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.

Tunneling conductance of connected carbon nanotubes

Abstract: A three-dimensional structure of two carbon nanotubes (CN) joined by a connecting region containing a pentagon and heptagon pair is given by the use of a projection method. The connecting joint is uniquely determined for the given two chiral vectors of CN by a vector which defines a three-dimensional dihedral angle. The tunneling conductance is calculated for a metal-metal CN junction and a metal-semiconducting CN junction. The calculated results clearly show that these junctions work as the smallest semiconductor devices.

D-Wave Collapse and Explosion of a Dipolar Bose-Einstein Condensate

Abstract: We investigate the collapse dynamics of a dipolar condensate of 52 Cr atoms when thes-wave scattering length characterizing the contact interaction is reduced below a critical value. A complex dynamics, involving an anisotropic, d-wave symmetric explosion of the condensate, is observed. The atom number decreases abruptly during the collapse. We find good agreement between our experimental results and those of a numerical simulation of the three-dimensional Gross-Pitaevskii equation, including contact and dipolar interactions as well as three-body losses. The simulation indicates that the collapse induces the formation of two vortex rings with opposite circulations.

Optical nanofiber as an efficient tool for manipulating and probing atomic fluorescence

Abstract: We experimentally demonstrate efficient coupling of atomic fluorescence to the guided mode of a subwavelength-diameter silica fiber, an optical nanofiber. We show that fluorescence of a very small number of atoms, around the nanofiber can be readily observed through a single-mode optical fiber. We also show that such a technique enables us to probe the van der Waals interaction between atoms and surface with high precision by observing the fluorescence excitation spectrum through the nanofiber.

Variational Method for the Analysis of Microstrip Lines

Abstract: This paper reports a method for computing the line capacitance of a microstrip line based on the application of Fourier transform and variational techniques. The characteristic impedance, guide wavelength, and the surface potential distribution in the microstrip line are obtained for a range of structure parameters and the dielectric constant. The results calculated from the expressions developed in the paper are compared with the theoretical results presently available in the literature and good agreement is found. Comparison with available experimental results is also made where feasible. Possible applications and limitations of the method are discussed.

Effects of antenna directivity and polarization on indoor multipath propagation characteristics at 60 GHz

Abstract: In millimeter-wave indoor communications systems, the radiation patterns and polarizations of the antennas at base stations and remote terminals have a significant influence on channel characteristics. The work reported in this paper investigated the effects of the radiation patterns of the antennas at remote terminals on multipath propagation characteristics. These effects were investigated by indoor propagation measurements at 60 GHz conducted in a modern office room and by ray-tracing simulations based on geometrical optics. Multipath channel characteristics are compared in terms of impulse responses and their root-mean-square (rms) delay spreads for an omnidirectional antenna and for three directive antennas with different beam widths. From the results of measurements and ray-tracing simulations, the use of a directive antenna at the remote terminal is demonstrated to be an effective method of reducing the effects of multipath propagation. Further reduction in the multipath effects is found to be achieved by the use of circular polarization instead of linear polarization with the directive antennas.