Sharif Digital Repository

Progress in analysis of multicomponent mixtures and processes focused on the interpretation of the multivariate responses, rely on the combination of sophisticated instrumental techniques and suitable chemometric methods. Among the present chemometric method, curve resolution techniques have a wide application in the analysis of multicomponent mixtures and processes. Chemometric resolution techniques are used in the present work. At the first, Essential oil of green and black cardamoms was extracted by hydrodistillation and was analyzed by gas chromatography–mass spectrometry (GC-MS). Due to the fact that the essential oils are complex mixtures, strong overlap is observed between the peaks.... 

In various industries as a solution to energy production for a short period of time in order to have a high instantanuse power pulsed sources are widely used. This resource is a relatively long period of energy stored in the energy storage element and then this energy in a short period of time the exhaust. Among the most important applications of these resources can be used in radar systems, linear accelerators, pulsed lasers, nuclear fusion, medical applications, etc. Among the most important targets are the following sources can be output pulse quality, reliability and longevity of these resources, efficiency and cost them. From the perspective of the quality of the output pulse, rise time... 

Artemia is a small crustacean which has adapted to live in high salty water.The name of Artemia has been chosen according to its appearance. The adult Artemia is viviparous in the proper conditions whereas in tough conditions it reproduces the cysts. About 20 hours after the floating of cysts in water, its crust splits and after a while nauplii is produced by the free swimming. The changes of the hatching percentage of cysts Artemia and also the changes of Artemia Urmiana's size have been evaluated in this report.
The hatching percentage of cysts have been studied under LED radiation of red, orange, green and blue wavelengths, under red diode laser radiation and also under the... 

The objective of this thesis is to design an electrically tunable array of rectangular waveguide slot antennas. Because of its simplicity in design and fan shaped radiation pattern, for many decades, this kind of antennas were used in many systems like radars. Conventionally, beam steering of these types of antennas is done by a frequency sweep of waveguide in vicinity of the center frequency. Because each element is a resonant slot, its low bandwidth puts limitations in the frequency sweep. In this project, instead of frequency sweep in slot array antennas, we will consider adjusting these antennas using varactor diodes. Apart from varactor’s adjusting capability and its effect on radiated... 

In this thesis, a new wind turbine scheme based on Electrically-Excited Synchronous Generator (EESG) and diode-bridge rectifier is proposed and developed. This new scheme is mainly based on the idea of generator excitation current employment as a means of wind turbine control. That is why the new scheme is called Excitation Controlled Synchronous Generator (ECSG) wind turbine. The most important aspects of the proposed ECSG wind turbine scheme are cost-effectiveness, simplicity and higher reliability, as well as higher efficiency. Considerable cost reduction for the converter unit of ECSG wind turbine is so important since costly converter has been one of the main challenges of the... 

Organic light emitting diodes (OLEDs) are one of the main subjects of research in the organic electronic advanced technology. There are many advantages for OLEDs like self-emitting, high efficiency, wide vision angle, high contrast, and rapid response time. The main challenge in this area is the long-time stability of performance in air ambiance. Although the encapsulation process could overcome the instability problem, it increases the final cost. In this project, metal oxides have been utilized for the injection of electrons and holes in hybrid light emitting diodes (HyLEDs). In the first stage, inverted structure of HyLEDs with ZnO and MgxZn1-xO layers was fabricated and characterized.... 

Luminescent semiconductor nanocrystals otherwise known as quantum dots (QDs) have attracted intense interest over the past decade due to their unique properties and great potential in various applications. In this work we have studied the growth and luminescence properties of CdTe QDs and CdTe/CdS core-shell QDs and their application in hybrid organic/inorganic light-emitting diodes (LEDs) and fluorescent sensors. CdTe QDs were synthesized using a thermochemical method in aqueous phase. Central composite design (CCD) was applied to obtain the optimized conditions of the synthesis. The effects of four independent parameters including molar ratios of Cd to Te ions, TGA to Te ions, pH of the... 

Conventional imaging systems composed of two linear arrays of antennas as a transmitter and receiver. These arrays of antennas electronically scan along their antenna elements and are mechanically moved along a second orthogonal direction for scanning large two-dimensional areas quickly. In this thesis, the transmitter antenna elements are Tapered slot-line Antenna operating at 20-30GHz. A multiplexer circuit is used to transmit wideband signals to each antenna in the array. The receiver is composed of Schottky diode and pick up antenna that they are printed onto the radiating end of the antennas on the edge of the transmitter circuit board.In the available imaging systems, for achieving the... 

Recent developments in improving lighting efficiency and cost reduction of LED’s have caused them to be a suitable alternative for the current lighting systems. In this thesis a novel off-line structure is proposed to drive LED’s. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn’t use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) flyback converter in order to have power factor correction (PFC), a buck converter is added to the third winding of the flyback transformer in order to create two paths for the electrical power. DC... 

