Controller placement in software defined networks using multi-objective antlion algorithm

Software defined network (SDN) is a new modern network technology which decouples control plane and data plane to simplify network management. The separation of control plane from data plane arises the control placement problem (CPP) in these networks. The main questions in the CPP are (1) how many controllers are required to be used in such networks and (2) where these controllers should be placed. To achieve an efficient solution for such problem in SDN, we define the CPP as a multi-objective combinational optimization problem in this paper and solve the CPP by applying the antlion optimization algorithm on it. We consider three metrics for the CPP: (a) Inter-controllers latency, (b) switch to controller latency, and (c) multiple disjoint connectivity paths between switches and controllers. We evaluate our proposed solution by performing several experiments using different real network topologies. Experimental results show that our proposed solution provides better performance compared to the existing solutions.

     

Accuracy and availability modeling of social networks for Internet of Things event detection applications

Wireless Networks - As Social networks are widely used by the people around the world, if this infrastructure can be used for event detection systems like fire forest detection, the overall cost of...     

Creep analysis of an earth embankment on soft soil deposit with and without PVD improvement

In this paper, an anisotropic creep constitutive model, namely Creep-SCLAY1S is employed to study the installation effects of prefabricated vertical drains (PVDs) on the behavior of a full scale test embankment, namely Haarajoki embankment in Finland. The embankment was constructed on a natural soft soil with PVD installed to improve the drainage under one half of it. The Creep constitutive model used in this study, incorporates the effects of fabric anisotropy, structure and time within a critical state based framework. For comparison, the isotropic modified Cam clay (MCC) model and the rate-independent anisotropic S-CLAY1S model are also used for the analyses. The numerical predictions are compared with field measurements and the results indicate that the creep model provides an improved approximation of field settlements, and excess pore pressure build-up and dissipations. In addition, the application of two commonly used permeability matching techniques for two dimensional (2D) plane-strain analysis of the PVD problem is studied and the results are discussed highlighting their limitations and advantages.     

The evolution of soot morphology in a laminar coflow diffusion flame of a surrogate for Jet A-1

An experimental study is performed to investigate the evolution of soot morphology in an atmospheric pressure laminar coflow diffusion flame of a three-component surrogate for Jet A-1. The laser extinction measurement method and the rapid thermocouple insertion technique are used to obtain soot volume fraction profiles and temperature profiles, respectively. Thermophoretic sampling followed by transmission electron microscopy and atomic force microscopy is used to study the morphology of soot particles at different locations inside the flame. Soot formation on the centerline appears to be different from conventional models. Liquid-like particles, which are transparent at the wavelength of 623 nm, are formed and grow up to a volume equivalent diameter of d_p = 60 nm at temperatures below T = 1500 K. When the temperature exceeds 1500 K, transition of the transparent particles to the mature agglomerated particles happens immediately, i.e. in less than 12 ms. The volume of the liquid-like particles just before the start of their transformation to solid is about five times larger than the volume of mature primary particles. This significant size difference suggests that a large liquid-like particle does not transform into a single primary particle. In addition, multiple dark nuclei are observed in the liquid-like particles prior to carbonization. The significant size discrepancy and the presence of multiple dark nuclei may indicate that primary particle formation and agglomeration on the centerline happen inside the liquid-like particles. In contrast to the centerline, on another streamline with a significantly different temperature history, soot particles form from relatively small liquid-like particles. These particles have the same size as mature primary particles. Carbonization happens early on the streamline. A single dark nucleus grows inside each liquid-like particle and primary particles agglomerate after carbonization is completed. Most of the currently used computational soot models consider a single evolution process for all of the streamlines inside the flame which may not be an accurate assumption. This study shows that soot evolution processes may be different across the flame and are a function of temperature and the concentration of specific species inside the flame.     

Chemical,morphological and structural characteristics of crossbred wool fibers

Abstract

Crossbreeding of a local sheep called Ghezel thick wool with Arkharmerino fine wool is one of the interest studies in the last decade to improve the local sheep’s products quality. In this study, the chemical and mechanical properties of Arkharmerino, Ghezel and their first and second-generation wool fibers were investigated. The diameter, length and tensile properties of wool fibers were studied. The Fourier transform infrared spectroscopy, scanning electron microscope, X-ray diffraction and energy dispersive X-ray spectrum were also performed to evaluate the morphological and physical characteristics of all samples. The results showed that crossbreeding Ghezel ewes with Arkharmerino rams led to improving the wool fiber characteristics from chemical and physical properties points of view in the final application. The higher fineness, higher length, lighter color and higher tenacity were resulting from Arkharmerino–Ghezel in the second generation in comparison with Ghezel wool fibers.     

Preserving Melons by Osmotic Dehydration in a Ternary System Followed by Air-Drying

In this study, the effect of different osmotic solution concentrations (20–60% w/w of sucrose with 10% w/w NaCl salt), fruit to solution ratios (1:9–1:3), immersion times (0.5–4 h), and temperatures (15–55°C) on the mass transfer kinetics during osmotic dehydration of melons (Curcumis melo L.) in ternary solution namely sucrose–salt–water followed by air-drying were investigated. The effective diffusion coefficients for sucrose and water during osmotic dehydration were determined, assuming osmotic dehydration to be governed by Fickian diffusion. The estimated parameters allowed optimizing the system to reduce total processing time. The optimum treatments were with 50% sucrose and 10% NaCl salt concentration, fruit to solution ratio of 1:4 for 1 h at 45°C. Samples non-treated and pre-treated in optimized conditions were dried in a hot-air dryer at 60°C until equilibrium was achieved after 2.5 h. Pre-treatment reduced the air-drying period in up to 6.8 h.     

