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Survey on Physical Layer Security in Downlink Networks
Abbas, Mohammed Adil,Hong, Jun-Pyo The Korea Institute of Information and Commucation 2017 Journal of information and communication convergen Vol.15 No.1
In this paper, we discuss physical layer security techniques in downlink networks, including eavesdroppers. The main objective of using physical layer security is delivering a perfectly secure message from a transmitter to an intended receiver in the presence of passive or active eavesdroppers who are trying to wiretap the information or disturb the network stability. In downlink networks, based on the random feature of channels to terminals, opportunistic user scheduling can be exploited as an additional tool for enhancing physical layer security. We introduce user scheduling strategies and discuss the corresponding performances according to different levels of channel state information (CSI) at the base station (BS). We show that the availability of CSI of eavesdroppers significantly affects not only the beamforming strategy but also the user scheduling. Eventually, we provide intuitive information on the effect of CSI on the secrecy performance by considering three scenarios: perfect, imperfect, and absence of eavesdropper's CSI at the BS.
Abbas H. Mohammed,Nildem Tayşi 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.5
During their life span, post-tensioned concrete structures may be exposed to thermal loads. Therefore, there has been a growing interest in research on the advanced analysis and design of post-tensioned concrete slabs subjected to thermal loads. This paper investigates the structural behaviour of post-tensioned one-way spanning concrete slabs. A nonlinear finite element model for the analysis of post- tensioned unbonded and bonded concrete slabs at elevated temperatures was developed. The interface between the tendon and surrounding concrete was also modelled, allowing the tendon to retain its profile shape during the deformation of the slab. The load-deflection behaviour, load-force behaviour in the tendon, and the failure modes are presented. The numerical analysis was conducted by the finite element ANSYS software and was carried out on two different one-way concrete slabs chosen from literature. A parametric study was conducted to investigate the effect of several selected parameters on the overall behavior of post-tensioned one-way concrete slab. These parameters include the effect of tendon bonding, the effect of thermal loading and the effect of tendon profile. Comparison between uniform thermal loading and non-uniform thermal loading showed that restrained post tensioned slab with bottom surface hotter has smaller failure load capacity.
Mohammed Abbas,Mohammed Alkaff,Asim Jilani,Haneen Alsehli,Laila Damiati,Mamdooh Kotb,Moahmmed Abdelwahed,Fahad Alghamdi,Gauthaman Kalamegam 한국조직공학과 재생의학회 2018 조직공학과 재생의학 Vol.15 No.5
BACKGROUND: Mesenchymal stem cells (MSCs) and/or biological scaffolds have been used to regenerate articular cartilage with variable success. In the present study we evaluated cartilage regeneration using a combination of bone marrow (BM)-MSCs, HyalofastTM and/or native cartilage tissue following full thickness surgical cartilage defect in rabbits. METHODS: Full-thickness surgical ablation of the medial-tibial cartilage was performed in New Zealand white (NZW) rabbits. Control rabbits (Group-I) received no treatment; Animals in other groups were treated as follows. Group-II: BMMSCs (1 9 106 cells) ? HyalofastTM; Group-III: BMMSCs (1 9 106 cells) ? cartilage pellet (CP); and Group-IV: BMMSCs (1 9 106 cells) ? HyalofastTM ? CP. Animals were sacrificed at 12 weeks and cartilage regeneration analyzed using histopathology, International Cartilage Repair Society (ICRS-II) score, magnetic resonance observation of cartilage repair tissue (MOCART) score and biomechanical studies. RESULTS: Gross images showed good tissue repair (Groups IV[III[Group II) and histology demonstrated intact superficial layer, normal chondrocyte arrangement, tidemark and cartilage matrix staining (Groups III and IV) compared to the untreated control (Group I) respectively. ICRS-II score was 52.5, 65.0, 66 and 75% (Groups I–IV) and the MOCART score was 50.0, 73.75 and 76.25 (Groups II–IV) respectively. Biomechanical properties of the regenerated cartilage tissue in Group IV closed resembled that of a normal cartilage. CONCLUSION: HyalofastTM together with BM-MSCs and CP led to efficient cartilage regeneration following full thickness surgical ablation of tibial articular cartilage in vivo in rabbits. Presence of hyaluronic acid in the scaffold and native microenvironment cues probably facilitated differentiation and integration of BM-MSCs.
