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61.
Eid M.S. Azzam Hanafy M. Abd El-Salam Reham A. Mohamed Samy M. Shaban Asmaa Shokry 《Egyptian Journal of Petroleum》2018,27(4)
In this work polyacrylamide (PACM) was prepared by radical polymerization technique using ammonium persulfate (APS) as initiator under nitrogen atmosphere. The viscosity average molecular weight of the prepared PACM was found to be 177858. The free amino groups of PACM, poly(2-methoxyaniline) was grafted by the oxidation of 2-methoxyaniline using APS in acidic medium under nitrogen atmosphere. The grafting percent is found to be 96%. The morphology of the obtained PACM and PACM-g-P2-MeOANI was studied by X-ray diffraction and scanning electron microscope. The grafting process enhances the morphology of both PACM and poly(2-methoxyaniline). The inhibiting effect of the three polymers on the mild steel corrosion in the 1.0?M HCl as aggressive environments have been measured gravimetrically at three different temperatures 25, 40 and 55?°C and electrically at 25?°C. The inhibition efficiencies of the three tested polymers were found to increase with temperature. The poly(2-methoxyaniline) is the most effective one as a corrosion inhibitor at all tested temperatures. The adsorption behavior of the polymers was found to follow Villamil isotherm and the values of the change in free energy refer to a mixed chemical and physical adsorption on the steel surface. Tafel curves indicate that the tested polymers act as mixed anodic and cathodic inhibitor. The double layer capacitance was found to decrease with increasing the inhibitor concentration. 相似文献
62.
63.
Selma Sbit Mohamed Béchir Dadi Belgacem Chibani Rhaimi 《Wireless Personal Communications》2018,100(4):1299-1311
Interference in cellular networks is one of the most common problems in the radio access network. In fact, it is the major issue in cellular networks that affects performances and quality of service. Indeed, interference can be caused by a call on the same frequency from neighboring cell, or a call on an adjacent channel in the same or in neighboring cell. So, we can classify interference on intra-cell interference and inter-cell interference. In 4G, thanks to the use of orthogonal frequency division multiple access and single carrier frequency division multiple access as access techniques in downlink and uplink respectively, intra-cell interference is reduced compared to the inter cell one which caused by the frequency reuse one mechanism and the femto cells deployment. In this work, we will evaluate the interference in different cellular network standards from 2G to 4G. 相似文献
64.
Adaptive modulation and decision feedback equalization for frequency‐selective MIMO channels 下载免费PDF全文
Mohamed Lassaad Ammari Kalthoum Zaouali Paul Fortier 《International Journal of Communication Systems》2014,27(11):3323-3338
In this paper, an adaptive modulation scheme for the multiple‐input multiple‐output (MIMO) frequency‐selective channels is investigated. We consider a scenario with precoded block‐based transceivers over spatially correlated Rayleigh multipath MIMO channels. To eliminate the inter‐block interference, the zero‐padding is used. The receiver is equipped with a MIMO minimum‐mean‐squared‐error decision feedback equalizer. The precoder aims to force each subchannel to have an identical signal‐to‐interference‐plus‐noise ratio (SINR). To adjust the constellation size, the unbiased mean square error at the equalizer output is sent back to the transmitter. To simplify our analysis, the feedback channel is considered as instantaneous and error free. We first derive the probability density function of the overall SINR for flat fading and frequency‐selective channels. On the basis of the probability density function of the upper bound of the SINR, we evaluate the system performance. We present accurate closed‐form expressions of the average spectral efficiency, the average bit error rate and the outage probability. The derived expressions are compared with Monte Carlo simulation results. Furthermore, we analyze the effect of the channel spatial correlation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
65.
Thi Minh-Thuyen Radwan Amr Huynh Thong Hwang Won-Joo 《Wireless Personal Communications》2019,109(4):2289-2303
Wireless Personal Communications - In the formulating of power control for wireless networks, the radio channel is commonly formulated using static models of optimization or game theory. In these... 相似文献
66.
