Sharif Digital Repository

Servo drive systems require a fast dynamic response for position control applications. Conventional cascade control structure has sluggish response due to bandwidth limitations on speed and current control loop. To achieve a fast output response, model reference adaptive control methods can be used to remove the dynamics of inner control loops. In this paper, feed-forward signals are generated using model predictive control which is combined with the conventional cascade structure. Using this approach, a fast transient response and satisfactory tracking ability can be achieved. The proposed control configuration is verified by the simulation results  

The lipase-immobilized polyethyleneimine (PEI)- and polyacrylic acid (PAA)–coated magnetic silica nanocomposite particles (L-PEI-MS and L-PAA-MS, respectively) were prepared and applied at various transesterification reaction conditions. The reactions were carried out with soybean, sunflower, canola, and palm oils along with methanol or ethanol in the solvent-free and n-hexane systems. The highest fatty acid methyl ester (FAME) and fatty acid ethyl ester (FAEE) synthesis yields were obtained from the transesterification of palm oil, i.e., almost 7.7–10.2% higher than other oils. At the constant reaction conditions, the application of ethanol leads to higher (6.0–8.7%) reaction yields in... 

In this study, apatite formation ability on TiO2 nanotubes (TNTs) synthesized by anodizing process were compared with TNTs decorated by MnO nanoparticles. The MnO nanoparticles used for decoration process were fabricated via thermal decomposition method. At first, it was strived to find the optimal condition of anodizing process and the effect of applied voltages (15 V, 20 V, and 25 V) and process times (15 min, 20 min, and 25 min) on the diameter of the synthesized TNTs was investigated. Results of microscopic characterizations showed that the completely uniform structure of nanotubes with a diameter in the range of about 100–130 nm was achieved after 20 min of anodizing process at an... 

A cost-effective design of reusable enzyme-functionalized particles with better catalytic activity is of great scientific interest due to their applications in a wide range of catalytic reactions in several industrial processes. In this work, a systematic approach for preparing amine-functionalized magnetic nanocomposite particles through the surface modification of core/shell type Fe3O4 cluster@SiO2 particles by the small molecules of 3-(2-aminoethyl)aminopropyltrimethoxysilane (AAS) or the large molecules of polyethyleneimine (PEI) with two different molecular weights, as the support materials for enzyme immobilization, has been demonstrated. The functional... 

A facile approach for the preparation of core-shell structured poly(acrylic acid) (PAA)-coated Fe3O4 cluster@SiO2 nanocomposite particles as the support materials for the lipase immobilization is reported. Low- or high-molecular-weight (1800 and 100 000, respectively) PAA molecules were covalently attached onto the surface of amine-functionalized magnetic silica nanoacomposite particles. The successful preparation of particles were verified by scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA), zeta potential measurement, and Fourier-transform infrared (FTIR) techniques. Once lipase is covalently... 

This study reports the importance of physicochemical characteristics of the core-shell structured polymer-coated Fe3O4 cluster@SiO2 nanocomposite particles for designing the biocatalysts used for transesterification of soybean oil. To demonstrate this issue, two different types of polymer molecules such as polyethylenimine (PEI) and polyacrylic acid (PAA) each with two different molecular weights are employed. The highest fatty acid methyl esters (FAMEs) synthesis yield values are achieved by the lipases immobilized onto the low- and high-molecular-weight PEI-coated particles as compared to those of the low- and high-molecular-weight PAA-coated particles (i.e., ∼64.8% and ∼73.1% versus... 

γ-Alumina is used to catalyze the Cannizzaro reaction in the absence of any base under microwave irradiation in high yields. In the case of terephthalaldehyde the reaction is carried out with high selectivity  

Enolizable ketones have been reacted in a one-pot method with aromatic aldehydes, acetyl chloride and acetonitrile at room temperature in the presence of SnCl4/SiO2 to furnish the corresponding β-acetamidoketones in improved yields. Acetylation of an aromatic hydroxyl group was observed while using 4-hydroxybenzaldehyde or vanillin and the corresponding β-acetamidoketones were isolated in an excellent yield  

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer assumptions and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order Adams predictor-corrector method. The free vortex and uniform velocity profiles are applied for the tangential and axial velocities at the inlet region, respectively. Due to the lack of experimental data for swirling flows in converging nozzles, the developed model is validated against the numerical simulations. The... 

The governing equations of two-dimensional steady density currents are solved numerically using a finite volume method. The v2̄-f turbulence model, based on standard k - s model, is used for the turbulence closure. In this method, all Reynolds stress equations are replaced with both a transport equation for v2̄ and an elliptic relaxation equation for f, a parameter closely related to the pressure strain redistribution term. The Simple-C procedure is used for pressure-velocity coupling. In addition, Boussinesq's approximation is used to obtain the momentum equation. The computed height of the progressive density current is compared to the measured data in the literature, resulting in good... 

