Sharif Digital Repository

In this paper, the problem of the waveform design for colocated multiple-input multiple-output (MIMO) radars is considered in two parts. In the first part, we design transmit waveform in order to approximate the desired beampattern with low number of samples in the transmitter. Unlike the traditional waveform design methods, in our solution, waveforms are designed for a specific number of samples. Also, the constant envelope constraint that is an important practical constraint is considered. In the second part, we jointly design the transmit waveform and receive filter by a sequential algorithm, considering a priori information of target and interference angle locations. We have evaluated... 

In this letter, we consider the problem of waveform design in colocated multiple-input multiple-output radars in order to obtain a desired beampattern. In this problem, practical constraints, such as constant envelope (CE) and low peak-to-average power ratio, are very important. Therefore, we propose a simple method to generate some practical waveforms, such as different versions of phase-shift keying and pulse-amplitude modulation. We map a non-CE to the desired finite alphabet by a mapping function (MP). In the proposed method, first, the values of cross-correlation relationship between the input and the output of MP are calculated in a few points, and then, using radial point... 

Components in cryogenic milieu with relative motion, like seals and pumps cannot be lubricated by using oils or other lubricants. Therefore materials wear in cryogenic condition is a great concern. To earn valid data about the wear properties of common and super useful material in cryogenic tribosystems, reconstruction wear test apparatus at cryogenic temperature is needed. Investigations on metal-metal couple show that austenitic stainless steels have favorable and auspicious sliding properties at cryogenic temperature. This research provides the wear parameters of austenitic stainless steel AISI type 316 in cryogenic environment. For this purpose two sets of test environment are prepared,... 

Efficient electron transport layers (ETLs) play a pivotal role in the performance of solar cells. In recent years, Indium sulfide (In2S3) has been studied as a promising ETL in CuInGaS(e)2, Cu2ZnSnS(e)4, and perovskite solar cells. Despite several studies on spray-deposited In2S3, there is no complete experimental investigation on In2S3 thin films. The effect of the molar ratio of S/In and the type of indium precursor on the structural, morphological, optical, and electrical properties of sprayed-In2S3 layers has been studied. Films were characterized using x-ray diffraction, scanning electron microscopy (SEM), optical transmission (UV-Vis), Mott-Schottky analysis, four-point probe, and... 

This paper presents the influence of the severe shot peening process on the fatigue life of the laser-cladded Inconel 718 specimens which can be employed during refurbishment of components enduring high mechanical cyclic loads such as gas turbine components. In order to quantitatively evaluate the destructive effect of laser cladding on the fatigue endurance, fatigue tests are first performed on the as-received and laser-cladded specimens. Then, microstructural analysis by scanning electron microscope (SEM) is carried out to identify the root causes of the drawback of laser cladding. Moreover, by employing a comprehensive laser-cladding FE analysis considering cyclic plastic material... 

Herein, we deposited CuInSe2(CISe) thin films by using aqueous spray deposition method and post selenization process. The effect of different indium precursor salts including indium chloride, indium nitrate and indium acetate on the structural, morphological, optical and electrical properties of sprayed CISe layers has been studied by using x-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM-EDS), optical transmission (UV–Vis), Mott-Schottky analysis, I–V dark measurements. Although all the deposited thin films show a chalcopyrite tetragonal ordering structure of CISe, the crystallinity, morphology, and electrical characteristics are strongly influenced by the type of... 

We introduce an effective method for copper indium sulfide selenide (CISSe) doping with different alkali metals (Li, Na and K) based on a pre-deposited alkali chloride layer. A simple and fast spray method is used for pre-deposition of alkali chloride layer (LiCl, NaCl, KCl) on substrate surface before spray pyrolysis deposition of copper indium disulfide CuInS2 (CIS) films followed by selenization. The different properties of alkali-doped CISSe films by the alkali chloride pre-deposition (ACPD) method were compared to the post-deposition treatment (PDT) method. Based on FESEM images, a highly compact film with large grains can be obtained for CISSe films doped with K(∼0.72 μm) and Na (∼0.56... 

