Spontaneous Formation of Liquid Crystals in Ultralarge Graphene Oxide Dispersions

A novel process is developed to synthesize graphene oxide sheets with an ultralarge size based on a solution‐phase method involving pre‐exfoliation of graphite flakes. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of the ultralarge graphene oxide sheets in water above a critical concentration of about 0.1 wt%. It is the lowest filler content ever reported for the formation of liquid crystals from any colloid, arising mainly from the ultrahigh aspect ratio of the graphene oxide sheets of over 30 000. It is proposed that the self‐assembled brick‐like graphene oxide nanostructure can be applied in many areas, such as energy‐storage devices and nanocomposites with a high degree of orientation.     

Study the flashover voltage for outdoor polymer insulators under desert climatic conditions

This work presents a study of flashover voltage for outdoor polyester and composite insulators under some desert climatic conditions. Cylindrical polyester composite samples have been prepared after incorporated with different concentrations of inorganic fillers e.g., alumina trihydrate [ATH], boric acid [H₃BO₃] and magnesium hydroxide [Mg(OH)₂] to improve the electrical, mechanical and thermal properties in addition to maximize the surface flashover voltage and decrease the tracking phenomena.Results showed that flashover voltage reaches to 38 kV for samples without filler and 47 kV for samples containing 50% of ATH filler in dry condition. A comparison between inorganic fillers under various environmental conditions showed higher flashover voltage values for samples containing ATH filler than that of samples containing H₃BO₃ and Mg(OH)₂ fillers at all filler concentrations. Flashover voltage increases 24% by adding ATH filler for polyester samples under sandstorm conditions. Also, in this study, the effects of sandstorm, ultra violet (UV) radiation, mechanical strength (compressive and tensile strengths) and thermal performance with respect to surface of the sample under test have been investigated in detail.     

Producer’s behavior analysis in an uncertain bicriteria AGV-based flexible jobshop manufacturing system with expert system

Here, an approach for finding an optimal path in a flexible jobshop manufacturing system considering two criteria of time and cost is proposed. A network is configured in which the nodes are considered to be the shops with arcs representing the paths among the shops. An automated guided vehicle functions as a material handling device through the manufacturing network. To account for uncertainty, time is considered to be a triangular fuzzy number and apply an expert system to infer the cost. The expert system based on fuzzy rule backpropagation network to configure the rules for estimating the cost under uncertainty is proposed. A multiple linear regression model is applied to analyze the rules and find the effective rules for cost estimation. The objective is to find a path minimizing an aggregate weighted unscaled time and cost criteria. A fuzzy dynamic programming approach is presented for computing a shortest path in the network. Then, a comprehensive economic and reliability analysis is worked out on the obtained paths to find the optimal producer’s behavior. Finally, an application of the model is illustrated by a numerical example. The results show the effectiveness of our approach for finding an optimal path in a manufacturing system under uncertainty.     

Modeling of nucleate boiling heat transfer under an impinging free jet

A model using an analytical/empirical approach has been developed to predict the rate of heat transfer in the stagnation region of a planar jet impinging on a horizontal flat surface. The model has been developed based on the hypothesis that bubble-induced mixing would result in enhanced or additional diffusivity. The additional diffusivity has been included in the diffusion term of the conservation equations. The value of the effective diffusivity has been correlated with jet parameters (velocity and temperature) and surface temperature using experimental data. The important aspects of the bubble dynamics (generation frequency and average bubble diameter) have been acquired using high-speed imaging and an intrusive optical probe. The applicability of the proposed model has been investigated under conditions of partial and fully-developed nucleate boiling. Experiments have been carried out using water at atmospheric pressure, mass flux in the range of 388–1649 kg/m² s, degree of sub-cooling in the range of 10–28 °C, and surface temperature in the range of 75–120 °C. Results showed that the proposed model is able to predict the surface heat flux with reasonable accuracy (+30% and ?15%).     

