Co_(41)Ni_(33)Al_(26)合金冷轧带材相变与阻尼能力

通过热轧和冷轧工艺制备了0.2mm厚的Co41Ni33Al26合金带材,采用1350℃×5h水冷对该带材进行了淬火热处理,用金相显微镜观察了其组织。用微分差热分析仪(DSC)测定了其马氏体转变温度,并用动态热机械谱仪(DMS)研究了其相变及阻尼能力。结果表明,0.2mm的Co41Ni33Al26合金带材的基体为竹节状的粗大再结晶晶粒,其马氏体相变温度比1.5mm厚的板材高约45℃;降温过程中合金带材在140~25℃温度范围出现阻尼峰,其阻尼峰宽明显大于马氏体相变温度范围,后者为121~78℃,表明有新的应力诱发马氏体相变出现;Co40Ni33Al27合金带材的阻尼能力超过0.04,并且温度范围宽,有望成为新型阻尼材料。     

High-potential magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media

The magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media, including higher energy terms, was studied as a function of film composition and seed layer materials. All series of CoPtCr films with various Cr content, deposited on Ru seed layers, show maximum values of total anisotropy K/sub u/ at 25-30 at%Pt. The maximum value for CoPt(Cr=0) films reaches /spl sim/15/spl times/10/sup 6/ erg/cm/sup 3/. The addition of SiO/sub 2/ to the CoPtCr films reduces the grain K/sub u/, however the grain K/sub u/ maintains a large value of 8/spl times/10/sup 6/ erg/cm/sup 3/ even when 10at%SiO/sub 2/ is added to (Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/, for instance, which indicates the high-potential thermal stability. Theoretical calculations for media designs of 400 Gbits/in/sup 2/ revealed that the ratio of the high-energy anisotropy term K/sub u2/ to K/sub u1/(K/sub u/=K/sub u1/+K/sub u2/) is required to be 0.2-0.35 to enhance the energy barrier for the remanent state, without a notable change in switching field. The films deposited on Ru seed layers were found to show negligibly small K/sub u2/ values, however, the values of K/sub u1/ and K/sub u2/ vary significantly with the seed layer material used. K/sub u1/ decreases almost linearly as the K/sub u2/ value increases. It is concluded that CoPtCr films have a sufficient potential in the values of K/sub u1/ and K/sub u2/ for high-density perpendicular media.     

Fabrication of size-controlled polyimide nanoparticles

Polyimide particles were fabricated through the two-steps imidization of poly(amic acid) particles prepared by using reprecipitation method. PAA and PI nanoparticles were all spherical, and the changes of particle size, its distribution, and morphology were not observed before and after the imidization. The preparation of PI nanoparticles size-controlled between ca. 20-500 nm was also achieved by changing the experimental conditions, temperature of the poor solvent, the composition of two kind of poor solvent, and PAA-NMP solution concentration.     

Risk-based reconfiguration of safety monitoring system using dynamic Bayesian network

To prevent an abnormal event from leading to an accident, the role of its safety monitoring system is very important. The safety monitoring system detects symptoms of an abnormal event to mitigate its effect at its early stage. As the operation time passes by, the sensor reliability decreases, which implies that the decision criteria of the safety monitoring system should be modified depending on the sensor reliability as well as the system reliability. This paper presents a framework for the decision criteria (or diagnosis logic) of the safety monitoring system. The logic can be dynamically modified based on sensor output data monitored at regular intervals to minimize the expected loss caused by two types of safety monitoring system failure events: failed-dangerous (FD) and failed-safe (FS). The former corresponds to no response under an abnormal system condition, while the latter implies a spurious activation under a normal system condition. Dynamic Bayesian network theory can be applied to modeling the entire system behavior composed of the system and its safety monitoring system. Using the estimated state probabilities, the optimal decision criterion is given to obtain the optimal diagnosis logic. An illustrative example of a three-sensor system shows the merits and characteristics of the proposed method, where the reasonable interpretation of sensor data can be obtained.     

A 1-Gb DRAM for file applications

A time-shared offset-canceling sensing scheme, a defective word-line Hi-Z standby scheme, and a flexible multimacro architecture have been developed for 1-Gb DRAM. These circuit technologies have been applied to a 1-Gb DRAM for file applications employing 0.25 μm CMOS process technology, a diagonal bit-line cell, and a two-stage pipeline circuit technique. In this DRAM, a 30% chip size reduction and a 400-MB/s data transfer rate have been achieved. A 100% improvement in yield has been estimated by Monte-Carlo simulation. The 1-Gb DRAM die size is 936 mm². The cell size is 0.54 μm². The operating current is 58 mA at 2 V and 100 MHz     

Development of the DQFM method to consider the effect of correlation of component failures in seismic PSA of nuclear power plant

