Sharif Digital Repository

We address the performance of the 802.11p protocol in terms of the packet delivery ratio (PDR) and the packet reception ratio (PRR) for broadcasting safety messages in highway environments. Regarding the semi-sparse and intermediate traffic, we try to answer to questions such as what are the upper, dominant and lower bounds of PDR and PRR in each traffic condition? How they may deviate from their average values? and What fraction of vehicles may experience such bounds? To answer to such questions, we propose to consider the communication graph formed among vehicles as a special type of the complex networks and we apply the recently proposed obligatory attachment ruleto synthesize such... 

The rapid developments in wireless communications have introduced the vehicular ad hoc networks as an efficient tool to improve the safety of traffic through Dedicated Short Range Communications systems on highways. This paper addresses the broadcast mode of the 802.11p protocol and it quantitatively analyzes the impact of the highway vehicular traffic on its performance in terms of the packet delivery ratio and the packet transmission delay. To this aim, we propose to consider the number of the contending vehicles as a traffic-dependent stochastic counting process, which can be computed by analyzing the inter-vehicle spacing distribution in different traffic conditions. Based on the... 

In the past few years, the study of complex networks has attracted the attention of researchers. Many real networks, ranging from technological networks such as the Internet to biological networks, have been considered as special types of complex networks. Through application of the network science, important structural properties of such networks have been analyzed and the mechanisms that form such characteristics have been introduced. In this paper, we address the structural characteristics of a technological network called Vehicular Ad hoc Networks (VANETs). Recent studies reveal that the communication graph of VANETs has some interesting characteristics including: the Gaussian degree... 

In this paper, we will propose a new methodology for performance modeling of IEEE 802.11p medium access control (MAC) sub-layer in broadcast mode. In most of the current works, it is assumed that the number of contending nodes is deterministic and constant. However, in vehicular ad hoc networks, we can observe a kind of uncertainty in number of contending vehicles, which try to get access to the shared wireless channel. This uncertainty can affect the performance analysis of MAC protocols in vehicular environments. In this paper, we will try to model the dynamicity of number of contending vehicles based on the distribution of vehicles' velocity. This model will be combined with the current... 

Particle dispersion in the vortex flow has been one of the most interesting subjects in recent years. Bidirectional vortex flow field is an industrial sample of the rotating flow which is used to obtain advantages of better mixing and combustion. In this work penetration and dispersion quality of the particles which are entering from various positions on the vortex engine walls have been numerically predicted. Head side, end side, and sidewall are considered as the entering positions. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, and density of entering the particles are assumed to be known. If the particle length scale is considered not to be comparable... 

this research chamber effective length, which is the minimum chamber length required for complete combustion, for a dilute monopropellant spray, constant area, one dimensional and fixed volume engine is analytically predicted. A new evaporation rate in the form of dk +1 relation, instead of d 2 law, is introduced. In case of controlling the vaporization by radiative heat transfer, k is equal to zero, and when molecular processes control the vaporization, k will be equal to unity and in some cases the vaporization data need the value of k greater than one to fit properly to related equation. Development of this approach can be used in design of combustion chambers with optimum length and with... 

Particle dispersion in the vortex flow has been one of the most interesting subjects in recent years. Bidirectional vortex flow field is an industrial sample of rotating flow which is used to obtain advantages of better mixing and combustion. In this work penetration and dispersion quality of particles which are entering from various positions on the vortex engine walls have been numerically predicted. Head side, end side, and sidewall are considered as the entering positions. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, and density of entering particles are assumed to be known. If the particle length scale is considered not to be comparable with the... 

In this research, effective length of one-dimensional combustion in a dilute monopropellant spray, constant area and fixed volume chamber is analytically predicted. A new evaporation rate in the form of d k+1 relation is introduced. In the case of controlling vaporization by radiative heat transfer, k is equal to zero, and when molecular processes control the vaporization, k will be equal to one and in some cases vaporization data need the value of k greater than one to fit properly to related equation. Development of this approach can be used in the design of combustion chambers with optimum length and with using vaporization rate of R = R0〈r〉 0 k/〈r〉k. Spray equation and distribution... 

In this research particle trajectory in a bidirectional vortex flow has been numerically predicted and the results experimentally validated. Scale analyses of forces show their order of magnitudes and give a criterion to recognize the order of magnitude of exerting forces on the particle. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, density, and position of entering particle are assumed to be known. If the particle length scale is considered not to be comparable with the chamber length and if particle number density is low, then influence of particle on the flow field is negligible and a one-way solution is applicable. The governing equation is converted to... 

