Sharif Digital Repository

In this paper, LQG/LTR controller is designed for attitude control of the geostationary satellite at nominal mode. Usage actuator is the reaction wheel and control torque is determined by the LQR regulator. LQR controller signal has good performance, if all states are considered in feedback, but does not include model and sensors noises. Usage sensors are sun and earth sensors and EKF is used for estimation of noisy states. Then, LQG and LQG/LTR controllers are designed based on the estimated states, and are compared with LQR controller. The results show that robustness and performance of LQG/LTR are better than LQG and its control overshoot is smaller than LQR. The term that is provided in... 

Composites of unsaturated polyester containing 5 wt% nanoclay and different amounts of lead monoxide particles (0, 10, 20, and 30 wt%) were prepared. XRD patterns showed the exfoliation of nanoclay layers in the polymer. Morphological properties of the composites were studied using SEM micrographs. The prepared composites were investigated for their thermal resistance and mechanical properties using thermogravimetric analysis and tensile testing method, respectively. Addition of lead monoxide to the polymer worsened its thermal resistance and tensile properties, whereas the observed negative effects could be moderated by the clay nanoparticle. Gamma attenuation performance of the composites... 

This study introduces two new, simple, and scalable methods for synthesis of “cysteine–graphene oxide” hybrid, namely nucleophilic and covalent methods. Produced adsorbents could uptake 500 and 600 mg Hg2+/g, respectively, which are larger than capacities of most of the commercial adsorbents. By means of different instrumental techniques, chemical structures of the obtained graphene products were disclosed, and two pertinent mechanisms for their formations were suggested. Time for attaining uptake equilibrium for nucleophilic/covalent samples was 30 min/150 min, and kinetics was controlled by liquid film resistance/chemical reaction mechanisms, respectively. High selectivity and good... 

Removal of fluoride ions was investigated using a new adsorbent of yttrium alginate biocomposite (YALG). Effect of various parameters such as pH, contact time, initial concentration of fluoride ions and temperature on the sorption capacity of adsorbent was studied. Performing a mathematical assessment of fluoride sorption, isotherm and kinetics models including Freundlich & Langmuir isotherms and pseudo first & second order kinetics were applied on experimental equilibrium results through this work. Isotherm analysis revealed that Langmuir model showed a better evaluation from sorption equilibrium data than Freundlich. Based on kinetics evaluation, the pseudo second-order equation was... 

Tributhyl phosphate (TBP) decomposition in supercritical water oxidation (SCWO) was performed with and without catalyst, at different temperatures ranging from 370 to 480 °C, and different reaction times. Ag2O, CuO, Fe2O3, MgO, and ZnO synthesized by supercritical water were examined in TBP decomposition as the catalyst. TBP structure decomposed under the non-catalytic reaction; nevertheless, the results indicated that the use of catalysts improved the reaction efficiency, which calculated based on total organic carbon (TOC) removal, by far. However, TOC removal using Fe2O3 was 20% higher than the non-catalytic reaction. Having the ability in completion of the redox cycle, iron oxide... 

Polyurethane (PU) nanocomposites with 0, 1, 3, 5, and 7 wt-% nanoclay contents were prepared. X-ray diffraction patterns, transmission electron microscopy images, tensile test, and thermogravimetric analysis were utilised to reveal the morphological, mechanical, and thermal-resistant properties of the prepared nanocomposites. The exfoliated structure was obtained for nanoclay contents up to 3 wt-%. Incorporation of nanoclay to the PU matrix prompted the thermal stability of the polymer. A nanocomposite filled with 3 wt-% nanoclay showed the best tensile strength in the prepared nanocomposites. Subsequently, the nanocomposite with the 3 wt-% nanoclay was reinforced with carbon and glass... 

Vacuum residue cracking has been successfully conducted under supercritical water condition in presence of various metal oxide nanocalysts, namely NiO, CuO, ZnO, Co2O3, and Cr2O3 synthesized at supercritical water. The cracking experiments were carried out at 450 °C. Three species of cracking: maltene, asphaltene, and coke were then weighed and their corresponding speciation was defined. Gas chromatography-mass spectrometry (GC–MS), nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA), and elemental analysis (CHNS) tests were utilized to prove the performance of upgrading reactions. It was revealed that NiO showed the best performance among other catalyst, in which... 

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit... 

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only... 

One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared  

It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite... 

By employing the MIMO (multiple-input-multiple-output) technology in radar, some new problems emerged, that, in order to benefit the MIMO gains in radar, it was necessary to solve them suitably. One of such obstacles is determining the positions of receive antennas in a MIMO radar system with widely separated antennas (WS MIMO radar), since it is shown that the antennas' positions affect the whole system's performance considerably. In this study, a proper receivers' positioning procedure is proposed. To do this end, four criteria are developed based on the proposed MIMO detector and the MIMO ambiguity function. The simulations verify that the proposed positioning procedure improves the...