Maazoun J.,University of Sfax |
Bouassida N.,University of Sfax |
Ben-Abdallah H.,Abdulaziz University
Journal of King Saud University - Computer and Information Sciences | Year: 2016
A software product line (SPL) represents a family of products in a given application domain. Each SPL is constructed to provide for the derivation of new products by covering a wide range of features in its domain. Nevertheless, over time, some domain features may become obsolete with the apparition of new features while others may become refined. Accordingly, the SPL must be maintained to account for the domain evolution. Such evolution requires a means for managing the impact of changes on the SPL models, including the feature model and design. This paper presents an automated method that analyzes feature model evolution, traces their impact on the SPL design, and offers a set of recommendations to ensure the consistency of both models. The proposed method defines a set of new metrics adapted to SPL evolution to identify the effort needed to maintain the SPL models consistently and with a quality as good as the original models. The method and its tool are illustrated through an example of an SPL in the Text Editing domain. In addition, they are experimentally evaluated in terms of both the quality of the maintained SPL models and the precision of the impact change management. © 2016 The Authors
Argyros I.K.,Cameron University |
Cho Y.J.,Gyeongsang National University |
Cho Y.J.,Abdulaziz University
Numerical Functional Analysis and Optimization | Year: 2014
In this article, we provide a semilocal analysis for the Steffensen-type method (STTM) for solving nonlinear equations in a Banach space setting using recurrence relations. Numerical examples to validate our main results are also provided in this study to show that STTM is faster than other methods ([7, 13]) using similar convergence conditions. © 2014 Copyright Taylor & Francis Group, LLC.
Zhu W.,Chongqing University of Posts and Telecommunications |
Zhu W.,New York University |
Jiang Z.-P.,New York University |
Feng G.,City University of Hong Kong |
Feng G.,Abdulaziz University
Automatica | Year: 2014
In this paper, the event-based consensus problem of general linear multi-agent systems is considered. Two sufficient conditions with or without continuous communication between neighboring agents are presented to guarantee the consensus. The advantage of the event-based strategy is the significant decrease of the number of controller updates for cooperative tasks of multi-agent systems involving embedded microprocessors with limited on-board resources. The controller updates of each agent are driven by properly defined events, which depend on the measurement error, the states of its neighboring agents and an arbitrarily small threshold. It is shown that the controller updates for each agent only trigger at its own event time instants. A simulation example is presented to illustrate the theoretical results. © 2013 Elsevier Ltd. All rights reserved.
Hayat T.,Quaid-i-Azam University |
Hayat T.,Abdulaziz University |
Yousaf A.,Quaid-i-Azam University |
Mustafa M.,National University of Sciences and Technology |
Chemical Engineering Communications | Year: 2012
This article addresses the squeezing flow and heat transfer between parallel disks when one disk is impermeable and the other is porous. Appropriate similarity transformations are invoked to convert the partial differential equations into ordinary ones. Expressions for velocity and temperature fields have been obtained by homotopy analysis method (HAM). The effects of embedding parameters such as squeeze number (S), Hartman number (M), Prandtl number (Pr), and Eckert number (Ec) are analyzed through graphs for the velocity and temperature profiles and tables for skin friction coefficient and local Nusselt number. It is observed that the series solutions are convergent only at third-order of approximation. The obtained results for velocity are also compared with the homotopy perturbation method (Domairry and Aziz, 2009). © Taylor & Francis Group, LLC.
