Positive Corona Pulse Characteristics from Two Interacting Needles in Air

A set of oscillograms has been obtained to investigate the development of pulse mode in the positive discharge from a single and twin interacting thin needles. The transition from burst pulses to continuous glow in laboratory air is discussed. When the needles are brought close together, the onset voltage increases with a subsequent decrease of the corona current for the same applied voltage. Not only the onset voltage but also the offset voltage (i.e., voltage at which the burst pulses disappear) increases as the needle-to-needle spacing decreases. The pulse repetition rate increases with the applied voltage reaching maximum and then showed a decrease with further increase of voltage. When the needles are brought very close to each other, the rate of increase of pulse repetition rate with voltage increases by about 15 percent more than the corresponding rate for single needle. Not only the rate of increase of pulse repetition rate but also the repetition rate itself reaches almost double the value for a single needle. The randomness of the pulse repetition rate was found maximum at voltages close to the onset value and decreases with increase of the voltage. On the contrary, the pulses had almost the same amplitude at voltages very close to the onset value.     

Cumin seed meal with enzyme and polyethylene glycol as an alternative to wheat bran in broiler diets

Iran produces about 7000 metric tons of cumin seed meal (CSM) as a by‐product of cumin oil extraction factories, annually. To evaluate the nutritional significance of cumin seed meal as a broiler feedstuff, an experiment was conducted using 288 male broiler chicks (14 days old) receiving diets containing 0, 25 and 50 g kg⁻¹ of CSM with and without polyethylene glycol (PEG) and enzyme (Grindazyme^™ GP 15000) for 28 days. Total body weight (BW), body weight gain (WG), feed intake (FI), feed conversion ratio (FCR), weight of carcass and percentage of legs, breast and edible parts of carcass were measured. The results showed that, inclusion of CSM in broiler diets had no negative influence on parameters evaluated compared to the control diet containing wheat bran (P > 0.05). PEG and enzyme had no influence on the bird performance (P > 0.05). There was an increase in relative weight of gizzard when the amount of CSM in the diet was increased (P < 0.01). An increase in relative weight of gizzard in birds that received the CSM diet was likely to be due to the increase in fibre content of CSM diets. In respect of the low price of CSM, it could be concluded that inclusion of CSM at levels used in this experiment has no negative effect on broiler performance and reduces the overall cost of broiler production. Copyright © 2006 Society of Chemical Industry     

The effects of fumed silica and barite on the aluminum resistance of alumina castables

A study of the effects of microsilica and barium sulfate as additives in high-tabular alumina castables on cold and hot modulus of rupture, porosity, thermal shock, and corrosion resistance to aluminum attack is reported in this article. This investigation underlined the importance of the quality of fumed silica on the physical and mechanical properties of refractory castables, and also confirmed the importance of celsian formation during firing in the protection of refractory against aluminum attack. For more information, contact Saied Afshar, CIREP-CRNF, école Polytechnique de Montréal, 8475 Christophe-Colomb Street, Montréal, QC, H2M 2N9, Canada; e-mail saied.afshar@polymtl.ca.     

A computer relaying algorithm for direct determination of the fault distance

The objective of this work is to present an algorithm for estimating the distance to the fault location for use in digital protection of transmission lines. The proposed scheme is based on the observation that for a line with zero shunt admittance, the fault current is inversely proportional to the fault distance. Assuming the current for a fault occurring at a distance of unity is available, the unknown distance to the fault can be estimated from the ratio of the assumed unity-distance fault current and the actual fault current. A detailed derivation of the algorithm is presented, and simulated test results on a 345 kV line are included. A comparison of the computational requirements, and hence the complexity of implementation and speed of response, is made vis-a-vis some of the well known approaches.     

Nature inspired meta‐heuristic algorithms for solving the service composition problem in the cloud environments

Many sorts of services in the cloud environments must be composited based on the user's requests to meet the requirements. Thus, the distributed services are joined to the cloud services through service composition. Also, it is known as NP‐hard problems and many researchers significantly are focused on this problem in recent years. Therefore, many different nature‐inspired meta‐heuristic techniques are proposed for solving this problem. The nature‐inspired meta‐heuristic techniques have an important role in solving the service composition problem in the cloud environments, but there is not a wide‐ranging and detailed paper about reviewing and studying the important mechanisms in this field. Therefore, this study presents a comprehensive analysis of the nature‐inspired meta‐heuristic techniques for the service composition issue in the cloud computing. The review also contains a classification of the important techniques. These classifications include Ant Colony Optimization, Bee Colony Optimization, Genetic Algorithm, Particle Swarm Optimization, Cuckoo Optimization Algorithm, Bat Algorithm, greedy algorithm, and hybrid algorithm. An important aim of this paper is to highlight the emphasis on the optimization algorithms, and the benefits to tackle the challenges are encountered in the cloud service composition. Also, this paper presents the advantages and disadvantages of the nature‐inspired meta‐heuristic algorithms for solving the service composition problem in the cloud environments. Moreover, this paper aims to provide more efficient service composition algorithms in the future. Finally, the obtained results have shown that the discussed algorithms have an important effect in solving the cloud service composition problem, and this effect has been increased in recent years.     

