Sharif Digital Repository

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using... 

In this study, the optimal location of baffle in the header of air-to-air plate heat exchangers and the geometry of the header and the effects of triangular fins arrays on the effectiveness were numerically investigated for different flow rates and Reynolds numbers on different models. The main purpose of inlet baffle and geometry changes is to improve the pattern of flow distribution and assist flow uniformity. The investigations show that the optimal location of the inlet baffle with high Reynolds numbers has an insignificant effect on effectiveness, while with Reynolds numbers 250-3000, the effectiveness is affected significantly by baffle location. On the other hand, the reduction in... 

One-dimensional nanostructures of tin oxide nanotubes were fabricated by carbothermal evaporation at 900°C in air. The synthesized film was grown on Au-coated (100) Si substrate. Heterogeneous catalysis by Au/Sn droplets assisted the formation of the tin oxide nanotubes of less than 40 nm diameter at Sn vapor pressures around 1.4×10 -7 Pa. In order to reduce the nanotube diameter further, an increase in the Sn vapor pressure by changing the source materials' ratio seemed viable. © 2009 Springer-Verlag  

Widespread growth in Android malware stimulates security researchers to propose different methods for analyzing and detecting malicious behaviors in applications. Nevertheless, current solutions are ill-suited to extract the fine-grained behavior of Android applications accurately and efficiently. In this paper, we propose ServiceMonitor, a lightweight host-based detection system that dynamically detects malicious applications directly on mobile devices. ServiceMonitor reconstructs the fine-grained behavior of applications based on their interaction with system services (i.e. SMS manager, camera, wifi networking, etc). ServiceMonitor monitors the way applications request system services in... 

In this paper we present and investigate a digital design and implementational details of a wireless optical CDMA (OCDMA) system based on generalized optical orthogonal codes (OOCs). A detailed digital implementation analysis and transmitter/receiver architectures in the context of the above design are fully studied. We analyze various subsystems for a wireless OCDMA system including detector and receiver structure, acquisition, and tracking blocks as well as evaluating their performance in a typical wireless OCDMA communication system. By analyzing two main parts of the system, namely, chip-level detector and OCDMA receiver blocks we evaluate the performance of the overall system.... 

In this paper we study and present an in-depth analysis on the operability and the viability of a typical wireless optical CDMA (OCDMA) local area network. Three receiver structures for OCDMA systems, using optical orthogonal codes (OOC) with minimum auto and cross-correlations as signature sequence, namely, correlation, correlation with hard-limiter, and chip-level detection are studied and proposed for such a network. For the synchronization circuit design the performance of two algorithms for OOC based OCDMA networks, namely, simple serial-search and multiple-shift in the context of wireless OCDMA LAN are studied. Furthermore, we study a synchronization method based on matched filtering... 

Dynamics of a drop under the influence of gravitational force was examined using lattice Boltzmann method and color-gradient model. The term associated with the buoyancy force caused by the density difference between the two phases was modified in the lattice Boltzmann equations and verified in some cases. The motion of n-butyl acetate drops in water was predicted in various deformation regimes. The modeling results were in good agreement with the experimental results, solutions obtained by common CFD methods and semi-empirical correlations. Contrary to the common multiphase models, the behavior of moving drops in oscillating regime was predicted with good accuracy using the present model.... 

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using this... 

In this paper, we present a novel multirate, differentiated quality of service (QoS) optical CDMA (OCDMA) system using multilevel signaling technique. The emphasis is on OCDMA systems employing multi-length variable-weight optical orthogonal codes (MLVW-OOC) as signature sequence. We begin by presenting a two-class variable-weight OCDMA system in which all users have the same energy level in one bit duration. As a consequence, high weight users transmit their corresponding optical pulses at a lower power while low weight users transmit their corresponding optical pulses at a higher power level. We show that using this multilevel signaling technique, while employing the well known optical AND... 

The brain is one of the vital organs in the body. The main cerebral distribution center of blood flow in the brain is the circle of Willis (CoW). In more than 50% of healthy brains and in more than 80% of dysfunctional ones, at least one artery of the circle of Willis is absent or underdeveloped. These variations reduce the collateral flow availability and increase the risk of stroke and transient ischemic attack in patients with atherosclerosis. Thus it is essential to simulate the circle of Willis and investigate the effects of stenosis. In this work the systemic arteries along with the circle of Willis are simulated using the finite volume method and one-dimensional equations of... 

A one dimensional model of the pulmonary arterial network along with systemic circulation was introduced to quantify the human pulmonary artery hemodynamics. A lumped parameter model of the right ventricle was used as the inlet boundary condition. A time varying elastance related the volume and pressure of the right ventricle was imposed in the model. By using a four element Windkessel model, blood flow rate throughout the right ventricle was in hand. An asymmetric structured tree was chosen as the outlet boundary conditions. Simulation was based on solving one-dimensional equations of conservation of mass and momentum by using finite volume method. Blood flow rate, pressure and velocity... 

