Sharif Digital Repository

We introduce the capture effect concept in microwave photonic links (MWPLs) for the first time to our knowledge. The capture effect or the small-signal suppression is the change in the amplitude ratio of the two signals between input and output of the intensity-modulation direct-detection (IMDD) MWPLs. An analytical explanation of the performance of external IMDD MWPLs due to the effects of nonlinearity combined with sum of several input sinusoidal signals is given.We have investigated the suppression of a weaker signal in these links. General analytic expression for the small-signal suppression is derived using a nonlinear analytical approach. We show that the small-signal suppression is... 

Transition metal lithium orthosilicates are of interest as cathode materials for lithium batteries. Density functional theory (DFT) calculations were performed to evaluate the structural and electrochemical properties of the different polymorphs of Li2MnSiO4. Our computational studies predict superior properties for the Pmn21 polymorph even after extraction of two Li per formula unit. We state that the shortcomings observed for Li2MnSiO4 as a cathode are caused by two mechanisms. Switching of the magnetic state occurs during the first cycles. The subsequent transition, under delithiated conditions, from the Pmn21 or Pmnb polymorphs to the electrochemically weakest P21/n polymorph is the... 

A new scheme for investigating electromagnetically induced grating in four-level cascade-Type of 87Rb cold atoms is presented. The novel result indicates that the diffraction efficiency of phase grating is dramatically enhanced due to the presence of an RF-driven field and a diffraction efficiency up to 34% can be obtained. Furthermore, it is found that the frequency detuning of the applied laser fields with the corresponding atomic transition and the interaction length can improve the efficiency of the phase grating in the present atomic model. This work has potential applications in all-optical communication processes  

A phenolic-based ionic liquid (IL), 1-(2-hydroxyethyl)-2,3-dimethylimidazolium phenoxide has been introduced for 1.5 molar carbon dioxide (CO2) absorption at ambient conditions without using special methodologies or precautions. The structure of the IL was characterized by various methods such as FT-IR, 1H NMR, 13C NMR, elemental analysis (EA) and thermogravimetric analysis (TGA). The ability of this IL for CO2 uptake reaches to its maximum value after 2 h. The IL has been reused fr several times with constant efficiency. Density functional theory (DFT) calculations at the B3LYP/6-311++G∗∗ level of calculation have been carried out to gain more structural knowledge... 

Motivated by recent laboratory and field observations, this paper reports the first quantitative measurements of the stabilization phase of interfacial instability in a two-layer fluid in surface wave motion. The instability results from the formation of a resonant triad between the surface wave and noise-level sub-harmonic interfacial waves. To exclude the effects of interfacial mixing on the interaction, the experiments were carried out with immiscible fluids. Carrying out a resonant interaction analysis to the third order of nonlinearity using a Lagrangian formulation, we also show for the first time that the three-wave resonance is inherently accompanied by a harmonic four-wave resonant... 

Both theoretical and experimental results of an optical beam shaping system are investigated in this report. The described system is a two-stage beam shaping device including a fiber-bundle and a prism-duct. A source light is used to illuminate the fiber-bundle and the image of output beam is captured by a CCD camera. The fiber-bundle output beam shape shows a linear arrangement of circular spots lights, which are placed in a rectangular cross section of about 21.37 mm×2.44 mm. In another study, the photograph picture of the prism output beam is taken by a digital camera. The prism output beam cross section is a square shape with a dimension of about 4×4 mm2. According to the experimental... 

In this work, we present a theoretical investigation of the thermal conductivity of hydrogen-passivated graphene antidot lattices. Using a fourth nearest-neighbor force constant method, we evaluate the phonon dispersion of hydrogen-passivated graphene antidot lattices with circular, hexagonal, rectangular and triangular shapes. Ballistic transport models are used to evaluate the thermal conductivity. The calculations indicate that the thermal conductivity of hydrogen-passivated graphene antidot lattices can be one fourth of that of a pristine graphene sheet. This reduction is stronger for right-triangular and iso-triangular antidots among others, all with the same area, due to longer... 

