Study concerning production of lightning overvoltages on low‐voltage power distribution lines

In order to study lightning problems of low‐voltage power distribution lines, lightning overvoltage waveforms were observed inside the homes of customers. The cause of lightning overvoltages was examined from observation of striking points by still cameras. Lightning overvoltages of 62 waveforms were recorded by observation over a period of about 3 1/2 years. Observed waveforms can be classified into three types of single polarity (positive or negative), both polarities (which change from positive to negative or negative to positive), and pulsive waveform. The causes of these lightning overvoltages which were estimated from striking points are shown as follows: (1) Induced lightning overvoltages on low‐voltage distribution lines. (2)   Electric potential rise due to discharge of surge arresters or current of overhead ground wire. (3)   Shift of lightning overvoltages from high‐voltage side of transformer to low‐voltage side, which is due to electromagnetic induction. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 66–75, 2000     

Automated fault tree synthesis by semantic network modeling, rulebased development and recursive 3-value procedure

A concept of flow is introduced to represent any material, information, energy, activity, or phenomenon which can move or propagate along flow paths to cause events specific to the system to be analyzed. A graphical equipment library is given to represent typical types of ‘generation rate’ and ‘aperture’ controllers. The system is modeled by a semantic network with labeled arrows showing effect to cause (backward) relationships between flow and equipment nodes. A correspondence between the equipment library and the system components is established, and the semantic network is constructed by integrating network fragments in the library. Fixed and/or free boundary conditions can be specified explicitly for flow or equipment nodes. Forward-chaining event development rules locally trace the labeled arrows, while a 3-value procedure guides the FT generation by recursive rule applications. The rules are obtained from tables and equipment definitions. The 3-value logic is used to truncate FTs according to the boundary conditions. Different FTs are generated for different top events and boundary conditions, given a semantic network model. FT modules and their hierarchies can be identified by examining network theoretic properties of flow nodes. The proposed approach is demonstrated for a relay system, a hypothetical swimming pool reactor and a chemical reactor.     

Observation of lightning effect on power distribution lines by still cameras

In order to clarify the cause of lightning outages of a distribution line, simultaneous observation of lightning discharge channels and types of damage on distribution lines were carried out with still cameras from July 1993 through July 1995. High-voltage lines located in the observation area did not suffer from induced voltages due to indirect lightning strikes, even if such lightning strikes were nearby. One instance of a direct lightning strike on a distribution line was observed. The striking point was the span center of the overhead ground wire, and only a transformer fuse was blown on the high-voltage line. Damage to surge arresters was observed in the case of a lightning strike on a building located near a distribution line. The cause is thought to have been lightning current which flowed into the nearby distribution line through the damaged arresters. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(1): 17–23, 1997     

Quantitative assessment of cerebral blood flow by 123I-IMP SPECT: venous sampling method with hand warming in the water bath

In order to establish a noninvasive, quantitative method for measuring regional cerebral blood flow (rCBF) by N-isopropyl-p-[123I]iodoamphetamine (123I-IMP) SPECT, we attempted to employ continuous venous sampling instead of arterial sampling. Forty two patients with cerebrovascular diseases were classified into two groups, with (group II: n = 35) and without (group I: n = 7) hand warming. In group II, either hand was warmed, wrapping in a hot blanket (group IIA) or immersed in a 44 degrees C water bath (group IIB). In each patient, immediately after intravenous bolus injection of 222 MBq IMP, arterial and venous blood samples were collected continuously for 5 min from the radial artery and the cubital vein, respectively. By octanol extraction, IMP was divided into the unmetabolized and metabolized fraction. The ratio of 123I-IMP radioactivity of venous blood compared to arterial blood (pass ratio, referred as %PR) was calculated in three fractions, whole blood, unmetabolized, and metabolized fraction. By using these parameters, we assessed the possibility to estimate the amount of unmetabolized IMP fraction of arterial blood, usually used as an input function, from venous samples. In group I, %PR demonstrated a considerable variation between individuals (whole IMP, 47.5 +/- 24.6% (mean +/- SD): unmetabolized IMP, 46.0 +/- 24.5%: metabolized IMP, 51.8 +/- 27.4%). In group II, especially in group IIB, both increase of %PR value and the decrease in variation (whole, 77.9 +/- 5.6%: unmetabolized, 75.7 +/- 5.7%: metabolized, 86.7 +/- 8.7%) were observed, which permitted the further calculation based on the assumption that %PR value was constant in each IMP fraction (whole blood and unmetabolized fraction).(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation for sintering of electrocatalysts and its effect on voltage drops in high-temperature proton exchange membrane fuel cells (HT-PEMFC)

Durability performance such as sintering and voltage drops of HT-PEMFC was theoretically evaluated under non-humid conditions at 150 °C, 170 °C and 190 °C. The quantum chemical molecular dynamics showed that the affinity of the platinum (Pt) electrocatalysts with carbon support decreased with increasing temperature. The degree of agglomeration of electrocatalysts over time simulated by three-dimensional kinetic Monte Carlo method was compared and quantitatively agreed with experimentally measured Transmission Electron Microscopy (TEM) results. Agglomeration of electrocatalysts due to the sintering caused losses of electrochemically active surface area, and found to be occurred more severe as temperature increased. Decreased rate of the proton conductivity due to the evaporation of phosphoric acid affected voltage drops as temperature increased. A theoretical breakdown of the voltage drops indicated that the voltage drops that occurred during the first several hundreds of hours and those occurring for the latter stage were due to different effects.     

