Ultrasonic Anomaly Near the Charge Ordering Transition in Sr-Doped Nd0.3La0.2Ca0.5−x Sr x MnO3 Manganites

Sr doping in the charge-ordered compound Nd_0.3La_0.2Ca_0.5?x Sr _x MnO₃ has been systematically studied to examine its effect on ultrasonic velocity and elastic moduli as well as magnetic and electrical transport properties. DC electrical resistivity, ρ and AC susceptibility, χ′ measurements showed all samples exhibit metal-insulator (MI) behavior accompanied by ferromagnetic-paramagnetic (FM-PM) transition where the MI transition temperature, T _MI and FM-PM transition temperature, T _C increased with Sr content indicating the enhancement of double-exchange mechanism. Analysis of the resistivity change with respect to temperature, dlnρ/dT ^?1 versus T indicates onset of charge-ordering (CO) state where its CO transition temperature, T _CO decreased with Sr content indicating weakening of the CO state. On the other hand, both absolute longitudinal and shear velocities as well as elastic moduli measured at 80 K increased significantly with Sr doping indicating improvement in elastic properties, which is suggested to be due to the increase in formation of ferromagnetic domains. A longitudinal velocity anomaly characterized by a slope change around the vicinity of T _CO was observed for all samples. The longitudinal elastic anomaly is attributed to the Jahn–Teller (JT) effect of Mn³⁺ ions where analysis of the anomaly using the mean-field theory suggests involvement of the JT effect in the samples, which transforms from dynamic to static type with decreasing temperature. The elastic anomaly shifted down from 222 K (x=0) to 205 K (x=0.05) indicating that the static JT effect was weakened with Sr content.     

Molecular attributes of an effective steric agent: Yield stress of dispersions in the presence of pure enantiomeric and racemate malic acids

The effects of pH on the yield stress and zeta potential behaviour of α-Al₂O₃ dispersions with addition of d-, l- and racemate (DL) malic acids were evaluated. Conformational structures and intramolecular hydrogen bonding of the adsorbed malic acids obtained via MM2 modeling were used to explain the surface forces operating in the dispersions. We found that the yield stress-pH behaviour is almost identical for d-, l- and racemate malic acids. At low surface coverage of adsorbed malic acid, the maximum yield stress was reduced by as much as 55%. At complete surface coverage the reduction decreased to ～40%. MM2 modeling showed the presence of intramolecular hydrogen bonding between the hydroxyl and the (free) charged carboxylate group within the malic acid molecule. Intra-molecular hydrogen bonding and the high number of strongly bound water molecules (hydration number of malic di-ionic species) were likely responsible for the di-ionic malic acid species acting as a very effective steric agent. At complete surface coverage, the inter-molecular hydrogen bond formed between the layers of adsorbed malic acid, is responsible for the small rise in the maximum yield stress. Racemate malic acid produced a smaller maximum yield stress at complete surface coverage compared to the pure enantiomers. This may be related to the two different types of hydrogen bonds found in the racemate. Only one type is found in the pure enantiomers.     

High triplet energy Al complex as a host material for blue phosphorescent organic light-emitting diodes

An Al complex, tris((2-(pyrazol-1-yl)pyridin-3-yl)oxy)aluminum (Al(pypy)₃), was synthesized as a high triplet energy host material for blue phosphorescent organic light-emitting diodes. A high triplet energy ligand, 2-(1H-pyrazol-1-yl)pyridin-3-ol, was coordinated to the Al to develop the high triplet energy host material derived from Al. The Al(pypy)₃ host showed a high triplet energy of 2.86 eV for efficient energy transfer to blue triplet emitter. A maximum quantum efficiency of 20.5% was achieved in blue device using the Al(pypy)₃ host material.     

Application of the Box–Behnken design to the optimization of process parameters in foam cup molding

Currently, foam molding technologies are widely adopted for most bra styles, which demonstrate the incomparable advantages in the contemporary intimate apparel industry. The determination of proper molding conditions, such as molding temperatures and length of time on the basis of cup sizes and styles, is crucial in achieving the required cup shape with high stability, which is regarded as the most challenging part of the molded bra making process. To determine the optimal process parameter settings, numerous process trials are generally required to evaluate the molding variables and their interactions. This study proposes a novel systematic methodology to identify the optimal molding process parameters based on design of experiment (DOE) and a parameterization-based remesh method to evaluate the 3D shape conformity of molded cups. By solving the regression equation obtained from a Box–Behnken design (BBD) and analyzing the response surface plots, the results prove that molding temperature has greater influence than the length of the dwell time on the 3D shape conformity of molded cups. The optimal molding conditions can be determined for the cup depths of different sized mold heads, which are validated by the experimental results.     

