Sharif Digital Repository

The Cu2ZnSnS4 (CZTS) quaternary compound, with suitable optical and electrical properties, is one of the most interesting materials for absorber layer of thin film solar cell. Since all constituents of CZTS, are abundant in earth’s crust and non-toxic, it is a proper replacement for the materials like CdTe and CuInSe2. The CZTS pellet was synthesized by the solid-state reaction and deposited on soda lime glass substrates by pulsed laser deposition (PLD) method. PLD technique has the advantages of offering stoichiometric preservation during the materials transformation from target to substrate and good crystallinity due to the highly energetic species. CZTS has was deposited in order to... 

The main aim of this study is to propose a new structure of compression surfaces of a supersonic inlet in order to improve target performance parameter i.e. total pressure recovery ratio. This idea resulted in developing a new type of supersonic inlet, utilizing four ramps and a cone as compression surfaces simultaneously.A prototype of this type of inlet has been designed for Mach 3 and its performance has been studied via numerical simulation in design point and off design conditions. Eventually the new inlet compared to experimental performance survey data from two cases of two-cone inlets and also analytical calculations of ideal performance of some types of supersonic inlets. Results of... 

The integration of radar and communication functionalities into a unified Joint Radar-Communication (JRC) system offers enhanced spectral efficiency and reduced hardware complexity. Recognized as a key enabler for next-generation wireless networks, JRC systems require a careful balance between radar and communication demands, where waveform design plays a pivotal role in achieving this equilibrium. Although waveform design has been extensively studied separately in radar and communication domains, the requirements of modern networks necessitate a unified approach that simultaneously addresses the needs of both systems. This thesis advances waveform design methodologies for JRC systems,... 

The implementation of high-order multiple-input multiple-output (MIMO) detectors in complex domain, which finds applications in advanced wireless standards such as WiMAX and Long Term Evolution (LTE) systems, has always been a challenge in the literature. To address this challenge, two novel detection algorithms with their high-throughput VLSI architectures for a 4×4, 64-QAM complex MIMO detector are proposed in this thesis. The proposed architectures can easily be extended to high-order constellation schemes. For the first algorithm Complexity analysis and the synthesis results in a 0.13μm CMOS technology show that compared to the reported VLSI implementations in the complex domain, the... 

The Cu2ZnSnS(e)4 (CZTS(e)) quaternary and Cu2SnS3 (CTS) ternary componds with suitable optical and electrical properties have been considered as an emerging semiconductors for fabrication of thin-fim solar cells. So far, two technologies based on CdTe and CuInGaS(e)2 absorbers have achived efficiencies above 20%. However, these compounds contain toxic element Cd and rare elements such as In and Ga which, limited the development of these solar cells.In this research a 3-stage method was used for fabrication of CZTS(e) thin Films. In the first stage, CTS layers were deposited by spray pyrolysis method, in the second one, ZnS layers were also deposited on CTS layers by spray pyrolysis method... 

Physical and chemical properties of tungsten oxide thin films change reversibly while exposure to hydrogen gas. This property is called gasochromic. To enhance optical properties of such films, nanostructured, amorphous and porous thin films of (WO3)1-x(MeO)x (MeO= TiO2, MoO3, NiO; x=0.09, 0.17, 0.23, 0.29, 0.33) were fabricated by Pulsed Laser Deposition. Molar percentage of Me/W (Me= Ti, Mo and Ni) was changed in films with respect to targets; for Ti and Ni always a reduction, but for Mo an enhancement for low percentages was observed. The reason is the existence of thermal ablation mechanism during deposition, in the other word is different vapor pressure effect. An increment in x for... 

In this dissertation, the application of frequency and space diversities in radar target parameter estimation are investigated. On this basis, multi-frequency signal is used to improve the range resolution, array structure is used to increase the angle estimation accuracy and the merger of the multi-frequency signal and array structure are used to increase the maximum number of targets that can be uniquely identified.Considering the desirable properties of multi-frequency signals such as high bandwidth efficiency, high range resolution achievement without chip length decrease and …, there has been increased interest in the vast area of research on the design of such signals that has... 

Target recognition techniques based on micro Doppler phenomenon are popular because they are applicable even on low resolution radars, in contrast to other techniques such as High Resolution Range Profile (HRRP) which need high resolution in range or angle. Usually, main purpose of such techniques is generating robust features against target initial state, velocity, aspect angle, etc. rather than features which exactly identify a target. Main approaches in the literature are based on time-frequency transforms (TFT) such as spectrogram in order to generate features to classify targets, but in this thesis, we propose a totally different method using Recurrence Plot for generating features... 

In this research with Finite Element Methods in ABAQUS, numerical modeling has done in three-dimensions, which can be used to determine the effect of different factors on the surface settlement. Also, various factors such as geotechnical conditions, tunnel diameter,tunnel depth, the impact of the thickness of the segments and the amount of eccentricity of the structure relative to the longitudinal axis of the tunnel considered in this study. Face Pressure Supports, and Grout Injection Pressures are taken into account, too.Tunnel drilling causes a change in the displacement area and creates a changing zone around the tunnel. In this regard, not only adjacent buildings will be affected by... 

