Sharif Digital Repository

In this thesis, an enhanced local mean-field (MF) model that is suitable for simulating the electroencephalogram (EEG) in different depths of anesthesia is presented. The main building elements of the model (e.g. excitatory and inhibitory populations) are taken from two pioneer MF models designed by Steyn-Ross et al and Bojak & Liley, and then a new slow ionic mechanism is included in the main model. Generally, in mean-field models, some sigmoid-shape functions determine firing rates of neural populations according to their mean membrane potentials. In the enhanced model, the sigmoid function corresponding to excitatory population is redefined to be also a function of the slow ionic... 

A new class of design has been introduced in the RF circuits and Frequency Synthesizers, which is based on the digital circuits. Implementation of the digital synthesizers suppresses the need to use loop filter and thus reduces the loop lock time. In this thesis different topologies of digitally controlled oscillators using inductor and capacitor tank and all digital architectures used in high frequency all digital synthesizers in 0.18um CMOS technology has been inspected and simulated. Novel techniques introduced to improve the ring oscillator-based design’s specifications which doesn’t need inductor. Using the introduced techniques, the phase noise has been lessened acceptably with respect... 

This thesis investigates various modulation recognition systems both in analogue and digital forms. We are looking for a recognition technique considering practical implementation issues. To recognize the modulation, the career frequency is supposed to be known and a bandpass signal is received. Besides, we investigate some digital Automatic Modulation Recognition (AMR) methods. The techniques based on the features of the signal have less computational complexity compared to Maximum Likelihood (ML) techniques; hence they are more desirable for practical implementation. In this project, analog modulations are implemented using C++ software. For the convenience of users, here, two graphical... 

In this thesis we have studied slotted and unslotted ALOHA random access optical CDMA packet switching networks with a chip-level receiver structure. We used generalized optical orthogonal codes (GOOC) and Overlapping PPM (OPPM) signaling technique to improve system performance. The impact of physical layer parameters such as GOOC code cross correlation value and OPPM overlapping index on key performance benchmarks such as network throughput and delay are analyzed. We have also studied the stability of the network based on the number of backlogged users, using expected state drift. It has been shown that using GOOC instead of strict OOC improves the network average delay and throughput.... 

Recent stringent HC and CO emission regulations are because of increasing consciousness of the perilous influences of exhaust emissions. The chief attempt to pass the standards is to decrease the emissions during cold-start, due to catalytic converters are not efficient until they arrive a light-off temperature. It has been discovered that 50% to 80% of the controlled HC and CO emissions are sent out from tailpipe of automotive during the cold-start. Therefore, in order to minimize the cold-start emissions and fast light-off of catalytic converters, it is important to understand the catalytic converter characteristics and techniques for rapid warm-up catalyst. This thesis describes a... 

Determining nonlinear dynamic behavior of structures is always one of the main goals of structure and earthquake engineers. The Modal Incremental Dynamic Analysis (MIDA) is one of the newest methods for analyzing the seismic behavior of structures. Indeed, this method has superseded the exact IDA method which is too complicated and prolix. Although, this method represents approximate results, high accuracy, fastness and low cost procedure made it an efficient and useful technique. Many researchers have used this method and investigated the accuracy of that and achieved proper results. Up to now no one has applied this method on structures which are equipped with dampers. In the procedure of... 

In this thesis, we study some connections between the graph-theoretic and algebraic properties of co-maximal graph of algebraic structures. We follow two purposes. First, what properties of algebraic structures can be found from co-maximal graph of algebraic structures. Second, what geometric or graph theoretical properties of co-maximal graph of algebraic structures can be found from specefic algebraic structures. Let G be a group and I(G)∗be the set of all non-trivial sub-groups of G. The co-maximal graph of subgroups of G, denoted byΓ(G), is a graph with the vertex set I(G)∗and two distinct vertices H and K are adjacent if and only if HK=G. We char-acterize all groups whose co-maximal... 

Security of cryptographic devices lies amongst the most important issues in the field of hardware security. It is frequently seen that in the process of designing cryptographic systems insufficient attention is paid to the physical implementation details. This is happening while a lot of secret information is known to be leaked through side-channels such as power consumption, electromagnetic emission and execution time. Side-channel attacks are able to reveal secret keys by using these side-channel leakages. Additionally, side-channel attacks are one of the most powerful but low-cost attacks that put the security of cryptographic systems in vain. It can be claimed that the most dangerous... 

Performance based design becomes an effective method for estimating seismic demands of buildings. Incremental dynamic analysis (IDA) based on a nonlinear response time history analysis (NL-RHA) is considered to be the most accurate method in seismic demand calculations. However, modal incremental dynamic analysis (MIDA), based on the equivalent single degree-of-freedom (SDF) oscillator, is also often used in studying structural engineering performances. The MIDA procedure for estimating seismic demands is extended to unsymmetric-plan buildings. In the MIDA procedure, the seismic demand due to individual terms in the modal expansion of the effective earthquake forces is determined by... 

Analog-to-digital conversion and signal processing has been increasing due to its many advantages. So that mostly we prefer to convert signal from analog area to digital samples, then they are processed and finaly put the result signal at the system output. How ever because the restriction of the sampling rate, Prevent the spread of digital processing for the high-frequency signal (RF). In recent years, ADCs sampling rate rise up to several GHz (for example ADC with 4 GSPS and 12 bits for TI) that output of the these ADCs by powerful and fast FPGAs are processed but According to Shannon theorem band width of these ADCs is not desirable.the goal of this thesis uses of the compressed sensing... 