The deposition behavior of fine sediment is an important phenomenon, and yet unclear to engineers concerned about reservoir sedimentation. An elliptic relaxation turbulence model (v2̄ - f model) has been used to simulate the motion of turbid density currents laden whit fine solid particles. During the last few years, the v2̄ - f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proved that the v2̄ - f model to be superior to other RANS methods in many fluid flows where complex flow features are present. Due to low Reynolds number turbulence of turbidity current,(its critical Reynolds... 

In this paper, an analytical solution for steady creeping motion of viscoelastic drop falling through a viscous Newtonian fluid is presented. The Oldroyd-B model is used as the constitutive equation. The analytical solutions for both interior and exterior flows are obtained using the perturbation method. Deborah number and capillary numbers are considered as the perturbation parameters. The effect of viscoelastic properties on drop shape and motion are studied in detail. The previous empirical studies indicated that unlike the Newtonian creeping drop in which the drop shape is exactly spherical, a dimpled shape appears in viscoelastic drops. It is shown that the results of the present... 

In this paper, creeping motion of a viscoelastic drop falling through a Newtonian fluid is investigated experimentally and analytically. A polymeric solution of 0.08 % xanthan gum in 80:20 glycerol/water and silicon oil is implemented as the viscoelastic drop and the bulk viscous fluids, respectively. The shape and motion of falling drops are visualized using a high speed camera. The perturbation technique is employed for both interior and exterior flows, and Deborah and capillary numbers are considered as perturbation parameters up to second order. The product of Deborah and capillary numbers is also used as a perturbation parameter to apply the boundary condition on the deformation on the... 

In this paper, we consider the problem of minimizing the uplink delays of users in a 5G cellular network. Such cellular network is based on a Cloud Radio Access Network (CRAN) architecture with limited fronthaul capacity, where our goal is to minimize delays of all users through an optimal resource allocation. Earlier works minimize average delay of each user assuming same transmit power for all users. Combining Pareto optimization and Markov Decision Process (MDP), we show that every desired balance in the trade-off among infinite-horizon average-reward delays, is achievable by minimizing a properly weighted sum delays. In addition, we solve the problem in two realistic scenarios;... 

Microwave induced Cannizzaro reaction, which was performed in presence of neutral γ-alumina as a polymeric catalyst, was discussed. Cannizzaro reaction was carried out on alumina surface and other unknown products were also obtained. Solvent extraction method was utilized to isolate mild and selective benzyl alcohol and carboxylic acids  

A well known method to reduce the intrinsic complexity of Multiple Input Multiple Output (MIMO) systems is to choose a subset of available antennas which have stronger links than the others, in order to perform the specified MIMO algorithm. The data resulted from the antenna selection process (at the receiver side) is sent back to the transmitter side via a feedback channel. There seems to be a need to reduce the number of feedack bits, specially when the number of antennas is not small. In this paper, we investigate the problem of reducing the number of feedback bits in antenna selection techniques. We've proposed two methods using vector quantization techniques to perform feedback bit... 

Nowadays, deployment of peer-to-peer video streaming systems over wireless mesh networks has attained raising popularity among large number of users around the world. In this paper, we present an efficient peer-to-peer live video streaming architecture over multi-hop wireless mesh networks. In our proposed architecture, we take the physical topology of network into account and based on a distributed distributed locality-aware neighbor selection algorithm in the overlay construction phase, we generate an efficient mesh-based overlay on top of wireless mesh networks. In locality-aware neighbor selection algorithm, instead of choosing randomly, peers find their best neighbors based on their... 

Standard sparse decomposition (with applications in many different areas including compressive sampling) amounts to finding the minimum ℓ 0-norm solution of an underdetermined system of linear equations. In this decomposition, all atoms are treated 'uniformly' for being included or not in the decomposition. However, one may wish to weigh more or less certain atoms, or, assign higher costs to some other atoms to be included in the decomposition. This can happen for example when there is prior information available on each atom. This motivates generalizing the notion of minimal ℓ 0-norm solution to that of minimal weighted ℓ 0-norm solution. On the other hand, relaxing weighted ℓ 0-norm via... 

Precipitation, aggregation, and breakup of asphaltene particles are studied under natural depletion and nitrogen injection processes by means of high pressure filtration and a photographic procedure coupled with image analysis. Filtration results show that nitrogen destabilizes asphaltenes extremely, and the problem is more severe for heavier crude samples. Bimodal histograms of particle size distribution show two agglomeration mechanisms: cluster aggregation dominant around bubble point pressure and diffusion limited far away. The fractal structure of aggregates is also altered by gas injection; it is observed that the flocculent masses grow in size and become more compact and organized...