Significant challenges has been introduced for IP networks with the advent of new emerging applications, such as VOIP and E-Commerce, that require delivering quality guarantees. However, IP networks were originally designed to support best effort delivery only. Two Quality of Service (QoS) standard models, IntServ, DiffServ have been standardized by the Internet Engineering Task Force (IETF). Although these methods guarantee delivery, they have drawbacks such as complexity, restrictions of predefined classes and higher end-to-end delay. In this paper, a new QoS mathematical model has been proposed. This model is based on the principles of Network Calculus in which an incoming traffic flow is regulated by an arrival curve that upper bounds its rate. Then, this traffic flow is lower bounded and delayed by a service latency time at each node on its way to the destination node. The worst case end-to-end delay is derived and illustrated by a numerical example. The proposed model has achieved acceptable end-to-end delay compared with the other models.

Abstract

This paper presents the effect of corrugation geometry on the crushing behavior, energy absorption, failure mechanism, and failure mode of woven roving glass fibre/epoxy laminated composite tube. Experimental investigations were carried out on three geometrical different types of composite tubes subjected to axial and lateral compressive loadings. On the addition to a radial corrugated composite tube, cylindrical composite tube, and corrugated surrounded by cylindrical tube were fabricated and tested under the same condition in order to know the effect of corrugation geometry. The results showed that the loading carrying capability is significantly influenced by corrugation geometry in axial crushing. However, no affect of corrugation geometry was observed for lateral crushing. Load–displacement curve was plotted for all conducted tests, thus clear comparison between different specimen's geometry was achieved. It is also found that radial corrugation could significantly applicable as a stable and effective energy absorber.

Abstract

A numerical simulation of a two-stage reciprocating compressor has replicated the operations of the compressor under various conditions for the development of diagnostic features for predictive condition monitoring. The simulation involves the development of a mathematical model of five different physical processes: speed–torque characteristics of an induction motor, cylinder pressure variation, crankshaft rotational motion, flow characteristics through valves and vibration of the valve plates. Modelling both valve leakage and valve spring deterioration has also been achieved. The simulation was implemented in a MATLAB environment for an efficient numerical solution and ease of result presentation. For normal operating conditions, the simulated results are in good agreement with the test results for cylinder pressure waveforms and crankshaft instantaneous angular speed (IAS). It has been found that both the IAS fluctuation and pressure waveform are sensitive detection features for compressor faults such as valve leakage and valve spring deterioration. However, IAS is preferred because of its non-intrusive measurement nature. Further studies using the model and experiments are being undertaken in order to develop fault detection features for compressor driving motors and transmission systems.

The purpose of this work is to investigate the effect of the dimensions of composite tubes on their specific energy absorption capacity. Experimental investigations were carried out on three geometrical different cylindrical composite tubes subjected to compressive loading. More over a radial corrugated composite tube was subjected to the same load conditions in order to examine the varying of shape influence on the energy absorption of composite materials. Initial results indicate that for cylindrical tubes, diameter to thickness ratio has a significant effect on the energy absorption. Reduction in tube d/t ratio results in an increase in energy absorption. More over results show also radial corrugated composite tubes exhibit higher total energy absorption than cylindrical composite tubes.

This paper presents a novel cellular handset design with a bottom-mounted short loaded-whip antenna. This new handset design is modeled and simulated using a finite difference time-domain (FDTD)-based platform SEMCAD. The proposed handset is based on a current commercially available bar-phone type with a curvature shape, keypad positioned above the screen, and top-mounted antenna. The specific absorption rates (SARs) are determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct model of a human head when exposed to the EM-field radiation of the proposed cellular handset and the handset with top-mounted antenna. The two cellular handsets are simulated to operate at both GSM standards, 900 MHz as well as 1800 MHz, having different antenna dimensions and intput power of 0.6 W and 0.125 W, respectively. The proposed human hand holding the two handset models is a semirealistic hand model consists of three tissues: skin, muscle, and bone. The simulations are conducted with handset positions based on the IEEE standard 1528-2003. The results show that the proposed handset has a significant improvement of antenna efficiency when it is hand-held close to head, as compared with the handset of top-mounted antenna. Also, the results show that a significant reduction of the induced SAR in the human head-tissues can be achieved with the proposed handset

This paper is intended to investigate intensely the impact of multipossible hand-hold positions on the electromagnetic (EM) interaction of handset antennas and a human by using a finite-difference time-domain (FDTD) method. Candy-bar handsets with different external and internal antenna positions operating in the GSM900, GSM1800/DCS, and UMTS/IMT-2000 bands are hereby simulated with configuration of the most parts in order to achieve the commercially available handset model design. Homogeneous and heterogeneous phantoms both are used to simulate the human head, whereas, a semirealistic model with three different tissues is designed to simulate a human hand holding a set. Both of the antenna performance including the total isotropic sensitivity (TIS) and the specific absorption rate (SAR) in tissues are examined for the different suggested applicable cases, where various positions of antenna, handset and hand are considered in simulations. This simulation study determines that both of the antenna performance and the SAR in tissues significantly alter owing to the positioning of the handset against user’s head at different hand levels; where a maximum alteration is observed due to the exposure of handset with internal antenna, as compared with the handset having external antenna.

This paper presents a through investigation into the effect of the external antenna and printed circuit board (PCB) positions in cellular hand-sets on the coupling between the handset and human-head at GSM-900 frequency standard. The antenna performance and the specific absorption rate (SAR) induced in a human head were computed using a Finite Difference Time-Domain based platform (SEMCAD). A numerical correct model of a European female head was adopted and a semi-realistic hand model was designed during the simulation. The results showed that the optimum position for the antenna and PCB in hand-set close to head is the far right-corner for the right-hand users and the far left-corner for the left-hand users, where a minimum SAR in head is achieved.

This research is devoted to investigate the effect of structural geometry on the crushing behaviour, energy absorption, failure mechanism, and failure mode of radial corrugated composite shells. A multi-discipline literature review on the use of composite materials in the field of crashworthiness was carried out. Based on the literature review findings, new composite structure (Radial Corrugated Composite Tube RCCT) was proposed to be fabricated and investigated experimentally.

In this article an investigation was conducted to evaluate the level of conformity of reinforcing steel rods produced from recycled scraps by Zliten Steel Factory (ZSF) with relevant to Libyan specifications and international standards. A series of experimental tests were conducted to find ultimate tensile strength (UTS), yield strength (YS), and hardness. Bending test has been conducted too. Reinforcing steel rods samples of 12 and 14 mm diameter were subjected to mechanical properties investigations. The tests were carried out for samples selected randomly through three batches at different time. Obtained results were compared with Libyan specifications (LNS-75) and ASTM standard (A-615). Results showed that the locally produced reinforcing steel were conform with the Libyan and international standards in terms of yield stress, ultimate tensile stress, and hardness.

Abstract:

A detailed experimental investigation of the quasi-static lateral crushing of composite cylindrical tubes between flat platens has been carried out. Tubes employed were made of glass fibre reinforced with epoxy. Behaviour of tubes as regards the peak crushing load, post collapse load, energy absorbed and mode of crushing has been discussed. The load displacement response is plotted graphically.