ ( $pp$ stands for punishment period). If the node $n_{j}$ repeats this action for $n$ time then the punishment period increases to $n*pp$ . The punishment in this algorithm is stopping the forwarding of the information received from a punished node $n_{j}$ . The simulation results show that the proposed techniques are both efficient and accurate while locating the diffusion source. Consequently, misinformation propagation is limited

HYDROGEN AND OXYGEN EVOLUTION WITH TEMPERATURE IN NANOPOROUS SILICON

In this work, a porous layer on an n+ emitter by a chemical route was realized. The MEB observation shows a nanoporous shape of the surface. The subsequent contact depositions needs a heat treatment that has an influence on hydrogen and oxygen distributions in the porous layer. After heat treatments, the porous silicon layer is analyzed by secondary ion mass spectroscopy. The concentration profile of light elements like H, O, C, F and N are measured and compared with untreated porous layer. The results show that oxygen is present at high level at ambient temperature and then decreases from 25°C to 775°C. This means that oxygen desorption is observed on the surface. At 800°C the oxygen content increases again showing an oxidation of porous layer surface. For hydrogen, the concentration decreases from the ambient temperature until 750°C was noted. Then the hydrogen is restored at its first concentration. The FTIR spectra correlate this hydrogen distribution. The absorption spectra show the appearance of Si–Hx bonds (with x = 1, 2, 3) at 2089, 2115, and 2140 cm-1, respectively. Both elements O and H are present deeply in the porous silicon layer as shown by the sputter time.Concentration profile, porous silicon, heat treatment, light elements

OPTICAL ASPECTS OF POROUS MC-SILICON UNDER HEAT TREATMENTS

The aim of this study is the formation of porous silicon (PS) and the heat treatment effect on the optical properties of the PS layer. An optimized HF:HNO3 chemical solution is used at ambient temperature on the n + p silicon surface. Scanning electron microscopy (SEM) pictures show the form of the nanopores. We studied the effect of the heating on the morphology and the reflection of the PS layer. A chemical analysis of the surface is also carried out. The measurements show that the pore shape and the oxygen content on the surface are changing with temperature. Specular reflection spectra under variable incidence angles are measured on each treated surface. Curves of weighted reflection Rw are drawn to illustrate the evolution with temperature. The modification of oxygen content of the porous surface is correlated with the sheet resistance of the emitter. Results show the lower the oxygen percent the lower the resistivity. The layout of Rw according to the temperature of annealing indicates that the shape of the curve is the same for the angles of incidences 20°, 30°, 40°, and 50°. At a low temperature Rw is minimal indicating the presence of an oxide coating on the porous layer an indication of optical adaptation between the air and the substrate of silicon.Porous silicon, reflection, solar cell, heat treatment