Sharif Digital Repository

Multiband absorption is the interest of the microwave communities due to several applications in sensing, filtering, and stealth. Usually, the stacking of metal and dielectric multilayered structures form a multiband absorber which makes the device bulky and costly. In this paper, we investigate a multiband absorber based on a single-layered fractal metasurface for the 5G applications. The unit cell of the fractal metasurface is comprised of six ring-shaped symmetric split-ring resonators (SRRs) connected back-to-back with each other. The absorptivity is investigated in the 5G microwave regime (22–36 GHz) for various obliquities at different substrate thicknesses. Simulation results show... 

Radiative sky cooling (RSC) systems have enjoyed a privileged position in the research community due to generating cooling energy without consuming electricity using the open atmospheric window and infrared emission to the sky. However, the system's justification occurs when it reaches a temperature below the minimum 24-hour ambient temperature. This study utilizes phase change materials (PCM) as the energy storage of a hybrid daytime photovoltaic-thermal and nighttime RSC module and investigates the nocturnal cooling energy-saving potential of the system at different phase transition temperatures. After being validated by the experimental data in the literature, the simulated model was used... 

Recent studies in information computation technology (ICT) are focusing on Next-generation networks, SDN (Software-defined networking), 5G, and 6G. Optimal working mode for device-to-device (D2D) communication is aimed at improving the quality of service with the frequency spectrum structure is of research areas in 5G. D2D communication working modes are selected to meet both the predefined system conditions and provide maximum throughput for the network. Due to the complexity of the direct solutions, we formulated the problem as an optimization problem and found the optimal working modes under different parameters of the system through extensive simulations. After determining the links'... 

Currently, materials with outstanding absorption abilities, such as thin size, better absorbing power, and light weight are the need of industry to resolve the electromagnetic issues. However, the research on optimizing the composition of the material, microstructure and the structure of the absorber are also the important factors for enhancing the absorption features. A metamaterial microwave absorber (MMA) based on nano ferrites with desirable absorption peaks is proposed and simulated. Sol-gel auto combustion route is used to prepare the nanosized Sm doped Co ferrite with Co1+xSmxFe2-2xO4 at x = 0.00, 0.03, 0.06, 0.09, respectively. XRD, VSM, FESEM, and VNA were employed to evaluate the... 

Removing space debris of various sizes, configurations, and properties from Earth’s orbits is one of the main missions of world space agencies. The existence of deactivated bodies within the path of other spacecraft increases the risk of collision. Althgough towing a satellite through a tether and taking it out of orbit may be a definite solution for space debris removal, most deactivated satellites have some fuel remaining in their fuel tank. This remaining liquid slosh within the tank directly affects satellite motion. To improve the mathematical modeling, the existence of unburned fuel is considered. More specifically, this research focuses on dynamic modeling and control of a selected... 

Multiple access methods are the backbone of today's most communication systems. Increasing the efficiency of these schemes is a challenging engineering task. This paper introduces dispersion-division multiple access, a novel multiple-access technique that can improve the efficiency of multiple-access communication systems. When two (or more) pulses experience different Group Delay Dispersion (GDD) values on a propagation medium, they can be synchronized to overlap in time for combining the phase and amplitude of those pulses. This paper suggests the recoverability of these pulses while being mixed in the transmitter by propagating the combined pulse in a negative Group Velocity Dispersion... 

This paper presents a cycle by cycle Frequency Shift Keying (FSK) demodulator, able to demodulate a FSK signal with 1% frequency modulation index (MI), in a single cycle. Based on the proposed demodulation scheme, a high rate data transmission link can be established through a high-Q inductive coupling link, breaking the basic tradeoff between the power transfer efficiency (PTE) and data rate in single carrier wireless power and data transfer systems. Designed and simulated with 0.18μ m CMOS process, the proposed FSK demodulator, detects successfully a 5Mbps data with a carrier frequency of 5MHz. A test chip is fabricated in 180nm CMOS technology. Measurement results shows that the... 

Low-noise amplifiers (LNAs) with low-noise performance are critical components in communication systems. However, reaching a high level of performance is difficult. This study introduces a LNA for radio frequency front-end receivers with a frequency range of 6–12 GHz. The planned LNA contains a two-stage high-electron-mobility transistor cascade amplifier with a minimum measured noise figure of 0.8 dB and a peak gain of 25 dB at room temperature. The proposed LNA is based on a gallium arsenide field-effect transistor transistor (CE3512K2) because of its good low-noise performance at microwave frequency bands. The measured results demonstrate that the proposed LNA is perfectly matched over... 

Background: Remote cardiac monitoring and screening have already become an integral telemedicine component. The wide usage of several different wireless electrocardiography (ECG) devices warrants a validation study on their accuracy and reliability. Methods: Totally, 300 inpatients with the Nabz Hooshmand-1 handheld ECG device and the GE MAC 1200 ECG system (as the reference) were studied to check the accuracy of the devices in 1 and 6-limb lead performance. Simultaneous 10-second resting ECGs were assessed for the most common ECG parameters in lead I. Afterward, 6-lead ECGs (limb leads), were performed immediately and studied for their morphologies. Results: Of the 300 patients, 297 had... 

