When sound meets quantum dots

THz acoustic phonons have wavelengths in the nm range and can be used as internal probes to investigate self-assemble quantum dots (QDs) structures. The interaction between delocalised acoustic phonons and an ensemble of localised electronic states yields interferences in the Raman scattering efficiency. Raman scattering interferences provide an image in reciprocal space of the electronic density and therefore allow one to probe the spatial ordering of QDs and the localisation of the electronic states. Spatial correlations functions are obtained by performing inverse Fourier transforms. Characteristic distances can be identified, provided that optical and acoustic wave reflexion effects are taken into account.     

Acoustic vibration modes and electron-lattice coupling in self-assembled silver nanocolumns

Using ultrafast spectroscopy, we investigated electron-lattice coupling and acoustic vibrations in self-assembled silver nanocolumns embedded in an amorphous Al2O3 matrix. The measured electron-lattice energy exchange time is smaller in the nanocolumns than in bulk silver, with a value very close to that of isolated nanospheres with comparable surface to volume ratio. Two vibration modes were detected and ascribed to the breathing and extensional mode of the nanocolumns, in agreement with numerical simulations.     

The Fate of Base Metals in the Environment and Water Quality in the Mellegue Watershed,Northwest Tunisia

The 130 Mm³-capacity Mellègue reservoir has a broad catchment area. Contaminants include sewage from cities, farm fertilizers, and metals released from mine tailings, all of which threaten Tunisia’s water supply. Forty surface water samples were collected from watercourses and 18 from the reservoir during the wet and dry seasons. To evaluate groundwater contamination, the Sarrat basin was considered as a case study, and well water was analysed. The total amounts of base metals and nutrients in the watercourses did not exceed international standards. Evaporites in broad Triassic outcrops and in tailings dissolve, and may fix lead as sulphates; however, sulphate and chloride can complex and increase the solubility of some metals. The nutrient and salt content were highest in the Rmel River, which receives sewage from el Kef. An opposing gradient of metals was observed in the reservoir water column: elements such as Zn, Pb, and Al were enriched upwards, while Mn, Fe, and Cr increased towards the sediment–water interface. The same behaviour was observed for NO₃ ^? and O₂, due to metal release under reducing conditions in bottom waters, and dissolution of Fe and Mn colloids. Fertilizers and sewage may be responsible for the potentially hazardous level of nutrients in the groundwater.     

DDCA-WSN: A Distributed Data Compression and Aggregation Approach for Low Resources Wireless Sensors Networks

Wireless Sensor Networks (WSN) have been as useful and beneficial as resource-constrained distributed event-based system for several scenarios. Yet, in WSN, optimisation of limited resources (energy, computing memory, bandwidth and storage) during data collection and communication process is a major challenge. Data redundancy involves a large consumption of sensor resources during processing and transferring information to an analysis centre. As a matter of fact, most of energy consumption (as much as 80%) for standard WSN applications lies in the radio module where receiving and sending packets is necessary to communicate between stations.  Thus, this paper proposes an approach to achieve optimal sensor resources by data compression and aggregation regarding integrity of raw data. Then, the main objective is to reduce this redundancy by discarding a certain number of packets of information and keeping only the most meaningful and informative ones for the reconstruction. Data aggregation discarded a certain sensing data packet, which lead to low data-rate communication and low likelihood of packet collisions on the wireless medium. Data compression reduces a redundancy in keeping aggregated data, in order to diminish resources consumption of wireless sensor nodes, which leads to storage saving and sending only a small data stream in the bandwidth of communication. The performances of the proposed approach DDCA-WSN are qualified using experimental simulation on OMNeT++/Castalia. The performance metrics were evaluated in terms of Compression Ratio (CR), data Aggregation Rate (AR), Peak Signal-to-Noise Ratio (PSNR), Mean Square Error (MSE) and Energy Consumption (EC).The obtained results have significantly increased the network lifetime. Moreover, the integrity (quality) of the raw data is guaranteed.

     

A linear optimization approach to the heterogeneous r-cyclic hoist scheduling problem

The cyclic hoist scheduling problem is encountered in electroplating facilities, when mass production is required. This class of problems is a branch stemming from the Hoist Scheduling Problem (HSP) where automatic hoist is used for moving electroplates through chemical baths. A repetitive sequence of moves is searched for the hoist in cyclic schedule. To minimize the cycle time of r different part-jobs, we propose a linear optimization approach. An illustrative example is given in order to show some feedback of our exact solving method. Afterward, two comparisons are presented: firstly, between a two 1-cycle homogenous schedule and a 2-cycle heterogeneous part-job and secondly, between 2-cycle and 4-cycle heterogeneous part-job. These comparisons show how, by considering r-cyclic scheduling, we can optimize the cycle length considerably and then the throughput rate of the electroplating line.     

Dépôt chimique CVD de silicium dopé in situ au phosphore. Partie 2: Analyse théorique et modélisation

The behaviour modelling of a CVD reactor is useful to better understand the involved complex mechanisms and determine the conditions required for the fabrication of depositions according to industrial standards. This approach was applied to the deposition of polycrystalline silicon doped in situ with phosphor. A model was developed to represent the deposition process which predicts correctly the excess of deposition thickness caused by silylene. The control of the deposition operation is mainly governed by the feed phosphine concentration and the inlet geometry where silylene is formed.     

Surface enhanced Raman scattering of silver sensitized cobalt nanoparticles in metal-dielectric nanocomposites

We report the preparation of a new type of nanocomposite containing cobalt and silver nanoparticles organized in parallel layers with a well controlled separation. This arrangement allows the observation of an enhanced low-frequency Raman signal at the vibration frequency of cobalt nanoparticles excited through the surface plasmons of silver nanoparticles. Numerical simulations of the electric field confirm the emergence of hot spots when the separation between silver and cobalt nanoparticles is small enough.     

A genetic algorithm approach for a single hoist scheduling problem with time windows constraints

This study considers a cyclic scheduling of hoist movements in electroplating industry. Several jobs have to flow through a production line according to an ordered bath sequence. They firstly enter the line at a loading buffer. Then they will be soaked sequentially in a series of tanks containing specific chemical baths. Finally, they will leave the line at the unloading buffer. The processing time duration of each job in each tank is not constant but confined within a time window bounded by a minimum and a maximum duration. If a job spends less than the minimum duration or more than the maximum duration it is considered defective. Moreover, not only the job operations in the soaking tanks have to be scheduled, but also the transportation of the jobs between tanks has to be considered. The problem now is to find an optimum or near optimum feasible cyclic scheduling such that the hard resource and time-window constraints are respected and the cycle time duration is minimized. A mathematical formulation is proposed for the multi-jobs cyclic hoist scheduling problem with a single transportation resource, and a Genetic Algorithm (GA) approach is presented to solve it. The performance of the proposed algorithm is evaluated with the objective value obtained with a linear programming model, on several literature instances. Computational experiments show the good performance of our GA in terms of solution quality, convergence and computation time.     

Dépôt chimique CVD de silicium dopé in situ au phosphore. Partie 1: Etude expérimentale

The fabrication of silicon layers doped in situ with phosphor using CVD technique is still poorly controlled by the microelectronics industry. Significant thickness heterogeneities are noticeable on circuit and load, which greatly limits the process utilization. An experimental study of this deposition was carried out. The influence of many parameters (temperature, pressure, feed composition) was studied in terms of deposition thickness and uniformity as well as crystalline structure and resistivity. The advantages and involved mechanisms are presented.