In this thesis we study three versions of K−theory. The most well-known vesrsion is topological K−theory, a generalization of Grothendieck works on algebraic varieties to the topological setting by Atyiah and Hirzebruch. Since its birth it has been an indespensible tool in topology,differential geometry and index theory. In the early 1970s C∗−algebraic version of K−theory introduced through associating two abelian groups,K0(A)and K1(A)to a C∗−algebra like A. These functors proved to be a powerful machine, making it possible to calculate the K−theory of a great many C∗−algebras. At last,algebraic K−theory is dealig with linear algebra over a ring R by associating it, a sequence of abelian... 

Sigma-delta modulators have largely been implemented as discrete-time (DT) circuits because of their low sensitivity to circuit nonidealities, and their frequency scaling specification, however a continuous-time (CT) design offers significant advantage in the design of high accuracy, high speed analog to digital converters (ADC). A CT design allows for relaxed amplifier(s) bandwidth and power requirements, which enables the realization of high accuracy modulators with bandwidths of several megahertz at low power consumption. Furthermore CT modulators provide inherent anti-aliasing filtering which becomes especially important at low oversampling ratios. This thesis reports the design of a... 

In the present work, numerical simulation of cross-flow microfiltration of non-alcoholic beer in a tubular membrane has been studied. Finite element analysis was used as a powerful tool for simulation. The feed stream, which flows mainly tangentially to the porous membrane surface, is modeled by the Navier-Stokes equations. Porous wall conditions are described by the Darcy equation that relates the pressure gradient within a flow stream to the flow rate through the permeable wall. A pilot-scale cross-flow membrane filter was developed to verify the model results. Ceramic tubular membranes were used in this study. The cross-flow velocity of the feed solution was controlled at the laminar... 

In this work we have investigated the methods of providing quality of service in cognitive radio networks. At first, we have explained the various algorithms of providing BER quality of service in wireless networks. Especially we have explained those algorithms which are known as the distributed power control algorithms. Then we have introduced methods of using adaptive modulation and we have used this kind of modulation to provide delay quality of service in cognitive radio networks. We have done this by maximizing the sum of effective capacities of secondary links under the power constraints and also the interference constraints set by the primary receivers. Finally, we have introduced... 

iN This thesis, Design and implementation of a low voltage, low power Delta-Sigma Modulator (DSM) is presented. System level considerations have been discussed thoroughly. In addition a systematic design flow in the context of continuous time delta sigma modulators is provided. While voltage-domain signal processing becomes more difficult in deep sub-micron processes, a finer time resolution is achievable. Time-domain quantizers can ameliorate the design challenges of flash quantizers which arises from lower supply voltages and higher fraction of comparator metastable region. VCO based quantizer such as voltage to frequency and voltage to phase considered as time domain quantizers can be a... 

Pile foundations suffered severe damages during the past earthquakes in all around the world. These damages were more severe in laterally spreading grounds and they mostly have been observed in gently sloping grounds and coastal areas. In these cases, Pile foundations not only are subjected to structures inertial loads and kinematic loads of liquefied soil but also lateral spreading intensifies damages. Thus, in the recent decade, several researches have been conducted to investigate the behavior of pile foundations in liquefiable and laterally spreading grounds, however, some uncertainties still remain in modeling of soil-pile interaction. In this study, the effects of liquefaction- induced... 

external radiation therapy is a methods of cancer treatment or improvement of cancer-related complications. various techniques have been developed for external beam radiation therapy. Among which, Intensity Modulated Radiation Therapy (IMRT), due to its ability to adjust the intensity of radiation beams, has a higher capacity to generate appropriate dose distribution based on tumor size and volume. Intensity Modulated Radiation Therapy is one of the most commonly used procedures of delivering radiation to cancerous tissues, with the aim of reaching the prescripted dose in the target volume while minimizing damage to nearby healthy organs. Two decisions are of fundamental importance: to... 

In this thesis, no-load and full-load performance of Permanent Magnet Vernier Generators (PMVGs) is investigated in fully-aligned condition and under different types of mechanical faults. The studied mechanical faults are Static Eccentricity (SE), Dynamic Eccentricity (DE), Inclined Rotor (IR), and Run-out (RO). Furthermore, an analytical model is also developed to calculate the permeance of the air-gap and the induced voltages in the health machine and under studied mechanical faults. Then, 2-D and 3-D non-linear, time stepping finite element method is utilized for performance evaluation of the generator in no-load and full-load (with resistive, inductive and capacitive loads). In continue,... 

In this thesis, pulsed power structures containing a step up high voltage transformer with large transformer ratio are investigated. In pulsed power applications, a step up pulse transformer is a proper choice in the cases in which a low primary voltage is available. The noticeable advantage of employing these transformers is the ability to use several modules in the primary side of the transformer. However, it should be noticed that the primary side current of the transformer is large. So to solve this problem, the number of primary windings could be increased and the primary large current can be shared between these windings. In this thesis, the sharing methods are investigated and the... 

Subwavelength metallic slit structures allow extraordinary transmission of light (EOT) at certein frequencies.In recent years, the effect of graphene layer on EOT has been investigated, which is used in the design of terahertz modulators. The electrostatic tuning ability of graphene electrical conductivity controls the resonance frequency and the amount of incident radiation absorption. Because of the single atomic thickness of graphene, the wide range control of incident light can not be achieved alone. However, by placing this layer with various 1-D and 2-D patterns on periodic metallic layers with EOT ability, high light modulations can be obtained. In particular, the structure of the...