Sharif Digital Repository

This study aims to investigate the micromixing performance of three basic types of spatial shaped micromixers. New configurations of T, Y, and oriented Y-spatial mixers were designed with change in the angles of the confluence and the outlet channel to achieve the efficient micromixing. These micromixers offer advantages that are not attainable with the typical types of these mixers. Experimental tests were carried out in the laminar flow regime and the mixing efficiency was evaluated using Villermaux/Dushman test reaction. The geometries of the channels were cylindrical with the length of 30 mm and the diameter of 800 μm. The experimental results show that the angle of outlet channel has a... 

This study aims to investigate the micromixing performance of three basic types of spatial shaped micromixers. New configurations of T, Y, and oriented Y-spatial mixers were designed with change in the angles of the confluence and the outlet channel to achieve the efficient micromixing. These micromixers offer advantages that are not attainable with the typical types of these mixers. Experimental tests were carried out in the laminar flow regime and the mixing efficiency was evaluated using Villermaux/Dushman test reaction. The geometries of the channels were cylindrical with the length of 30 mm and the diameter of 800 μm. The experimental results show that the angle of outlet channel has a... 

Density functional theory method and B3LYP/6-311++G(d,p) level of theory were used to determine the acidity of α-carbon in the hydroxyl derivatives of beta diketones in the gas phase. An investigation of acidity strength in the gas phase indicates that α-carbon of hydroxyl derivatives of beta diketones become stronger acids than the α-carbon of beta diketone itself as their conjugate bases gain more stability via both enolate and hydrogen bond formation. Natural bond orbital and quantum theory of atoms in molecules analyses also confirm the role of hydrogen bond interactions on increasing the acidity of α-carbon of hydroxyl derivatives of beta diketones. © 2020 John Wiley & Sons, Ltd  

Density functional theory method and B3LYP/6-311++G(d,p) level of theory were used to determine the acidity of α-carbon in the hydroxyl derivatives of beta diketones in the gas phase. An investigation of acidity strength in the gas phase indicates that α-carbon of hydroxyl derivatives of beta diketones become stronger acids than the α-carbon of beta diketone itself as their conjugate bases gain more stability via both enolate and hydrogen bond formation. Natural bond orbital and quantum theory of atoms in molecules analyses also confirm the role of hydrogen bond interactions on increasing the acidity of α-carbon of hydroxyl derivatives of beta diketones. © 2020 John Wiley & Sons, Ltd  

Low Grade Heat Driven Multi-effect Distillation and Desalination describes the development of advanced multi-effect evaporation technologies that are driven by low grade sensible heat, including process waste heat in refineries, heat rejection from diesel generators or microturbines, and solar and geothermal energy. The technologies discussed can be applied to desalination in remote areas, purifying produced water in oil-and-gas industries, and to re-concentrate process liquor in refineries.
This book is ideal for researchers, engineering scientists, graduate students, and industrial practitioners working in the desalination, petrochemical, and mineral refining sectors, helping them... 

In this paper, the variational method is employed for minimizing the gain ripple of multi-wavelength fiber Raman amplifiers. The variance of gain spectrum of the fiber Raman amplifier is regarded as the cost function, restriction on total pump power and average gain is given as the constraints of the minimization problem. It is shown that the minimization problem with any necessary constraints on the pump powers, average gain and signal to noise ratio, is reduced to a two-point boundary value problem. The method gives the entire possible local and global solutions. The method is applied to different examples of fiber Raman amplifiers with different lengths from 25 km to 100 km and different... 

In this article, the influences of ferrofluid and magnetic field on the reactive absorption in packed-bed contactors have been investigated. Because of importance of carbon dioxide emission as a global concern, absorption of carbon dioxide was chosen to investigate these effects. In this regard, multitube approach was applied to model the contactor. The simulation results were validated against experimental data reported in the literature in the absence of nanoparticles and magnetic field and good agreement was obtained. Moreover, influences of various operating conditions on the contactor performance were investigated. It was found that for 3.4 vol.% of magnetic nanoparticles (MNPs), the... 

Porous silicon samples were obtained by the electrochemical method and were impregnated with Pd by the electroless process. X-ray photoelectron spectroscopy illustrated that the surface of the samples is oxidized during the palladium deposition. Scanning electron microscopy showed how factors such as morphology and pre-oxidations of porous samples and the plating parameters including Pd-salt concentration, HCl concentration, temperature of the electroless solution and the time of process affect the growth and nucleation of Pd particles. Observations demonstrated that the illumination-assisted process on p-type samples has a drastic effect on the growth of palladium. Hydrogen sensing of these... 

Porous silicon samples obtained from p+-type silicon wafers were impregnated with Pd by electroless process in different conditions. Scanning electron microscopy was used to study the change in the features of the surface after palladium plating. Results showed how the factors like Pd-salt concentration, HCl concentration, temperature of the electroless solution and the time of process affect on the growth and nucleation of Pd particles. Observations demonstrated that illumination-assisted process and pre-oxidation of the surface before process have drastic effect on the growth of palladium. Variation of the electrical resistance in the presence of diluted hydrogen at room temperature... 

