Sharif Digital Repository

Topic detection is the task of determining and tracking hot topics in social media. Twitter is arguably the most popular platform for people to share their ideas with others about different issues. One such prevalent issue is the COVID-19 pandemic. Detecting and tracking topics on these kinds of issues would help governments and healthcare companies deal with this phenomenon. In this paper, we propose a novel, multi-agent, communicative clustering approach, so-called ComStreamClust for clustering sub-topics inside a broader topic, e.g., the COVID-19 and the FA CUP. The proposed approach is parallelizable, and can simultaneously handle several data-point. The LaBSE sentence embedding is used... 

GPUs are widely used for diverse applications, particularly data-parallel tasks like machine learning and scientific computing. However, their efficiency is hindered by architectural limitations, inherited from historical RISC processors, in handling memory loads causing high register file contention. We observe that a significant number (around 26%) of values present in the register file are typically used only once, contributing to more than 25% of the total register file bank conflicts, on average. This paper addresses the challenge of single-use memory values in the GPU register file (i.e. data values used only once) which wastes space and increases latency. To this end, we introduce a... 

In this paper, it is shown that the main source of mechanical energy of cardiovascular (CV) system i.e., rhythmic heart contraction is transformed to the oscillations of the CV walls and blood flow, and finally CV acoustical waves. These waves propagate through both blood flow (hemodynamical pathways) and tissues (viscoelastical pathways) toward the skin. Nonetheless, the CV walls could be assumed as the source of acoustical waves, since they act as the interface between blood flows and other tissues including skin. After obtaining the approximate accelerations of CV walls from pressure-flow (PF) models, we also needed to model the viscoelastical pathways until the skin. Some improvements on... 

The interactions between five amino acid based anions ([AA] - (AA = Gly, Phe, His, Try, and Tyr)) and N7,N9-dimethylguaninium cation ([dMG] +) have been investigated by the hybrid density functional theory method B3LYP together with the basis set 6-311++G(d,p). The calculated interaction energy was found to decrease in magnitude with increasing side-chain length in the amino acid anion. The interaction between the [dMG] + cation and [AA] - anion in the most stable configurations of ion pairs is a hydrogen bonding interaction. These hydrogen bonds (H bonds) were analyzed by the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis. Finally, several correlations... 

The aim of this study is to investigate the uniform cooling of a hot isothermal heated target surface, using four turbulent impinging air jets. Eight parameters including the width of jets, the space between the inner jets, the space between inner and outer jets, the distance of jets from the plate, the impingement angle of jets, and the overall volumetric flow rate of the cooling air per unit depth of the nozzle are considered as design variables. The normalized standard deviation of the local Nusselt number from the desired Nusselt number is considered as the objective function. An optimization algorithm based on pattern search method is utilized to obtain the optimum array of the jets.... 

Horizontal ground heat exchangers (GHEs) have a lower cost in comparison to vertical ones; however, they require more land area. For the sake of reducing the required land area for horizontal GHEs, flat-panel GHEs have been recently introduced. In this piece of research, a 3-D numerical model has been developed to predict the thermal performance of flat-panel GHEs. In this study, at first, the thermal performance of a flat-panel GHE has been compared with that of linear horizontal ones. The results demonstrate that the flat-panel GHE has a better thermal performance of about 27% in comparison to an arrangement of linear GHEs with a value of 0.5 m for pipe spacing. In the second part of this... 

As one of the cleanest energies, hydrogen has attracted much attention over the past decade. Hydrogen can be produced using water electrolysis in a Proton Exchange Membrane Electrolysis Cell (PEMEC). In the present study, the performance of the PEMEC, powered by the Photovoltaic-Thermal (PVT) system, is scrutinized. It is considered that the PVT system provides the required electrical power of the PEMEC and preheats the feedwater. A comprehensive numerical model of the coupled PVT-PEMEC system is developed. The model is used to investigate the effect of various operating parameters, including solar radiation intensity, inlet feedwater temperature, and feedwater mass flow rate, on the... 

As one of the cleanest energies, hydrogen has attracted much attention over the past decade. Hydrogen can be produced using water electrolysis in a Proton Exchange Membrane Electrolysis Cell (PEMEC). In the present study, the performance of the PEMEC, powered by the Photovoltaic-Thermal (PVT) system, is scrutinized. It is considered that the PVT system provides the required electrical power of the PEMEC and preheats the feedwater. A comprehensive numerical model of the coupled PVT-PEMEC system is developed. The model is used to investigate the effect of various operating parameters, including solar radiation intensity, inlet feedwater temperature, and feedwater mass flow rate, on the... 

Hydrogen bonding interactions between thymine nucleobase and 2'-deoxythymidine nucleoside (dT) with some biological anions such as F - (fluoride), Cl - (chloride), OH - (hydroxide), and NO 3 - (nitrate) have been explored theoretically. In this study, complexes have been studied by density functional theory (B3LYP method and 6-311++G (d,p) basis set). The relevant geometries, energies, and characteristics of hydrogen bonds (H-bonds) have been systematically investigated. There is a correlation between interaction energy and proton affinity for complexes of thymine nucleobase. The nature of all the interactions has been analyzed by means of the natural bonding orbital (NBO) and quantum theory... 

