Using the Embedding Atom Method (EAM) for highly undercooled Ni3Al alloy, the melting point and the specific heat were studied by a molecular dynamics simulation. The simulation of melting
point was carried out by means of the sandwich method and the NVE ensemble method, and the results show a good agreement,
whereas are larger than the experimental value of 1663 K. This difference is attributed to the influence of surface melting
on experimental results, which causes the smaller measurements compared with the thermodynamic melting point. The simulated
specific heat of Ni3Al alloy weakly and linearly increases with the increase of undercooling in the temperature range from 800 K to 2000 K.
Supported by the National Natural Science Foundation of China (Grant No. 50395101) 相似文献
We found, through extensive experimental studies, that the physical aging effects are absent in the relaxation of rubbing-induced
birefringence (RIB) in polystyrene (PS), and the relaxation involves very small length scale. A phenomenological model based
on individual birefringence elements is proposed for the RIB relaxation. The relaxation times (RTs) of the elements are found
to be independent of the thermal or stress history of the samples, either before or after the formation of the birefringence.
The RTs are also independent of the molecular weight, rubbing conditions, and film thickness, while the RTs distribution function
does depend on the molecular weight and rubbing conditions. The model provides quantitative interpretations that agree very
well with all the reported experimental results, and sheds important light on the novel behaviors of the RIB relaxation. The
absence of physical aging effects is probably due to the combined effects of small length scale of the RIB relaxation, and
the accelerated aging speed in the near surface region in which the RIB concentrates. 相似文献
The finite-difference time-domain method based on recursive convoltion method (RC-FDTD) for the electric anisotropic dispersive
medium is discussed in detail. To exemplify the availability of the three-dimensional RC-FDTD algorithm, the backscattering
Radar-Cross-Section(RCS) of a non-magnetized plasma sphere is computed, and the numerical results are the same as the one
of the Shift Operater-FDTD method, and show that the RC-FDTD method is correct and efficient. In addition, the co-polarized
and cross-polarized backscattering time-domain of a magnetized plasma sphere are obtained by the RC-FDTD algorithm. The results
show that when the external magnetic field is implemented, the cross-polarized component appear, evidently. 相似文献
We have studied the effect of a Bi underlayer on ordering and coercivity Hc of FexPt100-x thin films (atomic content of Fe x=40∼58). We found that the Bi underlayer enhances Hc remarkably. After annealing at 400 °C for 20 min, a Bi/Fe49Pt51 film can realize an Hc as high as 1.07×103 kA/m and a ratio of the remnant Mr to the saturated magnetization Ms as high as 0.93. The ordering process of FePt film was promoted by the diffusion of Bi atoms. Moreover, the Bi underlayer
broadens the range of x for high Hc from 49∼55 to 43∼55. Interestingly, with Bi underlayer, the high Hc is affected by x to a less extent.
PACS 75.50.Ss; 75.50.Vv; 75.60.Ej 相似文献
Single-crystal erbium silicate nanowires have attracted considerable attention because of their high optical gain. In this work, we report the controlled synthesis of silicon-erbium ytterbium silicate core-shell nanowires and fine-tuning the erbium mole fraction in the shell from x = 0:3 to x = 1:0, which corresponds to changing the erbium concentration from 4:8 × 1021 to 1:6 × 1022 cm-3. By controlling and properly optimizing the composition of erbium and ytterbium in the nanowires, we can effectively suppress upconversion photoluminescence while simultaneously enhancing near-infrared emission. The composition-optimized nanowires have very long photoluminescence lifetimes and large emission cross-sections, which contribute to the high optical gain that we observed. We suspended these concentration-optimized nanowires in the air to measure and analyze their propagation loss and optical gain in the near-infrared communication band. Through systematic measurements using wires with different core sizes, we obtained a maximum net gain of 20±8 dB·mm-1, which occurs at a wavelength of 1534 nm, for a nanowire with a diameter of 600 nm and a silicon core diameter of 300 nm.
We have experimentally demonstrated a tunable multi-wavelength Brillouin–erbium fiber laser with over 40 GHz spacing utilizing two cascaded double Brillouin-frequency-spacing cavities. In this laser configuration, two segments of 25 km-long single-mode fibers are used as Brillouin gain medium in each ring cavity, and a segment of 8 m-long erbium-doped fiber with 980 nm pump is employed to amplify Brillouin pump (BP). At BP wavelength of 1550 nm, BP power of 8.3 dBm (6.8 mW) and the maximum 980 nm pump power of 27.78 dBm (600 mW), seven output channels with fourfold Brillouin-frequency spacing, and the tuning range of 15 nm from 1545 to 1560 nm are achieved. The proposed multi-wavelength Brillouin–erbium fiber laser has wide applications, such as in microwave signal generation and optical communications. 相似文献