Sharif Digital Repository

One of the most important subsystems in the air-breathing engines is the atomizers, which break the fuel into many droplets. It is well known that atomization quality has a significant influence on combustion characteristics such as stability limits, efficiency, and pollutant emission. Both jet and swirl injectors are applicable in gas turbine engines. The latter have been widely used for combustion chambers and the former are usually employed for fuel injection in the afterburner part. Since experimental and numerical study of atomizers could be complex and costly, a design methodology of atomizers based on empirical relations is still very advantageous and effective in reducing... 

We study the degrees of freedom of the three-user Gaussian interference channel under the circumstance where one or more transmitters are non-causally cognitive, meaning they are aware of the messages of one or more transmitters in a non-causal manner. Our focus is on the total degrees of freedom of the three-user cognitive interference channel. Our first case is when only one of the transmitters is fully cognitive and knows the messages of the other users. We prove that using interference alignment and interference cancellation, the achievable total degrees of freedom is 11/6 and does not coincide with the calculated total degrees of freedom upper bound which is 2. In the second and third... 

Various agile software development methodologies, practices, and techniques have been proposed in the last decade; some present novel ideas, while many are simply made up of tasks and techniques borrowed from prominent agile methodologies. Each of these methodologies prescribes a set of practices and techniques which are deemed appropriate for application in a specific context. However, there exists no single method which fits all project situations. This has resulted in the advent of Situational Method Engineering (SME) approaches, which are used for developing software methodologies that are tailored to fit the specific circumstances of the project situation at hand. Since tool support has... 

By expansion of digital multimedia and networking technology, the problem of ownership protection has become increasingly important. Digital watermarking is an efficient way for copyright protection of digital images. Traditional watermarking techniques degrade the quality of host image by embedding a watermark logo. Facing this problem, a new watermarking approach called zero-watermarking has been proposed. In zero-watermarking methods, the watermark does not require to be embedded into the protected image but it uses both the watermark and the protected image to generate a verification map which is registered to a trusted authority for further protection. In this paper we propose a robust... 

Recently, protecting the copyright of digital media has become an imperative issue due to the growing illegal reproduction and modification of digital media. A large number of digital watermarking algorithms have been proposed to protect the integrity and copyright of images. Traditional watermarking schemes protect image copyright by embedding a watermark in the spatial or frequency domain of an image. However, these methods degrade the quality of the original image in some extend. In recent years, a new approach called zero-watermarking algorithms is introduced. In these methods, the watermark does not require to be embedded into the protected image but is used to generate a verification... 

Watermarking is a way that is used to protect the copyright of images. As the existing watermarking methods are not robust enough a new novel scheme is needed. In this paper, we propose a zero-watermark discrete cosine transformation-based copyright protection scheme, in which a normalization procedure is applied in both watermark embedding and extraction to make our scheme more robust to geometric distortions. This method is resistant to malicious signal processing and geometric attacks such as blurring, JPEG compression, noise adding, sharpening, scaling, rotation and cropping. Experimental results on images with different complexity show that our proposed scheme outperforms related... 

We consider an optomechanical system with two membranes when a bichromatic laser field with red-sideband and blue-sideband frequencies is applied in the single photon strong coupling regime. It is shown that using the mode selecting method and under the Lamb-Dicke approximation, motion of membranes can evolve to single or two mode squeezed number states. By considering the environmental effect, a Wigner function is plotted for understanding the conditions that lead to the generation of non-Gaussian states. The results show that, in this system, initial states of membranes are important to generation of non-Gaussian mechanical squeezed number states. © 2016 Elsevier B.V. All rights reserved  

In recent years, with the growth of software engineering, agile software development methodologies have also grown substantially, replacing plan-driven approaches in many areas. Although prominent agile methodologies are in wide use today, there is no method which is suitable for all situations. It has therefore become essential to apply Situational Method Engineering (SME) approaches to produce agile methodologies that are tailored to fit specific software development situations. Since SME is a complex process, and there is a vast pool of techniques, practices, activities, and processes available for composing agile methodologies, tool support-in the form of Computer Aided Method... 