Experimental and theoretical results of a two-stage beam shaping system based on a flexible plastic fiber-bundle and a prism duct are described in this study. An imaging technique is used to investigate the divergence effect on the output beam images and intensity profiles. Photograph pictures of the output beam at different axial distances are taken by a digital camera and the image data is converted into a response curve and presented in this study. According to the experimental results, the propagation in the free space transforms a square beam with a hat-top intensity distribution into a rectangular beam with a conical intensity distribution. For theoretical investigations, using VOB... 

Abstract: A metal-free method for activation of hydrogen peroxide (H2O2) is introduced using piperidinium trifluoroacetate (PPHTFA) ionic liquid as catalyst. The catalyst has been used for selective oxidation of thioanisole to its corresponding sulfoxide at room temperature. It was found that the selectivities were reduced by increasing the reaction temperature. In this work, no organic solvents or metallic salts were used for activation of H2O2. Mechanistic studies suggested that the reaction proceeds via in situ formation of trifluoro hydroperoxy species as an active catalytic intermediate. Formation of the catalytic intermediate was screened by NMR, IR and Mass Spectroscopy analysis.... 

In this study, the theoretical investigation of a novel heat pump assisted humidification-dehumidification desalination system has been carried out. The conventional dehumidifier of the humidification-dehumidification system was removed and the evaporator of the heat pump was utilized for direct dehumidification of air. Besides, the heat pump condenser was used as the saline water heater of the humidification-dehumidification cycle. First, the sizes of the components were calculated at design conditions for fixed input operational conditions namely the ambient air temperature, relative humidity, and inlet saline water temperature. However, the input operating conditions vary at off-design... 

This article presents the variation of structural, electronic, thermal and optical properties of a halide perovskite CsYbBr3with increasing pressure, employing density functional theory. The pressure effect was determined in range of 0-15 GPa. In which stability of CsYbBr3remains valid, as, verified from negative values of enthalpy of formation and phonon dispersion curves. A significant change was observed in lattice constant, bond lengths, bulk modulus and its pressure derivative, volume and ground state energy, with increasing pressure. The calculated electronic properties presented CsYbBr3as a semiconductor with direct band gap of 3.61 eV. However, pressure rise shift the Yb-d states... 

In this article, we report the computational examination of the impact of hydrogen bonding (HB) on the stereoselectivity of a series of Diels-Alder (DA) reactions. Four different types of diene/dienophile couples were studied including (a) cyclopenta-2,4-dien-1-ol and heteroatom-substituted cyclopentenes, (b) substituted cyclopentadienes andN-protonated 2,5-dihydro-1H-pyrrole, (c) furan andN-protonated 5-azabicyclo[2.1.1]hex-2-ene, and (d)N-protonated cyclopenta-2,4-dien-1-amine and α,β-unsaturated carbonyl compounds. These systems were designed such that the HB can only exist in theexoreaction pathway. The optimized structures of the transition states (TSs) and products, along with the... 

Interactions of α-D-glucose with gold, silver, and copper metal clusters are studied theoretically at the density functional theory (CAM-B3LYP) and MP2 levels of theory, using trimer clusters as simple catalytic models for metal particles as well as investigating the effect of cluster charge by studying the interactions of cationic and anionic gold clusters with glucose. The bonding between α-D-glucose and metal clusters occurs by two major bonding factors; the anchoring of M atoms (M = Cu, Ag, and Au) to the O atoms, and the unconventional M.H-O hydrogen bond. Depending on the charge of metal clusters, each of these bonds contributes significantly to the complexation. Binding energy... 

