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.

A perturbation of DC electric field caused by light ion adhesion to aerosols during the growth in seismic-related atmospheric radioactivity

Abstract: . The influence of variations in conductivity and external electric current variations in the lower atmosphere on DC electric field over a seismic region is investigated. The external current is formed with the occurrence of convective upward transport of charged aerosols and their gravitational sedimentation in the atmosphere. This effect is related with the occurrence of ionization source due to seismic-related emanation of radon and other radioactive elements into the lower atmosphere. An increase in atmosphere radioactivity level results in the appearance of additional sources of ionization, and altitude dependence of the ion formation rate is calculated. Ionization source varies the atmospheric conductivity and the external current through appearance of ions with equilibrium number density and their adhesion to aerosols. We have calculated the perturbation of conductivity and external electric current as a function of altitude. Variation of conductivity and external current in the lower atmosphere leads to a perturbation of electric current which flows in the global atmosphere-ionosphere circuit. Finally, perturbations of DC electric field both on the Earth's surface and in the ionosphere are estimated.

Electromagnetic precursors to the 2004 Mid Niigata Prefecture earthquake

Abstract: This paper summarizes the electromagnetic precursory phenomena for the 2004 Mid Niigata Prefecture earthquake on October 23, 2004. Three different kinds of seismogenic perturbations have been observed; (1) lithospheric DC/ULF emissions, (2) atmospheric radio noise in the VHF band and (3) ionospheric disturbances. The DC/ULF emissions as observed at Nakatsugawa (in Gifu Prefecture) are detected on October 2–6, and the direction finding result has indicated the possible observed azimuth very close to the epicentral region. Then, we have observed the atmospheric radio noises in the VHF band on October 15–18, which are found to have the azimuth from Chofu very close to the epicentral zone. Finally, nearly at the same time (about one week before the earthquake) we have observed significant ionospheric perturbations on the subionospheric VLF/LF propagation characteristics by means of the shift in terminator time and enhancement in signal fluctuation for one particular path from the JJY (in Fukushima Prefecture) to Kochi. These perturbations not only in the lithosphere, but also in the atmosphere and ionosphere, are likely to be precursors to the 2004 Mid Niigata Prefecture earthquake.

On the Thrashing Cusp in Slotted Aloha Systems

Abstract: We develop a new tool for performance evaluation of a multiaccess communication system. We give an explicit detailed analytic description of a cusp catastrophe in a computer communication system. An approximate model is formulated for a slotted Aloha system assuming a single buffer, based on the Markovian model studied by Lam [2] and Carleial [3]. Next, we outline the research on quantitative processing of thrashing and its results. Sudden changes, which can be observed in the throughput rate, the average delay, and the average number of backlogged users, are induced by smooth alterations of control parameters in the behavior of a slotted Aloha system. These catastrophic phenomena, such as long lasting periods of vanishing throughput rate and very high delays, are analyzed in line with catastrophe theory. The system behavior in a slotted Aloha system is characterized by the cusp catastrophe. In particular, introducing a new parameter σ in our model, we make it clear why and in what cases these catastrophic phenomena occur. The amount of change is also estimated.

Structure factors for tunneling ionization rates of molecules

Abstract: Within the weak-field asymptotic theory, the dependence of the tunneling ionization rate of a molecule in a static electric field on its orientation with respect to the field is determined by the structure factor for the highest occupied molecular orbital (HOMO). An accurate determination of this factor, and hence the ionization rate, requires accurate values of the HOMO in the asymptotic region. Techniques for calculating the structure factors for molecules in the Hartree-Fock approximation are discussed. For diatomics, grid-based numerical Hartree-Fock calculations which reproduce the correct asymptotic tail of the HOMO are possible. However, for larger molecules, to solve the Hartree-Fock equations one should resort to basis-based approaches with too rapidly decaying Gaussian basis functions. A systematic study of the possibility to reproduce the asymptotic tail of the HOMO in calculations with Gaussian basis sets is presented. We find that polarization-consistent basis sets with quadruple or pentuple-zeta quality greatly improve the tail of the HOMO, but only when used with variationally optimized exponents. This methodology is validated by considering the CO molecule for which reliable grid-based calculations can be performed. The optimized Gaussian basis sets are used to calculate the structure factors for the triatomic molecules CO${}_{2}$ and OCS. The results are compared with available experimental and theoretical results.

Fractal analysis for the ULF data during the 1993 Guam earthquake to study prefracture criticality

Abstract: . An extremely large earthquake (with magnitude of 8.2) happened on 8 August 1993 near the Guam island, and ultra-low-frequency (ULF) (frequency less than 1 Hz) electromagnetic fields were measured by 3-axis induction magnetometers at an observing station (with the epicentral distance of 65 km) with sampling frequency of 1 Hz. In order to study electromagnetic signature of prefracture criticality, we have undertaken the fractal (mono-fractal) analysis by means of the Higuchi's method for the ULF data during the 1993 Guam earthquake. Then, it is found that the fractal dimension exhibits five maxima 99, 75, 52, 21, and 9–4 days before the earthquake main shock, which suggests the ULF electromagnetic signature of nonlinear evolution (in the sense of self-organized criticality) taking place in the lithosphere just before the 1993 large Guam earthquake. That is, there take place step-like changes in the lithosphere during the long-term of the order of several months before the main shock.