Three-dimensional thermo-hydrodynamic analysis of gas turbine combustion chambers is of great importance in the power generation industry to achieve higher efficiency and reduced emissions. However, it is prohibitive to use a comprehensive full-detailed mechanism in their simulation algorithms because of the huge CPU time and memory space requirements. Many reduction approaches are available in the literature to remedy this problem. Here a new approach is presented to reduce large detailed or skeletal mechanisms of oxidation of hydrocarbon fuels to a low-cost skeletal mechanism. The method involves an integrated procedure including a Sensitivity Analysis (SA) and a procedure of Gradual... 

Network virtualization is a promising approach in which common physical resources are shared between service providers. Due to the substrate network limitations such as maximum available memory of each node of the substrate network as well as different service priorities and requirements, resource management in this setup is essential. On the other hand, SDN is bringing a considerable flexibility in resource management by introducing a centralized controller which can monitor all the substrate network states. In this paper, we propose a proactive admission control and dynamic resource management in SDN-based virtualized network in which the number of accepted high-priority virtual network... 

It is shown that the asymmetry coupling between two coupled optomechanical cavities leads to special class of PT-symmetric model for optomechanical structure. Under these conditions, Hamiltonian is considered in blue and red sideband regime. In these cases, the asymmetric coupling between two cavities has been transferred such that the asymmetric beam-splitter or squeezing interaction is generated between optical and mechanical modes. Then, the amount of entanglement between the different optical and mechanical modes is calculated. The results define that PT-symmetry can improve the entanglement in special conditions. The proposed system provides good condition to investigate the... 

In the present study, the antibunching effect is considered in a parity time (PT)-symmetric system, using the recently proposed non-Hermitian model for resonant cavities. The model consists of a cavity coupled to an optomechanical system by a chiral mirror, with both cavities being driven coherently. The nonreciprocal coupling strength between the two cavities leads to the generation of the non-Hermitian but PT-symmetric model. The optimal conditions of strong antibunching are calculated in this system, and then the antibunching effect is considered using the two-photon correlation function and the Wigner function. The results showed that this model presented the best control over the strong... 

In the study presented herein, a simple method for laboratory calcite cementation of a reconstituted gravelly sand was presented. This method was used to prepare cemented gravelly sand specimens, which have similar natural characteristics to alluvial deposit of the city of Tehran. The formation and distribution of calcite bonds, as well as the effectiveness of the presented calcite cementation method in increasing interparticle cohesion, as observed in weakly to moderately cemented soil in Tehran, were evaluated by means of chemical analysis, X-ray diffraction technique, and unconfined compressive strength tests. The cementation technique was used to prepare triaxial specimens with calcite... 

We propose an effective blind image steganalysis based on contourlet transform and Zernike moments that improves the detection accuracy of universal image steganalysis methods. The proposed method examines randomness in the test image to distinguish between the stego and non-stego images. The suspicious image is decomposed by contourlet transform, and then the absolute Zernike moments of contourlet subbands coefficients of the image and linear prediction error of each contourlet subband are extracted as features for steganalysis. These features are fed to a nonlinear SVM classifier with an RBF kernel to distinguish between cover and stego images. Experimental results show that the proposed... 

Three-dimensional analysis of combustion chambers in industrial gas turbines suffers from lack of simple and accurate reduced mechanisms for oxidation of hydrocarbon fuels. Here, an integrated procedure is introduced based on a differential evolution optimization technique. The procedure is flexible and modular and allows optimization of many rate parameters of a multistep global mechanism based on many different combustion criteria and inlet or operational conditions. The procedure uses any selected chemical reactor model and any reference combustion mechanism provided. Sample design criteria used here are flame temperature, ignition delay time, and concentration of selected species,...