Sharif Digital Repository

The Jajrood River watershed is on of the main drinking water resurces of Tehran, the capital city of Iran. In addition it provides many recreational usages. However, a variety of microbial pollutions is commonly perecived in the Jajrood River, among them a high concentration of coliform group bacteria that has caused strong concerns. In this article, different aspects of microbial pollution as well as the main microbial pollution sources in the region are discussed. Coliform group bacterial die-off rates have been evaluated as the key parameters that govern bacterial fate in the watershed and were estimated using both laboratory and field data investigations. The high values of the bacterial... 

The Latian dam reservoir is one of the most important drinking water sources for Tehran, Iran. Nitrate is a major water quality problem in this reservoir. The Jajrood River, the most important water source for the reservoir, discharges large amounts of nutrients to it every year including high levels of nitrate, a pollutant of particular concern. This study presents the results obtained from simulating different point source and nonpoint source impacts on the fate and transport of nitrate in the 470 km2 Jajrood watershed using the Soil and Water Assessment Tool (SWAT) model version 2000 (SWAT2000). The SWAT model was calibrated and validated over an extended time period (1997-2005) for this... 

Transitional boundary layer over an airfoil in the combined pitch-plunge oscillating motions at low Reynolds number is experimentally investigated. The study is based on the data obtained from both surface hot-film and surface static pressure. Different oscillation zones prior to, within, and beyond the static stall angle of attack of the airfoil are considered. The hysteresis loops for the laminar separation bubble, transition, relaminarization points, as well as the airfoil lift coefficient are investigated and are compared for different types of dynamic motions. Two different types of combined pitch-plunge motions, constructive and destructive, are considered. In the constructive motion,... 

A new technique for the laminar-turbulent intermittency measurement based on the surface hot-film data is presented. The existing techniques require data acquired from the calibrated hot-films which leads to the real wall shear stress values. However, calibration of the hot-films is usually very complex. In the proposed method, a technique based on the probability distribution function (PDF) of the acquired data using the uncalibrated hot-film sensors is presented and evaluated. The PDF is prepared for a reduced form of the quasi-wall shear stress value instead of the real shear stress value one. This leads to a standard normal distribution curve for the PDF in the turbulent flow region and... 

Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2:7 × 105) is experimentally investigated using space-frequency and time-frequency analyses of hot- film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomenon for turbulent and fully separated flows is presented based on the time-frequency analysis. A new technique based on time-frequency analysis of hot- film signals is introduced to measure the transition onset and relaminarization locations. This technique functions based on the analysis of high-frequency disturbances of the measured data. Significant attention has been drawn to the... 

Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2:7 × 105) is experimentally investigated using space-frequency and time-frequency analyses of hot- film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomenon for turbulent and fully separated flows is presented based on the time-frequency analysis. A new technique based on time-frequency analysis of hot- film signals is introduced to measure the transition onset and relaminarization locations. This technique functions based on the analysis of high-frequency disturbances of the measured data. Significant attention has been drawn to the... 

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... 

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... 

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... 

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... 

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  

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 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... 

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

We study a classical problem in communication and wireless networks called Finding White Space Regions. In this problem, we are given a set of antennas (points) some of which are noisy (black) and the rest are working fine (white). The goal is to find a set of convex hulls with maximum total area that cover all white points and exclude all black points. In other words, these convex hulls make it safe for white antennas to communicate with each other without any interference with black antennas. We study the problem on three different settings (based on overlapping between different convex hulls) and find hardness results and good approximation algorithms  

A method is developed for in situ generation of 1,3-dioxan-5-one derivatives 2. These compounds are simple precursors for accessing carbohydrate structures and previously had to be produced via stepwise procedures using excessive amounts of reagents. In the present work, three different derivatives of 2 were synthesized via the reaction of trialkoxyalkanes with dihydroxyacetone dimer 1 in the presence of acetic acid as the catalyst. In the same pot, derivatives of 2 were reacted with aromatic aldehydes and 30 mol% of pyrrolidine to obtain high yields of the respective bischalcones 3 within short time periods. © 2019 M. Javad Poursharifi et al., published by De Gruyter 2019