Accurate implementation of river interactions with subsurface water is critical in large-scale hydrologic models with a constant horizontal grid resolution when models apply kinematic wave approximation for both hillslope and river channel flow. The size of rivers can vary greatly in the model domain, and the implemented grid resolution is too coarse to accurately account for river interactions. Consequently, the flow velocity is underestimated when the width of the rivers is much narrower than the selected grid size. This leads to inaccuracy and uncertainties in calculations of water quantities. In addition, the rate of exfiltration and infiltration between the river and the subsurface may... 

On-time delivery of network flows is crucial to ensure the quality of service of deadline-constrained applications. Today, real time applications have various uses in multimedia communications, the Internet of Things (IoT), and 5G (5th generation mobile network) technology. In Software Defined Network (SDN) architecture, the controller has a global view of the network. Hence, it is possible to enrich the features of the controller and/or forwarding devices to support real time communication. In this paper, we propose a firm real time software-defined approach (FRT-SDN) for real time communication and present a novel solution for the real time forwarding/routing of time-sensitive applications... 

Establishing high-quality communication in construction projects is essential to securing successful collaboration and maintaining understanding among project stakeholders. Indeed, poor communication results in low productivity, poor efficiency, and substandard deliverables. While high-quality communication is recognized as contingent on the interpersonal skills of workers, the impacts of communication quality on job performance remain unknown. This study addresses this deficiency by developing a method to evaluate construction workers' communication quality. A literature review is undertaken to capture salient interpersonal skills. Leadership style, listening, team building, and clarifying... 

A switched capacitor circuit frequently appears in literature in form of sample and hold or master-slave sampling filter. We call this block Sample and Hold Master-Slave Sampling Filter (SH-MSSF). Considering the time varying nature of this circuit it is difficult to predict its behavior, though it looks like a very simple circuit. So there exists no formula describing its function in all of its applications. In this brief, we present a closed-form transfer function, explaining the operation of SH-MSSF, based on state-space analysis. Then by interpolating an infinite number of such transfer functions a continuous-time formula is derived that can exactly model the behavior of this (Linear... 

With thousands of new questions posted every day on popular Q&A websites, there is a need for automated and accurate software solutions to replace manual moderation. In this paper, we address the critical drawbacks of crowdsourcing moderation actions in Q&A communities and demonstrate the ability to automate moderation using the latest machine learning models. From a technical point, we propose a multi-view approach that generates three distinct feature groups that examine a question from three different perspectives: 1) question-related features extracted using a BERT-based regression model; 2) context-related features extracted using a named-entity-recognition model; and 3) general lexical... 

To alleviate costly data communication among processing cores and memory modules, parallel processing-in-memory (PIM) is a promising approach which exploits the huge available internal memory bandwidth. High capacity, wide row size, and maturity of DRAM technology, make DRAM an alluring structure for PIM. However, dense layout, high process variation, and noise vulnerability of DRAMs make it very challenging to apply PIM for DRAMs in practice. This work proposes a PIM structure which eliminates these DRAM limitations, exploiting a precharge-free DRAM (PF-DRAM) structure. The proposed PIM structure, called PIPF-DRAM, performs parallel bitwise operations only by modifying control signal... 

The studies on forced migrants' digitally mediated communication and transnational practices have not sufficiently addressed contexts in which migrants are imposed with strong regulations on their physical mobility and information and communication technology (ICT), Internet, and social media uses. This article studied Internet and social media uses, digital divides (access, use, and the impact of Internet and social media), and digital transnational practices among Afghans in Iran. More than three million Afghans live in different legal, economic, and social positions in Iran. The analysis was based on surveys with 2003 Afghan refugees, other legally authorized Afghan immigrants, and... 

Classifying the modulation type of radio signals plays an important role in current and future wireless communication systems. We present a modulation classification method based on convolutional neural networks that reaches high accuracy in face of various channel characteristics and signal conditions without requiring the network to have a very large depth. Experiment results show that the proposed method reaches accurate classification under different system impairment settings that include sampling rate offset, carrier frequency offset, multi-path fading, and additive white Gaussian noise. For instance, compared to a state-of-the-art method, accuracy is improved up to 25% in classifying... 

Convolutional neural networks (CNNs) are at the heart of several machine learning applications, while they suffer from computational complexity due to their large number of parameters and operations. Recently, all-optical implementation of the CNNs has achieved many attentions, however, the recently proposed optical architectures for CNNs cannot fully utilize the tremendous capabilities of optical processing, due to the required electro-optical conversions in-between successive layers. To implement an all-optical multi-layer CNN, it is essential to optically implement all required operations, namely convolution, summation of channels' output for each convolutional kernel feeding the... 

The wide range of wireless sensor network applications has made it an interesting subject for many studies. One area of research is the controlled node placement in which the location of nodes is not random but predetermined. Controlled node placement can be very effective when either the price of the sensor nodes is high or the sensor coverage is of a specific type and it is necessary to provide special characteristics such as coverage, lifetime, reliability, delay, efficiency or other performance aspects of a wireless sensor network by using the minimum number of nodes. Since node placement algorithms are NP-Hard problems, and characteristics of a network are often in conflict with each... 

In this article, time-varying formation tracking problem for multi-agent systems is investigated. It is assumed the number of agents is changing and obstacles should be avoided along the trajectory. In addition, the tracking formation should be reached while the leader trajectory is unknown and communication data are noisy. To reach the desired formation tracking, first, a virtual leader is constructed using the local neighbouring data. Second, the reference signal is created based on the virtual leader and the leader data (which is available for some agents). The data fusion at this stage is done based on Kalman filtering to reduce the effect of communication noise. Third, an integral state...