News Article | August 22, 2016
Novel devices feature improved carrier transport and operate under higher-order modulation schemes to enable increased data transmission rates. Ethernet protocols (i.e., the IEEE 802.3ba 100Gb/s and the forthcoming IEEE P802.3bs 400Gb/s standards) provide the definitions for data transmission systems that are used in long-range (10km) and extended-range (40km) fiber links. These transmission systems include multichannel 25GBd on-off keying (OOK)—the simplest form of intensity modulation in which digital information is represented by low (0) and high (1) amplitude levels—and four-level pulse-amplitude modulation (PAM4). Directly modulated lasers (DMLs) are an attractive option for a light source in such applications because of their low cost, small footprint, and low power consumption. In addition, they allow simple direct detection, while being operated in an intensity-modulation mode. DMLs, however, are strongly limited by their bandwidth. Indeed, much higher data rates are possible with coherent systems in which more advanced modulation schemes and complex transmitters are used. As an alternative to conventional quantum-well-based DMLs, quantum-dot lasers (QDLs) have been studied extensively. QDLs feature several unique properties, e.g., they have temperature-insensitive and ultralow threshold current, and low linewidth enhancement factors.1 Gallium-arsenide-based (GaAs-based) QDLs exhibit at least three confined electronic energy levels, i.e., a ground state (GS) and two very close excited states (ESs). The GS is twofold degenerate, whereas the ES is fourfold degenerate. The larger degeneracy translates to a larger differential gain and smaller nonlinear gain compression.2 Direct modulation of QDLs on the GS, at over 20Gb/s, has been demonstrated for both indium arsenide (InAs)/GaAs lasers at 1.31μm (O-band)3 and for InAs/indium phosphide (InP) devices at 1.55μm (C-band).4 The bandwidth of these structures, however, is limited by several factors, including inhomogeneous broadening (low modal gain),5 the hot-carrier effect, and the slow capture time into the quantum dots (large gain compression).6 To ensure sufficient gain, several quantum dot (QD) layers with wide spacers (limiting carrier transport across the active region) are usually incorporated into QDLs. The holes tend to accumulate on the p-side of the active region because of their short diffusion length. This inhomogeneous distribution of carriers limits the modulation response of the devices.7 In our work,8 we have designed a novel GaAs-based QDL in which we incorporate graded p-doping of spacers to compensate for the hole distribution. We have designed this grading so that there is a small amount of p-doping on the topside of the active region and a large amount of doping on the bottom (i.e., substrate) side. Our lasers feature a larger maximum modulation bandwidth (9.2GHz) compared with standard p-doped samples (7.2GHz). Furthermore, by modifying the reflectivity of one laser facet, our lasers (operating exclusively at the ES) exhibit an increased maximum modulation bandwidth of 11.7GHz. We can also realize InAs/indium gallium arsenide/InP QD structures at 1.55μm, which exhibit a –3dB bandwidth of 12.1GHz, by shortening the distance between the electrical contacts and the active region, and by incorporating seven QD layers. We can thus provide sufficient gain, but do not limit the carrier transport. Our O-band and C-band QDLs exhibit data transmission at a rate of 25Gb/s for direct modulation in the non-return-to-zero OOK scheme. To further increase the digital bandwidth of our devices, we also explored higher-order modulation formats, e.g., PAM4 and eight-level PAM (PAM8). PAM4 results for the O-band and C-band lasers—see Figure 1(a)—show that 17.5GBd (35Gb/s) data transmission was realized with both structures. We thus achieved a 40% increase in the maximum bit rate. Doubling the bit rate, however, was not possible. This is because in PAM schemes (particularly PAM8), the noise level of the lasers becomes the major limiting factor. The 7.5GBd (22.5Gb/s) PAM8 response of a standard p-doped laser structure across 10km of single-mode fiber (SMF) is shown in Figure 1(b). We successfully demonstrated PAM8 for this particular laser structure because it features a strongly damped (but linear) small signal response, an ability to operate at low currents (threshold of 3mA), and a relatively large modulation-current-efficiency factor.8 