Sharif Digital Repository

5-Ammonium valeric acid (AVA) is a frequently used additive in the preparation of lead halide perovskites. However, its microscopic role as passivating, cross-linking, or templating agent is far from clear. In this work, we provide density functional theory-based structural models for the Ruddlesden-Popper (RP) phases of AVA2(CH3NH3)n-1PbnI3n+1 for n = 1, 2, and 3 and validate with experimental data on polycrystalline samples for n = 1. The structural and electronic properties of the AVA-based RP phases are compared to the ones of other linker families. In contrast to aromatic and aliphatic spacers without additional functional groups, the RP phases of AVA are characterized by the formation... 

This paper is concerned with a quasi-3D design method for the radial and axial diffusers of a centrifugal compressor on the meridional plane. The method integrates a novel inverse design algorithm, called ball-spine algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain, of which unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, unknown walls are composed of a set of virtual balls that move freely along specified directions called spines. The difference between target and current pressure distributions causes the flexible boundary to deform... 

This paper describes a new quasi-3D design method for centrifugal compressor impeller. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a quasi-3D analysis. Euler equation is solved on the impeller meridional plane. The unknown boundaries (hub and shroud) of numerical domain are iteratively modified by BSA until a target pressure distribution in flow passage is reached. To validate the quasi-3D analysis code, existing compressor impeller is investigated experimentally. Comparison between the quasi-3D analysis and the experimental results shows good agreement. Also, a full 3D Navier-Stokes code is used to analyze the existing and designed compressor... 

Inverse design in external flow regimes usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this research, a novel iterative inverse design method is developed for inviscid subsonic and transonic external flow regimes. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a 2D inviscid analysis code. The Euler equations are solved for a physical domain of which some unknown boundaries are iteratively modified via BSA until a prescribed pressure distribution is reached. In BSA, the unknown walls are composed of a set of virtual balls that move freely along the specified directions called... 

In this paper, we analyze a Dynamic Object Manipulation (DOM) problem; throwing upward and catching a disc using two planar manipulators. The manipulators control the disc xy position dynamically and use its angular movement as a free parameter. We use a simple model for the system. Each manipulator has three links and three active joints. In addition, the disc has considerable radius and mass. Therefore, we design a simple mechanism in the palm to damp a portion of the impact. © 2006 IEEE  

In this paper, we try to interpret "Duality of Dynamic Locomotion and Dynamic Object Manipulation". Since our main goal in this paper is to offer the duality concept and to validate it with a case study, we deal with the problem in a simple and abstract system. As a case study, we describe the duality between the problem of 2D dynamic object manipulation of a sphere using two planar manipulators and 2D dynamic locomotion of lower part of a biped robot. Having obtained the equations of dynamic object manipulation, we change the boundary conditions of the problem in such a way that both radius and mass of sphere object tend to infinity. Simultaneously, both of size and mass of manipulators'... 

In this research, centrifugal compressor of a gas turbine is investigated experimentally and numerically. Operation line of the compressor as a component of the gas turbine is obtained experimentally by measurements of impeller rotational speed, and flow parameters at the compressor inlet and outlet during the gas turbine operation. The flow field inside the impeller and diffusers are analyzed numerically using a full 3D Navier-Stokes program with SST turbulence model. Boundary conditions for the numerical simulation are specified from the experimental measurements. The operation line of the compressor is obtained numerically, which is compared with that of the experimental results, and... 

This paper is concerned with a quasi-3D design method for centrifugal compressor impeller in the meridional plane. The method links up a novel inverse design algorithm, called Ball-Spine Algorithm (BSA), and a quasi-3D analysis code. The Euler equation is solved on the meridional plane for a numerical domain of which some unknown boundaries (hub and shroud) are iteratively modified under the BSA until a prescribed pressure distribution is reached. In BSA, the unknown walls are composed of a set of virtual balls that move freely along the specified directions called spines. The difference between target and current pressure distribution causes to deform flexible boundary at each modification... 

