GOP-SDN: an enhanced load balancing method based on genetic and optimized particle swarm optimization algorithm in distributed SDNs

Wireless Networks - One of the biggest challenges of distributed software defined networks (SDNs) is to create load balancing on controllers to reduce response time. Although recent studies have...     

Synthesis and characterization of alcogels based on ethylene glycol methyl ether methacrylate-vinyl phosphonic acid copolymers

Alcohol absorbents based on poly(ethylene glycol methyl ether methacrylate) and vinyl phosphonic acid (VPA) were prepared via solution polymerization using poly(ethylene glycol dimethacrylate) macrocrosslinker. Swelling capacity of these materials was measured in water, ethanol and methanol. Alcohol absorbency was increased with increase of VPA content that can be attributed to ability of VPA in formation of H-bonding and disassociation of phosphonic acid group to produce mobile ions. The alcogels could absorb ethanol and methanol up to 15.1 and 17.8 g/g respectively. Thermo-gravimetric analysis showed that increase in VPA concentration increased char yield and decreased the initial decomposition temperature (IDT) due to forming anhydride crosslinks during heating. Based on rheological measurements, the storage modulus was increased with increase in PEGMEMA content. The prepared alcogels were further characterized using FTIR, NMR and DMTA.     

Effects of structural variables on AUL and rheological behavior of SAP gels

The swelling properties of superabsorbent polymers (SAPs) under real conditions are extremely important for selecting the material suitable for a given application, e.g. feminine napkin or agriculture. This new practical research represents deeper synthetic and physicochemical studies on the structure–property relation in acrylic SAP hydrogels and composites. Thus, the values of saline‐absorbency under load (AUL; a measurable simulation of the real circumstances of SAP applications, at pressures 0.3–0.9 psi) were measured for the SAP or SAP composite samples prepared under different conditions, i.e. type and content of crosslinker, type and concentration of initiator, percentage of inorganic filler (kaolin), and type and percentage of porosity generators. The samples were subsequently used to determine the rheological and morphological characteristics. Dynamic storage modulus (G′) measurements were carried out at constant strain in a wide range of frequency. Linear correlations were frequently found to be active between AUL and G′ data over the rubber‐elastic plateau. Thus, for a given SAP: AUL = k_totalG′ + C. The coefficient k total is a function of (nature and content of crosslinker, initiator, inorganic component, particle morphology, etc.). Therefore, the easily measured AUL values could be simply correlated to the main synthesis variables and molecular structure of SAP gels through a rheological material function (G′). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dendritic macromolecules containing several types of functional groups

Dendritic macromolecules containing several types of functional groups were successfully synthesized through divergent method. Poly(ethylene glycol) was functionalized using cyanuric chloride and it was reacted with p‐toluidine at room temperature and a macromolecule containing chloride and methyl functional groups (PEG‐Cl₂‐Me₂) was obtained. Substitution of chloride functional groups of PEG‐Cl₂‐Me₂ by hydroxyl functional groups led to a macromolecule containing methyl and hydroxyl functional groups (PEG‐Me₂‐OH₄). Hydroxyl functional groups of PEG‐Me₂‐OH₄ were reacted with cyanuric chloride and PEG‐Me₂‐Cl₈ was obtained. Finally, PEG‐Me₂‐Cl₈ was reacted with p‐aminophenol at room temperature and a macromolecule containing methyl, hydroxyl, and chloride functional groups (PEG‐Me₂‐(PhOH)₄‐Cl₄) was obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of long-chain monoacrylate on the residual monomer content, swelling and thermomechanical properties of SAP hydrogels

Residual monomer is an important factor, particularly in hygienic materials such as superabsorbent polymer (SAP) hydrogels. Recently, we reported different approaches to minimizing residual monomer content in SAPs. In this paper, the effect of a long-chain monomer, poly(ethylene glycol) methylether methacrylate (PEG.MEMA), on the residual monomer content of SAP networks of partially neutralized acrylic acid–PEG.MEMA is investigated. The aim of using PEG.MEMA in SAP synthesis was to reduce the glass transition temperature (T _g) of SAP. As the temperature that is conventionally used to dry SAP (70–110 °C) is lower than the T _g of ordinary SAPs, the polymer is in the glassy state during the heating stage. It was assumed that converting SAP from the glassy state to the rubbery state during drying would facilitate the removal of acrylic acid monomer (AA) from the gel, thus reducing the residual monomer content. The results showed that the use of PEG.MEMA led to a reduction in residual AA when the drying temperature was 100 °C. The residual AA was decreased from 169 to 95 ppm when the drying time was increased from 3 to 15 hours at 100 °C. This positive effect of PEG.MEMA on the level of unwanted residual AA became insignificant at a higher drying temperature (140 °C). The effects of PEG.MEMA content on the thermal and mechanical properties (in the dried state) and the rheological properties (in the water-swollen state) of the SAP hydrogels were also investigated. The swelling capacity and rate was studied in relation to the PEG.MEMA content. It was found that a high level of PEG.MEMA restricted both the absorption capacity and the rate of water absorption.     

