Sharif Digital Repository

Plasma focus is a copious source of electrons, ions, neutrons, and X-rays. SUT-PF is a 7 kJ Mather type plasma focus device. In order to study soft X-rays emitted by this device a bent crystal spectrometer has been designed and constructed based on Johann method. Before recording spectral lines, using a photodiode detector and a pinhole camera, optimum parameters for maximum emission of soft X-rays have been studied and registered. Results show that ionized Argon atomic lines mostly have wavelengths between 3 and 4 Å. Among them 1s2–1s2p transition with a wavelength of 3.943 Å represents the most intense line  

Condensation of water vapor available in atmospheric air can be considered as a solution for water scarcity problem. In this paper, a comprehensive thermodynamic analysis of water production from humid air using thermoelectric coolers (TECs) is presented. The system consists of a number of thermoelectric coolers, a fan to supply the required air flow circulation, two cold and hot air channels, heat sinks and solar cells for powering the thermoelectric coolers and fan. Effects of various design parameters are investigated and discussed. The proposed design is optimized to get the maximum effectiveness which is defined as the amount of produced water per unit of energy consumption. Sensitivity... 

Tourism is one of the largest sources of economic revenue for many countries around the world. The historical and cultural treasures of Iran made it one the main destinations for international tourists. One of the biggest problems encountered by the tourists during the visit to monuments of Iran is the lack of information about the visited landmark. Given that cameras can be found in all of the smart phones, the use of the landmark's photos can be very important for obtaining information about the tourism sites. The detection of the landmarks in an image taken by the mobile phone camera can be a very complex task depending on the angle and the light situation in which the photo is taken. In... 

The present paper deals with different effects of homogenization time and cooling environment on Ni-42.5wt%Ti-7.5wt%Cu alloy. The alloy was prepared by vacuum arc melting. Afterwards, three homogenization times (half, one and two hour) and three cooling environments (water, air and furnace) at 1373 K were selected. Optical and Scanning Electron Microscopic methods, EDX, DSC and hardness tests have been used to evaluate the microstructure, transformation temperatures and hardness. Results indicate that specimens that were cooled in air are super-saturated. Also, the microstructure from furnace cooling has many disparities with the other cooling environments' microstructure and two types of... 

In this paper we consider a cooperative communication systems over Rayleigh fading channels. The system utilizes a combination of incremental and selective decode-and-forward (ISDF) relaying protocols. The symbol error rate (SER) of M-PSK modulation for the ISDF protocol is derived. Using an approximation of the SER expression, the optimal power allocation is investigated. In order to reduce the complexity of the receiver, we used a modified version of the ISDF protocol which does not use the storage or retransmission of the first phase signal. We also derived optimal power allocation coefficient for modified ISDF. It has been noted that for the optimal power allocation in the ISDF protocol,... 

In this paper we consider a relaying communication system over Rician fading channels. In this system we assume simple Incremental-Selective Decode-and-Forward (ISDF) protocol, which is jointly combining incremental and selective DF relaying protocols. In this protocol, storage or retransmission of the first phase signal are not allowed. We analyze the symbol error rate (SER) performance of the recommended protocol with M-PSK modulation. We evaluate the performance of the protocol in the frequency nonselective slow Rician fading channels. Using the approximation of the SER expression, the optimal power allocation is investigated. Our results show that at least 50% of total power must be used... 

The catalytic activity of potassium salts of phthalimide (PPI) and succinimide (PSI), as organonucleophilic catalysts, has been investigated for the cyclotrimerization of isocyanates under solvent-free conditions. PPI showed better catalytic activity in comparison with PSI. Diverse and challenging isocyanates afforded the respective symmetrical isocyanurates in good to quantitative yields in an atom economic reaction without any phase transfer catalyst. © 2005 Bentham Science Publishers Ltd  

Combination of sodium saccharin and tetrabutylammonium iodide as a novel anionic catalyst system promotes selectively the trimerization of isocyanates to give symmetrical isocyanurates under solvent-free conditions. © Springer-Verlag 2004  

Chatter suppression is of great importance in machining processes for achieving more material removal rate, high precision and surface quality. In this paper, an H∞ control algorithm is proposed for chatter suppression in the presence of tool wear and parameter uncertainties. Orthogonal turning process is modelled as a single degree of freedom model that includes the effect of tool flank wear. Control input of the system is the force provided by a piezo-actuator.The turning process model includes the uncertainties in cutting velocity, tool wear and dynamic model parameters. Using the μ-synthesis technique, an H∞ optimal controller is designed based on a DK-iteration algorithm. The... 