Figure 1. Eye diagrams and corresponding bit-error ratio (BER) curves of (a) the O-band (1.31μm) and C-band (1.55μm) lasers under 17.5GBd four-level pulse-amplitude modulation (PAM4) in back-to-back configuration and (b) of a standard p-doped laser under 7.5GBd eight-level PAM (PAM8) across 10km of single-mode fiber (SMF). In (a) the aggregated BERs were determined by direct detection with an error analyzer. In (b) the BERs were retrieved using digital signal processing of single-shot traces that were acquired with a real-time oscilloscope. The improved BERs at lower received powers were achieved by means of equalization. In another part of our work, we have packaged a 39.813GHz monolithic two-section mode-locked laser (MLL) that is based on the 1.31μm graded p-doped laser structure into a module. MLLs (which generate optical and electrical pulse trains) are ideal candidates for various applications, e.g., microwave photonics and radio-over-fiber systems. When combined with modulators, MLLs act as transmitters for optical time-division multiplexing (OTDM) systems in optical communication networks. MLLs operate at frequencies far beyond the intrinsic bandwidth of DMLs. In contrast to DMLs, they benefit strongly from an inhomogeneously broadened QD gain spectrum. When all the longitudinal modes are locked, sub-picosecond pulses are emitted. QD MLLs also exhibit ultrafast recovery, which enables pulse generation up to 100GHz. We achieve jitter reduction and frequency tuning through hybrid mode-locking. In addition, dual-tone injection gives rise to a narrow optical linewidth (essential for coherent systems). We observe a pulse width of 2ps and integrated jitter of 340fs, which makes our MLL suitable for OTDM.9 We generated return-to-zero (RZ) differential quadrature phase-shift keying (DQPSK) data signals by superimposing bit sequences on the MLL pulse train, via successively sequenced dual-drive Mach–Zehnder and phase modulators. We have also conducted data transmission experiments at 40GBd (80Gb/s) across 45km of SMF (see inset of Figure 2). Through the use of DQPSK and OTDM we were thus able to quadruple the bit rate (compared with standard OOK). The corresponding 80GBd (160Gb/s) RZ DQPSK bit-error ratio curves and eye diagrams are also shown in Figure 2.10 Figure 2. Illustration of 80GBd return-to-zero (RZ) differential quadrature phase-shift keying (DQPSK) in back-to-back configuration. Eye diagrams of tributary 1 (Tr 1) and tributary 2 (Tr 2) at the maximum received optical power were measured by a differential receiver, based on a delay interferometer. The signal-to-noise ratios are 6.7 and 6.5, respectively. BERs were detected by means of an electrical demultiplexer (DEMUX). The BER curves of both DEMUX output signals (0P and 1P) and tributaries show error-free performance (i.e., without error floor to below 10−10. Inset: Constellation diagram of 40GBd RZ DQPSK across 45km of SMF, for the maximum received power obtained with an O-band optical modulation analyzer. The error-vector magnitude is 10.1%. In summary, in our novel GaAs-based QDL we incorporate graded p-doping of spacers to compensate for carrier transport limitations across the active region, and thus bandwidth limitations, in DMLs. The ES emission has larger differential gain than the GS emission. These improvements lead to higher cut-off frequencies of 1.31μm-InAs/GaAs devices. In addition, our 1.55μm InAs/InP QD lasers, which have a narrowed active region and barriers, exhibit large 3dB bandwidths. We have demonstrated data rates of 35Gb/s using PAM4 for both wavelength bands, and PAM8 reveals that further optimization of the lasers (in terms of their noise performance) is required. This will therefore be the focus of our future research. We have also shown that integration of MLLs as sources in coherent OTDM systems enables 160Gb/s RZ DQPSK data transmission. Funding for this research was provided by the German Research Foundation in the SFB 787 framework. The authors would like to thank Finisar (Germany) for packaging the quantum-dot mode-locked laser module and C. Meuer at Sicoya for assistance with the digital signal processing. Department of Solid-State Physics and Center of Nanophotonics Technische Universität Berlin Dejan Arsenijević received his diploma in physics from the Technische Universität Berlin in 2009. His current research interests include higher-order modulation formats, as well as low-jitter optical and electrical pulse sources for