Sharif Digital Repository

In this paper we investigated the structural properties of the ultra high voltage power transmission network of Iran. We modeled the power grid as a network with 105 nodes and 142 connection links. We found that the Iranian power grid displays a relatively moderate clustering coefficient-much larger than that of corresponding random networks-and small characteristics path length comparable to that of corresponding random networks; i.e. the power grid is a small-world network with exponential degree distribution. Global efficiency was considered as an indicator of grid's performance and the influence of random and intentional nodal failures on the efficiency was investigated. We also studied... 

A novel method based on microextraction in packed syringe (MEPS) as sample preparation technique coupled off-line with gas chromatography-mass spectrometry was developed using electrospun nanofibers as sorbent. For electrospinning of polypyrrole/polyamide-based nanofiber, a homogeneous solution containing nylon 6, ferric chloride and pyrrole monomer was prepared and then was drawn into a 2.5-mL syringe. By applying a voltage of 13akV between the needle of the syringe and an aluminum-foil collector, the nanofibers could be formed on the surface of the collector. The prepared sheet was used as the sorbent for MEPS to analyze some selected organophosphorous pesticides. Important parameters... 

Numerical and analytical methods are two methods to evaluate the performance of electrical machines. This article provides a comparison between numerical and analytical methods. Electrical machine software typically uses numerical methods to solve the electromagnetic equations. On the other hand, analytical methods are faster and more intuitive. A general analytical modeling technique to evaluate the performance of axial flux machines including but not limited to wound rotor resolvers is presented here. The proposed model is based on the actual three-dimensional (3-D) magnetic equivalent circuit (MEC). The accuracy of the proposed model depends on the number of radial layers in the... 

A common solution for increasing the accuracy of wound-rotor (WR) resolvers is to increase the number of poles. To achieve a compact design, fractional slot concentrated winding is used for multi-pole WR resolvers. However, employing such windings leads to rich sub-harmonics in the induced voltages. To suppress these undesirable sub-harmonics, multi-layer windings with appropriate shifting angle between the layers is suggested. However, the said shifting angle is limited by the slot pitch so that the capability of the multi-layer winding is not utilized fully. To overcome the mentioned deficiency a slotless disk type configuration is proposed in this paper. Then, an optimization based on the... 

A common solution for increasing the accuracy of wound-rotor (WR) resolvers is to increase the number of poles. To achieve a compact design, fractional slot concentrated winding (FSCW) is used for multi-pole WR resolvers. However, employing such windings leads to rich sub-harmonics in the induced voltages. To suppress these undesirable sub-harmonics, multi-layer windings with an appropriate shifting angle between the layers are suggested. However, the said shifting angle is limited by the slot pitch so that the capability of the multi-layer winding is not utilized fully. To overcome the mentioned deficiency, a slotless disk type configuration is proposed in this article. Then, an... 

High pole number permanent magnet (PM) motors, due to their high torque density, have been receiving considerable attentions in recent years. To achieve an accurate position control in PM machines, resolvers are suggested for industrial applications. Mechanical and electromagnetic considerations in the case of high pole number resolvers lead the machine designers to choose small cores with low slot numbers. This paper proposes two different on-tooth winding configurations to achieve high pole number without increasing the slot numbers, while the accuracy of the detected position is intended to be the maximum value. Variable turn on tooth winding (VTTW) is compared with fractional slot... 

Axial flux resolvers (AFRs) are used in motion control of electrical machines. In this paper, the effects of physical parameters on the accuracy of detected position are studied. The examined parameters are width of slot opening and slot width, number of poles, number of slots per pole and per phase, and skewing of rotor slots. An analytical model based on the winding function method is proposed for the first time in to estimate the error of position signal. The results of the analytical method are verified with 3-D time stepping finite-element method. Finally, the prototype of the studied AFR is constructed and tested. Good agreement between simulation and experimental results confirms the... 

Among position sensors, resolvers are superior from reliability point of view. However, obtaining lower output voltage harmonics and simple manufacturing process is a challenge in the design and optimization of resolvers. In this paper, a metaheuristic optimization algorithm is used to minimize total harmonic distortion of the output signals, and consequently the estimated position error in concentrated coil wound field resolvers. Meanwhile, to minimize total coil numbers, manufacturing costs, and complexity of the winding process, modified objective function and constraints are proposed. In this way, a modified winding function method is employed for performance analysis of the axial flux... 

