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RLECN—A learning based dynamic threshold control of ECN
Shahzad,정은성,김형석 한국통신학회 2023 ICT Express Vol.9 No.6
Explicit congestion notification (ECN) enables the network routers to mark packets instead of dropping them. When the queue size reaches a certain threshold, the queued packets are marked to indicate predicted congestion. However, an optimal value of the ECN threshold is not defined. A pre-decided value is chosen either by estimation or by hit and trial and therefore, it does not generalize well under a wide range of network scenarios. We propose a reinforcement learning (RL)-based ECN mechanism that utilizes software-defined networks (SDN) to address this problem. Our solution enables the routers to keep a dynamic ECN threshold according to the current network conditions. SDN provides the network visibility and reach to train the RL model and to dynamically adjust the ECN threshold. We show through experimental results that our proposed model outperforms the current state of the art.
Multi-Objective Optimization for a Reliable Localization Scheme in Wireless Sensor Networks
Shahzad, Farrukh,Sheltami, Tarek R.,Shakshuki, Elhadi M. The Korea Institute of Information and Commucation 2016 Journal of communications and networks Vol.18 No.5
In many wireless sensor network (WSN) applications, the information transmitted by an individual entity or node is of limited use without the knowledge of its location. Research in node localization is mostly geared towards multi-hop range-free localization algorithms to achieve accuracy by minimizing localization errors between the node's actual and estimated position. The existing localization algorithms are focused on improving localization accuracy without considering efficiency in terms of energy costs and algorithm convergence time. In this work, we show that our proposed localization scheme, called DV-maxHop, can achieve good accuracy and efficiency. We formulate the multi-objective optimization functions to minimize localization errors as well as the number of transmission during localization phase. We evaluate the performance of our scheme using extensive simulation on several anisotropic and isotropic topologies. Our scheme can achieve dual objective of accuracy and efficiency for various scenarios. Furthermore, the recently proposed algorithms require random uniform distribution of anchors. We also utilized our proposed scheme to compare and study some practical anchor distribution schemes.
Sulfur doped graphene/polystyrene nanocomposites for electromagnetic interference shielding
Shahzad, Faisal,Yu, Seunggun,Kumar, Pradip,Lee, Jang-Woo,Kim, Yoon-Hyun,Hong, Soon Man,Koo, Chong Min Elsevier 2015 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.133 No.-
<P><B>Abstract</B></P> <P>In this paper, for the first time, we present a simple and straightforward method to improve not only electrical conductivity and complex permittivity but also electromagnetic interference (EMI) shielding effectiveness of reduced graphene oxide (rGO)/polystyrene (PS) nanocomposites through sulfur doping. Sulfur-doped reduced graphene oxide with thiophene-like structure (2.6at.% S), synthesized through a simple heating process of a mixture of graphene oxide and sulfur powder, revealed almost three times larger electrical conductivity (1095Sm<SUP>−1</SUP>) than undoped rGO (395Sm<SUP>−1</SUP>). The SrGO/PS nanocomposite showed not only 150% larger electrical conductivity and 50% larger complex permittivity, but also improved EMI shielding effectiveness (24.5dB) at a frequency of 18GHz than rGO/PS nanocomposite (21.4dB) at the same loading level of 7.5vol.%. Considering the simplicity and effectiveness of process, sulfur doping of graphene is expected to be used as a versatile method to improve EMI shielding efficiency of graphene/polymer nanocomposites.</P>
Shahzad, M. Aasif,Nisa, M.,Sarwar, M. Asian Australasian Association of Animal Productio 2011 Animal Bioscience Vol.24 No.7
The study was conducted to evaluate enzose (corn dextrose), a corn milling byproduct, as substitute for corn grain as energy in growing lambs. Five iso-caloric and iso-nitrogenous diets were formulated. The control diet (E0) had no enzose whereas enzose replaced 20, 40, 60 and 80% corn grain in E20, E40, E60 and E80 diets on the basis of energy supply, respectively. Fifty growing lambs were divided into 5 groups, 10 animals in each, in a randomized complete block design. Nutrients (dry matter, crude protein, neutral detergent fiber and acid detergent fibre) intake and digestibilities increased with gradual replacement of corn grain by enzose. Lambs fed E80 diet also retained higher nitrogen (N) than those fed E0 diet. Plasma glucose, $T_3$ and $T_4$ increased while urea N decreased in lambs receiving higher enzose content. Maximum weight gain was recorded in lambs fed diets containing maximum concentration of E as a replacement for corn grains. A better feed conversion ratio was recorded in lambs fed E80 compared with those fed E0 diet. The study suggests that enzose can be used as an economical feed ingredient to replace corn grain upto 80%, without any adverse effects on growth performance of growing lambs.