Optimization of millimeter wave system in ITER Equatorial EC H&CD Launcher

A high power (20 MW) and CW millimeter wave (mm-wave) injection is planned for Electron Cyclotron Heating and Current Drive (EC H&CD) in ITER. An optimization of the mm-wave system for the ITER EC H&CD Equatorial Launcher (EL) is performed. The optimization of the system is aimed to obtain the maximum transmission efficiency on the condition that 1.8 MW injection per waveguide, ∼20 cm in beam radius at the resonance layer and narrow opening of the Blanket Shielding Module (BSM). The transmission efficiency of 99.1% from the end of the waveguide inside the launcher to the output of the BSM is achieved.The mm-wave propagation with high order modes is also calculated by using an experimentally obtained high power mm-wave beam pattern that includes 95%HE₁₁, 0.6%LP₁₁, 0.2%LP₀₂ and 4.2% other higher order modes. The analysis predicts the 1–2% additional loss will be induced by the high order modes.     

Growth mechanisms of MgO nanocrystals via a sol-gel synthesis using different complexing agents

In the preparation of nanostructured materials, it is important to optimize synthesis parameters in order to obtain the desired material. This work investigates the role of complexing agents, oxalic acid and tartaric acid, in the production of MgO nanocrystals. Results from simultaneous thermogravimetric analysis (STA) show that the two different synthesis routes yield precursors with different thermal profiles. It is found that the thermal profiles of the precursors can reveal the effects of crystal growth during thermal annealing. X-ray diffraction confirms that the final products are pure, single phase and of cubic shape. It is also found that complexing agents can affect the rate of crystal growth. The structures of the oxalic acid and tartaric acid as well as the complexation sites play very important roles in the formation of the nanocrystals. The complexing agents influence the rate of growth which affects the final crystallite size of the materials. Surprisingly, it is also found that oxalic acid and tartaric acid act as surfactants inhibiting crystal growth even at a high temperature of 950°C and a long annealing time of 36 h. The crystallite formation routes are proposed to be via linear and branched polymer networks due to the different structures of the complexing agents.     

Facile synthesis of Ag3PO4 with the assistance of N,N-dimethylformamid and urea for high performance photocatalysis

Ag₃PO₄ was synthesized with the assistance of N, N-dimethylformamid (DMF) and urea for high performance photocatalysis. The photocatalytic activity of the as-synthesized samples was evaluated by photodegrading rhodamine B (Rh B) under visible light irradiation. As a result, the optimal Ag₃PO₄ synthesized with the assistance of DMF and urea exhibited enhanced photocatalytic activity for Rh B degradation under visible light irradiation. DMF and urea play vital roles in improving the photocatalytic activity of Ag₃PO₄. This study could provide a new perspective for the controllable synthesis of Ag₃PO₄.     

Green synthesis of Ag/ZnO nanohybrid using sodium alginate gelation method

Mesoporous Ag/ZnO nanohybrid material has been successfully synthesized using simple and green route via sodium alginate media. The as-synthetized nanomaterial was structurally characterized using various techniques such as X-ray powder diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and N₂ adsorption-desorption measurements (BET). The Ag/ZnO nanoparticles were quasi-spherical, crystalline with a size ranging from 40 to 50 nm. In addition, characterization results confirmed that calcined Ag/ZnO nanomaterial sample was stable and mainly consisting of both hexagonal ZnO and cubic silver nanoparticles.     

Numerical study on the evaluation of tunnel shotcrete using the Impact-Echo method coupled with Fourier transform and short-time Fourier transform

This study presents a simple but robust evaluation technique of the bonding state of shotcrete applied to tunnels using Impact-Echo (IE) method and thus explores the effect of the ground types, thickness of the shotcrete, undulating surfaces and impact sources on system vibration through numerical simulations based on the finite element method. All the signals obtained from numerical simulation for various conditions are analyzed at the frequency domain using Fourier transform (FT) and at the time–frequency domain using short-time Fourier transform (STFT). As the bonding condition worsens, the resonant frequency (f_n) and the resonance duration (T_R) increase and the geometric damping ratio (D_G) decreases. The results of a comprehensive numerical analysis suggest that the shape of the contour in the time–frequency domain, the level of f_n, and the T_R and D_G values can be used as effective indicators for the evaluation of the shotcrete thickness, ground type, and bonding state. Finally, this paper presents a procedure for evaluating the tunnel shotcrete state, the shotcrete thickness, and the ground type with the IE method coupled with Fourier transform and short-time Fourier transform. Limited field tests were also performed to verify the proposed evaluation chart for tunnel shotcrete states.