Proton precession magnetometers are one of the most sensitive scalar magnetic sensors. Their function is based on Zeeman effect and also nuclear magnetic resonance phenomena. In this project we have designed and implemented needed coils, swithching and signal detection circuits. Because of extremely high sensitivity of this sensor to induced noises and also gradient of earth’s magnetic fileld, detection of precession signal needs design of low noise electronic circuits with special EMC considerations. The implemented system in this project contains different blocks, such as switching circuit and its related control unit, amplifier, filter and frequency meter. Using this system, the obtained... 

Effective field theory is a practical method for model building and explaining experimental/observational data. These theories are constructed based on knowing low energy degrees of freedom and symmetries (accidental or fundamental). By construction, these theories are applicable up to a cut-off scale and their predictions beyond that are not reliable. For applications to higher energies a UV completion is needed through which modifications are applied or new heavy degrees of freedom are introduced. In order to complete a theory in a Wilsonian approach, scattering amplitudes must satisfy some constraints. These constraints are derived from basic assumptions like Lorentz invariance,... 

Given a divisible finite field extension KjF, the structure of Br(F), the Brauer group of F, is investigated. It is shown that, if F is indivisible, then Br(F) = Z2, which generalizes the Frobenius Theorem. As a consequence, when F is indivisible, the class of all finite dimensional non-commutative F-central division algebras D having radicable multiplicative groups D is determined. In fact, it is proved that the following statements are equivalent: (1) D is radicable, (2) D contains a divisible subfield KjF, and (3) D is the ordinary quaternion division algebra and F(p 1) is divisible  

Numerous structures which are involved in seismic soil-pile-structure interaction have been destroyed. Considering complexities which exist in soil-pile interaction problems and lack of precise methods without imperfect bases, it is necessary to use numerical methods for analyzing soil-pile interaction problems. In this research, three-dimensional modeling and studying the effect of changing soil and pile parameters on the behavior of pile under earthquake loading is performed using finite difference software, FLAC3D. The soil in this model has a softening behavior. Real earthquake spectrum has been applied into the model as the acceleration time history at the bedrock level. The results of... 

In this research, a new approach for TWS (Track While Scan) systems is introduced. Conventional TWS systems usually use target’s position (in Cartesian or polar coordinate systems), its velocity, and sometimes its acceleration (in main directions of coordinate system which is being used) as the elements of target’s state vector but the suggested algorithms use target’s velocity, course of motion and their rates of change as main tracking quantities and target’s position will be calculated after updating its velocity and course of motion. Hough transform is used as a powerful tool in detecting patterns which are identified with finite parameters (like lines, circles, ellipses, etc) to... 

The problem of guarding orthogonal art galleries with sliding cameras is a special case of the well-known art gallery problem when the goal is to minimize the number of guards. Each guard is considered as a point, which can guard all points that are in its visibility area. In the sliding camera model, each guard is specified by an orthogonal line segment which is completely inside the polygon. The visibility area of each sliding camera is defined by its line segment.Inspired by advancements in wireless technologies and the need to offer wireless ser- vices to clients, a new variant of the problems for covering the regions has been studied. In this problem, a guard is modeled as an... 

Copper-based semiconductors have received a great deal of attention due to their high absorption coefficient, direct and adjustable energy gap with stoichiometry, low frequency and toxicity. Multicomponent nanocrystals such as CuInS2, Cu (In, Ga) (S, Se) 2, Cu2ZnSnS4 and Cu2SnS3 (CTS) have been successfully synthesized by colloidal synthesis and have shown application potentials such as energy conversion, photocatalyst, thermoelectric and biomedical. Among these, the CTS ternary semiconductor with p-type conduction is one of the most well-known compounds of group I-IV-VI, which consists of abundant and non-toxic elements. In this research, thin-film solar cells with FTO / TiO2 / In2S3 / CdS... 

In algebra, division rings or skew fields are considered one of the basic building blocks in ring theory. So, a careful study of the properties of these rings is essential for the development of ring theory. All division rings, according to whether they are finite dimensional or infinite dimensional (as vector spaces) over their centers, are broadly classified into two types of centrally finite division rings and centrally infinite division rings.Herstein's conjecture about multiplicative commutators in these rings, is one of the unsolved problems that Herstein has proved it in the case when division ring is centrally finite, or the center of division ring is uncountable, but the... 

Our main purpose is introducing essential dimension and investigating properties of this concept and definition of it on different algebraic objects and proving some theories about it. In the beginning we define the concept of essential dimension on the extension fields which indeed it is expressing complexity of extension on the background field.Then with the meaning of noetherian extension which we will introduce it in the chapter three, we generalize the concept of essential dimension to finite groups. At last we investigate the connection between the essential dimension with generic polynomials and one of our important results is finding upper bounds for essential dimension of finite... 

The current global economy challenges and the importance of maintaining a sustainable development strategy has increasingly bolded the importance of construction productivity measures. This research describes the results of a running research that is to find the most critical factors affecting the productivity of high rise concrete building projects in developing countries. To achieve that, we have conducted Delphi method in two phases. In the first phase we had a brainstorming program with construction experts from owner organizations, construction contractors and designing engineers to identify factors that have influenced productivity in recent concrete building construction projects.50...