The silicide phase formation is examined in the Ni/Si system. The multiphase of NiSi and NiSi2 is confirmed in the specimen, in which a 30-nm-thick Ni film is sputter-deposited on Si(100) at 350°C and subsequently annealed at 400°C for 1 h. This is interpreted that the NiSi and NiSi2 phases nucleate from the amorphous alloys, as a super-cooled melt, at the composition corresponding to those of eutectic points in different composition, which appear in the intermixed Ni-Si alloy layer with a Ni concentration gradient owing to intermixing between Ni and Si at the interface. To confirm this consideration, we execute the Ni deposition on a 350°C-heated Si substrate with a thin SiO2 layer. The result indicates the direct formation of NiSi2 in a non-uniform fashion. This is because the thin SiO2 layer suppresses the Ni diffusion into Si, resulting in the formation of a Ni-Si alloy in a Si-rich composition, from which NiSi2 nucleates at a low temperature. We can demonstrate that the high-temperature phase of NiSi2 nucleates by the kinetic constraint from the amorphous alloy of suitable composition.
In the through Silicon via (TSV) process as a key technology for the 3-dimensional LSI, particularly in the ‘via-last process', SiNx films of high density are strongly required to prepare at low deposition temperatures. It, however, is generally known that the SiNx film prepared at low temperatures shows low film density, resulting in poor insulating barrier properties. As a solution of this issue, we propose the use of the SiNx films deposited by reactive sputtering. We can obtain the sputtered SiNx films of high density (2.78∼2.99 g/cm3) in spite of the deposition without substrate heating. The 20-nm-thick SiNx films succeed the experimental check on the barrier properties against Cu diffusion upon annealing at 700°C for 1 h. The films also show good step-coverage for a TSV with an aspect ratio of 1.5. The SiNx films prepared by reactive sputtering are a candidate for a good insulating barrier applicable to the via-last TSV process.
For realizing highly reliable Cu wiring in 3D/2.5D-IC, SiNx films formed by the reactive sputtering deposition and the plasma-enhanced chemical vapor deposition (PECVD) at low substrate temperatures are characterized and compared by use of X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The film density obtained by XRR shows clear difference between the sputtering and PECVD films. Si-H bonding concentrations obtained by analyzing FT-IR spectra show good correlations with the film densities independent of deposition methods and conditions. Lower density properties of PECVD films could be attributed to higher density of residual Si-H bonds in the films.
It is well known that doubly terminated LC filters are low sensitive to element value deviation in the passband. This property has been expanded to passive complex filters, however, only the case for tracking deviation between real and imaginary part elements has proved. Although numerical calculation methods for arbitrary deviations have proposed, there is no mathematical analysis on mismatch error. In this paper, a preliminary study for passive complex filter sensitivity to mismatch errors between real and imaginary pair elements is given. At first, we show that any mismatch error can be decomposed into tracking and differential errors and that the latter is the subject to be analyzed. Then, we consider a passive complex filter as a multi-port output real filter and analyze its sensitivity in passband.
For extracting coupling capacitances between through silicon vias (TSVs) in three dimensional integrated circuits (3D ICs), a method using the inverse of inductance matrix was investigated. We clarify the accuracy of the method by various structures such as same/different diameters and regular/irregular arrangements. When a huge number of TSVs were used, the inductance matrix gets very large. Therefore, we propose a method for getting coupling capacitances with reasonable accuracy by a small inductance matrix when a lot of TSVs with the same diameter were located regularly.
This paper presents the gate driver with fast switching and low switching loss for SiC-MOSFETs. The proposed driver consists of very simple gate boost circuit and speed up circuit and also it is cost-effective. Normally, conventional gate drive methods have some trade-offs between switching losses and noise. The proposed gate driver can reduce switching losses without increasing surge and ringing voltage and current. The proposed gate driver is able to break the trade-offs of switching characteristics.
This paper presents 10 kW SiC-MOSFET converter for driving SRMs. We proposed gate driver which can reduce switching losses and switching delay at the same time. The SRM converter with the proposed gate driver has higher efficient drive capability compared to silicon IGBT. Because of this high efficient drive advantage, we can apply higher switching frequency to reduce current ripple, or add more switching devices to improve converter performances. We improved current control characteristics with 80 kHz switching frequency, and also add some switching devices and boost capacitor to expand output torque range of SRMs.