Van der Waals (vdW) heterostructures of two-dimensional monolayers are a relatively new class of materials with highly tunable band alignment, bandgap energy, and bandgap transition type. In this study, we performed density functional theory calculations to investigate how a vdW heterostructure of heptazine-based graphitic carbon nitride (hg-C3N4) and graphitic zinc oxide (g-ZnO) monolayers is formed (hg-C3N4/g-ZnO). This heterostructure is a potential solar-driven photocatalyst for the water-splitting reaction. Upon the formation of the heterostructure, a type-I indirect bandgap (Eg = 2.08 eV) is created with appropriate conduction band minimum and valence band maximum levels relative to... 

Trucking plays a vital role in economic development in every country, especially countries where it serves as the backbone of the economy. The fast growth of economy in Iran as a developing country has also been accompanied by an alarming situation in terms of fatalities in truck-involved crashes, among the drivers and passengers of the trucks as well as the other vehicles involved. Despite the sizable efforts to investigate the truck-involved crashes, very little is known about the safety of truck movements in developing countries, and about the single-truck crashes worldwide. Thus, this study aims to uncover significant factors associated with injury severities sustained by truck drivers... 

Speech enhancement in real-time applications improves the quality and intelligibility of the speech and reduces communication fatigue. Nowadays, due to reactivity of the systems and spread of online real-time applications, including VoIP, state-space models have been used broadly. This paper presents a speech enhancement method based on adaptive Bayesian-Kalman filter and Bayesian-MAP estimation to improve the performance and the quality of the enhancement procedure. The enhancement method includes a combination of Bayesian-Kalman filter for noise reduction and Bayesian-MAP estimation for parameter estimation of the lost speech segments. Performance evaluation and result of the proposed... 

In this paper stabilizing unstable periodic orbits (UPO) in a chaotic fractional order system is studied. Firstly, a technique for finding unstable periodic orbits in chaotic fractional order systems is stated. Then by applying this technique to the fractional van der Pol and fractional Duffing systems as two demonstrative examples, their unstable periodic orbits are found. After that, a method is presented for stabilization of the discovered UPOs based on the theories of stability of linear integer order and fractional order systems. Finally, based on the proposed idea a linear feedback controller is applied to the systems and simulations are done for demonstration of controller performance... 

This study attempts to investigate a new way for cooling PV cell using natural vapor as coolant. The performance of solar cell was examined on simulated sunlight. The natural vapor encountered backside of PV cell vertically in various distribution and different mass flow rates. Also, the effect of natural vapor temperature in cooling performance was analyzed. Results indicated that the temperature of PV cell drops significantly with increasing natural vapor mass flow rate. In detail, the PV cell temperature decreased about 7 to 16°C when flow rate reaches 1.6 to 5grmin-1. It causes increasing electrical efficiency about 12.12% to 22.9%. The best performance of PV cell can be achieved at high... 

The short history of the philosophy of technology has witnessed different and sometimes contradictory views about the relationship between society and modern technology, from the approaches that believe in technological determinism to those which believe in the deep influence of society on technology [5]. One famous example of technological determinism has emerged from autonomist approaches toward technology. In this approach, the development of modern technology is based on a special kind of internal logic and cannot be controlled by any element other than modern technology itself, such as human society. The autonomous approach, as seen in the works of the French thinker Ellul [8],... 

The emergence of COVID-19 has been changing in the world since 2020 and prompted social, cultural, and economic systems to adjust their structures, routines, and processes. The economic aspects of the pandemic appeared soon, and many industries changed their workflow and procedures through a mandatory or recommended quarantine. Knowing the impact of COVID-19 on different areas of construction projects, concerns and considerations, and preparedness levels of corresponding entities helps construction managers to cope with the new situation. The main purpose of this study was to investigate the impact of COVID-19 on construction professionals’ perceptions over time. For this purpose, a... 

Tailoring band gap energies and band alignment types of heterogeneous photocatalysts is critical for their performance in particular applications. Here, by performing calculations in the framework of density functional theory, we study the role of interface in control and tuning band gap and band alignment characteristics of two-dimensional van der Waals (vdW) heterostructures of monolayers of triazine graphitic carbon nitride (tg-C3N4) and Janus tungsten sulfide selenide (WSSe) by varying either S or Se atomic layers. Then we investigate how the vdW heterostructures (i.e., tg-C3N4/SWSe and tg-C3N4/SeWS) over both tg-C3N4 and WSSe surface sides can serve as an efficient water-splitting... 

Optical fiber doped with lead salts quantum dots (QDs) of different radii, has previously been proposed as a wide-band amplifier in the optical communication range. The emission and absorption spectra of QDs are size-dependent. Optical fiber amplifier doped with QDs of different sizes is an inhomogeneous gain medium. This inhomogeneity is the principle of operation of wide-band quantum-dot-doped fiber amplifiers (QDFAs). To study the effects of inhomogeneity such as spectral hole burning on the amplifier behavior, a fiber amplifier with an arbitrary size distribution of QDs is taken into consideration. The light propagation equations and rate equations for the inhomogeneous medium are... 

This book focuses on a central question in the field of complex systems: Given a fluctuating (in time or space), uni- or multi-variant sequentially measured set of experimental data (even noisy data), how should one analyse non-parametrically the data, assess underlying trends, uncover characteristics of the fluctuations (including diffusion and jump contributions), and construct a stochastic evolution equation?
Here, the term "non-parametrically" exemplifies that all the functions and parameters of the constructed stochastic evolution equation can be determined directly from the measured data.
The book provides an overview of methods that have been developed for the analysis of...