Scientia Iranica
Volume:23 Issue: 6, 2016

Unstructured wireless networks such as mobile ad hoc networks and wireless sensor networks have been rapidly growing in the past decade. Security is known as a challenging issue in such networks in which there is no fixed infrastructure or central trusted authority. Further, node limitations in processing power, storage, and energy consumption add further complexity to addressing security in such networks. While cryptography has proven as an effective solution capable of satisfying most network security requirements, it requires the use of efficient key pre-distribution algorithms compatible with the limitation of unstructured wireless networks. Typically, a key pre-distribution algorithm forms a cryptographic overlay layer above the network routing layer and as such introduces the need for relying on two layers of routing for secure delivery of information. In this paper, we conduct a categorical review of key pre-distribution methods for unstructured wireless networks. We also compare different key pre-distribution schemes in terms of performance and security strength. Finally, we provide an overview of recent overlay routing algorithms relying on key pre-distribution.

The design challenges of voltage reference generators in CMOS technology have increased over the years in low voltage low power CMOS integrated circuits constituting analog, digital and mixed-signal modules. The emergence of hand-held power autonomous devices push the power consumption limit to nW regime. Along with these confrontations, limited full scale range of data converters at low supply levels demands accurate reference voltage generators. This paper reviews the allied design challenges and discusses the evolved methodologies to tackle them. This paper also prominently retrospect the sub -1V voltage reference topologies presented in the literature along with classic bandgap based voltage reference topologies. Non- bandgap (only CMOS) based reference architectures are proven to be area and power efficient but always have to be accompanied with auxiliary on/off chip trimming mechanism for high accuracy. We also provide insightful analysis of the voltage reference topologies, required by the designers.

This paper reviews the merits of modernizing the power grid and discusses the way electric utilities in various countries are directing their practices toward o ering enhanced sustainability, reliability, resilience, security, and economics to their respective consumers. The modernization of the electricity grid, which has evolved as the brainchild of electricity restructuring, has been made all the more urgent by the virtually pervasive dependence of modern lives on a reliable, clean, and secure supply of a ordable electricity. The electric utility industry restructuring, which has staged many institutional, regulatory, and business models, has enabled the modern electricity grid to take full advantage of a range of available energy sources and modern technologies pertaining to prosumers and transactive energy, renewable supply, storage, energy eciency, climate change and carbon capture, electri cation of the transportation industry, microgrids and resilience, and large fossil units that have helped the electric utility industry meet its global objectives. Understanding the dynamics of grid modernization, which can o er a clear appreciation for the use of innovation in electric power systems, and the impact that grid modernization will have on individual lives, is among the issues which will be discussed in this paper.

In J.D. Jackson''s Classical Electrodynamics textbook, the analysis of Dirac''s charge quantization condition in the presence of a magnetic monopole has a mathematical omission and an all-too-brief physical argument that might mislead some students. This paper presents a detailed derivation of Jackson''s main result, explains the signicance of the missing term, and highlights the close connection between Jackson''s ndings and Dirac''s original argument.

This paper presents a model for a Modular Multilevel Converter (MMC) using extended-frequency dynamic phasors. The model is based upon a series of harmonicfrequency representations that are obtained for the fundamental and dominant harmonic components. Depending on the requirements of the study to be conducted and the desired level of model accuracy, a low-order model (i.e., average-value) or an arbitrarily wideband model may be constructed. The paper describes the principles of modeling using extended-frequency dynamic phasors, and applies them to an MMC connected to a power system represented using a Thevenin equivalent. The model contains details of the MMC''s control system including its high-level control circuitry, as well as voltage balancing and synchronization components. The developed model is then validated by comparing it against a fully-detailed electromagnetic transient (EMT) simulation model developed in PSCAD/EMTDC simulator. Comparisons are made to establish the accuracy of the model (both its low-order and wide-band variants) and to assess the computational advantages it o ers compared to conventional EMT models.

