Sharif Digital Repository

Considering the generation of quasi-monoenergetic electrons with femto-second Lasers, producing X-Rays using these electrons is of interest. Lately, higher efficiencies of x-ray generation have been demonstrated by bombardment of different metal slabs, with quasi-monoenergetic electrons instead of Maxwellian electrons. The goal of this research is to study how changing the geometry of the target will affect efficiency and angular distribution of generated X-rays. The electron source is defined using a theoretical model and experimental data. MCNP4C code has been utilized to simulate the collisions of these electrons with a metal target. Intensity and quality of generated X-Rays are obtained... 

Security protocols may be provable secure when used alone, but these protocols lose their security under composition operation. Universal Composition framework (UC) is a tool for analyzing security protocols under composition. UC framework guarantees that the cryptographic protocols keep their security under this composition operation. In this paper we state a modeling for key-evolving signature protocol within the UC framework as a case study. To do this, the ideal functionality is proposed for key-evolving signature scheme that keeps the security requirements of this scheme. Finally, we show that UC definition of security is equivalent to definition of security which is termed here as... 

In this project, production of nano and micro particles with laser ablation of zinc, silver and copper sheet metals in the liquid medium has been experimentally studied. For this aim, homemade Nd:YAG pulsed laser at 1064nm wavelength, 60μs pulses with excellent stability with energies up to 700mj is used. By changing the pulse intensity on the target surface, the parameters such as size, shape and optical properties of nano and micro particles are studied by UV-visible spectroscopy, DLS, and SEM techniques. In this work, by microsecond pulses of Nd:YAG and using measuring devices such as Coherent power /energy meter, the appropriate optical table, the related experiments are implemented.... 

By using Mie theory and experimental data for complex refractive index of Au and Ag nanoparticles, the scattering and absorption efficiency of these nanoparticles in silicon medium (crystalline, Polycrystalline and amorphous silicon) was investigated. It was shown that Ag and Au nanoparticles can be used for confine the light, in desired wavelength band, inside the solar cell.The optimum nanoparticle size for using in this kind of solar cells was about 70-80 nm. In amorphous silicon confined photons cannot participate in electron-hole generation so the application of these metal nanoparticles in this kind of solar cells cannot be useful. Also the complex refractive index for equivalent... 

With the significant advances in software engineering and developing complicated systems, it’s important to investigate the interaction between systems. Agentoriented software engineering is a new paradigm for developing distributed intelligent systems. Agent technology currently plays an important role in complex software development. The underlying paradigm offers a large repertoire of original concepts, architectures, interaction protocols, and methodologies for the analysis and the specification of complex systems built as Multi-Agent Systems (MAS). Several efforts, originating from academia, industry, and several standardisation consortium, have been made in order to provide new tools,... 

A coupler free scheme for directly exited surface polariton (SP) using a negative-index metamaterial (NIMM) with a bottom layer of N type quantum emitters is presented. It is shown that by suppressing the ohmic loss the giant field enhancement could be achived in a broad electromagnetically induced transparency (EIT). And this field enhancement cause the excitation of surface polariton at the NIMM-Quantum emitter interfaces. For large range of probe detuning in EIT position and the tunable excitation of SP could be accomplished for special probe angle.It is revealed that the linear and nonlinear optical properties could be controlled effectively by modulating the phase of the microwave... 

Nd:YAG laser is one of the most applicable laser for researches and development where it's basic wavelength and harmonics are used on different laser project. It's basic output has a wide pulse duration and low peak power ,therefore in order to increase the peak power the pulse duration is reduced by Q-switching.In this project by means of passive Q-switch technique an energy equivalent to 500 mj with 10to 20 ns pulse duration is extracted from the oscillator and the output energy is amplified to about 850mj in a single pass through amplifier. In this project we used saturable absorber for Q-switching because it is more optimum and simpler than other Q-switching techniques like... 

Clustering algorithms are developed to provide general attitudes on database, recognizing latent structures and their more effective accessibility. Recently, broad studies are conducted on clustering since it is recognized as an important tool to explore and analyze data. Clustering is a fundamental learning operation without monitoring in data exploration which divides data into groups of objects so that objects in one group have the most similarity to each other and lowest similarity to objects in other groups. Some clustering algorithms such fuzzy clustering model (FCM) are widely used in clustering problem solution although this technique addresses local optimized searches. Additionally,... 

With the invention of the Chirped Pulse Amplification (CPA) technique in 1985, it became possible to amplify ultra-short laser pulses to high intensities with suitable pre-pulses contrast. By considering the importance of the short wavelengths radiation sources, the interaction of the intense laser with dense plasma is one of the most promising routs to reach this goal.This thesis is devoted to theoretical studies of the interaction of intense laser pulses with solid-state targets. The Relativistically Oscillating Mirror (ROM) models, which introduced in 2006, is presented and discussed. The reflection of a laser pulse from an overdense plasma surface as the oscillating mirror, to the speed... 

