Sharif Digital Repository

Keggin-type polyoxometalate (POM) nanoparticles based on [PW12O40]3- and [SiW12O40]4- with Ag+ and (ZrO)2+ cations were prepared under ultrasound irradiation. The results of SEM and XRD revealed the average size of particles in the range of 24–95 nm. The moles of crystallization water per mole of nanocatalysts were in the range of 3–9. EDX spectra confirmed the successful replacement of protons of H3PW12O40 and H4SiW12O40 with Ag+ and (ZrO)2+ cations. These nanoparticles were used as heterogeneous catalysts for the synthesis of a poly (amido-ester) at room temperature. All polymers were fully characterized. Although employing the nanocatalyst resulted in at least 22% improvement in the... 

The multi-path phenomenon is one of the main causes of error in Direction Of Arrival Estimation systems which are located in a complex environment. The received signal in this environment consists of Line Of Sight (LOS) and multi-path components which are delayed versions of the LOS signal with the amplitude and the phase depending on the path length. In order to eliminate the multi-path signal, it is necessary to estimate the amplitude, the phase, and the delay of the signal. To this end, a method based on correlation which has been already used to estimate amplitudes and delays of Line Of Sight and multi-path signals in GPS systems, is implemented. After this estimation process, a phase... 

The LLC resonant converter, as a promising solution for battery charger applications, has the ability to adjust its output voltage during Constant Current and Constant Voltage modes in the charging profile. However, its operation mode changes as switching frequency changes. Therefore, for efficiency-oriented optimizations in battery charger applications, the one-pointed efficiency is not an appropriate objective. To this end, in this paper, a multi-pointed averaged efficiency is considered for optimization along with the transformer volume. Another factor of a proper design for a wide output range LLC is the converter peak voltage gain that is calculated based on an accurate method. The... 

This paper solves the problem of searching a surveillance region and tracking possible radio emitters by multiple unmanned aerial vehicles cooperating through communication links in a decentralized manner. An innovative entropy-based approach is utilized to obtain the routes and tasks (search/track) for the vehicles. Another significant contribution of this research is the assumption of each vehicle being equipped with only one simple and cost-effective direction finding (DF) sensor. The routes and tasks are determined by minimizing a well-defined entropy-based cost function. The proposed surveillance scheme allows one to find a feasible and near-optimal solution. The algorithm’s efficiency... 

In this paper, the problem of cooperative search and tracking by multiple flying vehicles is studied. An algorithm is proposed based on optimal planning by minimizing a suitably defined cost function. In order to define the cost function, three maps are proposed: uncertainty map, detection probability map, and emitter map. In the uncertainty map, the geometrical status of the vehicle with respect to the region is considered and its suitability is measured. The detection probability map is defined such that the group of vehicles can detect new emitters that appear in their sensors’ coverage. Finally, the emitter map is a tool to keep tracking the detected emitters with acceptable error while... 

Nonlinear behavior of functionally graded (FG) sandwich circular sector plates with simply supported radial edges under transverse loading is investigated using the first-order shear deformation theory with von Karman geometric nonlinearity. The nonlinear governing equations are reformulated and solved via single-parameter perturbation and Fourier series methods. Verification is performed by comparing numerical results with the available ones in the literature and the ones obtained via ABAQUS code. The effects of non-linearity, material constant, lay-up, and boundary conditions on bending of FG sandwich sector plates with FG core/homogenous face sheets and metallic core/FG face sheets are... 

Standard-form contracts facilitate the sophisticated public-private partnership (PPP) procurement process. Special care should be taken during the preparation of these documents since any remaining flaws affect subsequent projects. Reviewing the standard-form contract capabilities after its application help to identify its major flaws and improve the contract clauses. This research proposed a novel structured method to address this need and verified its capability. In the proposed method, a comprehensive list of risks is first created for the PPP projects in the specified project environment. The identified risks are prioritised to highlight the priority of the required adjustments in the... 

Ultrafine particles of paracetamol were produced by Rapid Expansion of Supercritical Solution (RESS). The experiments were conducted to investigate the effects of extraction temperature (313353K), extraction pressure (1018MPa), preexpansion temperature (363403K), and postexpansion temperature (273323 K) on particles size and morphology of paracetamol particles. The characterization of the particles was determined by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Liquid Chromatography/Mass Spectrometry (LC-MS) analysis. The average particle size of the original paracetamol was 20.8m, while the average particle size of paracetamol after nanonization via the... 

The first diastereoselective synthesis of spirothiooxindoles is reported via the Michael reaction between thiooxindoles and dibenzalacetones. The reaction was conducted without any catalyst or additive under green conditions, i.e., ethanol as the solvent and at room temperature. In addition, the described robust method benefits from scalability, simple work-up, and column chromatography-free purification. This work demonstrates the art of governing regio- and stereoselectivity, which has been discussed in the light of Density Functional Theory calculations. Our method represents the first synthesis of spiro[cyclohexanone-thiooxindoles] with the relative configuration of the aryl moieties at... 

Accurate depth estimation from monocular images is critical for various applications such as robotics, augmented reality, and autonomous navigation. However, achieving high accuracy while maintaining computational efficiency is a major challenge, particularly for resource-constrained devices. In this paper, we present LightDepth, an approach that leverages curriculum learning to estimate depth efficiently while taking into account resource constraints. It modifies the ground truth sparse depth maps from the KITTI dataset by resizing them to 31 extents during training to reduce sparsity and control complexity. The resulting model achieves comparable accuracy to state-of-the-art large models... 

