Propagation of time-reversed Lamb waves in acrylic cylindrical tubes as cortical-bone-mimicking phantoms

The present study aims to investigate the propagation of time-reversed Lamb waves in acrylic cylindrical tubes as cortical-bone-mimicking phantoms. Time-reversed Lamb waves could be successfully launched in 6 acrylic tubes with wall thicknesses from 2 to 12 mm by using a modified time reversal method. The group velocities of the time-reversed Lamb waves in the acrylic tubes were measured by using the axial transmission technique. They decreased very slightly with increasing wall thickness, showing good agreement with the theoretical group velocity of the A0 Lamb wave in the acrylic plate. These results suggest that the time-reversed Lamb waves in the acrylic tubes would essentially behave as the A0 Lamb wave, consistent with the behavior of the slow guided wave in long cortical bones. It is expected that the application of the time-reversed Lamb waves in long bones would enhance clinical potential of ultrasonic technologies for the diagnosis of osteoporosis.     

A novel carbon source coated on C-LiFePO<Subscript>4</Subscript> as a cathode material for lithium-ion batteries

The poor electronic conductivity and low lithium-ion diffusion are the two major obstacles to the largely commercial application of LiFePO₄ cathode material in power batteries. In order to improve the defects of LiFePO₄, a novel carbon source polyacrylonitrile (PAN), which would form the hierarchical porous structure after carbonization, is fabricated and used. This work comes up with a simple and facile carbothermal reduction method to prepare porous-carbon-coated LiFePO₄ (C-LiFePO₄-PC) composite and to study the effect of carbon-coated temperature on ameliorating the electrochemical performance. The obtained C-LiFePO₄-PC composite shows a high initial discharge capacity of 164.1 mA h g^?1 at 0.1 C and good cycling stability as well as excellent rate capacity (49.0 mA h g^?1 at 50 C). The most possible factors that improve the electrochemical performance could be related to the enhancement of electronic conductivity and the existence of porous carbon layers. In a word, the C-LiFePO₄-PC material would become an excellent candidate for application in the fields of lithium-ion batteries.     

A new method for high-energy pulsed Gamma measurement within intense background x-rays

The accelerator-generating 6.13~MeV pulsed Gamma by ¹⁹F(p, αγ )¹⁶⁰ reaction usually synchronizes with an intense bremsstrahlung x-ray which has a maximum energy of 1~MeV. This paper proposes a new method, named the scattering and absorbing method, to diagnose the 6.13~MeV Gamma. This method includes two parts: the detector and a scatterer placed in front of the detector. The detector converts the Gamma to electrons and then collects the electrons by a scintillator. In order to restrain the interference of the low-energy background, the scintillator collects the electrons at a small angle. The scintillator is wrapped with electro-absorbing material to absorb the low-energy electrons generated by background x-rays. The theoretical sensitivity ratio of 6.13~MeV Gamma to 1~MeV x-rays is greater than 150. The scatterer is a pretreatment tool to scatter some background x-rays away from the radial beam before they enter the detector. By varying the length, the scatterer can reduce the background x-rays to an acceptable level for the detector.     

Dependence of substrate temperature of Zn0.8Co0.2O films deposited by pulsed DC magnetron sputtering

We have investigated the microstructure, electrical and magnetic properties of the ZnCoO thin films, which were prepared by the asymmetrical bipolar-pulsed DC magnetron sputtering as a function of substrate temperature. The structural properties of ZnCoO films were characterized with a high resolution XRD. The XRD patterns of the ZnCoO films showed a strong (0 0 2) preferential orientation. The average crystallite size was 23–35 nm, which was estimated from full width at half maximum of XRD results. The electrical resistivity of the films were measured by the van der Pauw method through Hall measurement and showed below 10⁻¹ Ω cm above 300 °C. The magnetic properties of the ZnCoO films were analyzed by the alternating gradient magnetometer at room temperature. All of the films were exhibited the ferromagnetic nature. The high conductivity and room temperature ferromagnetism of the ZnCoO films above 300 °C suggested that the possibility for the application to diluted magnetic semiconductors.     

Crystallization,Flame Retardancy and Mechanical Properties of Poly(Butylene Terephthalate)/Brominated Epoxy/Nano-Sb2O3 Composites Dispersed By High Energy Ball Milling

Nano-Sb2O3 particles and brominated epoxy resin (BEO) powders were dispersed in poly (butylene terephthalate) (PBT) by high energy ball milling (HEBM). Then the nanocomposites were prepared by a twin screw extruder. The influence of the nano-Sb2O3 particles on the crystallization, thermal stability, flame retardancy and mechanical properties of the PBT/BEO/nano-Sb2O3 composites were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 tests and scanning electron microscopy (SEM). The results showed that the nano-Sb2O3 particles improved the crystallizability, thermal stability and flame retardancy properties of the PBT/BEO/nano-Sb2O3 composites. When the content of nano-Sb2O3 particles was 2.0?wt%, the LOI of nano-Sb2O3/BEO/PBT composites increased from 22.0 to 27.8 and the tensile strength reached its maximum value (62.44?MPa), which indicated that the optimum value of flame retardancy and mechanical properties of PBT/BEO/nano-Sb2O3 composites were obtained.     

Theoretical studies on the optical absorption coefficients and refractive index changes in parabolic quantum dots in the presence of electric and magnetic fields

The optical absorption coefficients and the changes in the refractive index in GaAs/AlGaAs parabolic quantum dots(QDs) with applied electric and magnetic fields are studied in detail. Analytical expressions for the linear and nonlinear intersubband absorption coefficients and refractive index changes are obtained by using a compact density matrix approach and an iterative procedure. Finally, the calculated results show the incident optical intensity, the frequencies of the confined potential of the QDs and the applied electric and magnetic fields have a great influence on the optical absorption coefficients and refractive index changes in this system.     

High-throughput screening of ferroelectric materials for non-volatile random access memory using multilayer perceptrons

During the last several years, the development of combinatorial technology has enabled synthesis of a huge amount of chemical compounds in a short time. The large number of variables makes the direct human interpretation of data derived from combinatorial experimentation for high-throughput screening (HTS) very difficult. Artificial neural networks using multilayer perceptrons (MLP) have been successfully applied to the regression problems with various material data. In this work, MLP model was applied to HTS of ferroelectric materials including Bi_4−xLa_xTi₃O₁₂ (BLT) and Bi_4−xCe_xTi₃O₁₂ (BCT). The model using MLP was made to predict the ferroelectric properties of whole feasible experimental conditions. Once a neural network model with high accuracy and good generalization performance was established, we could predict the expected optimal reaction conditions with the best characteristics. The highest gradient value obtained using MLP model is higher than the maximum value found from experiments, thereby accelerating the discovery of the optimal compositions and post-annealing time of BCT and BLT.     

Improved method for loss measurements in planar waveguides

A method employing an isosceles prism and a right-angle one is developed for loss measurement in planar waveguides. During the measuring process, the isosceles prism is fixed and the right-angle prism fixed on the waveguide slides by following the waveguide. Only by adjusting the gap thickness we can realize the loss measurement in planar waveguides. The method is demonstrated with an Ag/Na ion-exchanged waveguide fabricated on BK7 glass from AgNO₃ melt diluted with NaNO₃ (mass ratio 1:9), with the condition of 4 h and . The experimental results show that the method has the advantages on convenient operation, accurate results and no required end polishing.