Sharif Digital Repository

Accurate knowledge of pure hydrocarbon and natural gas viscosity is essential for reliable reservoir characterization and simulation as well as economic design of natural gas processing and transport units. The most trustable sources of pure hydrocarbon and natural gas viscosity values are laboratory experiments. When there is no available experimental data for the required composition, pressure, and temperature conditions, the use of predictive methods becomes important. In this communication, a novel approach was proposed to develop for prediction of viscosity of pure hydrocarbons as well as gas mixtures containing heavy hydrocarbon components and impurities such as carbon dioxide,... 

A numerical study on mixing/segregation phenomena in a pressurized fluidized bed with large particles of Geldart D type of binary density but same diameter with high velocity gas was performed by the use of discrete particle simulation. Particle mixtures are composed of spherical particles with 2mm diameter and 1g/cm3 flotsam density and different jetsam densities of 1.25, 2 and 2.5g/cm3 with jetsam volume fraction of 0.5. The particles are initially packed approaching perfect mixing state in a rectangular bed and then fluidized by gas uniformly injected at the bottom of the bed. Effect of increase of pressure and density ratio was investigated and mixing/segregation behavior is discussed in... 

A sonochemistry-based synthesis method was used to produce nanocrystalline nickel oxide powder with ∼20 nm average crystallite diameter from Ni(OH)2 precursor. Ultrasound waves were applied to the primary solution to intensify the Ni(OH)2 precipitation. Dried precipitates were calcined at 320 °C to form nanocrystalline NiO particles. The morphology of the produced powder was characterized by transmission electron microscopy. Using sonochemical waves resulted in lowering of the size of the nickel oxide crystallites. FT-IR spectroscopy and X-ray diffraction revealed high purity well-crystallized structure of the synthesized powder. Photoluminescence spectroscopy confirmed production of a wide... 

This paper presents a structured dictionary-based model for hyperspectral data that incorporates both spectral and contextual characteristics of spectral samples. The idea is to partition the pixels of a hyperspectral image into a number of spatial neighborhoods called contextual groups and to model the pixels inside a group as members of a common subspace. That is, each pixel is represented using a linear combination of a few dictionary elements learned from the data, but since pixels inside a contextual group are often made up of the same materials, their linear combinations are constrained to use common elements from the dictionary. To this end, dictionary learning is carried out with a... 

Permeability as a fundamental reservoir property plays a key role in reserve estimation, numerical reservoir simulation, reservoir engineering calculations, drilling planning, and mapping reservoir quality. In heterogeneous reservoir, due to complexity, natural heterogeneity, non-uniformity, and non-linearity in parameters, prediction of permeability is not straightforward. To ease this problem, a novel mathematical robust model has been proposed to predict the permeability in heterogeneous carbonate reservoirs. To this end, a fairly new soft computing method, namely least square support vector machine (LSSVM) modeling optimized with coupled simulated annealing (CSA) optimization technique... 

A new neutron spectrum unfolding code TGASU (Two-steps Genetic Algorithm Spectrum Unfolding) has been developed to unfold the neutron spectrum from a pulse height distribution which was calculated using the MCNPX-ESUT computational Monte Carlo code. To perform the unfolding process, the response matrices were generated using the MCNPX-ESUT computational code. Both one step (common GA) and two steps GAs have been implemented to unfold the neutron spectra. According to the obtained results, the new two steps GA code results has shown closer match in all energy regions and particularly in the high energy regions. The results of the TGASU code have been compared with those of the standard... 

Porous NiTi-shape memory alloy (SMA) is a promising biomaterial with desirable mechanical property and appropriate biocompatibility for human implant manufacturing. In this research, porous NiTi-SMAs have been successfully produced by using thermohydrogen process (THP). This process has capability of production of homogenous structures, appropriate pore-size distributions and short sintering times. The THP-SMA samples produced in this research have a low Young's modulus (19.8 GPa) and a high tensile strength of 255 MPa. These properties are close to those of the natural bone and can meet the mechanical property demands of the hard-tissue implants for heavy load-bearing applications. The... 

This paper deals with the dynamic response and energy absorption of foam-filled aluminum parabolic tubes under axial impact loading. The numerical crush analysis of empty and foam-filled tubes is performed using non-linear finite element techniques. The effects of geometrical (wall thickness) and material parameters (foam density and Young's relaxation modulus) on the impact response and energy absorption capacity of foam-filled tube are investigated using numerical models. The results show that the foam properties have significant effect on the crushing behavior, force and impact acceleration magnitude, and energy absorption capacity. Furthermore, there is a critical foam density beyond... 

A computational code, based on the genetic algorithm and MCNPX version 2.6 code was developed and used to investigate the effects of some important parameters of HPGe detector (such as Al cap thickness, dead-layer thickness and Ge hole size) on optimum dimensions of marinelli beaker. In addition, the effects of detector material on optimal beaker dimensions were also investigated. Finally, the optimized beaker dimensions at various beaker volumes (300, 500, 700, 1000 and 1500 cm3) were determined for some conventional Ge detectors with different crystal sizes (16 sizes). These sets of data then were used to drive mathematical formulas (obtained by best fitting to data sets). The results... 

We report on the MoS2 and MoOx (x = 2 and 3) composite thin layers, electrodeposited, onto a Florine doped Tin Oxide (FTO) substrate. Our results show a change in relative content of these compounds in different thicknesses ranging from ∼20 to 540 nm. This change in the relative content at different thicknesses leads to a change in optical and electrical properties including bandgap and the type of semiconductivity. A sharp transition from p to n-type of semiconductivity is observed by scanning tunneling spectroscopy measurements. We find that the spin-orbit interaction of Mo 3d electrons in the MoS2 and MoO3 enhances by significant reduction of the MoO3 content in thicker layers. © 2017... 

