Dispersion and Setting of Powder Suspensions in Concentrated Aqueous Urea Solutions for the Preparation of Porous Alumina Ceramics with Aligned Pores

Highly concentrated alumina powder suspensions have been prepared in aqueous urea solutions of concentrations in the range 200–360 g/100 mL using an ammonium poly(acrylate) dispersant at 80°C. The dispersant concentration for the suspension viscosity minimum in the urea solutions is higher than that in water due to the higher processing temperature. The urea solutions having higher dielectric constant than that of water offer higher interparticle potential that resulted in better dispersion of the powder as evidenced from the lower viscosity and yield stress of the suspensions. The decrease in temperature increased the suspension viscosity and the suspension formed a strong gel when cooled to room temperature due to the crystallization of urea. The minimum urea solution concentration for a 55 vol% alumina suspension to form a dimensionally stable gel is 240 g/100 mL. The compressive strength and Young's modulus of the gels increased with the increase in urea solution concentration. The alumina ceramics prepared by the urea removal followed by sintering at 1500°C had porosity in the range 28–36 vol% with the rectangular rod‐shaped aligned pores.     

Clad-modified fiber optic sensor utilizing CdS nanoflower as cladding for the detection of ethanol

Nowadays, sensing and detection of ethanol is paramount one for numerous applications including production of ethanol, fuel processing, chemical processing in industry, traffic management, food package testing for safety and medical applications. On the other hand, the rapid growth of nanotechnology paves the way to develop highly sensitive, portable and low-cost sensors with less power consumption. In line with this fact, a cladding modified fiber optic ethanol sensor using CdS nanoflower has been reported in the present study. CdS nanoflower was prepared by one step hydrothermal synthesis and subjected for various characterization techniques to investigate the material properties. The sensor probe was developed viz cladding modification technology followed by dip coating of CdS nanoflower over an unclad section of an optical fiber. The potency of CdS nanoflower has been probed for 0–300 ppm of acetone, ethanol, methanol and isopropanol at ambient environment. The sensing results demonstrates that the sensor coated with CdS nanoflower manifested better sensing performances towards ethanol (~?4.6% at 300 ppm) with response/recovery of 90 s and 100 s than other gases. The unique sensing feature complied that CdS nanoflower is desirable candidate in effective quantification of ethanol.

     

Outage Probability Analysis of Multi-relay Cooperative Decode-and-Forward System Over Generalized η–μ and κ–μ Fading Channels

In present scenario of wireless sensor networks and communications, efficient sensed data transmission among nodes is being a great confrontation because of the impulsive and volatile nature of sensors in the network. For providing that and enhancing network lifetime, there are several approaches are developed, specifically using clustering techniques. Still, there are requirements for energy based efficient routing in WSN. With that note, this paper develops anEnergy Aware Efficient Data Aggregation (EAEDAR) and Data Re-Schedulingwith the incorporation of clustering techniques. Moreover, the model used energy based cluster formation and cluster head selection for increasing the network stability and data delivery rate. The model comprises four main phases, namely, Energy factor based cluster formation, Aggregator_SN (Sensor Node) Selection, Efficient Data Aggregation (EDA) and Data Re-Scheduling based on delay and processing time. Furthermore, the model is updated with respect to the status of the nodes and links, for providing consistent network with improved reliable data transmissions. The simulation results portrays the effectiveness of the proposed model over other compared works in terms of the performance factors such as, throughput, packet delivery ratio, network lifetime, transmission delay and packet drop.

     

Flow of power-law fluids in cone-plate viscometer

Summary The flow of a power-law fluid in a cone-plate viscometer has been considered. The first order solutions for velocity and pressure have been obtained. Effects of secondary flow on velocity components, pressure, rate of deformation tensors and apparent viscosity have been studied. Both the primary and secondary flows are influenced by flow behavior index n. In shear thinning fluids, the effects on both the primary and secondary flows are of similar nature, whereas in shear thickening fluids, they are of opposite nature. The net result is that for shear thinning fluids the effects of the primary and secondary flows are additive, whereas in shear thickening fluids they almost balance out each other and the resultant effect is insignificant. The other important observation is in Newtonian fluids the secondary flow makes a significant contribution at high value of Reynolds number, which depends on the radius, velocity, density, and viscosity. In power-law fluids, Reynolds number depends on an additional parameter n. With this change, the effect of secondary flows can be important even at low shear rates. A critical value of n is obtained at which flow is independent of shear rates.     

Stability of mixed type functional equation in normed spaces using fuzzy concept

S. M. Ulam once addressed the problem ‘when is it true that a mathematical object satisfying a certain property approximately must be close to an object satisfying the property exactly?’. This problem was solved by D. H. Hyers in 1941 using the functional equation and thereafter numerous research papers and monographs have been published for various types of functional equations in different spaces. The solution proposed by D. H. Hyers (1941) later developed into the famous generalized Hyers-Ulam-Rassias stability of functional equations. In this paper, we intend to attain the general solution to a new mixed type functional equation and interrogate the generalized Hyers–Ulam–Rassias stability in fuzzy normed spaces. Also, we seek to provide its application for generating secret keys in client–server environment.     