An Improved Model for Fiber Kinking Analysis of Unidirectional Laminated Composites

This paper focuses on the fiber-kinking failure mode of unidirectional laminated composites under the compressive loading. An available stress based fiber-kinking model is explained and improved on the bases of strain concept. In the improved model, a new fracture surface is considered and the stresses are updated according to this new fracture surface. By taking the advantage of damage variables, the models are implemented into a finite element code and the results of numerical analysis such as prediction of kink band angles are discussed in details and compared with the available results in the literature. It is shown that the predicted kink band angles using the improved model are in good agreement with the experimental results.     

Effect of specimen geometries on the C versus da/dt master curve for type 316L stainless steel

This work deals with engineering components made of stainless steels working at high temperature and subjected to creep-fatigue loading history. The defect assessment procedures generally use the crack growth properties curve da/dt versus C^∗ parameter for estimating the creep-crack growth. The ASTM E 1457-98 [ASTM E 1457-98. Standard test method for measurement of creep crack growth rates in metals, 1998] procedure proposes the rule to establish such a master curve. In particular, it is stipulated that this rule only applies for CT specimens. Previously [Laiarinandrasana L, Kabiri R, Drubay B. In: Gupta A, editor. Proceedings of the 16th international conference on structural mechanics in reactor technology, Washington, USA, 2001], some practical methodology to produce this crack growth curve on CT specimens has been described by introducing the way to determine the upper and lower limits of relevant experimental points and by adopting the ASTM E 1457-98 method to estimate the creep component of the load line displacement rate (dδ/dt_behavior). This latter is the interesting part of the total displacement rate recorded during the test. This paper focuses on the application of the procedure proposed in [Laiarinandrasana L, Kabiri R, Drubay B. In: Gupta A, editor. Proceedings of the 16th international conference on structural mechanics in reactor technology, Washington, USA, 2001] on specimen geometries other than CT, such as circumferentially cracked round bar (CCRB) and double edged notched in tension (DENT) specimens. The da/dt versus C^∗ curves issued from all of these specimens are compared. Discussion about the effect of geometry on these curves is carried out. Additionally, some finite element analyses have been performed in order to simulate the creep crack growth using the node release technique. These simulations allow to verify the validity of the proposed expressions of C^∗ and consequently the master curve of the 316L(N) stainless steel.     

Formation control of VTOL UAV vehicles under switching-directed interaction topologies with disturbance rejection

This paper addresses the adaptive formation control of a group of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV) with switching-directed interaction topologies. In addition, to tackle the adverse effect of disturbances, a couple of smooth bounded estimators are involved in the procedure design. Exploiting an extraction algorithm, we take advantage of the fully actuated rotational dynamics, to control the translational dynamics of each vehicle. We propose a distributed control scheme such that all vehicles track a desired reference velocity signal while keeping a desired prespecified formation. In this framework, the underlying topology of the agents may switch among several directed graphs, each having a spanning tree. The stability of the overall closed-loop system is proved through Lyapunov function. Finally, simulation results are given to better highlight the effectiveness of the proposed control scheme.     

Synthesis of cellulose/reduced graphene oxide/polyaniline nanocomposite and its properties

A series of conductive nanocomposites cellulose/reduced graphene oxide/polyaniline (cellulose/RGO/PANi) were synthesized via in situ oxidative polymerization of aniline on cellulose/RGO with different RGO loading to study the effect of RGO on the properties of nanocomposites. The results showed that when RGO is inserted into cellulose/PANi structure, its thermal stability and conductivity are increased. So that adding of only 0.3 wt% RGO into the cellulose/PANi structure, its conductivity is increased from 1.1 × 1 10^?1 to 5.2 × 110^?1 S/cm. Scanning electron microscopy results showed that the PANi nanoparticles are formed a continuous spherical shape over the cellulose/RGO template; this increases the thermal stability of nanocomposite.