future high-speed data communications. Department of Solid-State Physics and Center of NanophotonicsTechnische Universität Berlin Department of Solid-State Physics and Center of Nanophotonics Technische Universität Berlin Berlin, Germany and King Abdulaziz University Dieter Bimberg received his diploma in physics and PhD from Goethe University, Germany, in 1968 and 1971, respectively. Between 1972 and 1979 he was a principal scientist at the Max Planck Institute for Solid State Research in Germany. He was then appointed as a professor of electrical engineering at the Technical University of Aachen (Germany) and, in 1981, as the chair of the Technische Universität Berlin's Applied Solid State Physics department. From 1990 to 2011 he was the executive director of the Institute of Solid State Physics, and in 2004 he founded the Center of Nanophotonics. In addition, he was the chairman of the board of the German Federal Government's Centers of Excellence in Nanotechnologies between 2006 and 2011. His many honors include the Russian State Prize in Science and Technology (2001), the Max Born Award (2006), the William Streifer Scientific Achievement Award (2010), the United Nations Educational, Scientific, and Cultural Organization's Nanoscience Medal (2012), and the Welker Award (2015). Department of Solid-State Physics and Center of NanophotonicsTechnische Universität BerlinBerlin, GermanyandKing Abdulaziz University 2. D. Arsenijević, A. Schliwa, H. Schmeckebier, M. Stubenrauch, M. Spiegelberg, D. Bimberg, V. Mikhelashvili, G. Eisenstein, Comparison of dynamic properties of ground- and excited-state emission in p-doped InAs/GaAs quantum-dot lasers, Appl. Phys. Lett. 104, p. 181101, 2014. doi:10.1063/1.4875238 5. H. Dery, G. Eisenstein, The impact of energy band diagram and inhomogeneous broadening on the optical differential gain in nanostructure lasers, IEEE J. Quantum Electron. 41, p. 26-35, 2005. doi:10.1109/JQE.2004.837953
Eskander A.,University of Toronto |
Merdad M.,University of Toronto |
Merdad M.,Abdulaziz University |
Freeman J.L.,University of Toronto |
And 3 more authors.
Thyroid | Year: 2013
Background: There remains controversy surrounding the extent of lateral neck dissection required in patients with papillary thyroid cancer (PTC) and suspicious or confirmed metastatic lateral neck lymphadenopathy. The evidence for this clinical dilemma has never been reviewed systematically nor has there been an attempt to meta-analyze the data by lymph node levels to better characterize the pattern of spread. Methods: This meta-analysis used MEDLINE and EMBASE including all cohort studies reporting the pattern of lateral neck disease in patients who underwent a neck dissection for clinically, radiographically, or cytologically suspicious or confirmed metastatic lymphadenopathy for PTC. Our main outcome was the number of patients with positive involvement at a given level as a percentage of the cohort of patients with positive lateral neck disease, each level being measured separately. Results: Eighteen studies with a total of 1145 patients and 1298 neck dissections were included in our meta-analysis. Levels IIa and IIb had disease in 53.1% [95% confidence interval (CI) 46.6-59.5%] and 15.5% [CI 8.2-27.2%], respectively. Studies that did not distinguish between level IIa and IIb or in which both were collapsed into one category showed a total level II involvement of 53.4% [CI 49.7-57.1%]. Level III and level IV were involved in 70.5% [CI 67.0-73.9%] and 66.3% [CI 61.4-70.9%] of specimens. Studies that did not distinguish between level Va and Vb or in which both were collapsed into one category showed a total level V involvement of 25.3% [CI 20.0-31.5%]. Levels Va and Vb had positivity in 7.9% [CI 2.8-20.0%] and 21.5% [CI 7.7-47.6%], respectively, but had only three studies that could be meta-analyzed. Conclusions: This systematic review of the literature and meta-analysis of the pattern of spread indicates significant rates of lymph node metastasis to all lateral neck levels in patients with PTC with regional involvement. This evidence leads us to recommend a comprehensive selective neck dissection of levels IIa, IIb, III, IV, and Vb in patients with lateral neck disease from PTC. The evidence for level Va is lacking, as most studies did not distinguish between levels Va and Vb, and the border between the two levels was inconsistent. Future studies will need to address these sublevels separately. © 2013, Mary Ann Liebert, Inc.
