[en] The effect of calcium cyanamide (CaCN₂) additives on the grain growth and electric properties of liquid phase sintered AlN ceramics have been investigated using an X-ray diffractometer (XRD), a scanning electron microscope (SEM), a transmission electron microscope (TEM) attached with an energy dispersive X-ray microanalyzer (EDX) and an inductance-capacitance-resistance (LCR) meter. The grain sizes of the AlN compacts containing 1.5 wt.% CaCN₂ additive and sintered at 1700, 1750 and 1800 deg. C for 1 h are about 0.35, 0.40 and 0.56 μm, respectively. When the compacts are sintered at 1750 deg. C for 12 and 6 h, the grain size decreases from 1.20 to 0.87 and 1.06 to 0.80 μm with the CaCN₂ additive content increased from 0.50 to 3.0 wt.%, respectively. The grain size increases from 0.29 to 0.39 μm with the CaCN₂ content increased from 1.0 to 1.5 wt.% when sintered at 1750 deg. C for 1 h. When the AlN compact containing 1.0 wt.% CaCN₂ additive is sintered at 1750 deg. C for 6 h, the electric resistance is 5.0x10¹⁴ Ω. For the compacts containing 0.50 wt.% CaCN₂ additive and sintered at 1700, 1750 and 1800deg. C for 1 h, the electric resistances are 1.6x10¹⁴, 1.4x10¹⁴ and 6.3x10¹³ Ω, respectively. When measured at 1-10 kHz, the relative dielectric constant decreases from 7.0 to 3.5 for the AlN compacts containing 1.0 wt.% CaCN₂ additive and sintered at 1750 deg. C for 1 h. The relative dielectric constant decreases from 3.5 to 1.4 when the testing frequency is in the range of 10 kHz-1 MHz. The grain size of the sintered AlN compacts with 1.01 wt.% CaCN₂ additive is greater than 0.6 μm and the relative dielectric constant approaches 1.0

[en] The intermetallic compounds (IMCs) formed at the interface between Cu substrate and an Sn-9Zn-0.5Ag lead-free solder alloy have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED). The XRD patterns show that the main IMCs formed at the interface of Sn-9Zn-0.5Ag/Cu are γ-Cu₅Zn₈ and η'-Cu₆Sn₅. The Ag₃Sn IMC with orthorhombic structure was also observed at the Sn-9Zn-0.5Ag/Cu interface by TEM and ED analyses. The interfacial adhesion strength between the Cu substrate and Sn-9Zn-0.5Ag lead-free solder alloy is higher than that of the Sn-9Zn alloy due to the formation of Ag₃Sn IMC at the interface

[en] The kinetics of intermetallic compounds (IMCs) formation at the 91Sn-8.55Zn-0.45Al lead-free solder alloy/Cu substrate interface during soldering and subsequent aging have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and electron diffraction (ED). From the XRD results, γ-Cu₅Zn₈ and Cu₆Sn₅ are found in the eutectic 91Sn-8.55Zn-0.45Al solder alloy/copper interface, but no γ'-Cu₉Al₄ is formed in the wetted samples aged at 423 K for 250 h. However, by TEM observation and ED analysis, γ'-Cu₉Al₄ is found at the interface of the solder alloy and the Cu substrate, and the IMC growth can be expressed as X = (Dt)^1/2. The activation energy of the γ-Cu₅Zn₈ layer growth in 91Sn-8.55Zn-0.45Al solder alloy/Cu interface is determined as 53.77 kJ/mol

[en] Mycotoxins are fungal secondary metabolites with very diversified toxic effects in humans and animals. In the present study, patulin (PAT) and citrinin (CTN), two prevalent mycotoxins, were evaluated for their genotoxic effects and oxidative damage to mammalian cells, including Chinese hamster ovary cells (CHO-K1), human peripheral blood lymphocytes, and human embryonic kidney cells (HEK293). PAT, but not CTN, caused a significant dose-dependent increase in sister chromatid exchange (SCE) frequency in both CHO-K1 and human lymphocytes. PAT also elevated the levels of DNA gap and break in treated CHO-K1. In the single cell gel electrophoresis (SCGE) assay, exposure of HEK293 to concentrations above 15 μM of PAT induced DNA strand breaks; the tail moment values also greatly increased after posttreatment with formamidopyrimidine-DNA glycosylase (Fpg). This suggests that in human cells PAT is a potent clastogen with the ability to cause oxidative damage to DNA. However, no significant change in the tail moment values in CTN-treated cultures was found, suggesting that CTN is not genotoxic to HEK293. Incubation of HEK293 with CTN increased the mRNA level of heat shock protein 70 (HSP70), but not that of human 8-hydroxyguanine DNA glycosylase 1 (hOGG1). PAT treatment did not modulate the expression of either HSP70 or hOGG1 mRNA

