Sharif Digital Repository

In the present work, interaction of high power and ultra short laser pulse with plasma in both under relativistic and relativistic regimes is investigated. The accelerated ions and electron are studied. The effect of pulse laser shapes on generating of the optimum wakefield is studied to find the maximum generated wakefield amplitude. It is found that similar to the wakefield amplitude generated by single pulse, the wakefield amplitude produced by dual trailing depends on the pulse shape and their permutation. Furthermore, the interaction of sub-picosecond UV laser in sub-relativistic intensities with deuterium is investigated. At high plasma temperatures, based on the quantum correction in... 

In this thesis, plasam kinetic aspects causing production of high-energy super-thermal particles in strongly nonlinear perturbations, including relativistic electron waves and shock waves occurred respectively in astrophysical and laser produced plasmas, have been studeied. Importance of kinetic simulations in this area has been demonstrated. In this respect, passing serious challenges, we have prepared a kinetic particle-in-cell (PIC) code and applied it within our supplied computational-resources. Relativistic electron waves produced via interaction of laser with tenouse plasmas have been deeply studied. These studies have resulted in new findings in fluid description of these waves,... 

Due to the interaction of high power lasers with over-dense plasma high harmonics are generated. The increase in harmonics cause an increase in frequency to the level of x-ray frequency and is thus a new method for creating x-ray lasers. In this research, we seek to understand the physics of this problem . Some theories try to explain this phenomenon based on the Doppler shift caused from the reflection of the laser beam from surface of the plasma, which oscillates with relativistic velocity.some try to explain this phenomenon based on the similarity with synchrotronic emissions. In this research, the main theories on this subject are reviewed, and a modelling of the emission caused by the... 

Structures that change color in an adjustable way have been noticed in recent years. There are structures in nature such as the skin of chameleons and octopuses and other animals that can change color. In recent years, inspired by these structures, materials based on photonic crystals or surface plasmonics have been proposed to change color. In this research, a review is made on these structures in nature as well as recent efforts to make such materials. In fact, photonic crystals create a special color due to the interference between scattered waves. For example, the change in the distance between the nanoparticles in the photonic crystals inside the chameleon skin is the cause of its color... 

In this project, the ionization and dissociation of methane molecule by intense femto-second lasers has been studied. Dissociation probability is calculated for interacting CH4 molecule under Ti: Sapphire laser pulse with pulse durations of 10- 40fs in intensities at the range of 1014-1016 Wcm-2. Calculations are carried out with time-dependent density functional theory using Gaussian03 and Octopus packages as powerful computational chemical physics programs. Due to importance of the dependence of interaction dynamics to laser parameters, the effect of these parameters including different intensities, polarization, various pulse durations and pulse envelopes are investigated. The optimal... 

The most important aspects of extensive air shower studies are finding energy, mass and the arrival direction of primary cosmic ray particles. In order for these parameters to be established, the core position of extensive air showers should be determined. In this thesis, a new method has been introduced that utilizes trigger time information of particle detectors for finding extensive air showers core location and for correcting plane wave front approximation to reconstruct their arrival direction. This method, in its simplest form, does not depend on density-sensitive detectors which are sensitive to the number of crossing particles. It is also independent of lateral distribution models.... 

The picosecond (ps) pulses in a synchronously pumped optical parametric oscillator (SPOPO) is generated by a 20W and 81.1 MHz Yb fiber laser at 1064nm, providing 11.7 W of total average power in near to mid-IR at 73% efficiency so that the signal pulse with a wavelength of 1560 nm and 7.1W average power and 3330 nm idler pulse with an average power of about 4.6W has been produced. The optical parametric oscillator (OPO), based on a 50 mm MgO:PPLN crystal with 5 gratings which is capable of withstanding large average powers without thermal effects.
The duration of these ultrashort infrared signal pulse generated by the described SPOPO is measured by using homemade interferometric... 

In this study, membrane distillation process was used for treatment of high salinity waters. The focus of this study is to simulate and build a setup of membrane distillation process. Since the membrane distillation process is based on the driving force of the temperature difference, the required temperature is provided by both the use of heaters and the use of solar energy. To increase the feed temperature by solar energy, a black polymer coating on the main membrane is used. The main membrane used in this process is PVDF polymer and the polymer coated on the surface is the PAN polymer. After simulating and constructing the laboratory setup, the influence of a variety of parameters on the... 

Previous researches has established that retrofitting RC (reinforced concrete) columns with FRP (fiber reinforced polymer) jackets is an effective means of providing external confinement to the column cross section. In an effort to evaluate FRP jacketing technology, this study focused on the confinement effectiveness of FRP jackets for rectangular building-type RC columns. Variables investigated include the following: the type of fibers (AFRP, CFRP), the thickness of the jacket, the shape (rectangular or circular) and aspect ratio of the cross section, and the sharpness of the corners of the rectangular cross sections. The sample structures were designed initially without lateral forces and... 

One of the new paradigms in information retrieval is to develop textual Question-Answering systems. Question-Answering (QA) is an advanced IR process at which for a natural language question, the answer is extracted and issued in natural language. The QA systems are divided into two general groups: Open-Domain QA and Restricted-Domain QA.
In this research field, a number of different models and methods are developed in which a document collection is used to retrieve candidate answers and then different methods are deployed to detect and eliminate irrelevant ones from answer set. Most of these methods decide based on expected semantic answer type, which is determined using pre-defined... 

Protocol identification and reverse engineering have recently received much attention due to their importance in many communication and security applications. In this field, the main challenges are: protocol identification, clustering unknown protocols, extracting protocol fields, and finding the protocol format based on these fields and their relations. Most of the proposed methods for the first two parts (protocol identification and clustering) use machine learning and AI techniques. For the last part, some bioinformatics techniques like sequence alignment algorithms are used. In this thesis, after reviewing different methods for protocol identification and reverse engineering, some...