Sharif Digital Repository

Using Green's function of semi-infinite Weyl semimetals, we present the quantum theory of the collective charge dynamics of Fermi arcs. We find that the Fermi arc plasmons in undoped Weyl semimetals are linearly dispersing gapless plasmon modes. The gaplessness comes from proper consideration of the deep penetration of surface states near the end of the Fermi arcs into the interior of the Weyl semimetal. The linear dispersion - rather than square root dispersion of pure 2D electron systems with extended Fermi surface - arises from the strong anisotropy introduced by the Fermi arc itself, due to which the continuum of surface particle-hole (PH) excitations in this system will have a strong... 

Beenakker noticed that the peculiar band structure of Dirac fermions in two-dimensional (2D) solids allows for the specular Andreev reflection in these systems, which has no analogue in other 2D electron systems. An interesting deformation of the Dirac equation in the solid state is to tilt it, which has now been realized in materials. In this paper we report another peculiar feature of the Andreev reflection in tilted 2D Dirac cone systems. The tilt deformation of the Dirac equation is characterized by two parameters ζ=ζ(cosθ,sinθ). We show that when the tilt parameter is tuned to its "horizon value" ζ=1, irrespective of the incidence angle of electrons, the Andreev reflected hole is always... 

In this paper, we present a nano-quantum photonic approach for the calculation of normal dispersion phenomena in organic crystals such as N-(4-nitrophenyl)-L-prolinol(NPP). We assume that a laser beam consists of a flow of energetic particles that interact with the distorted π-electron system. We approximate the distorted π-electron cloud by an ellipse to simplify calculations. By the precise analysis of photon interaction with the π-electron system of benzene ring in the NPP crystal, we obtain the refractive index in any wavelength by Monte Carlo simulation. The maximum error between our simulation results and the measurement data is 0.058, which is agreeable. © 2007 IOP Publishing Ltd  

The most common technique for analysis and control of power electronics circuits is switch averaging. The model is not linear however, and often results in a multiplicative term in the state equations. Hence, it is common to perform a small signal linearization of the model about an operating point. Models obtained with such method involve considerable approximation, and produce results that are limited for higher performance designs. In this paper a Piecewise Affine Approximation (PWA) technique is introduced for modeling of switched circuits. Modeling of a DC-DC buck-boost converter is presented as an illustrative example to show the favorable properties and broad utility of this approach.... 

In May 1, 2008, researchers at Hewlett Packard (HP) announced the first physical realization of a fundamental circuit element called memristor that attracted so much interest worldwide. This newly found element can easily be combined with crossbar interconnect technology which this new structure has opened a new field in designing configurable or programmable electronic systems. These systems in return can have applications in signal processing and artificial intelligence. In this paper, based on the simple memristor crossbar structure, we propose new and simple circuits for hardware implementation of fuzzy membership functions. In our proposed circuits, these fuzzy membership functions can... 

Recently announcement of a physical realization of a fundamental circuit element called memristor by researchers at Hewlett Packard (HP) attracted so much interests and opened a new field in configurable or programmable electronic systems because it has properties of the perfect switch. Combination of this newly found circuit element with nanowire crossbar interconnect technology, creates a powerful platform which is called memristor crossbar. It has been demonstrated that this structure can offer the potential of creating configurable electronic devices which can have applications in signal processing and artificial intelligence. In this paper, we will highlight the rule that Genetic... 

Motivated by recent works indicating the role of AC current on the reliability of electronic systems, the microstructural characterization and mechanical properties of solder joints, as vulnerable parts of electronic packages, under different alternating current shapes were investigated. The sine-, square- and triangle-waveform currents were considered for the experiments. The simulation results showed that the triangle shape current creates the highest thermal fluctuations and stress variations in the solder joints. This event was due to the lack of any relaxation time at the critical states, induced by triangle shape current, which leads to the intensification of stress in the solder... 

Topology, symmetry, electron correlations, and the interplay between them have formed the cornerstone of our understanding of quantum materials in recent years and are used to identify new emerging phases. While the first two give a fair understanding of noninteracting and, in many cases, weakly interacting wave function of electron systems, the inclusion of strong correlations could change the picture substantially. The Kondo lattice model is a paradigmatic example of the interplay of electron correlations and conduction electrons of a metallic system, describing heavy fermion materials and also fractionalized Fermi liquid pertaining to an underlying gauge symmetry and topological orders.... 

Recently announcement of a physical realization of a fundamental circuit element called memristor by researchers at Hewlett Packard (HP) has attracted so much interest worldwide. Combination of this newly found element with crossbar interconnect technology, opened a new field in designing configurable or programmable electronic systems which can have applications in signal processing and artificial intelligence. In this paper, based on the simple memristor crossbar structure, we will propose a new mixed analog-digital circuit as a hardware implementation of the sign-sign least mean square (LMS) adaptive filter algorithm. In this proposed hardware, any multiplication and addition is performed... 

This paper presents a new method for implementing the direct torque control (DTC) on the brushless doubly fed induction machines (BDFM) in presence of turbulence in voltage grid. It is supposed irrupts in three phase voltage grid suddenly. Effects of these events on closed-loop operation are inevitable and in some cases could lead to system instability. It presumed that grid voltages disturbance effect on back-To-back converter's outputs is negligible. Control of a complex machine is problematic. Hence, firstly has explained performance of the control method on BDFM, Proposed a new method for reducing turbulence effects of system operation afterward. Simulation results on BDFM model with... 

An analog circuit for maximum power point tracking of a PV battery charger with minimum number of elements is proposed which works in a full range condition with a fixed switching frequency. In conventional MPPT algorithms which provide PV current or voltage reference value as output, fast climate changes may cause system instability. Here, a new variable is defined to eliminate the problem and improve the stability of the system. In order to compare the presented circuit with a conventional system, perturb and observe (P&O) MPPT algorithm which is well-known in PV systems is implemented on the same system. Simulation results (Conventional P&O algorithm and proposed structure) are presented... 

Multi-port converters (MPC), used in multi-input/multi-output power electronic systems have low cost, low weight and low mass integrated control system. Besides these converters offer bidirectional and isolated ports, which are inevitable in some applications. Three-Port Half Bridge Converters (TPHBC) are the ones which have the lowest component count. But these converters suffer from a low Zero Voltage Switching (ZVS) range that is lost in medium to low load powers. Low ZVS range cause low efficiency, especially in low output powers. In this paper a modified Pulse Width Modulation (PWM) technique is introduced to increase the ZVS range of main switches which results higher efficiency and... 

This paper presents a high performance real-time simulator for power electronic systems applications and primarily intended for controller hardware-in-the-loop (CHIL) testing. The novelty of the proposed simulator resides in the massively parallel hardware architecture that efficiently exploits fine-grained parallelism without imposing severe communication overhead time that can limit the performance. The simulator enables the use of a nanosecond range simulation timestep to simulate power electronic systems. Through the use of this nanosecond range simulation timestep, the simulator minimizes the error arising from the intersimulation timestep switching phenomenon associated with CHIL. The... 

Design technology is expected to rise to electronic system-level (ESL). This necessitates new techniques and tools for synthesizing ESL designs and for verifying them before and after ESL synthesis. A promising verification strategy for future very complex designs is to initially verify the design at the highest level of abstraction, and then check the equivalence of the lower level automatically generated models against that initial golden model. We present one such approach to simulation-based functional verification implemented in our ESL design methodology called ODYSSEY. Our ESL synthesis tool generates a transaction-level model (TLM) at TLM level 2 (i.e., design with partial timing)...