The transformation of gibbsite to α-alumina occurs in the range 1100 to 1300°C. The higher the calcination temperature, the larger the crystallites and this leads to abnormal grain growth. The main goal of this research was to reduce the transformation temperature of gibbsite to α-alumina by reducing the gibbsite particles size. The sodium content of the gibbsite used in the study was reduced to less than 0.1% by washing it in HCl solution. It was then ground in a fast mill at ambient conditions for different times then calcined at different temperatures. The microstructure, particles size and thermal behaviour of the samples were examined with SEM, XRD, XRF, PSA and STA, respectively. In a... 

In this research, the parameters affecting the Nusselt number of a generator rotor and stator under varying heat transfer rate are experimentally studied. In spite of the stator having no grooves, the rotor has four large triangular grooves. The temperature and then heat transfer rate of the rotor and stator are experimentally measured in three longitudinal and two angular positions. First, the effect of axial Reynolds number and rotor rotational speed on the rotor and stator Nusselt number with constant heat transfer rate ratio is studied. The range of the axial Reynolds number and rotational speed used is from 4000 to 30,000 and from 300 to 1500 rpm, respectively. Next, the effect of... 

The current study used the horizontal slices method to develop a new formulation to calculate active pressure on retaining walls. In this method, the failure wedge is assumed to be circular in cohesive-frictional soil. In addition to the formula, graphs are provided to determine the center and radius of failure without need for calculation to determine the pressure exerted on the retaining wall. A comparison of the results of the proposed method with previous methods shows that the active pressure calculated using a circular failure wedge was higher than when using a plate failure wedge; confirming the importance of the circular failure wedge. The proposed method can calculate the shear... 

The transformation of gibbsite to α-alumina occurs in the range 1100 to 1300°C. The higher the calcination temperature, the larger the crystallites and this leads to abnormal grain growth. The main goal of this research was to reduce the transformation temperature of gibbsite to α-alumina by reducing the gibbsite particles size. The sodium content of the gibbsite used in the study was reduced to less than 0.1% by washing it in HCl solution. It was then ground in a fast mill at ambient conditions for different times then calcined at different temperatures. The microstructure, particles size and thermal behaviour of the samples were examined with SEM, XRD, XRF, PSA and STA, respectively. In a... 

There is a long-standing question about the molecular configuration of interfacial water molecules in the proximity of solid surfaces, particularly carbon atoms, which plays a crucial role in electrochemistry and biology. In this study, the dielectric, structural, and dynamical properties of confined water placed between two parallel graphene walls at different interdistances from the angstrom scale to a few tens of nanometer have been investigated using molecular dynamics. For the dielectric properties of water, we show that the dielectric constant of the perpendicular component of water drastically decreases under sub-2-nm spatial confinement. The dielectric constant data obtained through... 

In this paper, we aim at an integrated approach to Dynamic Biped Walking (DBW) and Dynamic Object Manipulation (DOM) at an abstract level. To this end, we offer a unified and abstract concept with a dual interpretation as a DOM and as a DBW system. We validate the proposed approach by using a set of simulations on an illustrative case study and show how it can be used in modeling as well as design of planning and control algorithms for DOM and DBW systems. In the case study, we describe the proposed approach and show its dual interpretation by identifying the relations between 2D dynamic object manipulation of a disc using two planar manipulators and 2D dynamic object locomotion of lower... 

There is a long-standing question about the molecular configuration of interfacial water molecules in the proximity of solid surfaces, particularly carbon atoms, which plays a crucial role in electrochemistry and biology. In this study, the dielectric, structural, and dynamical properties of confined water placed between two parallel graphene walls at different interdistances from the angstrom scale to a few tens of nanometer have been investigated using molecular dynamics. For the dielectric properties of water, we show that the dielectric constant of the perpendicular component of water drastically decreases under sub-2-nm spatial confinement. The dielectric constant data obtained through... 

In this investigation, the Flexible String Algorithm (FSA) used before for the inverse design of 2D subsonic ducts is developed and applied for the inverse design of subsonic and supersonic ducts with and without normal shock waves. In this method, the duct wall shape is changed under a novel algorithm based on the deformation of a virtual flexible string in a flow. Deformation of the string due to the local fl.ow conditions resulting from changes in the wall geometry is performed until the target shape satisfying the. prescribed walls pressure distribution is achieved. The flow field at each shape modification step is analyzed using an Euler equation solution by the. A USM method. Some...