Effects of Space Charge on the Discharge Process in an Icicle/Iced-Plate Electrode System under Positive DC Voltage

Using an icicle/iced-plate system, the corona discharge at the icicle tip was investigated under positive DC voltage. The discharge pulses were recorded and analyzed. The relationship between the discharge magnitude and the time interval before the pulse was examined. The mechanisms underlying the corona discharges at icicle tips were investigated. The influence of space charge on the discharge and the effects of the applied voltage on the time interval between two pulses were also investigated. Finally, a model for calculating the drift and diffusion of the space charge cloud was presented.     

Role of air gaps on AC withstand voltage of an ice-covered insulator string

The influence of the number and position of air gaps on the 50% AC withstand voltage, V₅₀, of a short string of 5 IEEE standard insulator units covered with ice was experimentally investigated and numerically simulated. The results show that the V₅₀ is affected by the number and position of the air gaps. The results also show that the presence of a partial arc along the air gap close to the high voltage (HV) electrode leads to a redistribution of the voltage along the ice-covered insulator. Based on the obtained results, suggestions for improving the performance of line insulators under icing conditions were proposed     

A hybrid modified FA-ANFIS-P&O approach for MPPT in photovoltaic systems under PSCs

ABSTRACT

A modified firefly algorithm (MFO)-based adaptive neuro-fuzzy inference system (ANFIS) combined with the perturbation and observation (P&O) is used in this paper to track the maximum power point (MPP) in photovoltaic systems (PVs). The proposed method identifies and tracks the MPP in two stages. First, according to the irradiance on the solar panels, the ANFIS approximately identifies the MPP. In the second stage, the P&O method starts to act in the tracking cycle and initiates an accurate searching process from that point. The suggested hybrid method covers the problems of commonly-used methods, such as inability in detecting the global MPP under partial shading conditions (PSCs) and trapping in the local optima. Furthermore, the method provides significantly higher speed for the MPP tracking under various irradiance patterns. To prove the above-mentioned claims, the given approach is compared with the P&O method as a common method in the MPPT and particle swarm optimisation (PSO) which operates based on swarm intelligence. Simulation results obtained from MATLAB/Simulink environment show that the proposed method identifies and tracks the MPP under uniform irradiance and PSCs in a very short time of roughly 0.2 s.     

Performance Analysis of TCP with Delayed Acknowledgments in Multi-hop Ad-hoc Networks

The acknowledgment strategy has great potential to increase TCP throughput when it runs over 802.11 MAC protocol. In particular, TCP acknowledgments (ACK) carry out an extensive number of medium accesses as they compete in the same route as data packets for media. In this paper, we first propose a dynamic TCP-MAC interaction strategy which tries to reduce the number of induced ACKs by monitoring the channel condition. To this end, the total collision probability collected along the path from sender to receiver in MAC layer has been used to properly set the number of delayed ACKs (DA) in TCP. Based on the estimated collision probability, TCP sender dynamically adjusts itself to the channel condition by delaying less ACKs in high traffic conditions and more ACKs in low traffic conditions. The simulation results show a throughput improvement up to 15% over the existing method called Dynamic Adaptive Acknowledgment (TCP-DAA) and much more over the regular TCP in different scenarios dealing with a dynamic loss rate. In addition, we show that our proposed strategy does not always benefit from a fixed delay policy along with a fixed congestion window size. In fact, the optimal number of delayed ACKs is based on the path length of a TCP connection and a large delay window may solely improve TCP throughput in short ranges with less number of flows. However, in a longer path congestion window limit provides more throughput gain.     

Recyclable Magnetic Camphor Sulfonic Acid: A Reliable and Highly Efficient Ionic Organocatalyst for Benzothiazin-4-One Synthesis in Green Media

Catalysis Letters - Organocatalysts, like a minimalistic biocatalyst, pursue to reduce metal consumption with low cost, and low toxicity targeting to become a green strategy in organic...     

Variation of Catechin,epicatechin and their enantiomers concentrations before and after wheat cultivar-Puccinia triticina infection

Three wheat cultivars (Boolani, Roushan and Fornota) were inoculated with Puccinia triticina strain 140 and placed in greenhouse and concentrations of catechin, epicatechin and their enantiomers were monitored in three steps; healthy leaves before and after exposed and also diseased leaves after exposed. The concentration of catechin and epicatechin in infected plant ranged from 4.43 to 11.00 and 1.65 to 3.68 times higher than those in non-infected plant, respectively. Also, the healthy leaves of infected plants had more amounts of catechin and epicatechin than diseased leaves. Study of chiral separations by cellulose column, indicated that both enantiomers of catechin were found in healthy leaves of non-infected plants. However, in the leaves of wheat which were exposed to P. triticina, the concentration of (+) catechin increased while (−)-catechin disappeared in healthy and diseased leaves of infected plants. Furthermore, only (−)-epicatechin was found in all the samples. So, infection by pathogen caused a change in the biosynthesis and accumulation of catechin and also a change in the enantiomeric ration of catechin enantiomers in the leaves.     

Modelling of sintering during rotational moulding of the thermoplastic polymers

This paper concerns the study of sintering phenomenon during rotational molding of polypropylene(PP),Polyvinylidenefluoride (PVDF) and Polymethyl methacrylate (PMMA). First, the coalescence (first step of sintering) of two grains has been followed. Bellehumeur’s model has been tested as a model to explain this phenomenon. In order to study the effect of neighboring grains on coalescence of two grains, a third grain has been put in contact with these two grains. For modeling the phenomenon in this case, Bellehumeur’s model has been modified by a geometric parameter called Farz Factor (FF), being this model validated by experimental test. Concerning densification, two different stages have been observed. In the first stage, before welding of the grains and formation of interphases between them, the grains are not stuck yet. The air trapped between the grains escapes through free ways between grains. This first step of densification is directly related to the coalescence where the density of the polymer varies very quickly. A new tridimensional model, based on a Body Centered Tetragonal (BCT) configuration, has been proposed to explain the densification during this first stage. In the second stage, the migration of air is controlled by diffusion.