The aim of this thesis is to investigate one of the novel methods of accelerating particles such as electrons acceleration method. In intense femtosecond laser plasma interaction, a Wakefield is formed that trap electrons and accelerating them which this process will be fully addressed in this project. Due to the recent rapid development of technology for producing over dense plasma in laser-plasma interaction process in smaller sizes and the possibility of nuclear fusion reactions, the quantum effects are important and must be taken into account quantum effects in plasma. We study quantum effects by introducing the Bohmpotential and assuming the plasma as a one dimensional electron fermi... 

Distributed feedback dye lasers are among the suitable candidates for spectroscopic applications due to their capability of producing widely tunable picosecond pulses in UV-IR region. However, the pulsewidth sensitivity of the laser to pump intensity fluctuations hinders its suitability for precision applications. In this thesis, by utilizing widely used Self Q-Switching model, we showed that if the dye solution is pumped by a narrow (sub-nanosecond) pulse, the laser can operates in the single-pulse output mode with a better stability over a wide range of pump intensity. After that, we used a dynamical model based on the induced polarization and Maxwell equations, where the obtained results... 

In this study, how to create spectral singularity in amplitude and phase in the proposed hybrid system and controllable propagation of plasmon waves of nonlinear polaritons has been investigated. For this purpose, a nonlinear hybrid system consisting of an atomic layer and a metamaterial layer is investigated. The atomic layer can be a gaseous system like rubidium atoms that are cooled to few Kelvin by magnetic systems,or these atoms can be thought of as charged particles that are impurity doped into a clear crystal and cooled to a temperature of a few Kelvin.This quantum system is placed on a metamaterial layer in the form of Al2O3 which has a nano-fishnet structure.This frequency... 

Over the past two decades, scientists have been intensely interested in the development of metallic nanostructures for their applications in industry and medicine due to their attractive optical properties resulting from surface-localized plasmon resonance (LSPR).In this Thesis, plasmonic resonance modes in bridge dimer (Gold and Silver) are numerically investigated. Without the junction, A high-energy resonant mode called the bonding dimer plasmon (BDP) mode appears in the optical spectrum of the dimer, which is caused by the coupling of each of the nanoparticle plasmon modes. But in bridge dimer, two resonances called screened bonding dimer plasmon mode (SBDP) and charge transfer plasmon... 

Methane conversion into higher hydrocarbons has been investigated by non-thermal plasma. The most important advantages of utilizing this type of plasma are atmospheric pressure and ambient temperature of the operating system. Without any catalysts and with pure methane used as the feed gas, a stable 20 kilohertz spark discharge leads to an acetylene selectivity of 90.4 % with 54.5 % of methane conversion at a methane fow rate of 33 ml/min and a specific input energy of 54 kJ/L. Other components such as hydrogen, ethylene and ethane are also formed in the process as by-products. These remarkable results expose superiority of spark plasma in comparison with other types of non-thermal... 

In this study we consider a two-level supply chain, with a supplier and a number of identical retailers, demand process is Poisson with random rate. All retailers apply (R,Q) policy with backorder case for their inventory control supplier fulfills the orders of retailers according to FIFO discipline. At any point of time the supplier has online information about inventory position of all retailers.
Whenever the inventory position of a retailer reaches to a fixed value (s) above its reorder point, the supplier orders a batch of size Q to an outside source with infinite capacity. Lead-time of each retailer is equal to the sum of a constant transportation time and a delay time which is... 

Quantum interference and coherence are responsible for a novel set of physical phenomena, where Electromagnetically Induced Transparency is one of the most important of them. Each of these phenomena can make a new possibility for modifying the optical properties of a coherently prepared medium. Fast controllability of optical properties in one hand and flexibility of this control process in the other hand, are important factors that attract interests into coherent control of light .Coherent control of optical properties of the medium can be used in designing some advanced and challenging devices including All-Optical Switches. In this work , in a consistent picture, using a step by step... 

Due to the increase of computer networks and their application, the need for secure communication has become a very important concern. We introduce Cmail, a secure messaging system that works without any central party and in addition protects privacy of users. This system is on top of a cryptocurrency system such as Bitcoin. Bitcoin is cryptocurrency that works on the Internet. The suply of bitcoins and verification of transactions is done by Bitcoin miners, which are some typical client of Bitcoin system, in a decentralizd maner. In Cmail the miners have additional task, they should transfer messages of users and if needed, they hold it for a limited time. In order to increase incentive of... 

In recent years, nanoplasmonic quantum has been an active and developing field, resulting in several quanta and nonlinear qualities in the time-frequency interval, such as the creation of coherent single photons, nonlinear observation in nanometer dimensions, high-speed optical switch, etc. In the meantime, the controlled emission of surface polaritons resulted in the development of new devices such as nanolasers , subwavelength diodes, and high-speed phase and amplitude modulators , all of which have had a significant impact on the development of technology in very miniature dimensions. Numerous approaches have been proposed for the manufacturing of nanolasers, or reinforced plasmon...