This paper proposes an N-modular redundancy (NMR) technique with low energy-overhead for hard real-time multi-core systems. NMR is well-suited for multi-core platforms as they provide multiple processing units and low-overhead communication for voting. However, it can impose considerable energy overhead and hence its energy overhead must be controlled, which is the primary consideration of this paper. For this purpose the system operation can be divided into two phases: indispensable phase and on-demand phase. In the indispensable phase only half-plus-one copies for each task are executed. When no fault occurs during this phase, the results must be identical and hence the remaining copies... 

In this paper, we present a novel multirate, differentiated quality of service (QoS) optical CDMA (OCDMA) system using multilevel signaling technique. The emphasis is on OCDMA systems employing multi-length variable-weight optical orthogonal codes (MLVW-OOC) as signature sequence. We begin by presenting a two-class variable-weight OCDMA system in which all users have the same energy level in one bit duration. As a consequence, high weight users transmit their corresponding optical pulses at a lower power while low weight users transmit their corresponding optical pulses at a higher power level. We show that using this multilevel signaling technique, while employing the well known optical AND... 

A two-step pack cementation technique was used to cover nickel-based IN-738LC superalloy with a Cr-aluminide coating layer. The IN-738LC/Cr-aluminide samples were oxidized at 900 °C for 350 and 700 h, isothermally, and 175 and 350 h, cyclically. Each cycle lasted for 25 h. Effects of the isothermal and the cyclic oxidation on (a) morphology, (b) new-phase formation, (c) weight gain, and (d) oxidation reactions were investigated by scanning electron microscopy, electron dispersive spectroscopy, X-ray diffraction, and weight gain measurements. From results, it was concluded that the oxygen attack was more severe during the cyclic oxidation than the isothermal procedure. Kinetics of the... 

In this paper we introduce and propose novel signaling methods and receiver structures based on advanced binary optical logic gates for fiber-optic code division multiple access (FO-CDMA) systems using all-optical signal processing. In the proposed system the users of the network are categorized into multiple classes. Users of each class transmit at the same power level but different from the levels of the other classes' users. Using a combination of optical OR, AND and XNOR logic gates for the receiver structure we show that such a network not only takes the full advantages of all-optical signal processing but also demonstrates a considerable throughput efficiency when compared to ordinary... 

Recently, using Peer-to-Peer (P2P) overlay architectures have become a popular approach for live video streaming over the Internet. Since the peers in these systems are geographically distributed, the communication between them imposes huge redundant traffic into the Internet. One solution to address this problem is utilizing the locality aware algorithms to optimize the neighbor selection policy. However, for real-time applications like live video streaming we need to consider the trade-off between localizing the traffic and service quality. In this paper, we propose a novel pure P2P framework through two phases; (1) Local tracker selection, and (2) Overlay mesh construction. We introduce... 

Intensity modulation/direct detection (IM/DD) schemes are widely used in wireless optical applications. The interest in using IM/DD schemes stems from the fact that they can be easily implemented in transmitter and receiver sides  

In this paper we present and investigate a digital design and implementational details of a wireless optical CDMA (OCDMA) system based on generalized optical orthogonal codes (OOCs). A detailed digital implementation analysis and transmitter/receiver architectures in the context of the above design are fully studied. We analyze various subsystems for a wireless OCDMA system including detector and receiver structure, acquisition, and tracking blocks as well as evaluating their performance in a typical wireless OCDMA communication system. By analyzing two main parts of the system, namely, chip-level detector and OCDMA receiver blocks we evaluate the performance of the overall system.... 

Considering cache enabled networks, optimal content placement minimizing the total cost of communication in such networks is studied, leading to a surprising fundamental 0–1 law for non-redundant cache placement strategies, where the total cache sizes associated with each file does not exceed the file size. In other words, for such strategies we prove that any nonredundant cache placement strategy can be transformed, with no additional cost, to a strategy in which at every node, each file is either cached completely or not cached at all. Moreover, we obtain a sufficient condition under which the optimal cache placement strategy is in fact non-redundant. This result together with the 0–1 law... 

Considering cache enabled networks, optimal content placement minimizing the total cost of communication in such networks is studied, leading to a surprising fundamental 0-1 law for non-redundant cache placement strategies, where the total cache sizes associated with each file does not exceed the file size. In other words, for such strategies, we prove that any non-redundant cache placement strategy can be transformed, with no additional cost, to a strategy in which at every node, each file is either cached completely or not cached at all. Moreover, we obtain a sufficient condition under which the optimal cache placement strategy is in fact non-redundant. This result together with the 0-1...