Visualization of Anomalies Using Mixture Models

Anomaly detection is important to learn from major past events and to prepare for future crises. We propose a new anomaly detection method that visualizes multivariate data in a 2- or 3-dimensional space based on the probability of belonging to a mixture component and the probability of not belonging to any components. It helps to visually understand not only the magnitude of anomalies but also the relationships among anomalous and normal samples. This may provide new knowledge in the data, since we can see it from a different viewpoint. We show the validity of the proposed method by using both an artificial and an economic time series.     

Design of a CW 1 THz Gyrotron (Gyrotron Fu Cw III) Using a 20 T Superconducting Magnet

Design of a CW 1 THz gyrotron at second harmonic operation using a 20 T superconducting magnet has been described. The mode competition analysis is employed to investigate operation conditions of second harmonic mode, which is being excited at the frequency ranging from 920 GHz to 1014 GHz. The output power up to 250 watt corresponding to the efficiency of 4.16 percent could be achieved by using an electron beam with accelerating voltage 30 kV and current 200 mA. The important advantage of this gyrotron is that the single mode excitation at second harmonic, and extremely high frequency of the radiation, could be maintained even at high currents. It opens possibility to realize a high power radiation source at 1 THz. Such gyrotron is under construction at FIR Center, University of Fukui.     

Suppression of Dynamic On-Resistance Increase and Gate Charge Measurements in High-Voltage GaN-HEMTs With Optimized Field-Plate Structure

The dynamic on-resistance increase associated with the current collapse phenomena in high-voltage GaN high-electron-mobility transistors (HEMTs) has been suppressed by employing an optimized field-plate (FP) structure. The fabricated GaN-HEMTs of 600 V/4.7 A and 940 V/4.4 A for power-electronics applications employ a dual-FP structure consisting of a short-gate FP underneath a long-source FP. The measured on-resistance shows minimal increase during high-voltage switching due to increased electric-field uniformity between the gate and drain as a result of using the dual FP. The gate-drain charge Q _gd for the fabricated devices has also been measured to provide a basis for discussion of the ability of high-speed switching operation. Although Q _gd /A (A: active device area) was almost the same as that of the conventional Si-power MOSFETs, R _on A was dramatically reduced to about a seventh of the reported 600-V Si-MOSFET value. Therefore, R _on Q _gd for 600-V device was reduced to 0.32 OmeganC, which was approximately a sixth of that for the Si-power MOSFETs. The high-voltage GaN-HEMTs have significant advantages over silicon-power MOSFETs in terms of both the reduced on-resistance and the high-speed switching capability.     

A Robust Dispatching Algorithm for Autonomous Distributed Manufacturing of Mixed VLSI Products

This paper describes a new dispatching algorithm for dynamic allocation of work-in-process (WIP), named pseudo periodical priority dispatching (P3D). The algorithm is developed to manage a processing station in an autonomous distributed manufacturing system. The priority of dispatching is examined when each quantum starts, by considering both the amount of WIP in the input buffer of the processing station and the arrival rate of WIP. Here, a quantum is defined as a period, during which a single type of WIP is processed in a machine, and the machine for each type of WIP is fixed during the quantum. Performance parameters, i.e., adjustment rate, throughput, response time, and tardiness, when applying P3D are compared with the results of the first-come first-serve (FCFS) and the shortest processing time (SPT) in simulations assuming Poisson arrival. A fluctuation in arrival rate causes large inventories at the processing station. The adjustment rate is the lowest and the availability of machines is the highest with P3D; therefore, P3D can quickly dissolve a bottleneck. Both P3D and SPT produced shorter response times than FCFS in average, and both P3D and FCFS produced shorter tardiness than SPT. The small quantum size helps to shorten the response time in P3D. P3D with the minimized quantum size gives a good estimation when setting the due date. P3D achieves very fair dispatching even though the arrival rate differs by 40 times among mixed WIPs. The author concludes from the above results that P3D is a robust dispatching algorithm for manufacturing a broad mix of VLSI products.     

THz Generation From GaP Rod-Type Waveguides

Terahertz (THz) generation was demonstrated from GaP rod-type waveguides via difference-frequency-mixing of near-infrared light using a collinear phase-matching condition. THz output peaks were observed, and appeared at frequencies corresponding to the fundamental and high-order waveguide modes. Interestingly, the position of the fundamental mode shifted to a higher frequency for a smaller waveguide cross-section, which is attributed to the waveguide confinement of the THz wave. The conversion efficiency was enhanced in the waveguide with a cross section of 200 mumtimes160 mum as compared to that in bulk GaP crystals     

Low-frequency Raman spectra in κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br

The ordering of the terminal ethylene groups of the BEDT-TTF molecule, i.e., the staggered or eclipsed conformation, in κ-(BEDT-TTF)₂Cu(NCS)₂ and κ-(BEDT-TTF)₂Cu[N(CN)₂]Br was studied between 18 and 295 K by Raman scattering. The low-frequency spectra of these compounds are similar to each other. Broad peaks at about 55 cm⁻¹ extremely broadened and their intensities became weak with decreasing temperature. The anomalous behaviour was interpreted in terms of critical dynamics of the pseudospin-phonon coupled system, where the spin states represent the conformations of the terminal ethylene groups. It was found that the ordered state is formed around the superconducting critical temperature.     

Inhibition effect of metal cations to intergranular stress corrosion cracking of sensitized Type 304 stainless steel

Inhibition effect of metal cation to intergranular stress corrosion cracking (IGSCC) of sensitized Type 304 stainless steel has been investigated by slow strain rate technique (SSRT) with a dynamic crack observation system. The SCC tests were conducted in fully-deaerated aqueous solutions containing various metal sulfates of 10⁻⁵ kmol/m³ at 95 °C. Metal cations of Na⁺, Ca²⁺, Mn²⁺ and Zn²⁺ were selected in this study, and were characterized by a hardness based on the hard and soft acids and bases (HSAB) concept. As a result, it was found that a hard metal cation in the test solution increased crack initiation time and decreased mean crack initiation frequency. In other words, metal cations with larger hardness have an ability of suppressing initiation process of the IGSCC. On the other hand, apparent mean crack velocity was independent of the hardness of metal cation. The finding that the metal cations with large hardness inhibit initiation of the IGSCC was able to be rationally explained on the basis of the passive film model combined with the HSAB concept.     

亚微米颗粒对铝基复合材料基体显微结构的影响

选用0．15μm和5μm的Al2O3颗粒，采用挤压铸造法制备了体积分数为40％的铝基复合材料。利用选区电子衍射和高分辨电子显微技术研究了Al2O3P／1070Al界面附近基体的显微组织。结果表明，复合材料增强体颗粒为5μm时，基体存在大量的Eh热错配应力引发的位错，颗粒粒径为0．15μm时，基体表现为近无位错的组织特征，其缺陷形式为1～5nm的“微畸变区”，这主要是由于粒径小、分布弥散，微区应力均匀所致。     

High coercivity in Sm5Fe17 melt-spun ribbon

Sm–Fe binary alloy with the hard magnetic Sm₅Fe₁₇ phase was produced by melt-spinning followed by heat treatment. The magnetic properties of the Sm–Fe melt-spun ribbon depended on the annealing temperature. The highest coercivity, _iH_c = 1.90 MA m⁻¹, was obtained by annealing the Sm–Fe melt-spun ribbon for 1 h at 923 K. The coercivity of the Sm₅Fe₁₇ melt-spun ribbon was attributed to the grain size of the hard magnetic Sm₅Fe₁₇ phase.     

The Fatty Acid Composition in Tuna (Bonito,Euthynnus pelamis) Caught at Three Different Localities from Tropics to Temperate

The present paper describes the effect of habitat on the fatty acid composition of the lipid of bonito (Euthynnus pelamis), which was caught at three different localities, Philippine Sea (the tropical zone; seawater temperature at the fishing ground was 27·8°C), East China Sea (the subtropical zone; seawater temperature was 29·7°C), and the Pacific coast of Japan (the temperate zone; sea-water temperature was 20·3°C). The total lipids of various organs and stomach contents were extracted and their fatty acid composition analysed by gas chromatography (GC). Docosahexaenoic acid (DHA; 22: 6n-3) was the major unsaturated fatty acid in the lipid of all specimens examined from all localities. The mean DHA content accounted for more than 25% (mean±standard error: 26·0±0·6%) of the total fatty acids (TFA) in the lipids of all organs, a lipid profile markedly different from that of other fish species whose fatty acid composition is generally variable. Particularly, the mean DHA content of lipids in bonito caught in the northern sea-area sample (the temperate zone) was always high (28·4±0·7% TFA) in the lipid of every organ. Because the DHA contents of lipids of the stomach contents fluctuated between 9·9 and 31·9% TFA, bonito did not simply incorporate the fatty acid profile of the lipids of its prey fishes, but selectively accumulated the DHA. Though the mean DHA content in the lipid of all bonito from the tropical to the temperate zone was markedly higher than other marine fish species such as sardines and herrings, there was a small difference between those in the northern (28·4±0·7% TFA) and southern samples (the subtropical and tropical samples, 24·7±0·8% TFA) (P<0·05). It is suggested that the difference between them may be due to environmental effects, for example, the temperature of the seawater and the fatty acid composition of the lipids of prey organisms. © 1997 SCI.