Sharif Digital Repository

In this study, some properties of metallochlorophylls - compounds produced by replacing Mg2+ in tetrapyrrolic ring of chlorophyll b with divalent ions – of the forth period transit elements of the periodic table have been investigated. Using DFT/B3LYP method and DGDZVP basis set, structures of these compounds were optimized and the energy of electronic levels, Gibbs free energy of formation of complex, contribution of atomic orbitals to formation of molecular orbitals and partial charges in these molecules were computed. The results show that some properties of these complexes cannot be justified by the common theories of complexes. Among these properties is the negligible effect of... 

In recent years due to the advances in semiconductor technology and the ability to implement small-scale manufacturing, communication at 60 GHz band receive more attention than ever has been. The use of this frequency band is not only about 7-9 GHz unlicensed broadband access provided, but getting smaller devices make it possible to use multiple antennas at the transmitter and receiver, and thus taking advantage of multiple input – multiple output systems. Antennas used in these systems should have features such as small size , low weight, high gain and bandwidth and also they should keep their high efficiency and gainat high frequency range (about a few GHz ). To achieve these features... 

Due to small size, flexibility, and low cost of manufacturing, micorobots are potentially suitable for implementation in a broad range of applications. Control and inspection, medical utilities, manufacturing and micromanipulation of small-sized devices with nano-metric precisions, and precise measurements are some of the most important applications of microrobots. Mobile microrobots are one of the significant divisions of microrobots that are capable of movement with small steps and possess a motion range of at least several times the robot’s body length. In this project, Modulated Friction Inertial Drive (MFID) is utilized as a mechanism for creating a mobile microrobot. The micorobot is... 

Design and modeling of a micromechanism for generating planar, nano-scaled locomotion is the subject of this thesis. First, we introduced the concepts and fundamental definitions used throughout the thesis. Then, based on the classification of the locomotion principles employed in microrobots, the related literature about design and fabrication of different microrobots is investigated. Inertial slip generation and contact force variation, as the preferred group, is utilized for further analysis. Since friction force is the main propelling source in the microrobot’s locomotion principle, different models proposed for this phenomenon are investigated and the Coulomb friction model is selected... 

Millimeter wave technology may prove to be one of the key technologies of the 21st century, covering a broad range of applications including high-speed telecommunication, wireless sensing, and ultra-fast digital computing. The ultimate (commercial) success of these technologies depends on the ability to integrate mm-wave circuitry on a chip, bringing about significant size and cost reduction. Traditionally, mm-wave systems have made extensive use of waveguides based on hollow- or dielectric-filled metallic cavities for the transfer and processing of signals. Cavity waveguides exhibit very low loss, but are not well-suited to high volume manufacturing or on-chip integration due to their... 

In minimum cut problem we aim at finding a set of edges with minimum overall cost possible, such that removing them would separate two specific vertices, source and sink. This problem has been studied thoroughly, however the available algorithms were not proven to be time-wise optimal. Nowadays, planar graphs have attracted more attention because of their applications in cities and countries map. Moreover,their characteristics and properties, make some problems easier to solve in planar case. In this thesis, we will have a survey on algorithms for minimum cut on planar graphs. Our motivation to choose these algorithms is the balance between how easily they could be implemented and how fast... 

In creating a telecom battery charger there are three challenging factors which are high power density, high efficiency and modularity. A telecome battery charger consist of a rectifier with power factor correction capability and a DC-DC converter. The power stage of DC-DC converter with high output current and low output voltage has a vital role in the battery charger. The isolation transformer and magnetic component of LLC resonant tank are two huge and heavy parts of the DC-DC converter. With the emergence of GaN and SiC switches pushing frequency to to megahertz is possible which resulted in decreasing the volume of passive divices. But with increasing the frequency, designing of the... 