A study of micro-channel size and spatter dispersion for laser beam micro-milling

During micromachining the accuracy of micro-feature is always a major concern. Using laser beam micro-milling (LBMM) the produced size is generally larger than the input design size. Another important drawback of LBMM is the formation of melt spatter around the feature geometry. The spatter adheres within the premises of the machined feature and influences the machining results, especially the geometry of previously machined features by adhering inside or around the feature. Determination of spatter size is very important when the objective is to produce an array of micro-features such as micro-channels. Thus, the minimum distance between two consecutive micro-features is necessary to be known in order to achieve safe geometry for which the size of spatter plays a significant role. The knowledge of spatter scattering and pre-calculated distance of dispersing spatter could certainly assist the machinist in estimating the safe distance between adjacent micro-channels. In this study, the micro-channel size and average spatter size are studied during the micro-milling of Ti-6AL-4V by Nd:YAG laser beam machining (LBM). Response surface methodology (RSM) has been utilized to plan a set of experiments and mathematical models are proposed to pre-calculate the channel size and spatter dispersion. Finally, the models are validated through confirmatory tests showing an acceptable range of error.     

An Efficient Numerical Solution of Fractional Optimal Control Problems by using the Ritz Method and Bernstein Operational Matrix

This paper deals with the Ritz spectral method to solve a class of fractional optimal control problems (FOCPs). The developed numerical procedure is based on the function approximation by the Bernstein polynomials along with fractional operational matrix usage. The approximation method is computationally consistent and moreover, has a good flexibility in the sense of satisfying the initial and boundary conditions of the optimal control problems. We construct a new fractional operational matrix applicable in the Ritz method to estimate the fractional and integer order derivatives of the basis. As a result, we achieve an unconstrained optimization problem. Next, by applying the necessary conditions of optimality, a system of algebraic equations is obtained. The resultant problem is solved via Newton's iterative method. Finally, the convergence of the proposed method is investigated and several illustrative examples are added to demonstrate the effectiveness of the new methodology.     

Homogeneous polymerization of ethylene using an iron‐based metal catalyst system

An iron‐based catalyst of 2,6‐bis‐[1‐(2‐methylphenylimino)ethyl]pyridine iron dichloride was prepared. The ligand was prepared using 2,6‐diacetylpyridine as the starting chemical under controlled conditions. The preparation procedure was followed using ¹³C‐NMR, ¹H‐NMR, FT‐IR, MS (mass spectroscopy), and elemental analysis methods. The homogeneous polymerization of ethylene was carried out using the prepared catalyst in toluene media. Methyl aluminoxane (MAO) was used as a cocatalyst. The effect of the [Al] : [Fe] molar ratio, polymerization temperature, and monomer pressure of 202,000 to 454,500 Pa on the polymerization behavior were studied. The highest activity of the catalyst was obtained at 30°C, the activity decreased with increasing temperature, while increasing pressure linearly increased its activity. The molecular weight distribution of the polyethylene obtained was 1.25 to 1.72. A weight average molecular weight of 7.1 × 10⁴ and 1.5 × 10³ were obtained. The crystallinity of the polymer was about 19% and its melting point was about 65°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1517–1522, 2007     

Extraction of pomegranate (Punica granatum L.) seed oil using superheated hexane

Superheated hexane extraction (SHHE), Soxhlet extraction and cold pressing method were compared for the extraction of pomegranate seed oil. The extraction efficiencies of different temperatures (80, 100, 120 °C), mean particle sizes (0.25, 0.50 and 1.00 mm), and n-hexane flow rates (0.5, 1.0 and 2.0 mL/min) were investigated. The fatty acids profile of the seed oils were quantitatively determined by GC-FID. The optimum extraction temperature, mean particle size, and flow rate were selected as 80 °C, 0.25 mm, and 1 mL/min, respectively. The SHHE showed a higher extraction efficiency (22.18 wt%) within 2 h than Soxhlet extraction (17.94 wt%) for 24 h and cold pressing (4.29 wt%) for 72 h. The fatty acids profile for SHHE was more similar to that obtained by cold pressing method than Soxhlet extraction.     

Furnaces: Improving low cement castables by non-wetting additives

Aluminosilicate castables, which are widely used in aluminum transformation furnaces, are susceptible to chemical reactions between molten aluminum and the furnace refractory lining. To prevent those reactions, commercial additives such as BaSO₄, CaF₂, and AlF₃ are generally added in castables. This article presents and analyzes the effect of various amounts of the above additives as well as the influence of pre-firing temperatures on the corrosion behavior of an aluminosilicate low cement castable matrix in contact with liquid Al-5%Mg alloy. For more information, contact C. Allaire, CIREPCRNF, Ecole Polytechnique of Montreal (CRIQ campus), Department of Engineering Physics & Materials Engineering, 8475 Christophe Colomb Street, Montreal, QC H2M 2N9, Canada; (514) 858-6476; fax (514) 858-6469; e-mail claude.allaire@courriel.polymtl.ca.