University of Electro-Communications

About: University of Electro-Communications is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Laser & Robot. The organization has 8041 authors who have published 16950 publications receiving 235832 citations. The organization is also known as: UEC & Denki-Tsūshin Daigaku.

Topological defect formation in a quenched ferromagnetic Bose-Einstein condensates

Abstract: We study the dynamics of the quantum phase transition of a ferromagnetic spin-1 Bose-Einstein condensate (BEC) from the polar phase to the broken-axisymmetry phase by changing magnetic field, and find the spontaneous formation of spinor domain walls followed by the creation of polar-core spin vortices. We also find that the spin textures depend very sensitively on the initial noise distribution, and that an anisotropic and colored initial noise is needed to reproduce the Berkeley experiment [Sadler et al., Nature (London) 443, 312 (2006)]. The dynamics of vortex nucleation and the number of created vortices depend also on the manner in which the magnetic field is changed. We point out an analogy between the formation of spin vortices from domain walls in a spinor BEC and that of vortex-antivortex pairs from dark solitons in a scalar BEC.

Analysis of two-dimensional high-energy photoelectron momentum distributions in the single ionization of atoms by intense laser pulses

Abstract: We analyzed the two-dimensional (2D) electron momentum distributions of high-energy photoelectrons of atoms in an intense laser field using the second-order strong field approximation (SFA2). The SFA2 accounts for the rescattering of the returning electron with the target ion to first order and its validity is established by comparing with results obtained by solving the time-dependent Schr\"odinger equation for short pulses. By analyzing the SFA2 theory, we confirmed that the yield along the back rescattered ridge in the 2D momentum spectra can be interpreted as due to the elastic scattering in the backward directions by the returning electron wave packet. The characteristics of the extracted electron wave packets for different laser parameters are analyzed, including their dependence on the laser intensity and pulse duration. For long pulses we also studied the wave packets from the first and the later returns.

Spectroscopic and stimulated emission characteristics of Nd/sup 3+/ in transparent Y/sub 2/O/sub 3/ ceramics

Abstract: Nd:Y2O3 ceramic materials have been synthesized using the vacuum sintering technique with the raw materials prepared by the nanocrystalline methods. The TEM measurements reveal the excellent optical quality of the ceramic with low pore volume and narrow grain boundary. The radiative spectral properties of Nd:Y2O 3 ceramic have been evaluated by fitting the Judd-Ofelt model with the absorption and emission data. Individual Stark levels for 2s+1LJ manifolds are obtained from the absorption and fluorescence spectra and are analyzed to identify the stimulated emission channels possible in the Nd:Y2O3 ceramic. Laser performance studies reveal two stimulated emission channels at 1074.6- and 1078.6-nm wavelengths with stimulated emission cross sections of 7.63times10-20 and 6.35times10-20 cm2. With 1.5 at % Nd:Y2O3 ceramic acting as a laser medium, we obtained a slope efficiency of 32% with 160-mW output power and pump threshold of 200 mW at 1078.6 nm

Design and control of an all-direction steering type mobile robot

Abstract: This article describes a new type of mobile robot that has a spherical wheel, an arched body, and motion-controlling mech anisms installed inside the wheel. The robot can travel in every direction and perform unique actions by virtue of the wheel and the motion-controlling mechanisms. We call the latter the Inside Wheel Balancing System (IWBS). Postural stability con trol, omnidirectional steering, and locomotion of the robot were achieved by means of the compound gravity center feedback control. Postural stability and traveling control on a slope and on a flat plane were also attained experimentally. The experimental results coincide well with those obtained by the simulation performed on a personal computer. The omnidirec tion traveling robot proposed here provides great possibility to the mobile robots in the manufacturing and nonmanufacturing environments.