Computational complexity of graph problems is an important branch in the-oretical computer science. We introduce to some of ideas for computing the complexity of graph problems with some kind and beautiful examples. Next, we show hardness and inapproximability of some problems. Representation number of graphs has been introduce by Pavel Erdos by Number theory. We prove n1−ϵ inapproximability of that. Lucky number η has been studied by Grytczuk et.al . We show for planar and 3-colorable graphs, it is NP-Complete whether η = 2. Note that since a conjecture, for those graphs, 2 ≤ η ≤ 3. Also for each k ≥ 2, we show NP-completeness of η ≤ k for the graphs. Proper orientation number −→ is a... 

Nematic liquid crystal shells (droplets) containing cores have attracted considerable attention in recent years. Defect structures that form in such systems do not emerge in the bulk.These shells which could be created using double emulsion techniques in the laboratory have provided applications in microscale optical structures.In the past just boundary conditions and bulk parameters were noticed but recently the geometry of the core is considered likewise.In this work oblate ellipsoid cores are examined numerically using finite-element method. The boundary conditions in studied systems are perpendicular in outer surface of droplet and planar in the vicinity of the core. First by minimizing... 

The interferometer method, as one of the most accurate schemes for wideband direction finding (DF), is used. The interferometer method has various algorithms which can be implemented depending on the required specifications. The advantages and disadvantages of these algorithms have been evaluated and the appropriate algorithm for a general practical case in view of the ambiguity resolution is proposed. The receivers’ channel phase tracking error is of significant concern in practice, in interferometric DF systems. The induced error due to channels phase tracking error is estimated. Furthermore the use of physically realizable antennas, achievement of high accuracy, minimum number of antennas... 

The recent project can be considered as a subset of Telerehabilitation, in the field of Telerehabilitation can be defined as the need for long-term data recording in order to determine each individual's movement pattern and compare it to the individual's best model or best practice. With this perspective, it can be said that the recent project, in more detail, remotely targets the use of foot plantar pressure to determine locomotor parameters. With this description, the FSR or force sensitive resistor sensor was selected for a number of reasons, including low cost, low weight and low thickness, and the data acquisition circuit was used to convert the sensors' analog signal to digital output,... 

Nowadays, regarding the wide achievements in micro scale technology, it is possible to manufacture a micro robot. Micro swimmer have extensive applications in different fields especially in medical sciences. One of the most important problems of the micro robot is their propulsion system. The locomotion of microorganisms in fluids is ubiquitous and plays an important role in numerous biological processes. The physics of swimming governing life under the microscope is very different from the one we experience in the macroscopic world. This project is aimed at designing a propulsion system for a micro swimmer based on the swimming mechanism of the eukaryotic Spermatozoa. Simplicity to build is... 

Nowadays superconducting devices and especially high temperature superconductors (HTSs) have found very wide applications in microwave engineering. This technology is raised in the form of planar microwave structures and in the different shapes of superconducting microstrip transmission lines, strip lines and coplanar waveguide (CPW) lines and different kind of applications like resonators, couplers, filters, antennas, etc. Important advantage of these structures is very low loss, small size and high quality factor. However nonlinear behavior of superconducting microwave devices, due to the dependence of the surface impedance on the applied field, limits the power handling capability of... 

converters in electric vehicles, it is necessary to reduce their dimensions and increase their efficiency. It is expected that in the near future wide band gap semiconductors will be used to achieve these goals. On the other hand, usage of planar transformers is necessary to achieve slim and compact converter designs in electric vehicles. Clearly, planar transformers offer a significant advantage in replacing bulky wired transformers in high frequency LLC resonant converters with WBG transistors. planar transformers also have several other advantages, including low flux leakage, modular structure, and low thermal resistance.However, in planar transformers, due to the proximity and large area... 

Nowadays high efficiency and power density are desired for designing a power electronic converter. Technology advances in power semiconductor devices, makes it possible to design converters for operation in higher frequencies to reduce size of the converters. As the frequency is increased, switching losses and temperature is also increased, so designing a converter for high frequency operation needs some tradeoffs. LLC resonant converter as a promising solution for battery chargers has ability to adjust its output voltage during Constant Current and Constant Voltage modes. However, its operation mode would change based on switching frequency change. Therefore, for efficiency-oriented...