Structure,transport and magnetic properties of the double perovskite (Ca<Subscript>2-2x</Subscript>Sr<Subscript>2x</Subscript>)FeMoO<Subscript>6</Subscript>

In this paper we report the results of a detailed investigation of the double perovskite (Ca_2-2xSr_2x)FeMoO₆ system. Chemical size effects on structural, electrical, and magnetic properties caused by the substitution of isovalent, larger Sr ions into the smaller Ca sites, resulting in (Ca_2-2xSr_2x)FeMoO₆, have been examined. The compounds crystallize in the monoclinic space group P2₁/n for 0.0x<0.2, the orthorhombic space group Pbnm for 0.2x<0.4, and the tetragonal space group I4/m and I4/mmm for x0.4. Examination of the resistivity of all compounds reveals a metallic behavior which is well described by a Tⁿ dependence except for x=1.0. These n values change from 1 to 2 as T decreases lower than T_c. This is indicative of a variation in the transport mechanism at T_c. The ferrimagnetic transition temperature T_c increases with increasing x from 318 (x=0.0) to 393 K (x=1.0). For all samples, the saturation magnetization at 82 K obeys M_s3.5_B/(formula unit), compared to a theoretical spin-only moment of 4_B/(formula unit) for a perfectly ordered compound. PACS 74.25.Fy; 74.25.Ha     

Direct experimental limit on neutron-mirror-neutron oscillations

In case a mirror world with a copy of our ordinary particle spectrum would exist, the neutron n and its degenerate partner, the mirror neutron n', could potentially mix and undergo nn' oscillations. The interaction of an ordinary magnetic field with the ordinary neutron would lift the degeneracy between the mirror partners, diminish the n' amplitude in the n wave function and, thus, suppress its observability. We report an experimental comparison of ultracold neutron storage in a trap with and without superimposed magnetic field. No influence of the magnetic field is found and, assuming negligible mirror magnetic fields, a limit on the oscillation time taunn' > 103 s (95% C.L.) is derived.     

High-energy scale revival and giant kink in the dispersion of a cuprate superconductor

In the present photoemission study of a cuprate superconductor Bi1.74Pb0.38Sr1.88CuO6+delta, we discovered a large scale dispersion of the lowest band, which unexpectedly follows the band structure calculation very well. Similar behavior observed in blue bronze and the Mott insulator Ca2CuO2Cl2 suggests that the origin of hopping-dominated dispersion in an overdoped cuprate might be quite complicated. A giant kink in the dispersion is observed, and the complete self-energy containing all interaction information is extracted for a doped cuprate. These results recovered significant missing pieces in our current understanding of the electronic structure of cuprates.     

Role of cross section on the stability and electronic structure of Ag-doped ZnO nanowires

Semiconductor nanowires (NWs) exhibit tunable physical properties intrinsically related to their reduced dimensionality, quantum size effect, morphology, and surface effects. By using density functional theory, we investigated the cross-sectional effect on the electronic structure of Ag-doped ZnO NWs. Three types of NWs have been considered: hexagonal cross-sectional ZnO NWs with zigzag and armchair surfaces, respectively, and triangular cross-sectional ZnO NW with zigzag surface. The results show that Ag prefers to substitute surface Zn atoms and induces typical p-type characteristic for all kinds of NWs. Moreover, single Ag doping could create a much shallower acceptor with a smaller hole effective mass in triangular ZnO NW than in the two hexagonal ZnO NWs. With the increase of Ag concentration, the p-type doping becomes much less effective overall. However, double Ag substituting in the zigzag surface of triangular ZnO NW improves the p-type properties, while substituting in the angle site seriously damage the p-type conduction. As the triangular ZnO NWs and prismatic ZnO nanoparticles have been synthesized recently, on the basis of our results, we expect that effective p-type could be achieved via incorporating Ag in triangular ZnO NWs experimentally.     

Switchable wavelength generation by injection-locked fiber laser based on GS-RSOAs

This paper proposes a switchable wavelength fiber laser (SWFL) based on an arrayed waveguide grating (AWG) and a gain-saturated reflective semiconductor optical amplifier (RSOA). The SWFL was experimentally implemented in the C- and L-bands. In order to achieve narrow-linewidth oscillation, the SWFL was driven by bidirectional injection-locked RSOAs. The RSOA was operated in the gain-saturated region, using gain compression properties to obtain uniform power over a wide bandwidth. Based on this configuration, we obtained 40 C-band international telecommunication unit (ITU) wavelengths with 100-GHz channel spacing. The SWFL displayed a narrow 3-dB bandwidth (<0.06 nm), a high and uniform peak power (P _max > 0.22 dB, ΔP _max < 0.26 dB), and a high and uniform side mode suppression ratio (SMSR > 66 dB, ΔSMSR < 1 dB). The peak-power and wavelength stabilities were ±0.24 dB and ±0.01 nm, respectively, at room temperature over a 1 h period.     

"烧蚀模式"激光推进技术及其应用研究

随着激光技术的发展,激光推进技术越来越受到关注."烧蚀模式"激光推进是激光推进技术中一个重要的研究领域.本文在介绍了"烧蚀模式"激光推进的原理、研究现状和几个亟待解决的热点研究问题的基础上,对激光推进的进一步应用进行了探索与研究.     

Dielectric and NMR Studies of the superionic conductor AgI embedded in mesoporous silicate matrices

This paper reports on the results of studies of small particles of the superionic conductor AgI embedded in MCM-41 and SBA-15 molecular sieves with different sizes of pores (channels). The studies are performed by the dielectric and nuclear magnetic resonance techniques. The temperature of the superionic phase transition is shown to increase monotonically with decreasing pore size. The enthalpy of activation of the ion motion in β-AgI in restricted geometry is determined. It is shown that introduction of AgI into pores does not noticeably affect its structure.     

Flexible and accurate implementation of a binocular structured light system

This paper presents a practical implementation of a binocular system for three-dimensional (3D) surface measurement. Manufacturing procedures are easy to implement because this system does not require that the optical axes of two cameras’ lenses be coplanar and the structured light sheets be perpendicular to that plane. The method of structured light calibration is proposed to obtain the parameters of the structured light sheets. This calibration method can tolerate the surface condition of the calibration board. To eliminate the effect caused by the distortion of projector lens, each structured light sheet is fitted to a conicoid. Meanwhile, data acquired from two cameras are transformed into a unique coordinate system to avoid 3D data matching. Experiments are conducted to validate the flexibility, accuracy, and desirability of our system.