This paper addresses the problem of optimal state-feedback design for a class of non-linear systems. The method is applicable to all non-linear systems which can be linearised using the method of state-feedback linearisation. The alternative is to use linear optimisation techniques for the linearised equations, but then there is no guarantee that the original non-linear system behaves optimally. The authors use feedback linearisation technique to linearise the system and then design a state feedback for the feedback-linearised system in such a way that it ensures optimal performance of the original non-linear system. The method cannot ensure global optimality of the solution but the global... 

The preparation, characterization and catalytic application of a novel copper-loaded ionic liquid-based periodic mesoporous organosilica (Cu@PMO-IL) are described. The mesoporous structure of the Cu@PMO-IL material is characterized by transmission electron microscopy (TEM) and nitrogen adsorption-desorption analysis. The thermal stability of the material is also determined by thermal gravimetric analysis (TGA). The presence of copper species in the material framework is confirmed by X-ray photoelectron spectroscopy (XPS) and elemental analysis (EA). The catalytic application of Cu@PMO-IL nanocatalyst is then investigated in the Biginelli condensation of different aldehydes with urea and... 

Public procurement for innovation (PPI) is an assertive demand-side innovation policy. However, research is behind in understanding the know-how of designing and implementing successful PPI, particularly in developing economies. This study's primary goal is to provide a conceptual framework of influential factors in designing and implementing a successful PPI. To this aim, we did a case study on some projects under the PPI initiative, defined for Iran's oil industry. Reviewing the corresponding literature and analyzing the case materials, including interviews, observation, and documents, our findings suggest a conceptual framework that includes four categories of influential factors in the... 

Public procurement for innovation (PPI) is an assertive demand-side innovation policy. However, research is behind in understanding the know-how of designing and implementing successful PPI, particularly in developing economies. This study's primary goal is to provide a conceptual framework of influential factors in designing and implementing a successful PPI. To this aim, we did a case study on some projects under the PPI initiative, defined for Iran's oil industry. Reviewing the corresponding literature and analyzing the case materials, including interviews, observation, and documents, our findings suggest a conceptual framework that includes four categories of influential factors in the... 

The solubility of acetaminophen in SuperCritical-Carbon Dioxide (SC- CO 2) with and without menthol as a cosolvent was measured at various temperatures (313, 328 and 343) K, and within pressures ranging from (10 to 25) MPa. It should be stated that the cosolvent, menthol, has chiral isomers with different melting points. Therefore, the effects of both menthol (I) with a lower melting point and menthol (II) with a higher melting point, as cosolvents on the solubility of acetaminophen in SC- CO 2, were studied. The experimental data collected in this work were obtained using a static flow apparatus. The experiments were replicated at least three times and the data reported are the average of... 

Previous in-vivo investigations on the stabilizing efficacy of knee bracing for ACL reconstructed patients have been often limited to 20-30 degrees of knee flexion. In this study, the effectiveness of a uniaxial hinged functional brace to improve the knee stability was assessed at 30, 60 and 90 degrees of knee flexion. Arthrometry tests were conducted on 15 healthy subjects before and following wearing the brace and the tibial displacements were measured at up to 150 N anterior forces. Results indicated that functional bracing has a significant stabilizing effect throughout the range of knee flexion examined (p < 0.05). The rate of effectiveness, however, was not consistent across the... 

In the real world, there are complex decision-making problems in which a variety of intertwined factors and hierarchical structures exist, and it is difficult or impossible to solve these problems using classical methods. The prioritization of circular economy (CE) adoption barriers is one such complex problem that cannot be solved using current classical methods. Hence, in this paper, for the first time, a new method, namely, FBWDS, is developed. FBWDS derives from the combination of fuzzy best–worst method (BWM), fuzzy decision-making trial and evaluation laboratory (DEMATEL), and Supermatrix structure. This proposed method establishes weights of the intertwined factors in hierarchical... 

Solid-State Drives (SSDs) are recently employed in enterprise servers and high-end storage systems in order to enhance performance of storage subsystem. Although employing high speed SSDs in the storage subsystems can significantly improve system performance, it comes with significant reliability threat for write operations upon power failures. In this paper, we present a comprehensive analysis investigating the impact of workload dependent parameters on the reliability of SSDs under power failure for variety of SSDs (from top manufacturers). To this end, we first develop a platform to perform two important features required for study: A) a realistic fault injection into the SSD in the... 

Productivity of gas condensate reservoirs reduces significantly due to the near wellbore condensate/water blockage phenomenon. A novel, permanent solution to alleviate this problem is near wellbore wettability alteration of reservoir rocks to preferentially gas wetting conditions; industrial chemical materials are good candidates for this purpose, because of their eco-friendly characteristics, economical price, and mass production. In this paper, a comparative study is conducted on two industrial fluorinated chemicals, MariSeal 800 and SurfaPore M. Static and dynamic contact angle measurements, spontaneous imbibition, and core flooding tests were conducted to investigate the effect of... 

Benzoins are rapidly oxidised to benzils in high yields by iodic acid supported on alumina under solvent-free conditions and microwave irradiation