Goddi C.,Joint Institute for VLBI in Europe |
Henkel C.,Max Planck Institute for Radio Astronomy |
Henkel C.,Abdulaziz University |
Zhang Q.,Harvard - Smithsonian Center for Astrophysics |
And 2 more authors.
Astronomy and Astrophysics | Year: 2015
Context. This paper is the second in a series of ammonia (NH3) multilevel imaging studies in high-mass star forming regions. Aims. We want to identify the location of the maser emission from highly excited levels of ammonia within the W51 IRS2 high-mass star forming complex that was previously discovered in a single dish monitoring program. Methods. We have used the Karl Jansky Very Large Array (JVLA) at the 1 cm band to map five highly excited metastable inversion transitions of NH3, (J,K) = (6,6), (7, 7), (9, 9), (10, 10), and (13, 13), in W51 IRS2 with ∼0″.2 angular resolution. Results. We present detections of both thermal (extended) ammonia emission in the five inversion lines, with rotational states ranging in energy from about 400 K to 1700 K, and point-like ammonia maser emission in the (6, 6), (7, 7), and (9, 9) lines. For the point-like emission, we estimate lower limits to the peak brightness temperatures of 1.7 × 105 K, 6 × 103 K, and 1 × 104 K for the (6, 6), (7, 7), and (9, 9) transitions, respectively, confirming their maser nature. The thermal ammonia emits around a local standard of rest velocity of VLSR = 60 km s-1, near the cloud's systemic velocity, appears elongated in the east-west direction across 4″ and is confined by the HII regions W51d (to the north), W51d1 (to the east), and W51d2 (to the west). The NH3 masers are observed in the eastern tip of the dense clump traced by thermal NH3, offset by 0″.65 to the east from its emission peak, and have a peak velocity at ∼47.5 km s-1. No maser components are detected near the systemic velocity. The NH3 masers arise close to but separated from (0″.65 or 3500 AU) the rare vibrationally excited SiO masers, which are excited in a powerful bipolar outflow driven by the deeply embedded high-mass young stellar object (YSO) W51-North. This means that the two maser species cannot be excited by the same object. Interestingly, the NH3 masers originate at the same sky position as a peak in a submm line of SO2 imaged with the Submillimeter Array, tracing a face-on circumstellar disk or ring around W51-North. In addition, the thermal emission from the most highly excited NH3 lines, (10, 10) and (13, 13), shows two main condensations, the dominant one towards W51-North with the SiO and H2O masers, and a weaker peak at the NH3 maser position. Conclusions. We propose a scenario where the ring seen in SO2 emission is a circumbinary disk surrounding (at least) two high-mass YSOs, W51-North (exciting the SiO masers) and a nearby companion (exciting the NH3 masers), separated by 3500 AU. This finding indicates a physical connection (in a binary) between the two rare SiO and NH3 maser species. © ESO 2015.
Al-Tamimi A.-M.S.,Abdulaziz University |
Ghabbour H.A.,King Saud University |
Ghabbour H.A.,Mansoura University |
El-Emam A.A.,King Saud University
Zeitschrift fur Kristallographie - New Crystal Structures | Year: 2016
C16H19N3O, orthorhombic, Pna21 (no. 33), a = 8.0381(5) Å, b = 10.4499(8) Å, c = 17.1228(13) Å, V = 438.27(18) Å, Z = 4, Rgt(F) = 0.0499, wRref(F2) = 0.1105, T = 100 K. © 2016 Abdul-Malek S. Al-Tamimi et al., published by De Gruyter.
