First-principles investigation of the electronic,elastic and thermodynamic properties of VC under high pressure

An investigation of the electronic, elastic and thermodynamic properties of VC under high pressure has been conducted using first-principles calculations based on density functional theory （DFT） with the plane-wave basis set, as implemented in the CASTEP code. At elevated pressures, VC is predicted to undergo a structural transition from a relatively open NaCl-type structure to a more dense CsCl,type one. The predicted transition pressure is 520 GPa. The elastic constant, Debye temperature and heat capacity each as a function of pressure and/or temperature of VC are presented for the first time.

Formation and Compression Behavior of Two-Phase Bulk Metallic Glasses with a Minor Addition of Aluminum

A remarkable enhancement in room-temperature compressive deformability is realized by the minor-addition of 1.5 at.%Al in ZrTi-based bulk metallic glass.Two amorphous phases are observed by transmission electron microscopy in the Al-containing alloys and this explains the improvement of compression deformability.The studies suggest that phase separation might occur in glass forming alloys with a negative enthalpy of mixing.

Voronoi Structural Evolution of Bulk Silicon upon Melting

The Voronoi structural evolution of silicon upon melting is investigated using a molecular dynamics simulation.At temperatures below the melting point,the solid state system is identified to have a four-fold coordination structure(4,0,0,0).As the temperature increases,the five−fold coordination(2,3,0,0)and six−fold coordination structures(2,2,2,0)and(0,6,0,0)are observed.This is explained in terms of increasing atomic displacement due to thermal motion and the trapping of the moving atoms by others.At temperatures above the melting point,nearly all of the four-fold coordination structures grows into multiple-fold coordination ones.

Time-Resolved Photoluminescence Study of Silicon Nanoporous Pillar Array

A silicon nanoporous pillar array （Si-NPA） is thought to be a promising functional substrate for constructing a variety of Si-based optoelectronic nanodevices, due to its unique hierarchical structure and enhanced physical properties. This makes the in-depth understanding of the photoluminescence （PL） of Si-NPA crucial for both scientific research and practical applications. In this work, the PL properties of Si-NPA are studied by measuring both the steady-state and time-resolved PL spectrum. Based on the experimental data, the three PL bands of Si-NPA, i.e., the ultraviolet band, the purple-blue plateau and the red band are assigned to the oxygen-excess defects in Si oxide or silanol groups at the surface of Si nanocrystallites （nc-Si）, oxygen deficiency defects in Si oxide, and band-to-band transition of nc-Si under the frame of quantum confinement combining with the surface states like Si=O and Si-O^i bonds at the surface of nc-Si, respectively. These results may provide some novel insight into the PL process of Si-NPA and may be helpful for clarifying the PL mechanism.

Determination of spices in food samples by ionic liquid aqueous solution extraction and ion chromatography

In the present work, a novel method to extract three kinds of spices, namely vanillin, ethyl vanillin and ethyl maltol from food products such as biscuit, chocolate and milk powder was developed. 1-Octyl-3- methylimidazolium chloride （[Omim]Cl） aqueous solution was selected as the extracting medium. A 0.5 g powder of food product was extracted by 5.0 mL of [Omim]Cl aqueous solution （0.3 mol/L, pH 6.0） under ultrasonication at 50 ℃, and then the extract was centrifuged for 10 min at 4000 rpm. The extract was filtered through a syringe filter and injected into ion chromatography system for analysis. The separation of the three spices was carried out on an anion exchange column. The detection wavelength was set at 280 nm. Compared with traditional extraction solvents, [Omim]Cl aqueous solution displayed particular advantages. The applicability of the proposed method to real sample was confirmed. Under the optimal conditions, good reproducibility of extraction performance was obtained, with the relative standard deviation （RSD） values ranging from 1.9% to 6.3%. The recoveries of spiked samples were between ？9.8% and 95.8%. The detection limits （LOD, SIN = 3） of vanillin, ethyl vanillin and ethyl maltol were in the range of 20-45 μg/kg. The use of ionic liquid aqueous solution as extraction solvent was operationally easy and environmental-friendly.