Concurrent optimal allocation of geometric and process tolerances based on the present worth of quality loss using evolutionary optimisation techniques

Concurrent tolerancing becomes an optimisation problem to find out the optimum allocation of the process tolerances in the given design function constraints. In traditional optimisation methods, finding out the optimum solution for this advanced tolerance design problem is complex. The proposed algorithms (elitist non-dominated sorting genetic algorithm) and differential evolution extensively do better than the previous algorithms for attaining the optimum result. The aim of this paper is to suggest a model for optimal tolerance allocation by considering both tolerance cost and the present worth of quality loss such that the total manufacturing cost/loss is minimised. The suggested model takes into account the time value of money for quality loss and product degradation over time and consists of two new parameters: the planning horizon and the product user’s discount rate. From the outcome of this study, a longer planning horizon results in an increase in both tolerance cost and quality loss; however, a larger value of discount rate gives up a decrease in both tolerance cost and quality loss. Finally, a practical example is brought into reveal the effectiveness of the suggested method.     

Self-standing,hybrid three-dimensional-porous MoS2/Ni3S2 foam electrocatalyst for hydrogen evolution reaction in alkaline medium

Self-standing and hybrid MoS₂/Ni₃S₂ foam is fabricated as electrocatalyst for hydrogen evolution reaction (HER) in alkaline medium. The Ni₃S₂ foam with a unique surface morphology results from the sulfurization of Ni foam showing a truncated-hexagonal stacked sheets morphology. A simple dip coating of MoS₂ on the sulfurized Ni foam results in the formation of self-standing and hybrid electrocatalyst. The electrocatalytic HER performance was evaluated using the standard three-electrode setup in the de-aerated 1 M KOH solution. The electrocatalyst shows an overpotential of 190 mV at ?10 mA/cm² with a Tafel slope of 65.6 mV/dec. An increased surface roughness originated from the unique morphology enhances the HER performance of the electrocatalyst. A density functional approach shows that, the hybrid MoS₂/Ni₃S₂ heterostructure synergistically favors the hydrogen adsorption-desorption steps. The hybrid electrocatalyst shows an excellent stability under the HER condition for 12 h without any performance degradation.     

Preparation of low density carbon foams by foaming molten sucrose using an aluminium nitrate blowing agent

Low density carbon foams have been prepared by thermo-foaming of molten sucrose using aluminium nitrate as a blowing agent to produce solid organic foams followed by dehydration and carbonization. Gas bubbles are generated in the molten sucrose due to water vapour produced by the acid catalysed condensation between sucrose hydroxyl groups and NO_x gases produced by the thermal decomposition of the aluminium nitrate. Higher melt viscosity achieved by cross-linking of the condensation products of sucrose through co-ordination of the aluminium ions with the hydroxyl groups stabilizes the bubbles against coalescence and rupture. The foam volume, foaming time and setting time depend on the aluminium nitrate concentrations. The carbon obtained by the pyrolysis of the solid organic foams has turbostratic graphite structure. The foams produced have an interconnected near-spherical cellular structure. The carbon foams prepared at aluminium nitrate concentrations in the range of 0.5–4 wt.% have a density and average cell size in the ranges of 0.085–0.053 g/cc and 1.55–0.83 mm, respectively. The alumina (～0.17–1.34 wt.%) produced from the aluminium nitrate is concentrated more on the surface of cell walls, ligaments, and struts.     

A urea crystal templating method for the preparation of porous alumina ceramics with the aligned pores

A novel process for the preparation of porous alumina ceramics with an aligned pore structure has been reported. The urea dissolved in the aqueous alumina slurry at higher temperature formed rod shaped crystals aligned in the direction of gravity when cooled to room temperature. The gelatin used to set the slurry, controls the crystallization of urea such that the urea crystals produced in the suspension containing the gelatin had much lower width and thickness compared to that produced in the suspension without the gelatin. The alumina powder catalyzed the thermal decomposition of urea that enabled the removal of the majority of the urea crystals from the alumina green body by isothermal heating at temperature much lower than the melting point of urea. The void space created by the removal of the urea crystals remained as pores in the sintered ceramics.     

Preparation of carbon foams by thermo-foaming of activated carbon powder dispersions in an aqueous sucrose resin

Thermo-foaming of activated carbon (AC) powder dispersions in an aqueous sucrose resin followed by carbonization has been studied to prepare carbon foams. The dispersions were characterized by viscosity measurements and sedimentation studies. The OH to OH condensation reactions, leading to the cross-linking of the sucrose polymer, were retarded by the AC powder. The AC particles adsorbed on the gas–liquid interface stabilized the gas bubbles that resulted in foaming of the poorly cross-linked sucrose polymer resin having low viscosity. The carbon produced by the carbonization of the sucrose polymer binds the AC particles as in reaction bonding. The carbon foams have an interconnected cellular structure. Density (0.138–0.22 g/cc), cell size (0.62–3 mm) and compressive strength (0.42–3.4 MPa) of the carbon foams depends on the AC powder to sucrose weight ratio. Incorporation of the AC powder in the sucrose resin decreases the carbonization shrinkage that enables the preparation of large carbon foam bodies without warping. The carbon foam prepared at an AC powder to sucrose weight ratio of 0.1 shows the highest density and compressive strength and the lowest cell size.