Xiaofan Wang Keisuke Shinokita Hong En Lim Nur Baizura Mohamed Yuhei Miyauchi Nguyen Thanh Cuong Susumu Okada Kazunari Matsuda 《Advanced functional materials》2019,29(6)
Atomically thin‐layered ReS2 with a distorted 1T structure has attracted attention because of its intriguing optical and electronic properties. Here, the direct and indirect exciton dynamics of a three‐layered ReS2 is investigated by polarization‐resolved transient photoluminescence (PL) and ultrafast pump‐probe spectroscopy. The various time scales of the decay signals of the time‐resolved PL (<10 ps), with monitoring of the populations of electron–hole pairs (exciton), and the transient differential reflectance (≈1 and 100 ps), with monitoring of the populations of electrons and/or holes in the excited states, are observed. These results reveal the characteristic exciton dynamics: rapid relaxation of direct excitons (electron–hole pairs) and slow relaxation of the momentum‐mismatched indirect excitons accompanied by a one‐phonon emission process. These findings provide important information regarding the indirect bandgap nature of few‐layered ReS2 and its characteristic exciton dynamics, boosting the understanding of the novel electronic and optical properties of atomically thin‐layered ReS2. 相似文献
67.
This paper presents Quality of Service (QoS) based routing and priority class assignment algorithms. It introduces an end-to-end
delay margin balancing approach to routing, and uses it to formulate a nonlinear optimization problem. In a single-class network,
the formulation is shown to be convex; however in a multi-class priority network, it is only convex within specific regions,
and is infeasible otherwise. A centralized off-line computation technique is proposed to calculate both the route configuration
and end-to-end priority assignment. A gradient-based solution in the convex region and a heuristic to overcome the multi-class
discontinuity are derived. An approximation of the optimization problem is developed for on-line distributed processing is
then presented. Using the approximation, arriving traffic flows can use vector routing tables to search for routes. Compared
with minimum-hop, minimum-delay, and min-interference routing algorithms, the proposed approach enables the single-class network
to accommodate more users of different end-to-end delay requirements. In a multi-class priority network, results show that
using the objective function to combine route and priority class assignment further increases the supportable network traffic
volume.
Mohamed Ashour received his B.Sc. (1991) and M.Sc. (1997) in Electrical Engineering from Ain Shams University, Cairo, Egypt. He worked for
Hughes and General Dynamics as a Telecommunications Engineer. Currently, he is a Ph.D. Candidate in the Department of Electrical
and Computer Engineering of McGill University, Montreal, Quebec, Canada. His current area of research is focused on traffic
engineering, routing, and QoS provisioning in DiffServ and MPLS Networks. He is also interested in multi-class queuing analysis
of long-range traffic, and QoS provisioning in ad hoc networks and satellite communications.
Tho Le-Ngoc obtained his B. Eng. (with Distinction) in Electrical Engineering in 1976, his M.Eng. in Microprocessor Applications in 1978
from McGill University, Montreal, and his Ph.D. in Digital Communications 1983 from the University of Ottawa, Canada.
During 1977–1982, he was with Spar Aerospace Limited as a Design Engineer and then a Senior Design Engineer, involved in the
development and design of the microprocessor-based controller of Canadarm (of the Space Shuttle), and SCPC/FM, SCPC/PSK, TDMA
satellite communications systems.
During 1982–1985, he was an Engineering Manager of the Radio Group in the Department of Development Engineering of SRTelecom
Inc., developed the new point-to-multipoint DA-TDMA/TDM Subscriber Radio System SR500. He was the System Architect of this
first digital point-to-multipoint wireless TDMA system.
During 1985–2000, he was a Professor the Department of Electrical and Computer Engineering of Concordia University. Since
2000, he has been with the Department of Electrical and Computer Engineering of McGill University.
His research interest is in the area of broadband digital communications with a special emphasis on Modulation, Coding, and
Multiple-Access Techniques. He is a Senior Member of the Ordre des Ingénieur du Quebec, a Fellow of the Institute of Electrical
and Electronics Engineers (IEEE), a Fellow of the Engineering Institute of Canada (EIC), and a Fellow of the Canadian Academy
of Engineering (CAE). He is the recipient of the 2004 Canadian Award in Telecommunications Research, and recipient of the
IEEE Canada Fessenden Award 2005. 相似文献
68.
69.