Environmental degradation due to economic activities is a key challenge facing sustainable development. The fossil fuel production sector is a very polluting industry. In this research, the future trends of pollution accumulation in the region due to direct/indirect oily discharge into the semi-enclosed area of the Persian Gulf are studied. The purpose of the study was not only to alert policy-makers about potential future threats in the region but also to conduct a trial to develop potential solutions to these problems. Four different environmental cases were studied via the principle of system dynamic modeling simulation. The cases consisted of three situations: relaxed, simple policy, and... 

Unidirectional current flow is at the heart of modern electronics, which has been conceived by making p–n junctions or Schottky barriers between different kinds of materials. Within such elements, however, synthesis of thin film lateral heterostructures has so far remained challenging. Here, a one-step simple synthesis of p-type, n-type, and metallic lateral heterostructures using bipolar electrodeposition (BPE) technique is reported. Molybdenum oxides and sulfides with gradient of oxygen and sulfur are deposited at a metallic substrate. A lateral heterostructure is achieved with electrical properties that change from p- to n-type semiconductor and then to metal by moving in the plane of the... 

The modulation transfer function (MTF) is well known as a crucial parameter in quality assurance of computed tomography (CT) scanners, which provides detailed information of both contrast and resolution of CT images. Different methods have been introduced and developed to calculate the MTF of CT scanners. However, a robust methodology which accurately estimates the MTF of CT scanners under the use of every range of object electron density and tube current-time product (mAs) has not been reported so far. To this aim, a new wavelet-based circular edge method for MTF measurement has been presented in this work. Owning to the edge spread function (ESF) susceptibility to noise, the approach was... 

Computed tomography (CT) is one of the most valuable diagnostic imaging tools in the clinic and is widely used worldwide. One of the main motivations driving research and development in CT is to achieve better image quality while keeping the radiation dose to the patient as low as possible. In this regard, computer simulations play a key role in the optimization of CT design. In this work, a fan-beam source model (FBSM) for the simulation of multi-slice fan-beam CT scanners using the MCNP Monte Carlo code, has been developed and implemented. The use of this model removes the need for using the collimator in the system configuration and thus to overcome the perennial problem of particle... 

In the previous researches, several theoretical equations were presented for calculation of buildup factor of the single layer shields. Also, the theoretical equations were offered for the two-layered shield that consist of the known materials. For other possible modes of the multi-layered shield, the buildup factor are usually calculated via experimental or simulated data. The purpose of present study is the extraction of the new theoretical equation for the gamma ray buildup factor of three-layered spherical shield made of water, concrete and iron based on the Monte Carlo calculation. To this end, the gamma ray buildup factor of the three-layered spherical shield is calculated via... 

In the present paper, the effect of Nano silica on mechanical properties and durability of concrete containing polypropylene fibers has been investigated. Here, the length and length to diameter ratio of used polypropylene fibers were considered to be fixed and equal to 18 mm and 600 respectively and the cement content was 479 kg/m3. The effect of fibers and Nano silica in four different percentages for each one at 0.1, 0.2, 0.3 and 0.4 percent by volume for fibers and 3 percent for Nano silica in concrete with water to cement ratio of 0.33, 0.36, 0.4, 0.44 and 0.5 have been compared and evaluated. In total, more than 425 cubic and cylindrical specimens were made according to ASTM standards.... 

We produced bifurcated bone-like shape memory implant (BL-SMI) with desirable tooth-root fixation capability by compact-sintering of TiH2–Ni-urea mixture. The primary constituents of the porous product were Ni and Ti. We could adjust the pores' shape, size, and interconnectivity for favorite bone ingrowth by using urea as a space holder. Without urea, we obtained an average porosity of 0.30, and a mean void size of 100 μm. With 70 vol % urea, we got 62% interconnected pores of 400 μm average size. Aging allowed us to tune the austenite-martensite transformation temperatures towards the needed body tissue arouse. Differential scanning calorimetry measured the transformation temperatures.... 

Computed tomography (CT) simulators are versatile tools for scanning protocol evaluation, optimization of geometrical design parameters, assessment of image reconstruction algorithms, and evaluation of the impact of future innovations attempting to improve the performance of CT scanners. Computational human phantoms (CHPs) play a key role in simulators for the radiation dosimetry and assessment of image quality tasks in the medical x-ray systems. Since the construction of patient-specific CHPs can be both difficult and time-consuming, nominal standard/reference CHPs have been established, yielding significant discrepancies in the special design and optimization demands of patient dose and... 

Computed Tomography (CT) is one of the most widely used screening and diagnostic tools in medical imaging centers. Considering IAEA HUMAN HEALTH SERIES No. 19 and the American College of Radiology (ACR) Accreditation Program, quality assurance (QA) and quality control (QC) are mandatory programs to periodically monitor the system condition to promote the effective utilization of ionization radiation for a diagnostic outcome through obtaining and retaining appropriate image quality and reduction of patient dose. Computational phantoms (CPs) are the key tool to monitor system condition. The commercial QC phantoms are expensive products and are not flexible enough for user demands. In this... 

In order to determine the activity of C137s in soil resulting from nuclear accidents or fallouts, the best choice is to use HPGe detectors due to their best energy resolutions. In this regard, in order to enhance the detection efficiency, the Marinelli beakers have been used to increase the radiation interaction with the sensitive volume of the detector. In previous works, to optimize the dimension of Marinelli beakers, the assumption was that the emission rate of the source is homogeneous in beaker volume. In the present study, to investigate the effect of the inhomogeneous emission rate of the source on the optimum dimensions of the beaker, in a simple case, the beaker was divided into two...