Mechanism of proton anisotropic velocity distribution in the solar wind

Although it has been long that spacecraft observed the anisotropy of velocity protons in the solar wind, there is still not a reasonable explanation. In this paper we try to give an explanation from the diffusion plateau of protoncyclotron resonance predicted by the quasi-linear theory for the resonance between the protons and the parallel propagating waves. We consider the effect of dispersion relation on diffusion plateau and notice that the diffusion plateau we have got by using cold plasma dispersion relation accords with the density contours in the velocity phase space detected at 0.3 AU in fast solar wind. For explaining proton distributions obtained in the fast solar wind from 0.7 AU to 1 AU hot plasma dispersion relation should be considered. We also give a theoretical relation of proton thermal anisotropy A and plasma parameter β.     

Strong visible PL from the nc-Si thin film by Ni silicide mediated crystallization

We studied the growth of nanocrystalline silicon (nc-Si) thin film exhibiting a strong room temperature photoluminescence (PL) at 1.81–2.003 eV. The amorphous silicon was crystallized by Ni silicide mediated crystallization (Ni SMC) and then Secco-etched to exhibit the PL. The PL peak energy and intensity increase with increasing the metal density on the a-Si because of the reduction in the grain size down to 2 nm. The photoluminescence energy and peak intensity depend strongly on the Secco etch time because the grain size is reduced by etching the grain boundaries.     

Analytical study of a flattened Gaussian beam through multi-apertured optical imaging systems of B = 0

By using the methods of the matrix decomposition and expansion of the hard-edged aperture function into a finite sum of complex Gaussian functions, the recurrence propagation expressions for a flattened Gaussian beam (FGB) through multi-apertured optical imaging systems of B = 0 are derived and illustrated with numerical examples. Comparisons with the straightforward numerical integration of the Collins formula and with the previous work are made. It is shown that the main advantages of our methods and results are the more accuracy and great reduction of computer time.     

一种多波长OCDMA解码器方案及其性能分析

提出了一种多波长OCDMA（MW OCDMA）系统的光解码器方案,通过多个光硬限幅器来抑制多用户干扰.分析了使用该解码器的MW OCDMA误码率性能、频谱效率和归一化吞吐量性能.分析结果表明,该方案能有效改善MW OCDMA系统的误码率性能,在要求的误码率条件下增加同时用户数,从而能有效改善MW OCDMA系统的频谱效率.同时,采用光硬限幅器的MW OCDMA 系统的归一化吞吐量性能明显提高,特别是归一化吞吐量峰值提高了约一倍.     

Current-induced spin-wave excitations in a single ferromagnetic layer

Evidence for a current-induced spin-transfer torque effect has been investigated in a series of point contacts to single ferromagnetic layers. At specific current densities, abrupt resistance changes, similar to those attributed to current-induced spin-wave excitations in multilayers, have been observed for one current polarity. The critical current for these resistance changes depends linearly on the external field applied perpendicular to the layer. The observed effect is interpreted as a current-driven heterogeneous instability in an otherwise uniform ferromagnetic layer.     

Ultrasonic investigation of amorphous carbon in various frequencies at low temperatures from 2.1 to 300 K

Using pulse echo overlap measurement, the elastic behavior of amorphous carbon has been studied at ambient and low temperatures. The smaller ratio B/G of the bulk modulus to shear modulus and smaller Poisson's ratio σ at room temperature indicate that there is an intrinsic stiffening of transverse acoustic phonons in the amorphous carbon. The acoustic velocity and attenuation for longitudinal modes have been measured between 2.1 and 300 K at three frequencies of 7, 21 and 35 MHz, respectively. Their frequency and temperature dependence are observed. The elastic constant C₁₁ increases with decreasing temperature and show enhanced stiffening at low temperatures. In the 130-220 K region, the abnormal change and effect of longitudinal velocity and attenuation with temperature and frequency, and a phase transition associated with structure relaxations are discussed.     

锰氧化物团簇正离子与硫化氢反应的实验与理论研究 (cited: 2)

采用激光溅射法制备了同位素标记的氧化锰团簇正离子Mn_m¹⁸O_n⁺,并研究了其在快速流动反应管中与硫化氢在热碰撞条件下的反应,氧化锰团簇正离子与硫化氢反应前后的质量分布与强度变化由飞行时间质谱仪检测．实验表明,绝大多数氧化锰团簇正离子可与硫化氢发生氧-硫交换反应产生水分子,反应通式为：Mn_m¹⁸O_n⁺+H₂S→Mn_m¹⁸O_n-1S⁺+H₂¹⁸O．通过密度泛函理论计算了氧化锰团簇正离Mn₂O₂⁺、Mn₂O₃⁺和Mn₂O₄⁺与H₂S反应的机理,结果显示,在这些反应体系中氧-硫交换反应通道同时具有热力学和动力学优势,印证了实验中观察到的现象．气相团簇研究发现的氧-硫交换反应与相关凝聚相体系反应结果一致     

Temporal behavior of low-amplitude dark spatial solitons in two-photon centrosymmetric photorefractive media

We investigate the temporal behavior of low-amplitude dark spatial solitons in biased centrosymmetric crystals with two-photon photorefractive effects. The expressions of time-dependent space-charge field and dynamical evolution equation are derived. The temporal behaviors of the intensity profiles and the intensity full width at half maximum (FWHM) of dark solitons are investigated by numerical method. The results indicate that a broad soliton is generated at the beginning, and as time evolves, the intensity width of solitons decrease monotonously to a minimum value toward steady state. Within the same propagation time, the higher the ratio of soliton peak intensity to the dark irradiation intensity is, the shorter the FWHM of dark solitons is.     

Optimized absorption imaging of mesoscopic atomic clouds

We report on the optimization of high-intensity absorption imaging for small Bose–Einstein condensates. The imaging calibration exploits the linear scaling of the quantum projection noise with the mean number of atoms for a coherent spin state. After optimization for atomic clouds containing up to 300 atoms, we find an atom number resolution of $\varDelta_{\rm det}= 3.7$ atoms, mainly limited by photon shot noise and radiation pressure.     

2013年声频工程学术论坛暨学术交流年会在广州召开

中国电子学会声频工程分会和中国声学学会声频工程分会于2013年9月23日至9月26日,在广州举办了《2013年声频工程学术论坛暨学术交流年会》。