Dark pulse generation in a dispersion-managed fiber laser

We report an experimental observation of dark pulse generation in a dispersion-managed erbium-doped fiber laser with net anomalous cavity group-velocity dispersion. It is found that apart from the bright soliton pulses, dark pulses with spectral sidebands could be obtained in the laser under appropriate operating conditions. The generation of dark pulses may be attributed to soliton shaping in the cavity.     

Preparation of Nd-doped BiFeO3 films and their electrical properties

The Nd-doped BiFeO₃ thin films were prepared on SnO₂(FTO) substrates spin-coated by the sol–gel method using Nd(NO₃)₃·6H₂O, Fe(NO₃)₃·9H₂O and Bi(NO₃)₃·5H₂O as raw materials. The microstructure and electric properties of the BiFeO₃ thin films were characterized and tested. The results indicate that the diffraction peak of the Nd-doped BiFeO₃ films is shifted towards right as the doping amounts are increased. The structure is transformed from the rhombohedral to pseudotetragonal phase. The crystal grain is changed from an elliptical to irregular polyhedron. Structure transition occurring in the Bi_0.85Nd_0.15FeO₃ films gives rise to the largest Pr of 64 μC/cm². The leakage conductance of the Nd doped thin films is reduced. The dielectric constant and dielectric loss of Bi_0.85Nd_0.15FeO₃ thin film at 10 kHz are 190 and 0.017 respectively.     

完整系统Appell方程的Lie-Mei对称性与守恒量

研究了完整系统Appell方程的Lie-Mei对称性与守恒量.在完整系统Appell方程的基础上,给出了Appell方程的Lie-Mei对称性的定义和判据,得到了Appell方程的Lie-Mei对称性导致的Hojman守恒量和Mei守恒量.举例说明结果的应用.     

经典单色短峰水波理论的三阶完备解

针对经典的有限水深三阶单色短峰波,考虑环境均匀流效应,赋予一新的解析解,从而与原经典解析解构成完备的解析解.这就在第二阶解、第三阶解结构上显示出多种相互作用机制.     

A self consistent normalized calibration protocol for three dimensional magnetic resonance gel dosimetry

In a clinical setting, mixed and inconsistent results have been reported using Magnetic Resonance Relaxation imaging of irradiated aqueous polymeric gels as a three-dimensional dosimeter, for dose verification of conformal radiation therapy. The problems are attributed to the difficulty of identifying an accurate dose calibration protocol for each delivered gel at the radiation site in a clinical setting. While careful calibration is done at the gel manufacturing site in a controlled laboratory setting, there is no guarantee that the dose sensitivity of the gels remains invariant upon delivery, irradiation, magnetic resonance imaging and storage at the clinical site. In this study, we have compared three different dose calibration protocols on aqueous polymeric gels for a variety of irradiation scenarios done in a clinical setting. After acquiring the three-dimensional proton relaxation maps of the irradiated gels, the dose distributions were generated using the off-site manufacturer provided calibration curve (Cal-1), the on-site external tube gel calibration (Cal-2) and the new on-site internal normalized gel calibration (Cal-3) protocols. These experimental dose distributions were compared with the theoretical dose distributions generated by treatment-planning systems. We observed that the experimental dose distributions generated from the Cal-1 and Cal-2 protocols were off by 10% to 40% and up to 200% above the predicted maximum dose, respectively. On the other hand, the experimental dose distributions generated from the Cal-3 protocol matched reasonably well with the theoretical dose distributions to within 10% difference. Our result suggests that an independent on-site normalized internal calibration must be performed for each batch of gel dosimeters at the time of MR relaxation imaging in order to account for the variations in dose sensitivity caused by various uncontrollable conditions in a clinical setting such as oxygen contamination, temperature changes and shelf life of the delivered gel between manufacturing and MR acquisitions.     

A new-style phased array transducer for HIFU

Considering the complexity of common phased array, and relatively slow mechanical scanning of the single transducer, a new-style transducer that has a changeable focus and a simple control system is needed. The sector phased array transducer, which has many advantages including easy fabrication, movable focus, and a simple control system, can reach the desired requirements. This paper has demonstrated its feasibility by the computation of acoustic field in (y, z) plane. The 24-element phased array, of which the length of the focal region is about 10 mm, and the maximum lateral diameter is about 1.5 mm, can accomplish the adjustment of the focus position. The maximum lateral displacement is 1.5 mm, and the treatment area is about 9 multiples of the single transducer, and only six power amplifiers are needed.     

Quantum phase transition and entanglement in Heisenberg XX spin chain with impurity

In this paper,we study the quantum phase transition and the effect of impurity on the thermal entanglement between any two lattices in three-qubit Heisenberg XX chain in a uniform magnetic field.We show that the quantum phase transition always appears when impurity parameter is an arbitrary constant and unequal to zero,the external magnetic field and impurity parameters have a great effect on it.Also,there exists a relation between the quantum phase transition and the entanglement.By modulating the temperature,magnetic field and the impurity parameters,the entanglement between any two lattices can exhibit platform-like behaviour,which can be used to realize entanglement switch.     

A molecular dynamics simulation of segregation behaviours of horizontally vibrated binary granular mixture

This paper performs the two-dimensional, soft-sphere molecular dynamics simulations to study the granular segregation in a binary granular mixture with the same size but different density in the container with the sawtooth base under horizontal vibration. The segregation phase diagram is presented in the acceleration-frequency space. When the acceleration is high enough to result in relative motions of the particles, the system can be in various states (mixed state, vertical and horizontal segregation state), which depend on both acceleration and frequency. Due to the sawtooth base there is stratified flow effect besides density effect. The density effect raises the light particles. The stratified flow drives the particles in the upper levels to the right and the particles in the lower particles to the left, those fact results in the appearance of the left segregation state. The left segregation state can be changed to the right segregation by changing the shape of the sawtooth. As the vibration frequency increases, the stratified flow effect becomes weaker and weaker, so at high vibration frequencies the vertical segregation state appears instead of the left segregation state.     

Ultrafast nonlinear optical properties of dye-doped PMMA discs irradiated by 40 fs laser pulses

The two-photon absorption (TPA) characteristics of PMMA discs doped with three different dyes were studied using an fs-pulsed Ti-Sapphire laser as the pump source, and employing the open-aperture Z-scan technique. TPA cross-sections obtained for PMMA doped with the dyes PM597, DCM and rhodamine 6G–rhodamine B (co-doped) were found to be equal to 24.7, 33.3 and 32.3 GM, respectively (1 GM=10^?50 cm⁴ s phot^?1 mol^?1). Furthermore, two-photon fluorescence was measured for the samples containing DCM and rhodamine 6G–rhodamine B (co-doped). Compared to the one-photon fluorescence spectrum, the peaks in the two-photon fluorescence spectrum were red shifted and the extent of red shift increased with increasing doping concentration. We have also observed that the red shift in the two-photon fluorescence peak of the samples in the solid form is much larger than that in the solution state. This phenomenon could be explained by a twisted intra-molecular charge transfer model.