Resolvers, due to their robust structure, are widely used in automation systems. The need for accurate position estimation beside the precise control of present PM motors, persuade machine designers to select a resolver with high pole numbers. By the aid of concentrated winding topologies high pole numbers is accessible. Among different topologies of concentrated windings fractional slot (FS) type has been focused by a lot of researches. FS concentrated winding (FSCW) offers high pole number under limited slots, identical on tooth coils, short end winding, and compact design. However, depending on the topology, there are major drawbacks, such as magnetic noises, high sub-harmonics, high... 

In this paper, we present a randomized LOCAL constant approximation factor algorithm for minimum dominating set (MDS) problem and minimum total dominating set (MTDS) problem in graphs. The approximation factor of this algorithm for planar graphs with no 4-cycles is 18 and 9 for MDS and MTDS problems, respectively. © 2020 Owner/Author  

Fused Deposition Modeling with Polypropylene filament was employed to make a lap joint between Polypropylene and pre-punched Al-Mg alloy sheets, in the form of bonds between the polymeric substrate and the additive part and mechanical lock between the additive part and aluminum base sheet. Effects of the joint interface area (hole diameter of 5–13 mm) and preheating of the substrates (room temperature, 50 and 90℃) were investigated on the mechanical properties of the joints. Peak load in the tensile-shear and cross-tension tests increased with enhancement of the joint interface area (up to ˜280 N and ˜160 N, respectively). Higher joint strength in the tensile-shear test compared to the... 

For a set of n disjoint line segments S in R2, the visibility counting problem (VCP) is to preprocess S such that the number of visible segments in S from a query point p can be computed quickly. For this configuration, the visibility testing problem (VTP) is to test whether p sees a fixed segment s. These problems can be solved in logarithmic query time by using O(n4) preprocessing time and space. In this paper, we approximately solve this problem using quadratic preprocessing time and space. Our methods are superior to current approximation algorithms in terms of both approximation factor and preprocessing cost. In this paper, we propose a 2-approximation algorithm for the VCP using at... 

In real applications, there are situations where we need to model some problems based on uncertain data. This leads us to define an uncertain model for some classical geometric optimization problems and propose algorithms to solve them. The assigned version of the k-center problem for n uncertain points in a metric space is studied in this paper. The main approach is to replace each uncertain point with a clever choice of a certain point. We argue that the k-center solution for these certain replacements of our uncertain points, is a good constant approximation factor for the original uncertain k-center problem. This approach enables us to present fast and simple algorithms that give... 

We report on the response of a monolithic high Tc transition-edge bolometer to about 3 mmWave for the first time. The detector structure consisting of 400-nm YBa2Cu3O7-x(YBCO) film on buffered yttria stabilized zirconia substrate without any coupled antenna, shows bolometric type responsivity to the 3-mmWave radiation at its transition temperature. The YBCO thin film Ce0.9La0.1O2 buffer layer are both fabricated by the metal-organic deposition method. The meander line pattern of the bolometer is designed for obtaining maximum absorption and responsivity possible when the polarized radiation of the source is aligned with the pattern. Meander lines are 50 micrometers wide and 1.5-mm long. We... 

Increasing demand for wearable devices has resulted in the development of soft sensors; however, an excellent soft sensor for measuring stretch, twist, and pressure simultaneously has not been proposed yet. This paper presents a novel, fully 3D, microfluidic-oriented, gel-based, and highly stretchable resistive soft sensor. The proposed sensor is multi-functional and could be used to measure stretch, twist, and pressure, which is the potential of using a fully 3D structure in the sensor. Unlike previous methods, in which almost all of them used EGaIn as the conductive material, in this case, we used a low-cost, safe (biocompatible), and ubiquitous conductive gel instead. To show the... 

One of the most important applications of wireless sensor networks is data collection. This paper proposes as efficient approach for data collection in wireless sensor networks by introducing Member Forward List. This list includes the nodes with highest priority for forwarding the data. When a node fails or dies, this list is used to select the next node with higher priority. The benefit of this node is that it prevents the algorithm from repeating when a node fails or dies. The results show that Member Forward List decreases power consumption and latency in wireless sensor networks