The light emitting diodes is composed of an electron transport layer and hole transport layer. The electrons and holes go to the middle region called active region through these transmit regions, and they emit light from themselves by recombination in this area. In our structure, the active region consists of quantum dots. The emitted light characteristics depend on these dots to great extent. In this thesis, we first describe the processes in this type of device, and then we will review the well-known structures that have been reported so far. In chapter 4 discusses the important characteristics of the active region, including the size of the quantum dots and the wetting layer, and we... 

LED Drivers with near 1 power factor, Because of using electrolytic capacitors (to become flicker-free) have lifetime drawbacks. This research will focus on solutions to use magnetic energy storage instead of electrolytic capacitors (used for energy storage) to solve lifetime drawbacks and decrease output light flicker. Calculations show that magnetic energy density using iron powder cores are lower than electrolytic capacitors, also a little lower than ceramic capacitors, but obviously higher than film capacitors. After calculations, conventional isolated and non-isolated LED drivers will be reviewed and new non-isolated off-line 230v with 10w output power LED driver with magnetic energy... 

This thesis begins in an attempt to design an X band front-end receiver in GaAs pHEMT technology, suitable for microwave circuits which should be high frequency, low noise, high gain, as well as high power handling and should have stable characteristics at large number of productions. The front-end receiver consists of three blocks, namely limiter, low noise amplifier, and mixer, which are designed in ISDL group previously. The measurement result of the fabricated low noise amplifier was satisfactory, since it was close to its simulation result. However, due to the drawbacks of modeling the switching behavior of devices, the results of the two other blocks, i.e., limiter and mixer – which... 

Factor analysis based methods are one of the applied methods in the Chemometrics. In this regard, some modifications on one of the factor analysis based method named fixed size moving window evolving factor analysis were done and two new methods named variable size moving window evolving factor analysis and preselected variable size moving window evolving factor analysis were introduced. The performance of the new introduced methods were examined and compared by the fixed size moving window evolving factor analysis.
Pure variable selection methods are useful for curve resolution methods which need to define an initial estimate from chromatographic profile or spectra. In this aspect the... 

In this thesis we examine and study the transmission of Ultra Wide Band (UWB) signals over single mode fiber in a radio over fiber system. We begin by developing mathematical model for the key optical components employed in radio over fiber systems. The authenticity of these models is verified with experimental results. Following the above models as well as experiment results, the transmission of UWB signals over optical fiber is investigated. The impact of limited operating bandwidth and nonlinearity of the electrical to optical transfer function on UWB signals is examined. Two types of UWB signals, namely, multi-band orthogonal frequency division multiplexing (MB-OFDM) and impulse radio... 

Semiconductor nanocrystals act as a good luminescent layer in new coming electroluminescence devices. Research on luminescent devices based on nanocrystals such as silicon nanoparticles, has been progressed over the last decades. In this research, silicon nanoparticles have been synthesized from porous silicon layer that was created through an electrochemical process. The effective luminescent parameters like electrolyte contents, current density and reaction time have been investigated. The maximum luminescence has been captured when the current density and reaction time were adjusted at 30 and 20 min, respectively. In addition, volume ratio Ethanol:HF 14:8 was another modified... 

In this work, encapsulating cesium-based perovskite quantum dots (PQDs) in zeolitic imidazolate framework-8 (ZIF-8) was investigated in order to enhance their environmental, water and thermal stabilities. It was shown that physical mixing of pre-synthesized PQDs and nanocrystalline ZIF-8 (structure-I) does not have any influence on stability enhancement. In second structure, nanocrystals of perovskite were crystalized in ZIF-8 pores. These nanostructures kept 50% of their initial photoluminescence after 24 hours maintenance in water. In third structure, both perovskite nanoparticles and ZIF-8 structures were crystalized simultaneously which resulted in more efficient encapsulation and kept... 

In spite of developments in microwave mixers, reducing its noise figure is still a designers’ challenge in receiver applications. Due to generating intermodulations and saturating the following stages, the low noise amplifier cannot have a so much gain to decrease the noise of the following stages in a typical receiver. This problem is intensified in special applications because of low dynamic range of low noise amplifiers. Accordingly, the low noise amplifier is replaced sometimes by the mixer. Therefore, the design of a low noise mixer is an important issue in improving the noise performance of a total receiver.To this end, it is required to accurately analyse the nonlinear and noise... 

Visible light communication networks provide wide bandwidth due to the use of visible light. In these networks, high efficiency can be achieved with proper system design and the use of space division multiplexing, effectively utilizing the existing bandwidth. Design issues in these networks are usually raised in the form of optimization. In this thesis, we optimize the energy efficiency of a visible light communication network with space division multiplexing in the transmitter by determining how to allocate LEDs to users and the amount of power for each LED. To accomplish this, we first propose two heuristic algorithms for determining how to allocate LEDs, and then we use a global...