[en] Chlorophyll content, the most important pigment related to photosynthesis, is the key parameter for vegetation growth. The continuous spectrum characteristics of ground objects can be captured through hyperspectral remotely sensed data. In this study, based on the coniferous forest radiative transfer model, chlorophyll contents were inverted by use of hyperspectral CHRIS data in the coniferous forest coverage of Changbai Mountain Area. In addition, the sensitivity of LIBERTY model was analyzed. The experimental results validated that the reflectance simulation of different chlorophyll contents was coincided with that of the field measurement, and hyperspectral vegetation indices applied to the quantitative inversion of chlorophyll contents was feasible and accurate. This study presents a reasonable method of chlorophyll inversion for the coniferous forest, promotes the inversion precision, is of significance in coniferous forest monitoring

[en] In this paper, the homotopy perturbation method (HPM) is applied to solve a coupled system of two nonlinear differential with first-order similar model of Lotka-Volterra and a Bratus equation with a source term. The analytic approximate solutions are derived. Furthermore, the analytic approximate solutions obtained by the HPM with the exact solutions reveals that the present method works efficiently

[en] This paper presents a tri-axis MEMS gyroscope design with novel tetra-pendulum proof masses for X-, Y-axis and regular proof masses for Z-axis rate sensing, which are all coupled with and embedded in a conventional tuning fork driving frame. The four pendulum proof masses are suspended via the torsional springs to a common center anchor and can be driven to swing around the anchor via the tilted transforming springs as the driving frame is oscillated in an anti-phase mode. As an X-, Y-axis angular rate is applied, the tetra-pendulum proof masses will rotate around the torsional springs in pairs for X- and Y-axis differential sensing, respectively. In particular, we investigated the relationship between the tilting angle of the transforming spring and its transforming efficiency, i.e. the amplitude ratio of the pendulum's swing to the driving oscillation, which shows a straight impact on the sensitivity. By theoretical analysis and Ansys simulation, we achieved an optimal tilting angle of 22.5°, which extends along the angular bisector of the pendulum's and driving mass’ moving direction and demonstrates a significant increase in transforming efficiency by about 40%, compared with the trivial tilting angle of 45°. By employing an SOI-based bulk micromachining process, the prototype device with the optimal design of the transforming spring (type I) and that with the trivial design (type II) for reference have been successfully fabricated. As expected, the testing results indicate an increase of more than 20% in the X- and Y- sensitivities, which is mainly from the enhanced sensitive transforming springs. (paper)

[en] Titanium dioxide (TiO_2) nanotube arrays are attracting increasing attention for use in solar cells, lithium-ion batteries, and biomedical implants. To take full advantage of their unique physical properties, such arrays need to maintain adequate mechanical integrity in applications. However, the mechanical performance of TiO_2 nanotube arrays is not well understood. In this work, we investigate the deformation and failure of TiO_2 nanotube arrays using the nanoindentation technique. We found that the load–displacement response of the arrays strongly depends on the indentation depth and indenter shape. Substrate-independent elastic modulus and hardness can be obtained when the indentation depth is less than 2.5% of the array height. The deformation mechanisms of TiO_2 nanotube arrays by Berkovich and conical indenters are closely associated with the densification of TiO_2 nanotubes under compression. A theoretical model for deformation of the arrays under a large-radius conical indenter is also proposed

[en] A better understanding of lithium-silicon alloying mechanisms and associated mechanical behavior is essential for the design of Si-based electrodes for Li-ion batteries. Unfortunately, the relationship between the dynamic mechanical response and microstructure evolution during lithiation and delithiation has not been well understood. We use molecular dynamic simulations to investigate lithiated amorphous silicon with a focus to the evolution of its microstructure, phase composition, and stress generation. The results show that the formation of Li_xSi alloy phase is via different mechanisms, depending on Li concentration. In these alloy phases, the increase in Li concentration results in reduction of modulus of elasticity and fracture strength but increase in ductility in tension. For a Li_xSi system with uniform Li distribution, volume change induced stress is well below the fracture strength in tension.

[en] Graphene has been increasingly used as nano sized fillers to create a broad range of nanocomposites with exceptional properties. The interfaces between fillers and matrix play a critical role in dictating the overall performance of a composite. However, the load transfer mechanism along graphene-polymer interface has not been well understood. In this study, we conducted molecular dynamics simulations to investigate the influence of surface functionalization and layer length on the interfacial load transfer in graphene-polymer nanocomposites. The simulation results show that oxygen-functionalized graphene leads to larger interfacial shear force than hydrogen-functionalized and pristine ones during pull-out process. The increase of oxygen coverage and layer length enhances interfacial shear force. Further increase of oxygen coverage to about 7% leads to a saturated interfacial shear force. A model was also established to demonstrate that the mechanism of interfacial load transfer consists of two contributing parts, including the formation of new surface and relative sliding along the interface. These results are believed to be useful in development of new graphene-based nanocomposites with better interfacial properties