Effect of Ag addition on the thermal stability and glass-forming ability of Zr_(35)Ti_(30)Cu_(7.5)Be_(27.5) bulk metallic glass

The thermal stability and glass forming ability (GFA) of Zr35-xTi30Cu7.5Be27.5Agx (x = 0-10) alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and ultrasonic techniques. We found that the addition of 1 at.% Ag can considerably enhance the GFA as indicated by an increase in the critical glass dimension from 15 mm in the Zr35Ti30Cu7.5Be27.5 alloy to 20 mm in the Zr34Ti30Cu7.5Be27.5Ag1 alloy. However, with the addition of more Ag the supercooled liquid region (△Tx) and y parameter (defined as Tx/(Tg+Tl)) drastically decreased from 155 K and 0.436 to 76 K and 0.363, respectively, resulting in a decrease in the GFA. Additionally, the elastic constant (the ratio of shear modulus to bulk modulus or Poisson's ratio) was also used as a gauge to evaluate the GFA in Zr35-xTi30Cu7.5Be27.5Agx alloys.

Temperature-Dependent Photoluminescence from GaN/Si Nanoporous Pillar Array

A GaN/Si nanoheterostructure is prepared by growing wurtzite GaN on a silicon nanoporous pillar array （Si-NPA） with a chemical vapor deposition method. The temperature evolution of the photoluminescence （PL） of GaN/Si- NPA is measured and the PL mechanism is analyzed. It is found that the PL spectrum is basically composed of two narrow ultraviolet peaks and a broad blue peak, corresponding to the near band-edge emission of GaN and its phonon replicas, and the emission from Si-NPA. No GaN defect-related PL is observed in the as-prepared GaN/Si-NPA. Our experiments prove that Si-NPA might be an ideal substrate for preparing high-quality Si-based GaN nanomaterials or nanodeviees.

Scanning Tunneling Microscope Observations of Non-AB Stacking of Graphene on Ni Films

graphene 的显微镜的特征在化学 transferincluding 以前在 Ni 电影上分离了单层和 bilayers 的原子结构， Moir ? 敷敲映牯敭 ? 祢爠汯楬杮甠? 景琠敨愠湮慥敬 ? 佇 ? 湡 ? 桴 ? 楤浡瑥牥 ? 敷敲洠獯汴 ? 湩琠敨爠湡敧 ???

Modal cutoff in rare-earth-doped photonic crystal fibers with multi-layer air-holes missing in the core

The various mode effective indices of the doped photonic crystal fibers (PCFs) are compared, the mode field distributions of the fundamental mode and the second-order mode are analyzed, and the single-mode condition is presented. The mode effective indices of large-core doped PCFs with different core indices and structure parameters are simulated by the finite element method (FEM). The relations of the core index with the fiber structure parameters of pitch, hole-to-pitch ratio and core diameter are obtained for single-mode propagation. In the design and fabrication of the doped PCF, we can adjust the core index and fiber structure parameters to achieve large mode area and single-mode propagation.

Design of large-core single-mode Yb^(3+)-doped photonic crystal fiber

The effective index of the cladding fundamental space-filling mode in photonic crystal fiber (PCF) is simulated by the effective index method. The variation of the effective index with the structure parameters of the fiber is achieved. For the first time, the relations of the V parameter of Yb3+-doped PCF with the refractive index of core and the structure parameters of the fiber are provided. the single-mode characteristics of large-core Yb3+-doped photonic crystal fibers with 7 and 19 missing air holes in the core are analyzed. The large-core single-mode Yb3+-doped photonic crystal fibers with core diameters of 50 μm, 100 μm and 150 μm are designed. The results provide theory instruction for the design and fabrication of fiber.