Sharif Digital Repository

Transferred Electron Device is a semiconductor device being capable of generating oscillation in microwave frequencies. Applying a bias voltage to the device and putting it in a resonant circuit, a periodic waveform in the output current is observed. The cause of the generation of oscillation in the device is related to the characteristics of velocity-field in the device. In some part of the characteristics, it is observed that increasing the field inside the device causes the velocity of electrons to be reduced. This causes the generation of the negative conductance and the oscillation of the output current under some conditions. The purpose of this thesis is to represent an equivalent... 

An Ad-Hoc wireless network consists of a collection of geographically distributed nodes that communicate with each other over a wireless medium. These networks don’t use any infrastructure or base station to channel allocation. The important difference between wireless networks and wired networks is the broadcast nature of wireless communications. In these networks, each node transmits data to all of the nodes in the transmission range which may cause an increase in interference and data loss. On the other hand, due to mobility of users, fading the channel between them and change of routing, the probability of data loss increases. The extensive and successful employment of TCP variants in... 

Several applications have been envisioned for wireless sensor networks (WSNs). These range in scope from military applications to environment monitoring to biomedical applications. It is a widely accepted fact that the limited energy available at the nodes of a wireless sensor network must be used as efficiently as possible. If energy conservation techniques are used at different levels, the functional lifetime of both individual nodes and the network can be extended considerably.
Energy can be saved if the network topology itself is energy-efficient. The research in topology construction and connectivity has been approached independently along two paths. In one path, researchers aim to... 

Phospholipid vesicles are able to carry drugs or DNA to infected or cancerous cells. The blood flow can carry them to their target positions but their performance will be enhanced if they complete their attack by swimming in final stages of their journey. Vesicles built only by lipid molecules have rotational symmetry and undergo a random motion in their solvents without having a preferred direction. In this project, we break the symmetrical shape of phospholipid vesicles by a cluster of transmembrane proteins. We use a triangulated model of the membrane, apply the method of multi-particle collision dynamics to the motion of solvent particles, and simulate the motility of vesicles for... 

Temperature reduction from room temperature to liquid nitrogen temperature has a significant effect in improvement of semiconductor devices operation such as field effect transistors. Nowadays cryoelectronics as a considerable branch of electronics is concerned by several groups. In order to optimize the procedure of low temperature IC design and fabrication we investigated the temperature effects on different parameters of MOSFET in this thesis. Several transistors in a variety of channel lengths were fabricated in different technology files. Wide measurement experiments were done on these transistors in order to find their drain current vs. drain to source voltage characteristics. From... 

In the present study, synthesis, preparation, and application of bimetallic iron/nickel nano-particles were experimentally investigated with the aim of groundwater remediation. Firstly, iron/nickel nano-particles were synthesized according to chemical reduction and stabilization with starch biopolymer, and then characterized. Results confirmed the formation of bimetallic iron/nickel nano-particles with mean size of 75 nm that starch placed around of them. The more stability characteristic and also enough mobility ensure their diffusion through porous media. Secondly, reactivity of synthesized nano-particles for removal of various contaminants including nitrate, chromium, and lead were... 

Issues arising from host-centric nature of IP-based networks lead to emerging Informationcentric networks (ICN). One the most promising architectures of ICN is named data networking (NDN). Unlike IP-based networks, the foundation of NDN is the content not the location which it resides. Voluminous growth of mobile devices necessitates supporting mobility in NDN. Although consumer mobility is supported natively by NDN, the support of producer mobility is yet an open challenge in NDN design. Since producer mobility affects both network performance and end-users satisfaction, it is crucial to handle this problem. The solution is proposed in this paper is based on virtual coordinate-based... 

Excessive water production is one of the common problems during oil recovery that causes the production to decline, the operating cost to increase, and the well to shut in. The heterogeneities such as fractures in the reservoirs causes waterfingering and decrease waterflood efficiency, recovery factor and increase production costs and lead to high watercut. On of the methods used to prevent producing undesireable water from reservoirs is using Preformed Particle Gels (PPGs) that is known as plugging agent. These particles are injected into the hydrocarbon reservoirs and plugged the flow of water and prevent the production of water.In recent years, it has been recognized that the use of... 

In recent years, the subject of student mobility has become one of the most important areas of migration studies. The growing number of students moving from developing countries to developed ones has raised many concerns. Governments and institutions related to this issue have always tried to adopt policies to encourage the return of their diaspora students after graduation. However, to propose evidence-based policies there is a need to understand what shapes the intention of the Iranian international students to return or stay. This study tries to look at the factors that shape the intention of Iranian international students after graduation using the theory of planned behaviour.In the... 

During the covid-19 pandemic, in many countries, women's employment sector received more impact than men's. Some researchers consider this incident due to a decrease in the supply of women due to the closure of childcare centers and absenteeism in schools. Some consider this to be due to a reduction in the demand for women's labor due to the damage to the service sector. In this research, using the transition matrix, we showed that, during the epidemic period, the households in which women were employed in the pre-epidemic period (first group) had a greater reduction in income mobility than the households in which only men were employed (second group). Then, using the ordered logit of... 

Natural selection in structured populations is considered a crucial subject in evolutionary and population genetics. There is no explicit relationship between discrete-time stochastic models such as the Moran process and continuous-time models such as the Fisher-Kolmogorov equation. However, under specific conditions and within the limits of natural selection and weak selection, a connection can be found between these two models. To gain a better understanding of the specific relationship between these two models, we obtain partial differential equations for the spatiotemporal dynamics of natural selection by extending the birthdeath and death-birth processes of the Moran process to a...