Network dilation is a way of o ering system families, at a range of sizes and computational powers, which share an underlying communication architecture and routing algorithm. We consider indirect networks that connect processing nodes via intermediate switch nodes. In the simplest such indirect networks, there is a switching network of some regular topology, where each switch is connected to d other switches and to exactly one processing node. A variant, which we adopt here because it is more robust in the sense of not losing any processing capability to single-switch failures, is the use of 2-port processing nodes that connect to two neighboring switches. This alternate architecture also has the advantage of increasing the number of processing nodes from n to (d=2)n with a factorof- 2 increase in internode distances. A k-dilated version of the latter architecture replaces each processing node with a path network (linear array) of length k, thus growing the network size to k(d=2)n and also further increasing internode distances. In this paper, we study topological and performance attributes of such dilated network architectures, proving general theorems about worst-case and average internode distances and deriving the routing algorithm from that of the underlying switch network.

In this paper, we propose and investigate several crosstalk reduction techniques for hybrid quantum-classical densewavelength- division-multiplexing systems. The transmission of intense classical signals alongside weak quantum ones on the same fiber introduces some crosstalk noise, mainly due to Raman scattering and nonideal channel isolation, that may severely a ect the performance of quantum key distribution systems. We examine the conventional methods of suppressing this crosstalk noise, and enhance them by proposing an appropriate channel allocation method that reduces the background crosstalk e ectively. Another approach proposed in this paper is the usage of orthogonal frequency division multiplexing, which o ers ecient spectral and temporal filtering features.

A novel CT imaging structure based on compressive sensing (CS) is proposed. The main goal is to mitigate the CT imaging time and thus x-ray radiation dosage without compromising the image quality. The utilized compressive sensing approach is based on radial Fourier sampling. Thanks to the intrinsic relation between captured radon samples in a CT imaging process and the radial Fourier samples, partial Fourier sampling could be implemented systematically. This systematic compressive sampling helps in better control of required conditions such as incoherence and sparsity to guarantee adequate image quality in comparison to previous CS based CT imaging structures. Simulation results prove the superior quality of the proposed approach (about 4% better PSNR), achieving the smallest CT scan time and the best image quality.

Wide-area monitoring, protection, and control (WAMPAC) is a key factor in the implementation of smart transmission grids. WAMPAC has a crucial role in detection and prevention of widespread events with an ultimate goal of improving the electricity service reliability. Several mathematical techniques were proposed for the optimal phasor measurement units (PMU) placement (OPP) problem which represents the first step toward the development of WAMPAC. These techniques consider either the solution to the network observability or realization of specific PMU applications. This paper proposes a multi-objective framework for OPP which emphasizes the reliability of power systems. The objective functions minimize the investment cost and maximize the system reliability. Since the objectives are in conflict, the non-dominated sorting genetic algorithm II approach is adopted as an intelligent state sampling tool to find non-dominated solutions (Pareto front). The final placement scheme among Pareto points is chosen by a Fuzzy decision making approach.

The Di erential Transfer Matrix Method is extended to the complex plane, which allows dealing with singularities at turning points. The results for real-valued systems are simpli ed and a pair of basis functions are found. These bases are a bit less accurate than WKB solutions but much easier to work with because of their algebraic form. Furthermore, these bases exactly satisfy the initial conditions and may go over the turning points without the divergent behavior of WKB solutions. The ndings of this paper allow explicit evaluation of eigenvalues of con ned modes with high precision, as demonstrated by few examples.

Left Ventricular Assist Devices (LVAD) have received renewed interest as a bridge-to-transplantation as well as a bridge-to-recovery device. Ironically, reports of malfunction and complications have hindered the growth of this device. In particular, the main concern is LVAD''s susceptibility to excessive backlash and suction as a result of ows that are either too low or high, respectively. This study utilizes a wellestablished physiological model of the cardiovascular system as a reliable platform to study a proposed adaptive robust controller for a rotary motor based LVAD which overcomes such shortcomings. Proposed controller performance is evaluated by comparing simulated natural heart model with LVAD assisted diseased heart in various states, extending from 60 to 130 beats per minute (bpm). Simulation results of the proposed LVAD controller show that for heart rate of 75 bpm, systolic and diastolic blood pressures are 112  18 mmHg and 7316 mmHg, respectively. Furthermore, for the light exercise condition of 130 bpm, systolic and diastolic blood pressures increase to 155  19 mmHg and 96  14 mmHg, respectively. These results closely match natural heart clinical measurements, con rming proposed LVAD model and its adaptive robust controller to be a possible solution to current issues confronting the LVAD drives.