The solution for bulk fluid motion of a bidirectional coaxial vortex for application in vortex engine has been derived. The vortex engine is a novel combustion chamber in which swirl motion of reactants are used to maintain the chamber walls cool. The flow field has been considered both analytically and numerically. The model is based on incompressible, steady, axisymmetric, and non-reactive flow conditions. The governing PDEs are reduced to a system of nonlinear ODEs and then, by a coordinate transformation, their singularity has been relaxed. Solution domain has been decomposed into the inner viscous and outer inviscid regions, then, the velocity and pressure fields are obtained... 

The drug discovery process faces challenges due to its length, cost, and experimental failures. Researchers are addressing these issues through 'drug repurposing,' seeking new applications for existing pharmaceuticals. To predict drug-target interactions, computational methods, like drug-target interaction prediction, utilize bipartite graphs and link prediction. In this paper, we propose BiProSimGCN, a framework based on convolutional graph neural networks, to predict drug-protein interactions. BiProSimGCN integrates data from the bipartite drug-protein network and the protein similarity network, aiming to reveal latent factors of drugs and proteins. The performance of BiProSimGCN is... 

Identifying sub-networks showing similar properties, referred to as community detection, is a challenging task in network analysis. This challenge becomes even more formidable in bipartite networks. The focus of this study is the patients with problems in their Peripheral Nerve System. To this aim, we engaged the assistance of spinal specialty clinics in the collection of necessary Data. We employ the bipartite network to represent the relationship between the patients and their symptoms and disorders. The resulting bipartite network showcases unequally sized sets of nodes, making community detection more challenging. The principal purpose of this study is to develop a new, practically... 

In order to improve titanium corrosion behavior, we can increase the thickness of oxide layer on titanium surface during anodizing process and by electrochemistry. In this research, self-color anodizing of Ti in sulfuric acid was done, and anodizing layers were created in different colors. The highest value of chromaticity was 37.8 for the anodized sample in 10 V, and the lowest value was 8.6 at 15 V. The oxide layer thickness was calculated by optical method (light refraction). The anodic film thickness increased by increasing the anodizing voltage. The highest thickness of anodic film was 190 nm in sulfuric acid solution for the anodized sample in 80 V. Corrosion resistance of anodized Ti... 

Text classification in imbalanced datasets poses a significant challenge in natural language processing (NLP) applications. In this paper, we address this issue by treating text data as graphs, with words as nodes, and employ two strategies for establishing connections between words within these graphs. The first strategy employs a fixed-size context window to connect words that lie within the same window, while the second strategy leverages word embedding vectors and a k-nearest neighbors (KNN) approach to connect each word to its k most similar neighbors. To further enhance the classification performance, we combine Graph Convolutional Neural Networks (GCNs) and Long Short-Term Memory... 

Depth estimation is critical for autonomous vehicles (AVs) to perceive their surrounding environment. However, the majority of current approaches rely on costly sensors, making wide-scale deployment or integration with present-day transportation difficult. This issue highlights the camera as the most affordable and readily available sensor for AVs. To overcome this limitation, this paper uses monocular depth estimation as a low-cost, data-driven strategy for approximating depth from an RGB image. To achieve low complexity, we approximate the distance of vehicles within the frontal view in two stages: firstly, the YOLOv7 algorithm is utilized to detect vehicles and their front and rear... 

In this study, we apply the monitoring master equation describing decoherence of internal states to an optically active molecule prepared in a coherent superposition of nondegenerate internal states interacting with thermal photons at low temperatures. We use vibrational Raman scattering theory up to the first chiral-sensitive contribution, i.e., the mixed electric-magnetic interaction, to obtain scattering amplitudes in terms of molecular polarizability tensors. The resulting density matrix is used to obtain elastic decoherence rates  

Gas turbine shaft is generally exposed to high temperature gases and may seriously be affected and overheated due to temperature fluctuations in the combustion chamber. Considering vortex flow in the combustion chamber, it may increase the heat release rate and combustion efficiency and also control location of energy release. However, this may result in excess temperature on the combustor equipments and gas turbine shaft. Vortex flow in the vortex engine which is created by the geometry of combustion chamber and conditions of flow field is a bidirectional swirl flow that maintains the chamber wall cool. In this study a new gas turbine combustion chamber implementing a liner around the shaft...