Effect of the Te/Si ratio on the electrical characteristics of the amorphous chalcogenide switches

The effect of composition on amorphous chalcogenide threshold switches of the system Si _x Te_60-x As₃₀Ge₁₀, wherex = 5, 10, 12 and 20, has been studied. The compositionx = 5 shows the best switching characteristics, e.g. the smallest holding voltage (V _h = 0.4V), the highest ON state current (I _h = 45A) and smallest threshold voltage (V _s = 1.5V). Applying the three mechanisms of conductance of Mottet al. (Phil. Mag. 37 (1975) 961), it is found that for a particular composition ₂ < ₁ < ₀ (the pre-exponential factors) andW ₂ < (E _a –E ₁ +W ₁) < (E _c –E _f) (whereE _a,E _c andE _e = activation energies at band edge, fermi level and conduction band;W ₁ andW ₂ = activation energy for hopping). It was found that the density of states at the fermi levelN(E _f) increases with the decrease of silicon content. The results provided further evidence against thermal interpretations and thereby support electronic models of threshold switching for these glass systems.     

REBTAM: reliable energy balance traffic aware data reporting algorithm for object tracking in multi-sink wireless sensor networks

Recently, Multi-sink Wireless Sensor Networks (WSNs) have received more and more attention due to their significant advantages over the single sink WSNs such as improving network throughput, balancing energy consumption, and prolonging network lifetime. Object tracking is regarded as one of the key applications of WSNs due to its wide real-life applications such as wildlife animal monitoring and military area intrusion detection. However, many object tracking researches usually focus on how to track the location of objects accurately, while few researches focus on data reporting. In this work, we propose an efficient data reporting method for object tracking in multi-sink WSNs. Due to the limited energy resource of sensor nodes, it seems especially important to design an energy efficient data reporting algorithm for object tracking in WSNs. Moreover, the reliable data transmission is an essential aspect that should be considered when designing a WSN for object tracking application, where the loss of data packets will affect the accuracy of the tracking and location estimation of a mobile object. In addition, congestion in WSNs has negative impact on the performance, namely, decreased throughput, increased per-packet energy consumption and delay, thus congestion control is an important issue in WSNs. Consequentially, this paper aims to achieve both minimum energy consumption in reporting operation and balanced energy consumption among sensor nodes for WSN lifetime extension. Furthermore, data reliability is considered in our model where the sensed data can reach the sink node in a more reliable way. Finally, this paper presents a solution that sufficiently exerts the underloaded nodes to alleviate congestion and improve the overall throughput in WSNs. This work first formulates the problem as 0/1 Integer Linear Programming problem, and proposes a Reliable Energy Balance Traffic Aware greedy Algorithm in multi-sink WSNs (REBTAM) to solve the optimization problem. Through simulation, the performance of the proposed approach is evaluated and analyzed compared with the previous work which is related to our topic such as DTAR, NBPR, and MSDDGR protocols.     

Heat transfer and fluid flow characteristics in flash desalination units

The present work investigates the effects of different operating and geometrical parameters on the flashing efficiency of water in a single stage flashing chamber. This chamber uses a submerged rectangular orifice as flow control area. Experiments were performed to investigate the effects of flow rate, liquid level in the flashing chamber, liquid inlet temperature and flashing range, on the flashing efficiency under various design conditions. These comprise flow with baffle placed in the flashing chamber, and wire meshes placed at the orifice to increase the turbulence level.It was found that the efficiency increased with the increase of the turbulence levels, flashing range and liquid inlet temperature; the efficiency deceased with the increase of the flow rate and liquid level in the flashing chamber. The application of numerical procedure to predict flow pattern and heat transfer in the flashing chamber is introduced as a powerful design tool.     

Thermal induced transformations in glassy chalcogenides SixTe60−xAs30Ge10

Temperature-induced transformations are considered to be interesting characteristic properties of amorphous materials including the Si _x Te_60–x As₃₀Ge₁₀ system, withx=5, 10, 12 and 20. Density (), X-ray diffraction and differential thermal analysis (DTA) were used to characterize the compositions. DTA traces of each glass composition at different heating rates from 5 to 30° C min^–1 were obtained and interpreted. Fast and slow cooling cycles were used to determine the rate of structure formation. Cycling studies of materials show no memory effect but only ovonic switching action. The compositional dependence of the crystallization activation energy (E) and the coefficient of glass-forming tendency (K _gl) have been calculated. The thermal transition temperatures and associated changes in specific heat have been examined as a function of the Te/Si ratio by differential scanning calorimetry. It was found that andE increase linearly with increasing tellurium content, while the heat capacity (c _p) andK _gl, decrease with increasing tellurium content.E=1.54 eV andc _p=0.246 J g^–1 K^–1 forx=20 whileE=2.74eV andc _p=0.22 J g^–1 K^–1 forx=5.     