Zafar A.,Abdulaziz University |
Hasan S.H.,Abdulaziz University
Malaysian Journal of Computer Science | Year: 2015
The repository of any learning management system (LMS) keeps growing and becomes a rich source of learning materials with the passage of time. This learning resource may serve subject experts by allowing them to reuse the existing material while preparing online insnvctional materials. At the same time it may help the learners by allowing them to retrieve the relevant documents for efficiently achieving their learning goals. We have proposed a novel scheme for searching documents relevant to concept knowledge to be imparted to students, which assists subject experts in synthesizing the course material, by facilitating them to reuse existing learning objects available in e-learning repository. It also helps students in finding relevant learning resources efficiently for interactive e-learning. This paper presents an efficient way of retrieving information related to the teaching domain from a vast reservoir of documents. We have employed fuzzy clustering, fuzzy relation along with information retrieval techniques to discover the underlying structure of knowledge and identify knowledge based relationship between learning material and retrieving the relevant documents. The experiments conducted to judge the suitability of fuzzy clustering for discovering good document relationships and to evaluate the peifonnance of the proposed information retrieval system, show encouraging results. A practical implementation of this technique has also been demonsn'ated in the implementation of eLGuide, a frameworkfor an adaptive e-learning system.
Abuhasel K.A.,Abdulaziz University |
Bin P.S.,Abdulaziz University
Proceedings - Annual Reliability and Maintainability Symposium | Year: 2016
Traditionally, environmental factors have been utilised in assessments of electronic systems reliability (ESR) of electronic components, systems or devices. Most of these available interpretations are, however, confined to descriptions of the environment being 'Ground', 'Airborne' 'Naval', 'Commercial' and so on, which only describe the 'condition' of the environment and not the 'physical' or 'geographic' location that the electronic system is deployed for use in. Environments that combine different types of ambiance (dust, humidity, etc.) are known to be among the most detrimental to ESR. For example, moisture, considered as a chemical agent, is responsible for the deterioration of many types of materials including electronic components, systems and devices. In this work, arguments regarding the use of psychrometry, the study of the composition of air, its properties and their effects on different materials from place to place, in order to reinterpret the impact of physical nature of the environment on a device's reliability are advanced. Humidity connotes the amount of an invisible water vapour in the air and is at the centre of all psychrometric analysis. Generally, humidity could be considered inimical to ESR because low values are known to cause condensation and the build-up of static electricity in electronic equipment, which results in brittleness, dielectric breakdown and ultimately permanent damage to devices. At the other extreme, high values of humidity lead to increased conductivity, which leads to numerous hazards to both the device and surrounding environment. Aridity is another physical attribute used to characterise the extent of dryness or availability of water in an area, using which environmental conditions peculiar to any location can be deduced. Therefore, arid areas are characterised by high temperatures, low humidity, medium to large amounts of dust, solar and atmospheric pressure, etc. Geographically, the values of these psychrometric parameters anywhere on the global can be easily discerned. For example, it is well-known that areas surrounding the equator are the most arid, while humidity increases as we leave the equator towards the poles; thus, providing a model to estimate lifespan of electronic systems based on the location the device is deployed for use. When the physical attributes of the environment are efficaciously cogitated they can help to better interpret contributions of (physical or geographic) environmental conditions to the smooth, reliable and prolonged operation of electronic equipment. Building on an earlier work that formulated contributions of aridity in assessing environmental impacts on ESR and broadening this assessment from the established environmental 'conditional' interpretations to more 'physical' (or geographic) descriptions vis-a-vis its influence in terms of a device's failure rate, a property loosely referred to as the lifespan of an electronic system; in this study an attempt is made to model the impact of relative humidity on the lifespan of a biomedical electronic device, specifically the electrocardiogram, a device widely used to monitor and manage cardiovascular ailments. To validate the proposal, a conscientious and veridical analysis of psychrometric data gathered (in Riyadh, the capital city of the Kingdom of Saudi Arabia) over a 12-month period was undertaken in order to ascertain the relationship between some psychrometric (environmental) variables. Based on these relationships, an apposite formulation for electronic system lifespan was attained. Comparisons between the expected lifespan of the aridity based assessment of the lifespan of an ECG device with that based on the reformulation of lifespan based on the psychrometric conditions prevalent in Riyadh show an 80% correlation with the overall device lifespan reducing to 11 years. The results provide a more detailed and accurate assessment of the ECG lifespan confirming that that ESR is influenced by the geographical location (physical environment) that it is deployed for use. © 2016 IEEE.