Microstructure and phase composition of cordierite-based co-clinker

The aim of this work is to study the effect of phase composition and microstructure of cordierite-based co-clinkers on the electrical properties and coefficient of thermal expansion of cordierite briquettes. To achieve this aim talc and kaolinite samples were collected from quarries in the Egyptian desert. The samples are characterized using XRD, XRF, polarized light, cathodoluminescence and SEM microscopy attached with EDAX, in addition to X-ray micro-computed tomography (3D- µXCT). The electrical properties and coefficient of thermal expansion of the cordierite briquettes are determined using HiTESTER instrument and automatic Netzsch DIL402 PC dilatometer, respectively.Five talc-based batches were shaped and fired in the temperature range 1000–1350 °C for 2 h. The microstructural and physical characteristics of the resulted cordierite-based co-clinkers depend mainly on the viscosity of the liquid phase developed during firing. The microchemistry of the cordierite briquettes confirms their enrichment of both cordierite and ferroan-cordierite crystallized directly from locally developed melts. The dielectric constant and loss factor values for cordierite briquettes allow their possible use as insulator components in electronic applications.     

Reducing of heat loss of rubber compound using natural zeolite filler: effect of partially substitution of fillers on compound properties

The main objective of this work was reducing the heat loss of styrene butadiene rubber by partial substitution of carbon black with natural zeolite as a filler. Reducing the usage of carbon black in the rubber industry is a good strategy to decrease fossil fuel usage and global warming. There are different mineral fillers like silica and clay to be used instead of carbon black. Effect of application of natural zeolite on reducing the heat loss of rubber compound based on SBR was investigated by melt mixing of natural zeolite in rubber matrix in an internal mixer. Natural zeolite was selected as 5, 10, 15, and 20 phr. Carbon black was partially substituted with zeolite and the effect of natural zeolite content and structure on different aspects of the compound including heat buildup, hardness, elongation, and modulus were evaluated. It was shown that although cross-link density and mechanical properties of the compounds decreased a little, but a significant improvement was observed in the fatigue resistance of the compounds beside a favorable decrease in the heat buildup and abrasion loss with an increase in the natural zeolite loading. The rate of improvement in properties was slowed down at zeolite contents higher than 5 phr.     

Differential Scanning Calorimetry of Aspartame-Caffeine Mixture

The possible interaction between aspartame and caffeine was investigated by comparing the thermal behavior, using differential scanning calorimetry, of physical mixtures of aspartame and caffeine along with mixtures, in the same molar ratios, obtained as the co-precipitate. Caffeine was found to form several complexes with aspartame. These complexes were found to be dependent on the molar ratios of aspartame to caffeine. The stoichiometry of the aspartame-caffeine complexes were determined from the enthalpy change of the DSC transitions resulting from the complex formation.     

Impedance studies on plasticized PMMA-LiX [X: CF3SO3, N(CF3SO2)2−] polymer electrolytes

Plasticized polymer electrolytes composed of poly(methylmethacrylate) (PMMA) as the host, propylene carbonate (PC) or ethylene carbonate (EC) as a plasticizer and LiX (X: CF₃SO₃⁻ or N(CF₃SO₂)₂⁻) as a salt were prepared by the solution cast technique. Impedance spectroscopy was performed in the temperature range between 303 and 383 K. In this paper, we report the electrical properties of polymer electrolytes with different lithium salts and plasticizers. The polymer electrolytes investigated exhibited high ionic conductivity at room temperature in the range of 10^− 6 to 10^− 4 S cm^− 1. The temperature dependence studies showed that the samples were ionic conductors and seemed to obey the Vogel-Tamman-Fulcher (VTF) rule. FTIR spectroscopy studies confirmed the polymer-salt interaction.     

Synthesis of high purity Tl1212 superconductor with ultrafine grains from coprecipitated Tl-free precursor route

In this study, high purity and fine-grained Tl1212 superconductor samples were successfully synthesized from Tl_0.8Bi_0.2Sr₂Ca_0.8Y_0.2Cu₂O₇ starting composition by a two-step solid-state reaction method using Tl-free precursor powder prepared from coprecipitation method. XRD pattern of the sample, which was sintered at 1,000 °C for 6 min essentially showed formation of high purity 1212 phase. The sample’s zero resistance critical temperature, T _{c zero} was 91 K and bulk critical current density, J _c measured at 40 K in zero magnetic field was 11.2 A/cm². SEM investigation on the sample revealed ultrafine homogeneous grains that are randomly orientated with grain sizes of approximately 0.5–1 μm. Resintering the sample did not affect its superconducting properties but induced clustering of grains as observed by SEM. It is suggested that the sample be used in specialized measurement techniques such as in ultrasonic studies where high purity and ultrafine-grained samples are required.