Synthesis,characterization and charge transport properties of Pr–Ni Co-doped SrFe2O4 spinel for high frequency devices applications

Ferrites are materials of interest due to their broad applications in high technological devices and a lot of research has been focused to synthesize new ferrites. In this regard, an effort has been devoted to synthesize spinel Pr–Ni co-substituted strontium ferrites with a nominal formula of Sr_1-xPr_xFe_2-yNi_yO₄ (0.0 ≤ x ≤ 0.1, 0.0 ≤ y ≤ 1.0). The cubic structure of pure and Pr–Ni co-substituted strontium ferrite samples calcinated at 1073 K for 3 h has been confirmed through X-ray diffraction (XRD). Average sizes of crystallites (18–25 nm) have been estimated from XRD analysis and nanometer particle sizes of synthesized ferrites have been further verified by scanning electron microscopy (SEM). SEM results have also shown that particles are mostly agglomerated and all the samples possess porosity. It has been observed that at 298 K, the values of resistivity (ρ) increase, while that of AC conductivity, dielectric loss, and dielectric constants decrease with increasing amounts of Pr³⁺ and Ni²⁺ ions. The values of dielectric parameters initially decrease with frequency and later become constant and can be explained on the basis of dielectric polarization. Electrochemical impedance spectroscopy (EIS) studies show that the charge transport phenomenon in ferrite materials is mainly controlled via grain boundaries. Overall, synthesized ferrite materials own enhanced resistivity values in the range of 1.38 × 10⁹–1.94 × 10⁹ Ω cm and minimum dielectric losses, which makes them suitable candidates for high frequency devices applications.     

Developing a stochastic model to predict the strength and crack path of random composites

We characterize fracture and effective stress–strain graphs in 2D random composites subjected to a uniaxial in-plane uniform strain. The fibers are arranged randomly in the matrix. Both fibers and matrix are isotropic and elastic–brittle. We conduct this analysis numerically using a very fine two-dimensional triangular spring network and simulate the crack initiation and propagation by sequentially removing bonds which exceed a local fracture criterion. In particular, we focus on effect of geometric randomness on crack path of random composites. Based on that two stochastic micro-mechanic models are presented that can predict with confidence the failure probability of random matrix–inclusion composites.     

Antifungal activity of films and solutions based on chitosan against typical seed fungi

The use of eco-freindly polymers as antimicrobial materials is in growth due to the need to reduce the negative impact of conventional treatments on the environment and the human health. The purpose of the present study was to assess the antifungal properties of films and solutions based on chitosan with different molecular weight at different concentrations. Surfactants were added to the formulation to assess their impact on treatment efficiency. The antifungal activity was conducted against tree fungi, Aspergillus niger, Alternaria alternata and Rhizopus oryzae. Results indicated important and significant differences of the antifungal activity between chitosan based solutions and chitosan based films. Furthermore, the antifungal activity of the different treatment depended on the type of fungus treated. Thus, chitosan film treatments were significantly more effective on A. niger than solution treatments. On the other hand, solution treatments resulted in higher radial inhibition when applied against A. alternata or R. oryzae. The highest radial inhibition was observed against A. alternata (97%) using a chitosan solution. The influence of the other parameters (concentration, molecular weight and surfactant type) on treatment efficiency was not as important and their significance depended on treatment type and fungus nature.     

Contrast behavior of a field lens with a wire‐grid PBS

Abstract— In an LCOS projection system, a wire‐grid PBS may be used to improve contrast and a field lens may be employed to simplify the projection lens. However, the combination of the two leads to a reduced contrast, which decreases with increasing field angle in one direction. In a representative arrangement, measured contrast with a mirror varied from over 10,000 in the center to 450 at the left and right edges. Contrast loss can be improved with a weaker field lens. The problem arises due to a phase delay between polarization states introduced by the wire grid. Polarization measurements show a +53‐nm phase delay with an axis parallel to the wire‐grid surface normal. Various compensation schemes are proposed in order to reduce the aforementioned loss of contrast.     