Gold nanoparticles are widely used as high efficient photon-thermal energy converters in a broad range of applications. This paper presents a theoretical investigation on using the optothermal properties of gold nanoparticle arrays to generate nanoscale molten and rubbery regions on the surface of an amorphous polymeric film. Nanoparticles are assumed to be embedded in a transparent silica layer and illuminated with a 7.5 ns pulsed laser at 532 nm. Simulation results are presented for systems with single gold nanoparticles, dimers and chains. Both electromagnetic and thermal interaction between nanoparticles are found to be important factors in determining the result of surface processing.... 

Understanding the nature of interaction between metal nanoparticles and biomolecules such as amino acids is important in the development and design of biosensors. In this paper, binding of M3 clusters (M = Au, Ag and Cu) with neutral and anionic forms of histidine amino acid was studied using density functional theory (DFT-B3LYP). It was found that the interaction of histidine with M3 clusters is governed by two major bonding factors: (a) the anchoring N-M and O-M bonds and (b) the nonconventional N-H⋯M and O-H⋯M hydrogen bonds. The nature of these chemical bonds has been investigated based on quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. In the next... 

Fe3O4 magnetic nanoparticles (MNPs) were prepared by co-precipitation method. The nanoparticles were silica coated using TEOS, and then modified by the polymeric layers of polypropylene glycol (PPG) and polyethylene glycol (PEG). Finally, the core-shell samples were decorated with Ag, Au, and Cu nanoparticles. The products were characterized by vibrating sample magnetometry (VSM), TGA, SEM, XRD, and FTIR methods. The antibacterial activity of the prepared samples was evaluated in inactivation of E. coli and S. aureus microorganisms, representing the Gram-negative and Gram-positive species, respectively. The effect of solid dosage, bacteria concentration and type of polymeric modifier on the... 

In the present work, the spray characteristics of bio-ethanol and its blends have been experimentally and theoretically investigated. To have a comprehensive study, the effects of ambient condition and injection pressure on the spray of different blends have been considered. Macroscopic and microscopic characteristics of spray such as tip penetration length, cone angle, projected area, volume, Sauter Mean Diameter (SMD), and Ohnesorge number are investigated precisely. Besides, air entrainment and atomization analyses have been carried out to improve mixture formation process. Using curve fitting and least squares method, theoretical correlations have been suggested in such a way to predict... 

Polymer-layered silicate nanocomposites have been observed to demonstrate enhanced mechanical properties particularly at low weight fractions of silicate. Experimental and theoretical investigations reveal that numerous structural parameters strongly influence the modulus of such nanocomposites. A multiscale micromechanical model is developed which considers a wide range of different affecting parameters including the particle aspect ratio, the number of silicate layers per stack, the d-spacing ratio between the layers, the penetration of polymer chains along silicate sheets, the intercalation feature, and the particle volume fraction. The developed model illustrates the accuracy and... 

Optical fiber torsion sensors have significant importance for structural health monitoring. In this paper, an optical fiber torsion sensor based on computer-generated-hologram (CGH) is proposed and investigated theoretically. In the proposed structure a dual mode fiber (DMF) is used as a sensing element. An acoustic source can be employed to induce a fiber grating. The acoustic induced fiber grating (AIFG) causes the fundamental LP01 mode of DMF couples to LP11 o and LP11 e fiber modes. In the presence of torsion in DMF, the profiles of LP01, LP11 o and LP11 e modes rotate relative to the absence of fiber torsion. At the end of DMF a suitable CGH can be employed to resolve spatially the... 

Prediction of compressor performance is a basic step in design of this turbomachine, while designer can optimize plan by considering various conditions and calculating machine performance. Flow field in centrifugal compressor is threedimensional and intricate. Since 2-D and 3-D methods are very costly, consequently the mean line method usually is used for predicting compressor performance. The energy loss coefficients are used for this method. Because of the intricacy in flow and analysis of losses, most energy loss coefficients are attained by experimental procedures, however just some of them are determined according to theory and nature of the flow field. The purpose of this work is...