We have developed an educational support system for NAND-based logic circuits. However, there exists some redundancy with respect to the NAND-circuit generation algorithm which is the main part of the system. Hence, in this paper, we try to improve the system. First, we explain how a NAND circuit is generated for the case of four variables using a concrete example. Next, we discuss how to reduce (1) the number of input-variable lines to NAND gates and (2) the number of NAND gates in the circuit. The newly developed system was compared with the old one. For the purpose, we set the number of variables n to 5∼10 and then generated ten functions with truth-table density r=0.6 for each case. As a result, reduction by 30 percent was realized with respect to (1) and some reduction was also observed with respect to (2).

View full abstract

We verified by analyses of new and used paper base phenolic insulators and an acceleration test that the main reason for surface resistivity reduction in paper base phenolic insulators was the permeation of deliquescent ion compounds into the insulators. The main elements were Na and Cl, which were detected by element mapping analysis both on the cross section and surface of insulators, though Al and Si were detected only on the insulators' surface. The mechanism was presumed from the results of these analyses as follows. (1) Deliquescent ion compounds such as sodium chloride, calcium sulfurate, etc. adhere to the insulators' surface. (2) They absorb water in the air. (3) Aqueous solutions of sodium chloride, calcium sulfurate, etc. permeate into the insulators. (4) Though the deliquescent ion compounds adhering to insulators can be removed by cleaning, it is difficult to remove the permeated compounds. Therefore, the insulators deteriorate progressively over time. To verify this mechanism, a deliquescent ion compound (ex. sodium bromide) was put on the used insulators and a composite temperature/humidity cyclic test was executed. The above mechanism could be verified because Na and Br elements were detected by element mapping analyses on the cross section of the accelerated test samples and the permeated Na and Br elements could not be removed by cleaning.

View full abstract

This paper describes an analysis of high frequency electromagnetic field by the finite element analysis of Maxwell equations including the displacement current. A stationary vector wave equation for the high frequency electromagnetic field analysis is solved taking an electric field as unknown functions. Then, to solve subdomains by the direct method, the direct method based on the LDL^T decomposition method is introduced in subdomains. If the direct method is applied for solving subdomain problems, the computation time seems to be reduced by the improved accuracy of subdomain problems, and storing matrices that are results of the decomposition on main memory.

View full abstract

Recently, white Light Emitting Diodes (LEDs) are receiving attention worldwide as new lighting devices. This study examined effects of a lighting application on performance using white LEDs. The light color—the correlated color temperature (CCT) —was assessed. It affected to psychological states and physiological conditions. Three CCT conditions were respectively set for the experiment: 2500 K, 5000 K, and 8200 K. In all, 20 younger subjects (20-30 years old), 15 middle-aged to elderly subjects (45-60 years old) and 12 elderly subjects (over 65 years-old) participated. They were presented a Numerical Verification (NV) task for performance measurement. The psychological states on performance were evaluated using the lighting assessment questionnaire. The physiological conditions were recorded using an electrocardiograph. Results show that the effects of CCT differ among age groups. Especially, the performance of younger subjects might differ from CCT conditions; elderly subjects are affected by CCT condition because of their visual acuity or response to contrast of objects.

View full abstract

International Electrotechnical Commission (IEC) prescribes immunity tests (IEC610000-4-2) of electronic equipment against electrostatic discharges (ESDs), and specifies indirect discharges from an ESD-gun onto a vertical coupling plane (VCP) in the vicinity of equipment under test (EUT) for simulating personnel discharges to conductive materials being adjacent to the EUT. According to IEC 61000-4-2 2001-04, the VCP shall be placed at a distance of 0.1m from the EUT, and the indirect discharge of an ESD-gun should be conducted to the centre of a vertical edge of the VCP, while the reference arrangement of EUT and the angles of inclination and rotation of the ESD-gun are not specifically determined. In order to clarify to what extent EUT arrangements affect test results, using a simple printed circuit board (PCB) with a trace in lieu of EUT, we measured the voltages induced on the trace for indirect discharges from an ESD gun with different angles of inclination and rotation. As a result, we found that the peaks of induced voltages vary by a factor of 1.7 for indirect discharges onto the centre of a vertical edge of a VCP, while the indirect discharges onto the vertical edge from the back side of a VCP reduce the uncertainty of peak voltages by ±5%. The latter finding provides a new method for indirect discharges onto a VCP, whose test results are unlikely to be affected by EUT arrangements.