Activities of oxygen in liquid Bi,Sn, and Ge from electrochemical measurements

Modified coulometric titrations on the galvanic cell: O in liquid Bi, Sn or Ge/ZrO₂( + CaO)/Air, Pt, were performed to determine the oxygen activities in liquid bismuth and tin at 973, 1073 and 1173 and in liquid germanium at 1233 and 1373 K. The standard Gibbs energy of solution of oxygen in liquid bismuth, tin and germanium for 1/2 O₂ (1 atm) →O (1 at. pct) were determined respectively to be ΔG° (in Bi) = −24450 + 3.42T (±200), cal· g-atom⁻¹ = − 102310 + 14.29T (±900), J·g-atom⁻¹, ΔG° (in Sn) = −42140 + 4.90T (±350), cal· g-aton⁻¹ = −176300 + 20.52T (± 1500), J-g-atom⁻¹, ΔG° (inGe) = −42310 + 5.31 7 (±300), cal·g-atom⁻¹ = −177020 + 22.21T(± 1300), J· g-atom⁻¹, where the reference state for dissolved oxygen was an infinitely dilute solution. It was reconfirmed that the modified coulometric titration method proposed previously by two of the present authors produced far more reliable results than those reported by other investigators. TOYOKAZU SANO, formerly a Graduate Student, Osaka University     

Boojums Connecting Singular and Continuous Vortices in Two-Component Bose-Einstein Condensates

A boojum is a topological defect that can form only on the surface of an ordered medium such as superfluid ³He and liquid crystals. By analogy with superfluid ³He, we numerically create boojums between two phases with different vortex structures in two-component BECs where the intercomponent interaction is spatially dependent. The detailed structure of the boojums is revealed by investigating its density distribution, effective superflow vorticity and pseudospin texture.     

Evaluation of Solute Clusters Associated with Bake-Hardening Response in Isothermal Aged Al-Mg-Si Alloys Using a Three-Dimensional Atom Probe

Temporal changes in the number density, size distribution, and chemical composition of clusters formed during natural aging at room temperature and pre-aging at 363 K (90 °C) in an Al-0.62Mg-0.93Si (mass pct) alloy were evaluated using atom probe tomography. More than 10 million atoms were examined in the cluster analysis, in which about 1000 clusters were obtained for each material after various aging treatments. The statistically proven records show that both number density and the average radius of clusters in pre-aged materials are larger than in naturally aged materials. It was revealed that the fraction of clusters with a low Mg/Si ratio after natural aging for a short time is higher than with other aging treatments, regardless of cluster size. This indicates that Si-rich clusters form more easily after short-period natural aging, and that Mg atoms can diffuse into the clusters or possibly form another type of Mg-Si cluster after prolonged natural aging. The formation of large clusters with a uniform Mg/Si ratio is encouraged by pre-aging. It can be concluded that an increase of small clusters with various Mg/Si ratios does not promote the bake-hardening (BH) response, whereas large clusters with a uniform Mg/Si ratio play an important role in hardening during the BH treatment at 443 K (170 °C).     

Conversion of Solution‐Derived Perhydropolysilazane Thin Films into Silica in Basic Humid Atmosphere at Room Temperature

Spin‐on perhydropolysilazane (PHPS) thin films were converted into mechanically hard silica thin films by an exposure to the vapor from aqueous ammonia. Infrared absorption and X‐ray photoelectron spectroscopic analyses were conducted to clarify the details of the PHPS‐to‐silica conversion and the nature of the silica thin film products. The PHPS‐to‐silica conversion was found to proceed rapidly between 2 and 3 h of exposure via a reaction‐limited process, where the refractive index and the pencil hardness greatly decreased and increased, respectively. Finally, the O/Si mole ratio close to 2 was achieved, which has never been realized in literature for PHPS‐derived silica thin films. It was also found that the condensation of Si–OH groups proceeds in films immediately after PHPS hydrolysis, which is similar to the base‐catalyzed hydrolysis–condensation reaction of silicon alkoxides. Although the silica thin films obtained had refractive indices similar to that of silica glass, high pencil hardness over 9H on Si(100) substrates, and O/Si mole ratios close to 2, it was concluded that they are nonidentical to silica glass, containing trace amounts of Si–OH and Si–H groups.     

Adaptive control of Wiener-type nonlinear systems using neural networks

This paper proposes new adaptive control schemes with neural networks for Weiner-type nonlinear systems which have output nonlinearity. First, by adopting a robust adaptive control law and a functional link network (FLN), we present an adaptive linearizing scheme as a primary step for a model reference control scheme, where the FLN compensates the output nonlinearity. Second, we analyze the stability of the adaptive linearizing scheme by using a robust adaptive control technique, and demonstrate that all of the parameters are bounded and that the boundedness of all of the signals in the closed loop is guaranteed under some reasonable conditions. Third, based on the linearizing scheme, we present a new direct model reference adaptive control scheme by choosing the reference output appropriately. The stability of the system is guaranteed under several conditions in a similar manner. Finally, we illustrate the effectiveness of the proposed scheme through some numerical examples. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 37–48, 1998