This paper presents a new calculation method for considering the effect of correlation of component failures in seismic probabilistic safety assessment (PSA) of nuclear power plants (NPPs) by direct quantification of Fault Tree (FT) using the Monte Carlo simulation (DQFM) and discusses the effect of correlation on core damage frequency (CDF).In the DQFM method, occurrence probability of a top event is calculated as follows: (1) Response and capacity of each component are generated according to their probability distribution. In this step, the response and capacity can be made correlated according to a set of arbitrarily given correlation data. (2) For each component whether the component is failed or not is judged by comparing the response and the capacity. (3) The status of each component, failure or success, is assigned as either TRUE or FALSE in a Truth Table, which represents the logical structure of the FT to judge the occurrence of the top event. After this trial is iterated sufficient times, the occurrence probability of the top event is obtained as the ratio of the occurrence number of the top event to the number of total iterations.The DQFM method has the following features compared with the minimal cut set (MCS) method used in the well known Seismic Safety Margins Research Program (SSMRP). While the MCS method gives the upper bound approximation for occurrence probability of an union of MCSs, the DQFM method gives more exact results than the upper bound approximation. Further, the DQFM method considers the effect of correlation on the union and intersection of component failures while the MCS method considers only the effect on the latter. The importance of these features in seismic PSA of NPPs are demonstrated by an example calculation and a calculation of CDF in a seismic PSA.The effect of correlation on CDF was evaluated by the DQFM method and was compared with that evaluated in the application study of the SSMRP methodology. In the application study, Bohn et al. showed that correlation had a significant effect on CDF and may vary it by up to an order. However, in the results calculated by the DQFM method correlation varied CDF by at most 2 or 3 times compared with CDF for a case where no correlation was assumed. Although some factors should further be examined, this implied that the MCS method may have overestimated the effect of correlation on CDF and the effect of correlation on CDF may not be so significant as that evaluated in the SSMRP.     

Self-organized one-axis-oriented PZT films with nano-domain structure

{100} One-axis-oriented PZT films with a thickness of 2 μm were obtained on (111)Pt/TiO₂/SiO₂/(100)Si substrates by metal organic chemical vapor deposition (MOCVD). These were obtained irrespective of the film thickness up to 2 mm and with a Zr/(Zr + Ti) ratio from 0.20 to 0.75. This was found to be due to the higher growth rate of these orientation grains than {110} and {111)} orientation grains. These films had columnar grains 50–100 nm in width. Moreover, they were found to include 908 nano-domains 10–20 nm in width. Dielectric constant, ε_r and the field induced-strain were maximum around a Zr/(Zr + Ti) ratio of 0.5, which was in good agreement with previous reports on sintered bodies with 100 times larger domains. This means that the domain size had any effect on ε_r or field-induced strain.     

Discontinuous coarsening of the lamellar structure of γ-TiAl-based intermetallic alloys and its control

Discontinuous coarsening (DC) of the primary lamellar structure (PLS) occurring at lamellar colony boundaries (LCBs) and in surface layers of various Ti-(40 to 45) at. pct Al binary and Ti-46 at. pct Al-X (X=Si and C) ternary alloys was systematically investigated by using optical microscopy and scanning and transmission electron microscopy. The compositions of the α ₂ and γ phases in the primary lamellar structure were estimated based on the weight fractions of the two phases, determined by X-ray diffraction. When the solution-treated Ti-(40 to 45) at. pct Al binary alloys were subsequently soaked at 1000 °C, the primary lamellae in the Ti-40 at. pct Al alloy were the most stable, while those in the Ti-44 at. pct Al were the most unstable. Both the thermodynamic analysis and experimental results confirm that the driving force of the coarsening is mainly derived from the reduction of the chemical free energy (i.e., out-of-equilibrium chemical composition) and the interfacial energy of primary lamellae, whereas the coarsening resistance is mainly from the increase of the elastic strain energy of lamellar interfaces and the surrounding during coarsening. It is found that Si has an exceptional ability to hinder the coarsening of the primary lamellar structure at high temperatures, but the precise mechanism for this improvement is uncertain now. Based on this study, a proposal is finally addressed to improve the thermal stability of the primary lamellar structure of titanium aluminides.     

A 10-GHz Optoelectronic Oscillator at 850 nm Using a Single-Mode VCSEL and a Photonic Crystal Fiber

We demonstrate an optoelectronic oscillator using a gain-switched single-mode vertical cavity surface-emitting laser and a single-mode photonic crystal fiber. A 10-GHz optical pulse train at 850 nm with a timing jitter of 1.2 ps was successfully generated.     

Optimal structure of sensor systems composed of nonidentical sensors

The sensor system has two types of contradictory failures; a fail-dangerous failure and a fail-safe failure. A method of obtaining the optimal structure is developed for the sensor system which is composed of general components. The optimal structure minimizes an expected damage, considering all possible boolean structures including noncoherent systems. A simple optimality criterion is obtained and several properties of the optimal structures are derived; a noncoherent structure can be optimal in some cases. A simple systematic search algorithm can be used effectively to determine the optimal system. Analytic solutions are obtained for systems composed of identical components. Illustrative examples are given.