This paper analyzes the gate noise performance using simulation and experimental test focused on parasitic inductances of power semiconductor devices' terminals. The gate noise which is over the threshold voltage makes non-active FETs turn on and leads the FETs to a breakdown. Next generation devices which have very high speed switching characteristic are difficult to be dealt with due to the false turn-on problem. The false turn-on mechanism in conventional theory is related to parasitic capacitors and a gate resistor and false turn-on occurs by the current flowing through a reverse transfer capacitor. However, the novel mechanism we proposed is mainly linked to parasitic inductors and recovery current and a non-active FET is switched on due to the oscillation which the energy charged by the current flowing from the source to the gate makes. We verified our theory by experiments, simulations and simplistic circuit equations.
The DC-DC converter using integrated magnetic components that may achieve high power density has gained attention in environmentally-friendly cars such as electric vehicles (EVs) and hybrid electric vehicles (HEVs). This paper focused on interleaved boost converters using close-coupled inductors and loose-coupled inductors that are the integrated magnetic components. Following, detailed electromagnetically analysis for these circuit types were conducted in order to calculate volume of inductors and capacitors that are occupied the large part of space in the converters. The total volume of inductors and capacitors in these circuits were demonstrated clearly through comparison with conventional circuits such as an interleaved boost converter and a single-phase boost converter. As a result, it became clear that interleaved boost converter using loose-coupled inductors was effective for miniaturization of total volume. Further, duty ratio of the minimum volume of close-coupled inductors method is different from the duty ratio of the minimum volume of loose-coupled inductor method.
The author has previously proposed a new multi-point optical sensing system (MPOSS) based on remote optical power supply technology. This system enables us to drive variety of electric sensors and collect their sensing data even if there is no power equipment at their installation site. The system adopts optical pass control technique using optical switches to collect the sensing data from a lot of node by using only two optical fibers. In the previous research, it was demonstrated the prototype MPOSS with wired and wireless sensors had good performance. In this report, results in improving an optical node and evaluating its temperature resistance were shown. A new method using 2-by-2 and 1-by-2 optical switches to reduce optical devices was proposed and successfully demonstrated. Furthermore, it was confirmed an optical node can normally operate in wide temperature range of -25 to 50 degrees, and it shows the node can be used in outdoor environments.
The central pattern generator (CPG) in the spinal cord oscillates a motor command to produce rhythmic movement, whereas several studies have described the movement frequency coding in the primary motor cortex and other motor area. However it is still unclear that the modulation of excitability in the cortico-spinal tract during rhythmic movement. We assessed cortico-spinal excitability during rhythmic movement using transcranial magnetic simulation (TMS), and analyzed the changing CPG frequency characteristic. When the subject performed rhythmic finger flexion-extension movements, TMS was applied on the primary motor cortex. Then the amplitude of the motor evoked potential (MEP) was measured on the target muscle. The frequency of the movement was varied between 0.5 and 4 Hz. We confirmed attenuated MEP was observed at 3 Hz for the finger rhythmic movements. We concluded that the motor command producing the rhythmic movement from motor cortex was decreased during specific rhythmic movement.
Event-related potential (ERP) was measured when subjectively judging the preference for displayed pictures by three opinions; First preference, Second preference, and Others. And the relationship between subjective evaluation and ERP was discussed. In Exp. A, combinations of color shirts with pants were evaluated, in which only the color of the shirt was changed. In Exp. B, five kinds of animals in a zoo were evaluated. After the ERP measurement, a preference test by questionnaire was demonstrated. In result, the P300 area (surrounded by ERP waveform from 250 to 600 ms) is large in some cases where the degree of the preference is small. But the P300 area for a picture corresponding to `First preference' is larger in both experiments, which indicates a potential to distinguish the subject's preference by ERP.
