Sharif Digital Repository

Balance theory proposed by Heider for the first time modeled triplet interaction in a signed network, stating that relationships between two people, friendship or enmity, is dependent on a third person. The Hamiltonian of this model has an implicit assumption that all triads are independent, meaning that the type of each triad, being balanced or imbalanced, determined apart from the state of other triads. This independence forces the network to have completely balanced final states. However, there exists evidence indicating that real networks are partially balanced, raising the question of what is the mechanism preventing the system to be perfectly balanced. Our suggestion is to consider a... 

During the low salinity waterflooding (LSWF) of a viscous asphaltic oil reservoir, fluid-fluid interactions have a large influence on the fluid flow, pore-scale events, and thus oil recovery efficiency and behavior. In-situ water-in-oil (W/O) emulsion formation is a consequence of crude oil and brine interfacial activities. Despite the published studies, the pore-scale mechanisms of W/O emulsion formation and the role of injected brine salinity, injection rate, and pore-scale heterogeneity on emulsion formation and stability requires a deeper understanding. To address these, a series of static and dynamic micro-scale experiments were performed. The salinity dependent oil-brine interactions... 

The response of a rod-stabilized, V-shaped, premixed flame to upstream velocity and equivalence ratio perturbations was characterized as a function of excitation frequency. The response of the flame to equivalence ratio perturbations was calculated, assuming that the heat release response is controlled by contributions from three disturbances. These disturbances include flame speed, heat of reaction and flame area. Using an analytical model, based on linearization of the front tracking equation for inclined flames, the kinematics of a V-flame anchored on a central obstacle was investigated and its response was compared with that of a conical flame. The results suggest that the phase response... 

Simulation of x-ray generation from bombardment of various solid targets by quasimonoenergetic electrons is considered. The electron bunches are accelerated in a plasma produced by interaction of 500 mJ, 30 femtosecond laser pulses with a helium gas jet. These relativistic electrons propagate in the ion channel generated in the wake of the laser pulse. A beam of MeV electrons can interact with targets to generate x-ray radiation with keV energy. The MCNP-4C code based on Monte Carlo simulation is employed to compare the production of bremsstrahlung and characteristic x rays between 10 and 100 keV by using two quasi-Maxwellian and quasimonoenergetic energy distributions of electrons. For a... 

In this work, the 3D proton dose profile is calculated in a homogenous water phantom using a Monte Carlo application developed with the Geant4 toolkit. The effect of the ridge filter material (for SOBP widths of 6, 9 and 12 cm) on the homogeneity of the dose distribution, secondary neutron production and beam efficiency are investigated in a single ring wobbling irradiation system. The energy spectrum of secondary neutrons per primary proton at various locations around the phantom surface is calculated. The simulation revealed that most of the produced neutrons are released at slight angles which enable them to reach the patient and consequently to be hazardous. Also, the homogeneity of the... 

Based on the determination of protons fluence at the phantom's surface, a 3D dose distribution is calculated inside a water phantom using a fast method. The dose contribution of secondary particles, originating from inelastic nuclear interactions, is also taken into account. This is achieved by assuming that 60% of the energy transferred to secondary particles is locally absorbed. Secondary radiation delivers approximately 16.8% of the total dose in the plateau region of the Bragg curve for monoenergetic protons of energy 190 MeV. The physical dose beyond the Bragg peak is obtained for a proton beam of 190 MeV using a Geant4 simulation. It is found that the dose beyond the Bragg peak is <... 

The use of adjusted/optimized saline water categorized into two different classes namely smart water (SW) and low salinity (LoSal) water injection has been proposed for more oil recovery from specific types of oil reservoirs. There are possible mechanisms concerning SW flooding that have been proposed in the literature, some of them are still subject to more examination. In this study, an experimental investigation is performed to determine the influence of type and amount of salt to the surface properties including interfacial tension (IFT) and contact angle (CA) of aqueous solution + acidic and asphaltenic crude oil + carbonate rock systems. For this purpose, the concentration of different... 

Gas injection process for more oil recovery and in particular CO2 injection is well-established method to increment oil recovery from underground oil reservoirs. CO2 sequestration which takes place during this enhanced oil recovery (EOR) method has positive impact on reducing the greenhouse gas emission which causes global warming. Direct gas injection into depleted oil reservoirs, encounters several shortcomings such as low volumetric sweep efficiency, early breakthrough (BT) and high risk of gas leakage in naturally fractured carbonate oil reservoirs. Carbonated water injection (CWI) has been recently proposed as an alternative method to alleviate the problems associated with gas... 

This study investigates dynamic interfacial tension (DIFT) of acidic crude oil (ACO) and non acidic/basic crude oils (BCO) + deionized water (DW) as a function of pressure from 500 to 4000 psi, and temperature from 30 to 80 °C using an axisymmetric drop shape analysis (ADSA) technique. DIFTs are also modeled using dynamic adsorption model, mono-exponential decay model, and empirical equations. The results showed that if a reduction in the surface excess concentration due to increasing temperature overlooks the total entropy of the molecules in the system, an increase in IFT would be expected  

The concerns for water availability, affordability and environmental consideration have motivated more research on the development of smart water injection for enhanced oil recovery process. Although wettability alteration has been considered as the dominant mechanism, there is an ample space in this area needs to be explored more. Therefore, a systematic series of experiments is designed and performed to examine the effect of salinity and ion type on the wettability of the carbonate rock surface to find the active mechanisms. For this purpose, the concentrations of different salts including NaCl, KCl, CaCl2 and MgCl2 are examined during 10 days of soaking for salts concentrations range of... 

Due to increasing demand for natural gas, storage plan development in order to cope with seasonal gas fluctuations and ensure constant gas supply during a year, has recently become highly indispensable. However, developing underground gas storage (UGS) facility is so costly which may sometimes discourage the investment.One of the main cost items while fulfilling a UGS project can be attributed to cushion gas; this is part of gas inventory which remainspermanently in the storage field in order to maintain pressure and provide adequate deliverability rate during production cycles.For this reason, UGS in low quality gas reservoirs has been recentlyproposed. In such a case, native reservoir gas... 

Enhanced oil recovery (EOR) methods are mostly based on different phenomena taking place at the interfaces between fluid–fluid and rock–fluid phases. Over the last decade, carbonated water injection (CWI) has been considered as one of the multi-objective EOR techniques to store CO2 in the hydrocarbon bearing formations as well as improving oil recovery efficiency. During CWI process, as the reservoir pressure declines, the dissolved CO2 in the oil phase evolves and gas nucleation phenomenon would occur. As a result, it can lead to oil saturation restoration and subsequently, oil displacement due to the hysteresis effect. At this condition, CO2 would act as in-situ dissolved gas into the oil... 

This paper addresses a conceptual study on different aspects of a novel smart treatment method for a relatively new challenge of saline water production from low permeability lenses of high flow gas wells. Selective sealing of such lenses along with minor effect on gas productivity usually faces practical difficulties due to the inherent permeability contrast. Engineered application of salt sensitive gellan biopolymer through a smart treatment scenario that includes a protective gas flow proved its ability for treating such challenge. This paper investigates the importance of the gel rigidity and its coverage in the smart treatment scenario through considering the brine salinity and the... 

In this paper we report experimental results for the performance and rate of heat transfer in copper tubes in solar water heaters with thermosyphonic flow in continuation of experimental data reported in previous publications (Solar Energy, 2003, vol. 74, pp. 441-445, and Energy Sources, 1997, vol. 19, pp. 147-152). We also show a comparison between performances of three kinds of tubes: copper, polypropylene and steel under similar conditions. An analytical relation for calculation of rate of heat transfer in copper tubes is also presented in terms of Nusselt versus Reynolds and Prantdl numbers. A comparison of experimental data showed that performance of copper tubes is slightly better than... 

By displacing oil in porous media with other fluid, different mechanisms of fluid displacing occur. The importance of understanding the trapping mechanisms like pore body filling is irrefutable. Pore body filling mechanism with a coordination number of four has different events like I0, I1, I2 and I3. Previous studies showed that the event of I0 occurs when the pore is only filled by a compressible non-wetting phase, but this study showed that this event could also occur by an incompressible non-wetting phase. Trapping mechanisms can be examined in a glass micro-model. In this research, a glass micro-model with three different patterns was used. Results showed that at two spots of the... 

Improving oil recovery and decreasing greenhouse gas emissions are two important attractive features of CO2-enriched water injection into oil reservoirs. Regarding these unique features, the main objective of this study was concentrated to evaluate the swelling behavior of crude oil as a fundamental mechanism of carbonated water (CW) flooding. To achieve these goals, the swelling and Bond number of light and heavy crude oils (namely LCO and HCO, respectively) are measured and compared to each other. The results obtained from the measured swelling factors of crude oil/CW show some complicated behaviors. That is, as temperature increases the swelling factor decreases at low pressure... 

Propagation of a chirped laser pulse with a circular polarization through an uprising plasma density profile is studied by using 1D-3V particle-in-cell simulation. The laser penetration depth is increased in an overdense plasma compared to an unchirped pulse. The induced transparency due to the laser frequency chirp results in an enhanced heating of hot electrons as well as increased maximum longitudinal electrostatic field at the back side of the solid target, which is very essential in target normal sheath acceleration regime of proton acceleration. For an applied chirp parameter between 0.008 and 0.01, the maximum amount of the electrostatic field is improved by a factor of 2.... 

Naturally fractured reservoirs (NFRs) contribute in large extent to oil and gas production to the ever increasing market demand of fossil energy. It is believed that the vertical displacement of oil during gas injection assisted by gravity drainage (GAGD) is one of the most efficient methods for oil recovery in these reservoirs. Hence, in this work, unconsolidated packed models of cylindrical geometry surrounded by fracture were utilized in order to perform a series of flow visualization experiments during which the contribution of different parameters such as the extent of matrix permeability, physical properties of oil (viscosity, density, and surface tension) and the withdrawal rate was...