View full abstract

Skin depth of electromagnetic (EM) wave depends on frequency of EM wave ν and electrical properties of rocks and minerals. Previous studies have theoretically assumed that the skin depth L_α(ν) can be expressed as a function of frequency ν by L_α(ν) ∝ ν ^-φ and φ = 1 at high frequency or φ = 1/2 at low frequency. Based on fractal theory of rocks, we point out that the frequency exponent φ reflects internal fractal structures (i.e., occupancy, distribution and connectivity) of dielectric/conductive matrices of rocks such as pores, cracks, grain boundaries, inclusions and various fluids. Laboratory measurements of dielectric constant and conductivity of granite and previous studies on various rocks as a function of frequency show that φ is an exponent ranging from 1/4 to 1. By extrapolation of the skin depth by laboratory measurements at a given frequency into at other frequencies, the skin depth with variation in φ becomes longer or shorter than that by previous studies. Moreover, at a given frequency, the skin depth decreases with increasing a fractal dimension of fracture systems (decreasing φ). Thus, the skin depth of EM wave through the crust for detecting seismo-EM radiations and through rock salt domes for detecting ultra-high energy neutrinos depends on fractal structures of dielectric/conductive matrices in heterogeneous crust.

View full abstract

This paper proposes numerical techniques to distil waveform parameters out of digitally measured data of oscillatory impulse current. The first method, to be used for liner circuit, based on a curve-fitting technique in which a smooth analytical curve is defined to fit the noise-superposed measured data. The waveform parameters are derived from the curve. The algorithm is examined its performance using a measured waveform data which is obtained from a circuit composed of linear elements only. It is not rare when impulse current is measured in a circuit with non-linear element, namely an arrester. After carefully observed behaviours of the circuit current when the non-linear element turns on and off, authors developed two algorithms capable to determine the parameters from the recorded data obtained from a circuit having a ZnO arrester. The developed algorithm processed the waveform data generated by TDG which is to be issued in 2009 as a part of IEC 61083-2. The details of the algorithm are to be demonstrated in the paper.

View full abstract

Concerning about the pulsed current discharge in water which used for rough machining process of wire electric discharge machining, we performed measurements of single pulsed arc voltage, observed the developing process of arc discharge by using ICCD camera and examined discharge crater dependence on the discharge current. Based on these result of measurements of transient arc phenomena, we constructed a simple discharge model of arc plasma extension. As a result, we proposed the optimal pulsed discharge current under various processing conditions to improve the machining performance for Wire-EDM. The analysis of the pulsed arc discharge phenomena will form the basis of technology for realizing high-performance drive control schemes for Wire-EDM.

View full abstract

In our research group, multi-gas ICP (inductively coupled plasma) source was developed for industrial plasma processing and traced elemental analysis. With the multi-gas ICP source, not only Ar but He, O₂, N₂, CO₂, air and their mixture gas plasmas can be stably generated in atmospheric pressure. In this study, the plasma source was applied for decomposition of anesthetic gas which effect on global warming as involving N₂O. N₂O/air mixture gas plasma was generated by the plasma source then the composition of treated gas was measured. Effect of the RF input power on decomposition rate of N₂O was investigated. As a result, 99.98 % of decomposition rate 99.98 % of decomposition rate and 117 g/kWh of energy efficiency were achieved at 800 W of the RF input power and 1 % of NO₂ was generated as a by-product.

View full abstract

Epoxy resins with controlled high-order structure have higher thermal conductivities than conventional ones, because the crystal-like domains, self-arranged ‘mesogen’ groups of the epoxy monomers, promote smooth phonon transportation. Although thermal conductivities of these epoxy resins are 1.0 W/m·K at a maximum, these are not enough to apply to electric devices which require high heat dissipation efficiency. In this paper, we composed these resins and alumina fillers, to accomplish the epoxy resin composites which have both isotropic high thermal conductivities and electrical insulation. Though these epoxy monomers are difficult to handle because of their crystallinity and poor solubility in solvents, we conclude that the conventional forming process for thermosetting resins such as transfer molding are applicable to these composites by optimizing the molecular architectures of hardeners. Both high thermal conductivity as 5 W/m·K and excellent flow property were accomplished for molding compounds using developed composites. And developed molding compounds were applied to the plastic ball grid array (P-BGA) semiconductor packages and the bobbins for concentrated winding motors, then good heat dissipation properties were shown for both applications. We conclude that developed molding compounds are effective for thermal management of electric and electronic devices.

View full abstract

When the circular polarized wave incidents on an absorber panel obliquely, the cross-polarized wave components of the reflected wave remain. In this paper, the improvement method of oblique incidence properties for the absorber panels is proposed. By using the wire array sheet, the cross-polarized wave reflection coefficient of the circular polarized wave can be matched.

View full abstract

RuO₂ nanoparticles were supported on arc-black (AB) with different pH of Ru colloidal solutions. For lower pH, RuO₂ particles in nanometer size were dispersed on AB, although for higher pH, RuO₂ particles were aggregated. The RuO₂-supported-AB prepared at pH 5 had the highest amount of RuO₂ and showed the highest capacitance.

View full abstract