The newly generated neurons in adult animals are known to enhance the pattern separation capability. However, it remains unclear how the new-born neurons change the activity patterns in neuronal networks during the pattern separation. To verify the change of the whole neuronal network activity, the in vitro neurogenesis model is useful because of its observability and controllability. To develop the in vitro neurogenesis model, we modulated the amount of newly generated neurons in cultures by applying basic fibroblast growth factor (bFGF), or cytarabine (Ara-C). To investigate the pattern separation capability, the neural cultures were tetanized with two spatial-pattern stimuli, and then the change in neural response evoked by different pattern was evaluated using microelectrode array. We confirmed that the doublecortin expression in cultures with bFGF was up-regulated than that with Ara-C, indicating that bFGF promoted the neurogenesis. We found that the enhanced neurogenesis contributed the clusters of neuronal networks to specialize their responses to one of two spatial-pattern stimuli after tetanization, while the entire response tended to shift toward the immediately preceding pattern without the neurogenesis. These results suggest that the property of newly generated neurons that they only respond to the specific pattern unlike mature neurons enhances the pattern separation capability of the entire network.
The sympathetic neurons (SN) and the parasympathetic neurons (PN) have important roles in regulation of the cardiac activity. Imbalance of the SN and the PN activities results in abnormal cardiac electrophysiology and can cause several diseases such as atrial fibrillation. While activities of SN and cardiomyocytes have been studied using microfabrication technique, relationship between activities of PN and cardiomyocytes remains unclear. In this study, we developed a device for co-culture of intracardiac ganglion (ICG) neurons which are parasympathetic neurons and atrial myocytes (AMs) using microfabrication technique. Morphological connections between ICG neurons and AMs were observed by immunostaining. Inter-beat-intervals (IBI) were modulated after electrical stimulation of ICG neurons. This modulation completely blocked after applying atropine, a muscarinic receptor antagonist. These results suggest that the co-culture system can be utilized in the research of cell-cell interactions between parasympathetic neurons and cardiomyocytes.
Delay-induced oscillations are widely observed in biological systems such as gene regulation and neural activities. Synchronization among delay-induced oscillations plays important roles in physiology. Therefore, it is significant to establish a method to analyze synchronization properties of delay-induced oscillations. Phase reduction is a mathematical method to analyze such synchronization phenomena. Recently, phase reduction was extended to analyze mathematical models of delay-induced oscillations. However, derivation of synchronization properties of an experimental delay-induced oscillation from phase reduction of its mathematical model has yet to be demonstrated. Here, we demonstrated the validity of a method to derive synchronization properties of a delay-induced oscillation from phase reduction. We generated a delay-induced oscillation experimentally by an electrical circuit. We derived phase response curve and synchronization conditions with periodic external forces by two methods: phase reduction and electrical experiment. We compared the results of the two methods, then phase response curves and synchronization conditions were generally consistent between the two methods. In conclusion, the validity of a method to derive synchronization properties of a delay-induced oscillation from phase reduction was indicated.
The event-related potential (ERP) P300 is an electroencephalographic correlate of target recognition in decision-making tasks. The P300 is used in several brain-computer interfaces (BCIs) as a non-motor signal of decisions, such as letter choice in the P300-Speller utility. Accuracy in choice specification depends on the difference in P300 amplitude evoked by target versus non-target stimuli. In this study, we describe two novel visual attention stimuli, motion-modulated and complexity-modulated, both of which enhance the difference in P300 magnitude between target and non-target stimuli for P300-based BCIs. In the motion-modulated stimulus condition, subjects were asked to focus on a subtarget randomly appearing between two positions inside the main target. In the complexity-modulated stimulus condition, the spatial frequency of a red-green checkered pattern was modulated (low vs. high). Eight healthy subjects viewed these stimuli while brain signals were recorded by electroencephalography. Under all stimulus conditions, P300 amplitudes were significantly larger in response to targets as measured at a single electrode site (Cz). The high-complexity modulated condition produced the greatest difference in P300 between target and non-target stimuli and significance was reached after only four trials. Stimulus arrays incorporating these stimulus forms may be used for the design of improved P300-based BCIs with greater choice accuracy and speed.