In this paper, an active filtering technique is presented which is capable of filtering the out-of-band blockers in wireless receivers. The concept is based on the feedforward cancellation technique where a blocker replica is subtracted at the output of the low-noise amplifier (LNA). In contrast to the previously reported feedforward cancellation methods, exact gain and phase matching are easily obtained in the proposed architecture to produce a highly selective narrowband frequency response at the output of the LNA with wide rejection bandwidth. For the proof of concept, the system is implemented in a 65 nm CMOS technology. It occupies a total area of 0.8 mm2 and the current consumption is 24 mA from a 1.2 V supply. The system post-layout simulations showed a blocker rejection of more than 33 dB for blocker signals 100 MHz away from the desired signal when the feedforward path is activated. The noise figure (NF) of the entire system is 3.8 dB that degrades to 5.8 dB when the feedforward path is activated. 相似文献
70.
Salah M Ramadan Ahmed El Sherbini Mahmoud Marie Mohamed Zaki 《Wireless Personal Communications》2007,41(1):57-75
One of the challenging tasks in Personal Communication Services (PCS) is to efficiently maintain the location of PCS subscribers
who move from one region to another (hereafter called mobile users). When a mobile user receives a call, the network has to
quickly determine its current location. The existing location management scheme suffers from high signaling traffic in locating
the mobile users. Two-level forwarding pointer scheme has been proposed from per-user forwarding pointer scheme to reduce
the cost of signaling traffic. In this paper, we enhance the two-level forwarding pointer scheme. When a mobile user moves
from its current Registered Area (RA), which is served by Mobile Switching Center (MSC), to another RA the local switch that
acts as a parent of those two MSCs maintains this movement in its memory (hereafter called cache entry). A cache entry is
used to locate rapidly the mobile user instead of querying the Home Location Register (HLR) and waiting for its reply. HLR
is centralized in the network and far away from the mobile users so that the signaling traffic crossing it is expensive. Sometimes
the cache entry may be failed to reach the mobile user then a two-level forwarding pointers will be created from the corresponding
Visitor Location Register (VLR), attached to its MSC, through a correct path to locate the mobile user. Thus, there is a saving
in cost of querying the underlying HLR. The analytical results indicate that such proposal efficiently reduces the signaling
traffic cost for all values of Call to Mobility Ratio (CMR), this is especially considerable when CMR ≥1, without any increase
in the call setup delay.
Salah M. Ramadan (samohra@yahoo.com) received the BS and MS degrees from Computers Engineering Department, Al-Azhar University, Cairo, Egypt,
in 1995 and 2002, respectively. From 2002, he was a Ph.D. student in Computers Engineering Department at Al-Azhar University
and is currently pursuing the Ph.D. degree, where he is a research assistant in the Wireless Networks Branch. His research
interests include traffic management in ATM networks, routing protocols, mobility management in PCS networks, and mobile computing.
He is currently an instructor in Cisco Academy, Egypt.
Ahmed M. El-Sherbini (Sherbini@mcit.gov.eg) received the Ph.D. in Electrical and Communication Engineering, Case Western University, U.S.A. March
1983 and M.Sc. in Communication Engineering, Cairo University, Giza, Egypt, June 1980. (M. Sc. Research Studies at the Ecole
Nationale Superieure des Telecommunications (ENST), Paris, France). He is the Director, National Telecommunication Institute
– Ministry of Communications and Information Technology, Egypt and Professor of Electrical and Communication Engineering Dept.
Faculty of Engineering, Cairo University, Egypt.
M. I. Marie received his B.Sc., M.Sc. and Ph.D. in electronic and communication engineering from Cairo University on 1972, 1981, 1985,
respectively. Now he is a professor of communications at Computer and System Engineering department Al-Azhar University, Cairo,
Egypt. His fields of interest includes digital communication, computer networks and protocols development.
M. Zaki (azhar@mailer.scu.eun.eg) is the professor of software engineering, Computer and System Engineering Department, Faculty of
Engineering, Al-Azhar University at Cairo. He received his B.Sc. and M.Sc. degrees in electrical engineering from Cairo University
in 1968 and 1973 respectively. He received his Ph.D. degrees in computer engineering from Warsaw Technical University, Poland
in 1977. His fields of interest include artificial intelligence, soft computing, and distributed system. 相似文献