Investigation of chirality and diameter effects on the Young’s modulus of carbon nanotubes using non-linear potentials

The main goal of this research is to predict Young’s modulus of carbon nanotubes using a full non-linear finite element model. Spring elements are used to simulate molecular interactions in atomic structure of carbon nanotube. All interactions are simulated non-linearly. A parametric study is performed to investigate effects of chirality and diameter on the Young’s modulus of single walled carbon nanotubes. Unlike the results of presented linear finite element models, the results of current model imply on independency of Young’s modulus from chirality and diameter. Obtained results from this study are in a good agreement with experimental observations and published data.     

Experimental investigation and detailed modeling of soot aggregate formation and size distribution in laminar coflow diffusion flames of Jet A-1, a synthetic kerosene,and n-decane

A fully-coupled soot formation model is developed to predict the concentration, size, and aggregate structure of soot particles in the atmospheric pressure laminar coflow diffusion flames of a three-component surrogate for Jet A-1, a three-component surrogate for a Fischer–Tropsch Synthetic Paraffinic Kerosene (SPK), and n-decane. To model the chemical structure of the flames and soot precursor formation, a detailed chemical kinetic mechanism for fuel oxidation, with 2185 species and 8217 reactions, is reduced and combined with a Polycyclic Aromatic Hydrocarbon (PAH) formation and growth scheme. The mechanism is coupled to a highly detailed sectional particle dynamics model that predicts the volume fraction, structure, and size of soot particles by considering PAH-based nucleation, surface growth, PAH surface condensation, aggregation, surface oxidation, fragmentation, thermophoresis, and radiation. The simulation results are validated by comparing against experimental data measured for the flames of pre-vaporized fuels. The objectives of the present effort are to more accurately simulate the physical soot formation processes and to improve the predictions of our previously published jet fuel soot formation models, particularly for the size and aggregate structure of soot particles. To this end, the following improvements are considered: (1) addition of particle coalescence submodels to account for the loss of surface area, reduction of the number of primary particles, and increase of primary particle diameters upon collision, (2) consideration of a larger PAH molecule (benzopyrene instead of pyrene) for nucleation and surface growth to enhance the agreement between the soot model and the measured chemical composition of soot particles, and (3) implementation of a dimerization efficiency in the soot inception submodel to account for the collisions between PAH molecules that do not lead to dimerization. The results of two different particle coalescence submodels show that this process is too slow to account for the growth of primary particles, mainly because of the limited rate of particle collisions. Soot volume fraction predictions on the wings and at lower flame heights are considerably improved by using benzopyrene, due to the different distribution of the soot forming PAH molecule in the flame. The computed number of primary particles per aggregate and the diameters of primary particles agree very well with the experimentally measured values after implementing the dimerization efficiency for PAH collisions, because of the reduced rate of soot inception compared to growth by PAH condensation. Concentrations of major gaseous species and flame temperatures are also well predicted by the model. The underprediction of soot concentration on the flame centerline, observed in previous studies, still exists despite minor improvements.     

Review on effective parameters in electrochemical hydrogen storage

Today, energy has become one of the most important concerns of developing countries. The use of non-renewable energy sources, as well as the production of pollution, has led to growing efforts to replace fossil fuels, which are the most important energy sources in the modern world. Hydrogen as a clean fuel has attracted a lot of attention in recent years. Various methods have been reported for the production and storage of hydrogen. According to their advantages and disadvantages, it can be said that electrochemical hydrogen storage method is superior to other methods in terms of cost, safety, and optimum condition. The electrochemical hydrogen storage is done in a variety of techniques, and in recent years, the chronopotentiometry method has become one of the most popular methods for scientists. In chronopotentiometry technique, several parameters such as the reference electrode, the counter electrode, the working electrode, electrolyte, and current density are important. In this review, we investigated the articles that have been done in this regard from 2000 to 2020. This review can help scientists to better understand the electrochemical hydrogen storage system.     

Options-based negotiation management of PPP–BOT infrastructure projects

The success of public–private partnership (PPP)–build–operate–transfer (BOT) projects largely depends on effectively mitigating the impact of a variety of risks and uncertainties, especially those influencing the revenue over time. Revenue instability is one of the main obstacles of PPP form of procurement. Government support, which is established as a clause in the concession agreement, should be carefully designed and well formulated. Options which arise from certain clauses in the contract are more valuable for risky projects. The purpose of this paper’s proposed model is to evaluate early fund generation options and also to calculate equitable bounds for a guaranteed revenue for the project sponsor under uncertainty and risk. The model is specially designed to alleviate the concern of revenue risk. To illustrate its applicability the methodology is then applied to a freeway PPP project and a power plant PPP project in Iran. The results show that the value of these options can indeed be significant and by applying the proposed systematic negotiation mechanism both public and private sectors can take advantage of its flexibility at the negotiation table. The proposed mechanisms can facilitate negotiations on the verge of a break down as well as accelerating ongoing negotiations that have become moribund.