Pitting corrosion of lead in sodium carbonate solutions containing NO3 ions

Pitting corrosion of Pb in Na₂CO₃ solutions (pH=10.8) containing NaNO₃ as a pitting corrosion agent has been studied using potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques, complemented with scanning electron microscopy (SEM) examinations of the electrode surface. In the absence of NO₃⁻, the anodic voltammetric response exhibits three anodic peaks prior to oxygen evolution. The first anodic peak A₁ corresponds to the formation of PbCO₃ layer and soluble Pb²⁺ species in solution. The second anodic peak A₂ is due to the formation of PbO beneath the carbonate layer. Peak A₂ is followed by a wide passive region which extends up to the appearance of the third anodic peak A₃. The later is related to the formation of PbO₂. Addition of NO₃⁻ to the carbonate solution stimulates the anodic dissolution through peaks A₁ and A₂ and breaks down the dual passive layer prior to peak A₃. The breakdown potential decreases with an increase in nitrate concentration, temperature and electrode rotation rate, but increases with an increase in carbonate concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases with increasing the applied anodic potential, nitrate concentration and temperature.     

MICROWAVE VACUUM DRYING OF BANANA SLICES

Vacuum drying of banana slices was studied in a domestic microwave oven. The results show that banana temperature rises uniformly and rapidly to the saturation water vapor temperature corresponding to the vacuum used then rises slowly until most of the free moisture is lost. The thermal and drying efficiencies were found to drop from almost 100% at the beginning of the drying (high moisture content) to as low as 40% and 30% respectively at the end of drying. Both efficiencies were found to increase with the use of vacuum, especially at low moisture content.     

2D grid architectures for the DFT and the 2D DFT

New algorithms for the DFT and the 2-dimensional DFT are presented. The DFT and the 2-dimensional DFT matrices can be expressed as the Kronecker product of DFT matrices of smaller dimension. These algorithms are synthesized by combining the efficient factorization of the Kronecker product of matrices with the highly hardware efficient recursive implementation of the smaller DFT matrices, to yield these algorithms. The architectures of the processors implementing these algorithms consist of 2-dimensional grid of processing elements, have temporal and spatial locality of connections. For computing the DFT of sizeN or for the 2D DFT of sizeN=N ₁ byN ₁, these algorithms require 2N multipliers and adders, take approximately computational steps for computing a transform vector, and take approximately computation steps between the computation of two successive transform vectors.     

Service Violation Monitoring Model for Detecting and Tracing Bandwidth Abuse

Bandwidth abuse is a critical Internet service violation. However, its origins are difficult to detect and trace given similarities between abusive and normal traffic. So far, there is no capable and scalable mechanism to deal with bandwidth abuse. This paper proposes a distributed edge-to-edge model for monitoring service level agreement (SLA) violations and tracing abusive traffic to its origins. The mechanism of policing misbehaving user traffic at a single random early detection (RED) gateway is used in the distributed monitoring of SLA violations, including violations carried out through several gateways. Each RED gateway reports misbehaving users who have been sent notifications of traffic policing to an SLA monitoring unit. Misbehaving users are considered suspicious users and their consumed bandwidth shares are aggregated at every gateway to be compared with SLA-specified ratios. Bandwidth is abused when SLA-specified ratios are exceeded. By reporting bandwidth abuse, illegitimate users can be isolated from legitimate ones and source hosts of abusive traffic may be traced. Approximate simulation results show that the proposed model can detect any SLA violation and identify abusive users. In addition, the proposed model can trace user violations back to their source machines in real time.     

A survey and tutorial of wireless relay network protocols based on network coding

Ever since the wireless relay network (RN) was introduced, it has led to the discovery of several new protocols, which have been consistently improved by researchers to overcome many constraints such as throughput, capacity bound, symbol error rate, outage probability, and power allocations. Meanwhile, network coding (NC) was invented as an efficient technique to address these problems. To the best of our knowledge, there has been no comprehensive discussion about wireless-RN modes in the literature. We therefore provide a tutorial concerning the basic concepts of NC, dealing with the classification of particular relay modes, and presenting new wireless-RN protocols with/without NC in this paper. Under appropriate categories (i.e., fixed and dynamic), much attention has been given to various proposed wireless-RN protocols because they may differ individually depending on their processing at relay nodes and network topology. We compare the available wireless-RN protocols with/without NC, and conclude that the wireless-RN based on NC outperforms the traditional wireless-RN in certain scenarios.     

Efficient route optimization scheme for nested-NEMO

Network mobility (NEMO) basic support protocol maintains the connectivity when mobile router (MR) of a mobile network changes its point of attachment to the Internet by establishing a bi-directional tunnel between the MR and the home agent (HA). A packet from a correspondent node (CN) traverses through the tunnel to reach the mobile network. Nesting occurs in NEMO when a MR's new attachment point is in another mobile network that has also moved away from its home link. The level of tunneling increases as the level of nesting increases. Multiple levels of tunneling in nested NEMO adds multiple legs to a non-optimized routing path that the IP packets have to traverse in order to reach the final destination. As per our study, an efficient route optimization technique in NEMO, particularly in nested NEMO, is still a research challenge. In this paper, we propose an efficient route optimization scheme for nested NEMO. We use two care-of Addresses for each MR, as well as two types of entries, such as fixed and visiting, in the routing table in each MR. Our route optimization scheme removes the tunnels completely from the nested NEMO in a single step using only one binding update message irrespective of the number of levels in the nest. Our route optimization scheme also works for non-nested NEMO.     

The power manipulability – A new homogeneous performance index of robot manipulators

Jacobian-based performance indices such as the manipulability ellipsoid, the condition number and the minimum singular value, have been very helpful tools both for mechanical manipulator design and for determining suitable manipulator postures to execute a given task. For a manipulator having complex degrees of freedom (translations and rotations), Jacobian matrix becomes non-homogeneous, i.e. it contains elements with different physical units; therefore, the evaluation of its determinant, eigenvalues or singular values needs the combination of quantities of different nature, which is physically inconsistent and moreover it corresponds to a noncommensurable system. In this paper, a new performance index of robot manipulators is proposed. It is fully homogeneous and it constitutes a physically consistent system whether the manipulator contains joints of different natures, or the task space combines both translation and rotation motion. The development is concerned with the study of power within the mechanism. Given that the power has the same physical units in translation and rotation, it can be used as a homogeneous or natural performance index of manipulators by examining the behaviour of its basic components namely, force and speed, at different kinematics configurations. Furthermore, the new concept of vectorial power is introduced, followed by to the quadrivector of apparent power, and leading to the final homogeneous performance index of the power manipulability (PM). This new approach matches perfectly with mechanisms having joints of different natures, as well as with a task space combining both translation and rotation.     

The Jacobi elliptic function method and its application for two component BKP hierarchy equations

The periodic wave solutions for the two component BKP hierarchy are obtained by using of Jacobi elliptic function method, in the limit cases, the multiple soliton solutions are also obtained. The properties of some periodic and soliton solution for this system are shown by some figures.