The effect of thallium addition on differential thermal analysis of glassy selenium. Part 1

The effect of thallium on the phenomena accompanying the thermally induced structural changes in different compositions of the chalcogenide system Tl _x Se_1–x, withx = 0.0 to 0.9, has been investigated using differential thermal analysis measurements. It is possible to prepare massive homogeneous glassy samples with thallium contents up to 10 at %. Glasses with some embedded crystallites are obtained up to 40 at % Tl. The coefficient of the glass-forming tendency (K _gl) increases with increasing selenium content. In the binary system Tl-Se, one (or more) of the phases are likely to be more unstable with respect to crystallization than was the initially homogeneous system. The activation energy of crystallization for the glasses fromx = 0.0 to 0.3, varies from 1.0 to 4.5 eV for the low-temperature phase and from 1.7 to 2.5 eV for the high-temperature phase.     

A new optimization model for distribution substation siting, sizing, and timing

This paper presents a new planning optimization model for distribution substation siting, sizing, and timing. The proposed model involves using linear functions to express the total cost function. The developed model includes different electrical constraints such as voltage drops, substation and transformer capacities, power flow, and radial flow constraints. The proposed planning problem is formulated as a Mixed Integer Linear Programming (MILP) problem to avoid the use of nonlinear programming and thus avoiding the possibility of getting trapped in local solutions. A numerical example is presented to validate the effectiveness of the developed model.     

The effect of thallium addition on differential thermal analysis of glassy arsenous selenide. Part 2

The effect of thallium on the phenomena accompanying the thermally induced structural changes in various glasses of the chalcogenide system (As₂Se₃)_1-x Tl _x , withx = 0.0 to 0.7, has been investigated using DTA measurements. The crystallization kinetic parameters of the glasses (e.g. crystallization mode,n, rate of reaction,K, and activation energy,E) have been evaluated applying a single-scan technique, and compared with those obtained from the shift in the exothermic peaks (Kissinger model). The kinetic parameter results indicate a discontinuity near thallium concentration of 2.25×10²¹ atoms cm^–3 (x = 0.25) where there is a peak in bothE(3 eV) andn (2.7) and a corresponding dip inK(6.7×10^–3).     

Structural studies of amorphous and crystalline Tl-As-Se compounds

X-ray diffraction and microstructure studies for amorphous samples of composition (As₂Se₃)_1–x Tl _x , wherex varies between 0 and 0.7, show that up tox=0.25 the short-range order is similar to that of As₂Se₃. A change in the structure is observed asx increases. Diffraction from samples crystallized by annealing confirms that a thallium content up tox=0.25 is not enough to alter a characteristic matrix similar to crystalline As₂Se₃; however, it results in a decrease of crystallization tendency. Forx>0.25 up to 0.7 the structural matrix features are almost similar to those of crystalline TlAsSe₂. The observed structural changes could rationalize reported changes in the electrical and thermal transport properties of the amorphous ternary system compounds.     

Improved Grey predictor rolling models for wind power prediction

A new technique for one step ahead average hourly wind speed forecasting and wind turbines' output power prediction based on using the Grey predictor models is presented. The required mathematical formulation for developing the Grey predictor models is also presented. The obtained results from the proposed models are compared with the corresponding results obtained when using the persistent model. Utilising the traditional Grey model, GM(1,1) was first investigated and showed good improvement over the persistent model. However, the generated results demonstrate the presence of intervals with overshoots in the predicted values. To reduce such overshoots, a modified version for the Grey predictor model referred to as the adaptive alpha GM(1,1) model is investigated and two new models are proposed, hereafter, referred to as the improved Grey model and the averaged Grey model. The presented results demonstrate the effectiveness, the accuracy and the superiority of the proposed averaged Grey model for wind speed and wind power prediction.     

Higher and better yields with less environmental pollution in Egypt through balanced fertilizer use

Nitrogen use per unit area in Egyptian agriculture is over 300 kg ha^–1. An annual average increase of about 2% till year 2000 was estimated. Fertilizers use is characterised by excessive N application, moderate P use and neglection of K and micronutrients. Consequently, nutrient imbalance occurs in crop plants. Subsidising N fertilizers resulted in their misuse and increasing losses. Efficiency of N use in different areas and crops is low. High nitrate concentrations were detected in drainage as well as ground water. Subsidy was removed and fertilizers handling was left to the free market in 1992/93, which resulted in drastic price increases. It could be demonstrated for many years and in farmers fields that yields can be considerably increased (20%) through balanced fertilizers use based on soil testing and plant analysis and adjusted according to the prevailing farming system, leading to more return and less N-use. Use of micronutrients foliar fertilizers leads to increase in root growth and higher uptake of macronutrients. Use of relatively high rates of fertilizers is still a must, however it should be optimised to obtain the highest possible efficiency. Making crop and location specific fertilizer recommendations available to farmers helps in increasing high quality yields, which results in high economic benefits, keeping agricultural production sustainable and decreasing pollution.