Mohammed Bouremana,Abdelouahed Tounsi,Mohammed Sid Ahmed Houari,Abdelhakim Kaci,El Abbas Adda Bedia 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.15 No.5
In this paper, a new first-order shear deformation beam theory based on neutral surface position is developed for bending and free vibration analysis of functionally graded beams. The proposed theory is based on assumption that the in-plane and transverse displacements consist of bending and shear components, in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. The neutral surface position for a functionally graded beam which its material properties vary in the thickness direction is determined. Based on the present new first-order shear deformation beam theory and the neutral surface concept together with Hamilton's principle, the motion equations are derived. To examine accuracy of the present formulation, several comparison studies are investigated. Furthermore, the effects of different parameters of the beam on the bending and free vibration responses of functionally graded beam are discussed.
Abbas, Mohammed Adil,Song, Hojin,Hong, Jun-Pyo IEEE 2019 IEEE transactions on information forensics and sec Vol.14 No.4
<P>In this paper, we consider user scheduling and power allocation techniques for downlinks where transmitted message must be kept confidential from all other unintended users and the number of users is larger than that of access point (AP) antennas. In order to maximize network secrecy rate with a limited number of antennas, the AP schedules a user who can achieve the largest secrecy rate and exploits multiple antennas for transmitting artificial noise to the unintended users. We derive the closed-form expressions of the optimal power allocation for the artificial noise and the average network secrecy rate through asymptotic analysis. The analysis results provide the insightful information on the behaviors of the user scheduling and the effect of system parameters on the network secrecy rate performance. It is shown that opportunistic scheduling with artificial noise transmission technique is more effective than the conventional precoding techniques for multiple confidential message transmissions in terms of network secrecy rate. Furthermore, we have also discussed a transmission strategy for the worst case scenarios where all unintended users are treated as colluding eavesdroppers. The simulations confirm the validity of the analysis results and provide additional information on the network performance in general cases.</P>
Nonlinear Finite Element Model for the Optimization of Post-Tensioned One-Way Concrete Slab
Abbas H. Mohammed,Dia Eddin Nassani,Nildem Tayşi,Ali K. Hussein 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.7
Optimization in its wide sense can be used to solve many engineering problems and to find the best solutions so that designers cangain a maximum benefit from the available resources. In this research a nonlinear Finite Element (FE) model was developed for theoptimization of Unbonded Post-Tensioned (UPT) one-way slab. ANSYS program was used to find the optimum total weight of Post-Tensioned Tendon (PTT). In the optimization analysis, the objective function is the total weight of PTTs. The area of PTT, tendoninitial stress, and tendon eccentricity are considered as the design variables. Concrete normal stress, steel tendon stress, concrete shearstress, and mid-span deflection of concrete slab are considered as constraints. The optimization result indicates that the total weight ofPTTs can be reduced about 33% for the UPT slabs using an appropriate optimization algorithm.
Derivation and Differentiation of Bone Marrow Mesenchymal Stem Cells from Osteoarthritis Patients
Mamdooh Gari,Haneen Alsehli,Abdullah Gari,Mohammed Abbas,Mohammed Alkaff,Mohammed Abuzinadah,Fatin Al-Sayes,Mazin Gari,Ashraf Dallol,Adel M Abuzenadah,Kalamegam Gauthaman 한국조직공학과 재생의학회 2016 조직공학과 재생의학 Vol.13 No.6
Osteoarthritis (OA) of the knee is a degenerative joint disease caused by the progressive reduction of the articular cartilage surface that leads to reduced joint function. Cartilage degeneration occurs through gradual loss in extracellular matrix components including type II collagen and proteoglycan. Due to limited inherent self repair capacity of the cartilage, the use of cell-based therapies for articular cartilage regeneration is considered promising. Bone marrow mesenchymal stem cells (BM-MSCs) are multipotent cells and are highly capable of multilineage differentiation which render them valuable for regenerative medicine. In this study, BM-MSCs were isolated from OA patients and were characterized for MSC specific CD surface marker antigens using flowcytometry and their differentiation potential into adipocytes, osteocytes and chondrocytes were evaluated using histological and gene expression studies. BM-MSCs isolated from OA patients showed short spindle shaped morphology in culture and expressed positive MSC related CD markers. They also demonstrated positive staining with oil red O, alizarin red and alcian blue following differentiation into adipocytes, osteocytes and chondrocytes, respectively. In addition, chodrogenic related genes such as collagen type II alpha1, cartilage oligomeric matrix protein, fibromodulin, and SOX9 as well as osteocytic related genes such as alkaline phosphatase, core-binding factor alpha 1, osteopontin and RUNX2 runt-related transcription factor 2 were upregulated following chondrogenic and osteogenic differentiation respectively. We have successfully isolated and characterized BM-MSCs from OA patients. Although BM-MSCs has been widely studied and their potential in regenerative medicine is reported, the present study is the first report in our series of experiments on the BMSCs isolated from OA patients at King Abdulaziz University Hospital, Jeddah, Saudi Arabia.