Chatter suppression is an important topic in any type of machining process. In this paper, orthogonal cutting process is modeled as a single degree of freedom dynamic system. A nonlinear delay differential equation is presented that models flank wear of the tool. Uncertainties in cutting velocity, tool wear size and parameters of the dynamic model are included in the model of cutting process. The force provided by a piezo-actuator is taken as the control input of the system. A sliding mode control scheme is used and an effective control law is derived which suppresses the chatter vibration. Results for two distinct cases of a sharp tool and a worn tool are presented and compared which shows... 

Chatter suppression is an important topic in any type of machining process. In this paper, orthogonal cutting process is modeled as a single degree of freedom dynamic system. A nonlinear delay differential equation is presented that models flank wear of the tool. Uncertainties in cutting velocity, tool wear size and parameters of the dynamic model are included in the model of cutting process. The force provided by a piezo-actuator is taken as the control input of the system. A sliding mode control scheme is used and an effective control law is derived which suppresses the chatter vibration. Results for two distinct cases of a sharp tool and a worn tool are presented and compared which shows... 

Nanocomposites containing ZrO2 and HA have been considered in various fields due to their unique mechanical properties. The principal purpose of this paper is to select the models with the maximum accuracy for the prediction of microhardness of CHA/ZrO2 nanocomposite. For this purpose, three models, including gene expression programming (GEP), gray wolf optimization algorithm (GWOA), and least squares support vector machine (LS-SVM), were implemented to predict and optimize the microhardness of the CHA/ZrO2 nanocomposite. Finally, the results showed that the data obtained from the LS-SVM model were closer to the preliminary data than the others. According to the results, the LS-SVM could... 

Chitosan was modified with polyacrylonitrile (PAN) through ceric-initiated graft copolymerization. The chitosan-g-PAN product was saponified using sodium hydroxide aqueous solution to prepare a novel superabsorbent hydrogel, H-chitoPAN. Duration of completing the saponification reaction as well as the water absorbency capacity of the hydrogel was decreased with increasing the alkaline concentration. Either chitosan-g-PAN or H-chitoPAN was characterized by FTIR spectroscopy and DSC, TGA, and DTG thermal methods. According to FTIR, all the nitrile groups were converted to carboxylate and carboxamide groups. Both modified chitosans exhibited enhanced thermal stability over chitosan. The... 

Probabilistic Context-Free Grammars (PCFGs) are useful tools for syntactic analysis of natural languages. Availability of large Treebank has encouraged many researchers to use PCFG in language modeling. Automatic learning of PCFGs is divided into three different categories, based on the needed data set for the training phase: supervised, semi-supervised and unsupervised. Most current inductive methods are supervised, which need a bracketed data set in the training phase. However, lack of this kind of data set in many languages, has encouraged us to pay more attention to unsupervised approaches. So far, unsupervised approaches have achieved little success. By considering a history-based... 

Several methods have been developed in the past for analyzing the porosity and other types of well logs for large-scale porous media, such as oil reservoirs, as well as their permeability distributions. We developed a method for analyzing the porosity logs φ(h) (where h is the depth) and similar data that are often nonstationary stochastic series. In this method one first generates a new stationary series based on the original data, and then analyzes the resulting series. It is shown that the series based on the successive increments of the log y(h)=φ(h+δh)-φ(h) is a stationary and Markov process, characterized by a Markov length scale hM. The coefficients of the Kramers-Moyal expansion for... 

In this paper, the soave-Redlich-Kwong (SRK) Eos is modified based on perturbation theory. The parameter of the new cubic equation of state considered reduced temperature and a centric factor dependent. The average of absolute deviations of predicted vapor pressure, vapor volume and saturated liquid density of 30 pure compounds are 0.814.2.G14 and 5.814%, respectively. Also comparison with the new equation of vaporization of pure compounds are given. The florry-Hugines (FH) model is similarly modified by an adjustable parameter. This parameter is defined based on molecular weight of asphaltene to molecular weight of heavy oil ratio in form of polynomial function. The phase behavior of... 

Chatter suppression is of great importance for achieving high precision and surface quality in machining processes. A single degree of freedom model of orthogonal turning process is used to set up the nonlinear delay differential equation of motion. Tool wear effect is considered as the contact force between the workpiece and tool flank surfaces. Uncertainties in parameters of dynamic model and machining conditions are included in the model. An adaptive control strategy is applied for chatter suppression in cutting process. The force provided by a piezoactuator is the control input of the system. Results of stability analysis and adaptive control for two distinct cases of sharp and worn...