The optimal design of stiffened plates for buckling under in-plane forces and bending moments was presented. The virtual work principle was applied in order to calculate the buckling coefficient and the critical load factor of the stiffened plates. It was observed that the buckling coefficient is a function of the displacement coefficients  

This study represents the investigation of In2S3 thin films, which have been deposited with different Indium salts (Chloride, Acetate, and Nitrate) using the Chemical Spray Pyrolysis (CSP) method. The Mott-Schottky analysis has been used in case of studying the electrical properties of films such as conduction and valence band, carrier densities, Fermi level (Efn), flat band potential, and semiconductor type. In the next step, the Rb1MAFA perovskite solar cell has been simulated, and the results have been validated by the experimental data (with the least parameters for fitting). Finally, In2S3 layers have been inserted on the SnO2 layer to decrease the recombination rate and enhance the... 

The dynamic behavior of a closure bolting system was predicted using a spring-mass-damper model. The loading was assumed to be an initially peaked, exponentially decaying internal pressure pulse acting on the closure. It was observed that optimal pre-stress values that minimized the peak bolt deformation and stress, existed for relatively high levels of applied force and low pre- stress  

The individual and combined effect of shear deformation and rotary inertia on the columns was discussed. It was shown that the shear deformation effect always tends to reduce the buckling load. It was observed that rotary inertia for supported columns has no effect on the buckling load. The critical buckling load of perfect columns subjected to static axial loading was calculated using the Euler-Bernoulli theory  

In this paper, the application of an actuator wire made of shape memory alloy (SMA) and externally attached to a cantilever beam is analyzed. To this end, an integrated model that includes the constitutive equations of the SMA, the phase transformation equations from martensite to austenite and vice versa, the heat transfer equation for the SMA that also includes the input energy from an electric source, and the equations of the elastic deformation of the cantilever beam as well as the SMA wire, is presented. The simultaneous solution of the mentioned set of equations can result in the evaluation of the system response to an electrical activation of SMA  

The overlapping generations (OLG) model of micro-based macroeconomics has been utilized in order to calculate the optimal sequence of inter-generational transfer payments and evaluate its effects on the operation of an economy which suffers from the poverty trap. Each generation has been assumed to live for two periods and aims to find the optimal relationship between its borrowing from the previous generation and its lending to the next generation so that its discounted utility function is maximized. This optimization is subjected to budget constraints, the competitiveness of labor and capital markets and the equilibrium condition of savings and capital. Individuals in all of the... 

One of the main subjects in automotive industries is to enhance the efficiency of internal combustion engines. Wear between cylinder and ring is one of the major parameters reducing the engine performance. So many parameters are affecting the wear losses. Temperature plays a key role on the severity of wear condition in internal combustion engines. In conventional cast iron cylinders, it is not possible to increase the temperature from a defined level, as it causes excessive wear in contact area between cylinder liner and piston ring. One of the major benefits of using ceramic coating is their ability to withstand in higher temperatures, while having adequate hardness to improve wear rate... 

A thermo-mechanical finite element model is developed to accurately predict residual stresses of the multiple beads laser cladding process, incorporating the cyclic plasticity into the analysis by utilizing the nonlinear kinematic hardening behavior. Finite Element results are presented for Inconel 718, a material for which the laser cladding process is widely used. The FE results are compared with the results of incremental center hole drilling conducted on three specimens with different clad beads to evaluate the effect of cyclic plasticity modeling on the residual stresses. The results indicate that incorporating the nonlinear kinematic hardening model into the analysis can reduce the... 

The mathematical modeling of a bolted joint with a Shape Memory Alloy (SMA) actuator ring is presented. In this way, phase transformation, constitutive and displacement compatibility equations are used. The obtained model is utilized to show how the application of the SMA actuator ring in the bolted joint can help the joint to recover a significant amount of its lost clamping force. The model is run using the experimental data obtained for the Ni-55.7%wt Ti SMA in the companion paper (Part 1). The mechanical properties of SMA are calculated using the mentioned equations and compared to the experimental findings. It is observed that the final clamping force obtained theoretically is close to... 

One of the main problems with a bolted joint is losing its preload. In this situation, it cannot provide the required clamping force needed to keep the joint members together or prevent fluid leakages. Although every effort is usually made at the design stage to prevent such failure, because of the numerous factors present in the problem, these efforts are not always successful. After loosening occurs, the joint should be retightened to regain its preload. However, there are circumstances where the joint is very important but it is not easily accessible and retightening cannot be done manually. The shape memory effect (SME) property can be used in such circumstances to produce the necessary...