Carbon nanofluids flow behavior in novel composites

Nanocomposite materials have broadened significantly to encompass a large variety of systems, made of distinctly dissimilar components and mixed at the nanometer scale. This rapidly expanding field is generating many exciting new advanced composites with promising properties. However, during the fabrication of nanocomposites, many problems could arise and remain as challenging tasks. One such problem is controlling of the nanofluid flow behavior around the microfiber perform as in case of Resin Transfer Molding (RTM) process because of the high resin viscosity and the low preform permeability. In this paper, a two-dimensional simulation model based on the Eulerian multiphase approach has been performed and solved to investigate and predict the flow characteristics of a carbon nanofluid around a staggered microfiber matrix. ‘The interactions between the microfiber walls and the interfacial nanofluid layers during the flow process have been also studied. Based on the predicted results an energy “imbalance” technique has been applied between the microfiber walls and the interfacial nanofluid layers allowing them the potential to flow more smoothly around the microfiber walls to prevent any potential sticking on the microfiber walls.     

Modeling the customer in electronic commerce

This paper reviews interface design of web pages for e-commerce. Different tasks in e-commerce are contrasted. A systems model is used to illustrate the information flow between three subsystems in e-commerce: store environment, customer, and web technology. A customer makes several decisions: to enter the store, to navigate, to purchase, to pay, and to keep the merchandize. This artificial environment must be designed so that it can support customer decision-making. To retain customers it must be pleasing and fun, and create a task with natural flow. Customers have different needs, competence and motivation, which affect decision-making. It may therefore be important to customize the design of the e-store environment. Future ergonomics research will have to investigate perceptual aspects, such as presentation of merchandize, and cognitive issues, such as product search and navigation, as well as decision making while considering various economic parameters. Five theories on e-commerce research are presented.     

Buffer Behavior for Mixed Arrivals and Single Server with Random Interruptions

A queueing model with finite buffer size, mixed input traffic (Poisson and burst Poisson arrivals), synchronous transmission and server interruptions through a Bernoulli sequence of independent random variables is studied. Using average burst length, traffic intensity and input traffic mixture ratio as parameters, the relationships among buffer size, overflow probability and expected message queueing delay are obtained. An integrated digital voice-data system with synchronous time division multiplexing (STDM) for a large number of voice sources and mixed arrival process for data messages is considered as an application for this model. The results of this study are portrayed on graphs and may be used as guidelines in buffer design problems in digital voice-data systems. The queueing model developed is quite general in a sense that it covers pure Poisson and burst Poisson arrival processes and the mixture of the two as well.     

Microstructure and characterization of phases in TIG welded joints of Zircaloy-4 and stainless steel 304L

Tungsten inert gas (TIG) welded joints between Zircaloy-4 and stainless steel 304L have been studied by scanning electron microscope (SEM) having energy dispersive system (EDS) as an attachment. Intermetallic compound Zr(Cr, Fe)₂ and Zr₂Fe–Zr₂Ni eutectic phase have been observed in the molten zone. The surface area occupied by intermetallic compound Zr(Cr, Fe)₂ is about twice compared to Zr₂Fe–Zr₂Ni eutectic phase. The shape of the intermetallic compound is rod like. The phases were also identified by using X-ray diffraction (XRD) technique. EDS and XRD results are quite in agreement.     

Synthesis of multi-walled carbon nanotube/silica nanoparticle/polystyrene microsphere/polyaniline based hybrids for EMI shielding application

Novel polystyrene microsphere (PSMS)-based PSMS/Si and polystyrene/silica nanoparticle/multi-walled carbon nanotube (PS/Si/MWCNT) nanocomposite has been prepared using in situ sol-gel and chemical amalgamation methods. Aniline monomer was introduced by in situ route to form PSMS/PANI, PSMS/PANI/Si and PSMS/PANI/Si/MWCNT nanocomposite. FESEM of nanocomposite indicated core-shell spherical and tubular morphology. Glass transition temperature (T_g) and maximum decomposition temperature (T_max) of PSMS/PANI/Si/MWCNT nanocomposite were found as 295°C and 524°C, respectively, which were higher than the PSMS/PANI (T_g = 245°C; T_max = 387°C) and PSMS/PANI/Si (T_g = 257°C; T_max = 388°C) nanocomposite. For nanocomposite dispersion, tetrahydrofuran was studied as fine solvent. XRD depicted amorphous nature of PSMS/Si and PSMS/PANI/Si; however MWCNT reduced amorphous character of PSMS/PANI/Si/MWCNT. Electromagnetic interference (EMI) shielding effectiveness improved from 0.1 dB (PSMS) to 12.3 dB (PSMS/PANI/Si) to 24.5 dB (PSMS/PANI/Si/MWCNT). The increase in EMI shielding effectiveness was also observed with variation in log of conductivity from ?14 mho m^?1 (PSMA) to 1.17 mho m^?1 (PSMS/PANI/Si/MWCNT).