Shahzad, Aasim,Kim, Woo-Sik,Yu, Taekyung The Royal Society of Chemistry 2016 Dalton transactions Vol.45 No.22
<P>This paper describes a simple and fast aqueous-phase route to the synthesis of Ag/AgCl hybrid nanostructures. These hybrid nanostructures were synthesized by reduction of AgCl nanoparticles with controlled shapes prepared by reacting Ag+ with Cl-in the presence of polyethyleneimine (PEI) in an aqueous-phase. We could easily control the morphology and composition of the nanostructures by varying the experimental conditions, including the reaction temperature and the amount of the reducing agent. The as-synthesized Ag/AgCl hybrid nanostructures exhibited enhanced photocatalytic activity and stability during the degradation of methyl orange under visible light irradiation because of their strong surface plasmon resonance (SPR) effect.</P>
Shahzad Munir,Muhammad Israr Siddiqui,Morgan Heikal,Abdul Rashid Abdul Aziz,Guillaume de Sercey 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.11
The Proper orthogonal decomposition (POD) method has seen increasingly used in the last two decades and has a lot of applicationsfor the comparison of experimental and numerically simulated data. The POD technique is often used to extract information about coherentstructures dominating the flow. The two-dimensional and two-component instantaneous velocity fields of both liquid and gas phasesof a slug flow were obtained by Particle image velocimetry (PIV) combined with Laser induced fluorescence (LIF). POD was applied tothe velocity fields of both phases separately to identify the coherent flow structures. We focused on POD eigenmodes and their correspondingenergy contents of both liquid and gas phases. The sum of first few eigenmodes that contain maximum turbulent kinetic energyof the flow represents the coherent structures. In the case of liquid phase the first eigenmode contained 42% of the total energy, while inthe gas phase the decaying energy distribution was flat. The POD results showed that the coefficient of mode 1 for the liquid phase oscillatedbetween positive and negative values and had the highest amplitude. For the visualization of coherent motion different linear combinationsof eigenmodes for liquid and gas phases were used. The phenomena of turbulent bursting events associated with Q2 events(low momentum fluid moving away from the wall) and Q4 events (high momentum flow moving towards the wall) were also discussedto assess its contribution in turbulence production.
Shahzad, Faisal,Kumar, Pradip,Kim, Yoon-Hyun,Hong, Soon Man,Koo, Chong Min American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.14
<P>Electrically conductive thin carbon materials have attracted remarkable interest as a shielding material to mitigate the electromagnetic interference (EMI) produced by many telecommunication devices. Herein, we developed a sulfur-doped reduced graphene oxide (SrGO) with high electrical conductivity through using a novel biomass, mushroom-based sulfur compound (lenthionine) via a twostep thermal treatment. The resultant SrGO product exhibited excellent electrical conductivity of 311 S cm(-1), which is 52% larger than 205 S cm(-1) for undoped rGO. SrGO also exhibited an excellent EMI shielding effectiveness of 38.6 dB, which is 61% larger than 24.4 dB measured for undoped rGO. Analytical examinations indicate that a sulfur content of 1.95 atom % acts as n-type dopant, increasing electrical conductivity and, therefore, EMI shielding of doped graphene.</P>
Shahzad, Aamir,Udagepola, Kalum Priyanath,Lee, Young-keun,Park, Soojin,Lee, Malrey SAGE Publications 2015 INTERNATIONAL JOURNAL OF DISTRIBUTED SENSOR NETWOR Vol.2015 No.-
<P>This study examined the security of SCADA system and its protocols, more specifically, SCADA/DNP3 protocol security. To achieve the study goals, a SCADA simulation environment is designed for water pumping process through connectivity of intelligent sensors, the payload is constructed, and security is deployed inside DNP3 protocol stack and then bytes are multicast to subcontrollers.</P>
Sulfur-doped graphene laminates for EMI shielding applications
Shahzad, Faisal,Kumar, Pradip,Yu, Seunggun,Lee, Seunghwan,Kim, Yoon-Hyun,Hong, Soon Man,Koo, Chong Min The Royal Society of Chemistry 2015 Journal of Materials Chemistry C Vol.3 No.38
<▼1><P>Herein, for the first time, we demonstrate that a laminated structure of sulfur-doped reduced graphene oxide (SrGO) provides significant potential for electromagnetic interference shielding applications.</P></▼1><▼2><P>Herein, for the first time, we demonstrate that a laminated structure of sulfur-doped reduced graphene oxide (SrGO) provides significant potential for electromagnetic interference shielding applications. In this study, SrGO was prepared through the reaction between graphene oxide and hydrogen disulfide (H2S) gas at elevated temperatures. The doping degree of S was controlled through varying the time and temperature of the reaction and the maximum doping content of 5.6 wt% was achieved. Because of the n-type doping contribution of the S atom to the doped graphene, SrGO laminate not only revealed a 47% larger electrical conductivity (75 S cm<SUP>−1</SUP>) than undoped reduced graphene oxide laminate (51 S cm<SUP>−1</SUP>) but also revealed 119% larger EMI shielding effectiveness (33.2 dB) than the undoped one (15.5 dB) at the same sample thickness.</P></▼2>