Density functional theory (DFT) method and B3LYP/6-311++G(d,p) basis set were used to determine coordination geometries, binding strength, and metal ion affinity (MIA) for interaction of 2′-deoxythymidine (dT) with alkali metal cations including Li+, Na+, and K+. Calculations demonstrated that the interaction of dT with these cations is tri-coordinated η (O2, O4′, O5′). Among these cations, Li + cation exhibited the most tendency for interaction with dT. Cations via their interaction with dT can affect the N-glycosidic bond length, the values of pseudorotation of the sugar ring, the orientation of base unit with respect to sugar ring and the acidity of O5′H, O3′H, and N3H groups in 2′-dT... 

TiO2 layers were grown via pulse type microarc oxidation process under different applied voltages, frequencies, and duty cycles. Surface chemical composition and phase structure of the synthesized layers were studied utilizing X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Furthermore, scanning electron microscope (SEM) and atomic force microscope (AFM) were employed to investigate surface morphology and topography of the layers. It was revealed that the layers had a porous structure with both anatase and rutile phases. The anatase relative content in the layers increased with the applied frequency; meanwhile, it decreased with duty cycle at low applied voltages, but... 

Dust deposition on the surface of solar systems is one of the main parameters that significantly affects the performance of such systems. In this study, the effect of dust deposition density on the performance of photovoltaic modules (PV) and photovoltaic-thermal systems (PVT) is numerically investigated. Accordingly, all layers of a monocrystalline silicon PV module for both systems are simulated. Moreover, the effect of various system parameters on the performance of both clean and dusty PV module and PVT system are studied. The studied parameters included: solar radiation intensity, ambient temperature, coolant inlet temperature, and coolant inlet velocity. The obtained results indicate... 

Heat pumps as the only end-use cooling/heating technology with a Coefficient of Performance (COP) greater than one, have attracted a great deal of attention over the past decade. In this study, the long-term energy and exergy analysis of four different types of heat pump systems: a common Air Source Heat Pump (ASHP), an ASHP with Ground Air Heat Exchanger (GAHE), a Ground Source Heat Pump (GSHP) with Horizontal Ground Water Heat Exchanger (HGWHE), and a GSHP with Vertical Ground Water Heat Exchanger (VGWHE) is performed. It is considered that all systems are used for space cooling and heating of a residential building. A mathematical model that takes into account the variations of building... 

Ejector refrigeration system has many advantages over traditional compressor-based systems, including: simplicity, low installation and operating costs and the ability to operate with low-grade thermal energy sources. However, its main drawbacks are low Coefficient of Performance (COP) and failure at high ambient temperatures. To overcome these problems, a novel methodology for designing a multi-ejector refrigeration system is proposed. This system utilizes a parallel array of ejectors instead of one ejector. Therefore, the system can continuously operate at its optimum efficiency. Each ejector works within a specific range of condensing pressures. The condenser pressure governs the... 

In recent years horizontal Ground Heat Exchangers (GHEs) has attracted a growing interest as heat source/sink for ground source heat pump systems. Horizontal GHEs initial installation costs are lower than the vertical ones; however, they require larger land area and more pipes. Therefore, it is necessary to reduce their required land area and pipe length by improving their thermal performance. In this study, a numerical modal based on 3-D simulation of GHE with computational fluid dynamics methods is developed. The model is used to evaluate the thermal performance and initial installation cost of horizontal GHEs. Four different types of horizontal GHEs: linear, spiral, horizontal and... 

Solar Chimney (SC) can play a significant role in energy consumption reduction of ventilation applications. The primary purpose of this study is to ameliorate the performance of an inclined rooftop SC integrated with the Phase Change Material (PCM) and Photovoltaic (PV) module, called the SC-PCM-PV system. To this aim, the effects of using finned absorbers and composite PCMs on the performance of the SC-PCM-PV system are investigated for the first time. A 3D-CFD model is developed via the finite volume method to examine the impact of various design parameters, including fin number, fin thickness, PCM type, and PCM mass on natural ventilation duration, ventilation capacity, and power output.... 

Solar-driven ejector refrigeration (SER) systems have been granted special attention as a green and sustainable replacement for conventional vapor compression cooling systems. However, despite their significant advantages, SER systems suffer from a relatively low coefficient of performance and failure at high ambient temperatures and low solar radiations. Therefore, the need for an auxiliary heat source and cooling system has hindered their adoption in practice. In an attempt to eliminate the need for an auxiliary heat source and cooling system, this contribution puts forward a novel Solar-driven Multi-Ejector Refrigeration (SMER) system with an internal heat exchanger, a regenerator, and a... 

Horizontal Ground Heat Exchangers (HGHE) as a means of exploiting geothermal energy has come to the fore for a few decades. Various analytical and Computational Fluid Dynamics (CFD) methods have been proposed to predict the performance of the HGHEs. The available analytical approaches are fast; however, they are based on various simplifications and assumptions, affecting their accuracy. On the other hand, CFD methods are more accurate, but their computational cost is a burden. Therefore there is an acute need for an accurate and fast method for predicting the long-term performance of HGHEs. To this aim, this study puts forward a novel hybrid analytical-numerical model for predicting the... 

In this study, the performance of a Photovoltaic Thermal-Organic Rankine Cycle (PVT-ORC) system combined with a Proton Exchange Membrane Electrolysis Cell (PEMEC) is investigated. A combined numerical/theoretical model of the system is developed and used to evaluate the effect of various system design parameters. In addition, the effects of using water, ethylene glycol, and a mixture of water and ethylene glycol (50/50) as the working fluid of the PVT system and R134a, R410a, and R407c as the working fluid of the ORC cycle on the performance of the PVT-ORC-PEMEC system are studied. Based on the results, R134a and water demonstrated the best performance as the working fluid of the ORC and PVT...