Abstract Ad-hoc networking is a concept in computer communications, which means that users wanting to communicate with each other form a temporary network, without any form of centralized administration. Each node participating in the network acts both as host and a router and must therefore be willing to forward packets for other nodes.In a multi-hop wireless packet network, a packet traverses more than one wireless link in traveling from its source to its destination. Such wireless networks have received considerable attention recently in the context of ad hoc networks. Ad-Hoc networks are self-organizing multi-hop wireless networks where not all links along the path of a packet can be activated simultaneously. Hence the performance of a higher level mechanism, such as congestion window or Transport Layer protocol (TCP) will depend crucially on how the links are scheduled for transmission. In multiple access networks, such as the IEEE802.11 wireless LAN, the scheduling of transmissions is done by the medium access control (MAC) protocol. This transmission scheduling is completely unaware of the needs of the TCP congestion window protocol. This thesis is concerned with the poor interaction between the TCP adaptive window protocol, the IEEE 802.11 MAC protocol, and the IEEE 802.11 Ad-Hoc routing protocol. Our thesis follow on the work done by the researchers K. Nahm and C. Kuo in the paper entitled “TCP over 802.11 Multihop networks issues and Performance Enhancement” [1]. Our contributions are two-fold. First we have repeated and confirmed the simulation results reported by K.Nahm and C.Kuo using NS-2 network simulator. Second we have introduced a simple modification in the 802.11 DSR routing protocol which reduces the unnecessary VI reroutings triggered by MAC packet collisions and enforces the TCP to enter the fast retransmit / fast recovery phase to quickly recover the packet loses. This modification has been simulated using NS-2 network simulator and from the results we have found that it provides a substantial improvement in TCP performance in the situations that we have considered in the simulation models
يحي الشارف المبروك (2009)

Prediction of the present and future state of Reinforced Concrete (RC) structures suffering from chloride-induced corrosion is important if proper planning for inspection and maintenance is to be made. The majority of research studies have thus far focused on the diffusion process of chloride ions through the concrete cover, the time to corrosion initiation and on the prediction of the surface condition of the structure. However; practical evidence and theoretical analysis suggests that many structures can tolerate considerable corrosion damage without serious reduction to their load carrying capacity. Therefore, visual impression-based maintenance is not an optimum solution particularly when financial resources are limited. To support this notion, accurate models are needed to predict the deterioration rate of the structural load carrying capacity over time. This paper uses existing empirical RC deterioration models to predict the loss in the load carrying capacity of a typical RC T-beam using a reliability based approach. The approach takes into consideration the spatial variability of the deterioration parameters, thereby demonstrating the importance of its inclusion in any such analysis. arabic 13 English 97
Omran Kenshel(1-2009)

Abstract Measurements of in-situ data for geomechanical parameters are very essential part of geotechnical engineering design, but the time and the budgets are major issues, The design engineer must make critical decisions at several steps throughout the design stages to obtain the most reliable and realistic soil and rock property information. Because of that, the empirical equations are increased in use during the early stages of engineering design work. In any geotechnical investigations, most probably, will be involved in using Standard Penetration Test (SPT). It is a very popular test among geotechnical engineers. Therefore, it will be economically very useful if the results of SPT as N-values could be used to calculate the other geomechanical parameters. The sites of investigation are the Zawia Combined Cycle Power Plant, West Mountain Power Plant at Rowies, Tripoli and Tunisa. The data were collected from 13 boreholes, and more than 160 points. Which gave wide reliable results. Field investigations include Cross-Hole, Down-Hole seismic techniques, Standard Penetration Test SPT, Cone Penetration Test CPT and pressuremeter test PMT. The variation of seismic waves velocity (Vs & Vp) and dynamic modulus (shear modulus, young modulus, and bulk modulus) of sand and weak rock were studied and some correlations were developed. Also the effects of depth on the correlations were investigated. The correlations compared with previous relationships. The results showed that the power function provides the best fit for correlation between seismic wave’s velocity and dynamic modulus data with SPT N-value. The correlation coefficient (r) range 0.77-0.54 for sand and for weak rock. Range is 0.82-0.58. The multiple power regression analysis enhanced the correlation coefficient of sand and weak rock to ranges 0.82-0.58 and 0.97-0.92 respectively. These results are higher than the previous results. A single value of geotechnical parameters is very difficult to determine because the properties of material vary from point to point in the way that, it depends on a set of conditions so geotechnical parameters (seismic waves velocity and dynamic modulus) were determined between an upper and lower limits. The results of statistical analysis of relationship between SPT N-value and Cone Penetration Test (tip resistance qc) for all available data show that a linear regression with zero intercept as best fit correlation. of r=0.77. This result is equivalent to previous work. The logarithmic regression gave the best fit for the correlation analysis between the pressuremeter modulus EPMT and N value by r=0.81. The relationship between the limit pressure PL and N value was shown that, the linear regression was the best fit. The best-fit regression indicated a logarithmic relationship between the pressuremeter modulus (EPMT) and limit pressure (PL), with r=0.81 and 0.66 respectively.
ملاك عبد اللطيف ابوعرقوب (2010)