Exposure to a high intensity sound damages the inner ear, leading to hearing loss and tinnitus. Previous studies have found that such acoustic trauma also changes neural activities in the auditory cortex. However, to the best of our knowledge, no study investigated the effect of acoustic trauma on the synchrony of steady-state activities in the auditory cortex. In this study, at pre- and post-exposure of an intense sound (16 kHz pure tone; 96 dB SPL; 90 minutes), we investigated Phase Locking Value (PLV) to measure the synchrony of the activities in the auditory cortex of anesthetized rats. Acoustic trauma was confirmed by the auditory brainstem responses (ABR) exhibiting reduced amplitude and prolonged latency. Consequently, we found decreased PLV during presentation of continuous pure tones. In addition, we found an increased contrast of θ-band PLV between silence and tone presentation conditions. These results suggest that an acoustic trauma changes the representation of sound in the auditory cortex in terms of the steady-state phase synchrony.
Sway of transmission lines under typhoon and heavy snow sometimes causes short and break of tower. Short and break of tower make black-out. When they estimate the reason, they investigate the sway mode of cables. This paper presents the analysis of sway mode by combination of Combination of galloping, which is one of phenomenons of sway cables, video in checking power line facilities and cable sway simulation. Using real galloping video, one example of analysis of estimation of cable sway mode is also presented.
In this paper, we aim to propose an eye blink artifact rejection technique for single-channel electroencephalographic (EEG) devices. Independent component analysis (ICA) is usually employed for eye blink artifact rejection. However, ICA cannot be used for the artifact rejection when we recorded EEG signals by single-channel EEG devices, since this method requires multichannel signals for source estimation. On the other hand, single-channel EEG devices have been attracted attention since 2000 because of its usability for measurement and portability. In this paper, we propose positive semi-definite tensor factorization (PSDTF) with 2 step learning method as a new eye blink artifact rejection technique for single-channel EEG analysis. We investigate its validity using signal-to-noise ratio (SNR) between eye blink artifact signals estimated by our proposed method or ICA. Average value of SNR across subjects and trials is 16.13dB. For the value, the validity of our proposed method for eye blink artifact rejection of single-channel EEG signals was confirmed.
The H∞ loop shaping method is known as one of the robust controller design methods. In this method, the design procedure consists of two steps; the weight design and the derivation of a controller. The controller is derived for the weighted plant to suppress the H∞ norm of the transfer matrix consisting of a sensitivity function, a complementary sensitivity function, etc. Therefore, the closed-loop system achieves good tracking and robustness. However, there is only a guideline for the weight design, and an explicit design index of the weight has not been given. As a result, a time-consuming and tedious process is often required to tune the weight. This paper provides a new weight design method for a stable SISO plant. The resulting weight guarantees the upper bound of the performance level before the controller design. This means that the controller design and the weight design are completely separated in contrast to the Lanzon's work. Moreover, the weight is designed using only frequency responses. Accordingly, we can avoid the process of the system identification and reduce the conservativeness caused by an overestimate of the system uncertainty.
In this paper, a continuous-time, finite-time horizon Nash game for a class of stochastic systems is investigated. First, necessary condition attaining Nash equilibrium is derived by means of the existing stochastic optimal control policy. As a result, it is shown that the existence conditions consist of the cross-coupled forward-backward stochastic differential equations. Second, in order to obtain a strategy set, computational algorithm is discussed. In particular, four step scheme is adopted. Finally, simple examples are solved to show the validity of the proposed methodology.
This paper analyzes influence of resource allocation in R&D of solar cells in Japan. Firstly, it estimates solar cell price in Japan in the case resource allocation for R&D of crystalline silicon solar cells was not significantly reduced, but maintained almost constant level. For the projection, it does not use experience curve, but models technological progress, price reduction, of solar cell in Japan with a variable technology knowledge stock by excluding mass production effects. Secondly, solar cell prices in other countries are estimated based on their market share in the world solar cell production. The estimated solar cell price in Japan under the assumed resource allocation decreases by about 30% compared to the actual one and it, therefore, could competitive to the estimated solar cell prices in China and Taiwan. In this case, Japan could maintain its top market share in the world solar cell production several years longer. