Sharif Digital Repository

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... 

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... 

Carbonated water injection (CWI) is known as an efficient technique for both CO2 storage and enhanced oil recovery (EOR). During CWI process, CO2 moves from the water phase into the oil phase and results in oil swelling. This mechanism is considered as a reason for EOR. Viscous fingering leading to early breakthrough and leaving a large proportion of reservoir un-swept is known as an unfavorable phenomenon during flooding trials. Generally, instability at the interface due to disturbances in porous medium promotes viscous fingering phenomenon. Connate water makes viscous fingers longer and more irregular consisting of large number of tributaries leading to the ultimate oil recovery... 

Carbonated water injection (CWI) is known as an efficient technique for both CO2 storage and enhanced oil recovery (EOR). During CWI process, CO2 moves from the water phase into the oil phase and results in oil swelling. This mechanism is considered as a reason for EOR. Viscous fingering leading to early breakthrough and leaving a large proportion of reservoir un-swept is known as an unfavorable phenomenon during flooding trials. Generally, instability at the interface due to disturbances in porous medium promotes viscous fingering phenomenon. Connate water makes viscous fingers longer and more irregular consisting of large number of tributaries leading to the ultimate oil recovery... 

The flow behavior of a semi-solid A356 alloy at high solid fraction was studied. The mushy zone was considered as an effective two-phase, so that the solid continuum can be compressible porous media, and the liquid phase interaction with the solid skeleton was of Darcy type. The semi-solid flow through the upsetting test was modeled in ABAQUS finite element method software. The Gurson yield criterion has been developed for the modeling process of the flow behavior of solid porous medium. Specimens were globulized by a thermomechanical process and then were tested for various percentages of upsetting. The distribution of solid fraction along the radius of the specimens at different height... 

The flow behavior of a semi-solid A356 alloy at high solid fraction was studied. The mushy zone was considered as an effective two-phase, so that the solid continuum can be compressible porous media, and the liquid phase interaction with the solid skeleton was of Darcy type. The semi-solid flow through the upsetting test was modeled in ABAQUS finite element method software. The Gurson yield criterion has been developed for the modeling process of the flow behavior of solid porous medium. Specimens were globulized by a thermomechanical process and then were tested for various percentages of upsetting. The distribution of solid fraction along the radius of the specimens at different height... 

Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar  

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function... 

Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance... 

It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive... 

There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas  

By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only... 

One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared  

It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite... 

By employing the MIMO (multiple-input-multiple-output) technology in radar, some new problems emerged, that, in order to benefit the MIMO gains in radar, it was necessary to solve them suitably. One of such obstacles is determining the positions of receive antennas in a MIMO radar system with widely separated antennas (WS MIMO radar), since it is shown that the antennas' positions affect the whole system's performance considerably. In this study, a proper receivers' positioning procedure is proposed. To do this end, four criteria are developed based on the proposed MIMO detector and the MIMO ambiguity function. The simulations verify that the proposed positioning procedure improves the... 

Phenols and alcohols are silylated with hexamethyldisilazane (HMDS) under microwave irradiation in solvent-free condition in good to excellent yields  

Modified couple stress theory is a size-dependent theorem capturing the micro/nanoscale effects influencing the mechanical behaviors of the micro- and nanostructures. In this paper, it is applied to investigate the nonlinear vibration of carbon nanotubes under step DC voltage. The vibration, natural frequencies and dynamic pull-in characteristics of the carbon nanotubes are studied in detail. Moreover, the effects of various boundary conditions and geometries are scrutinized on the dynamic characteristics. The results reveal that application of this theory leads to the higher values of the natural frequencies and dynamic pull-in voltages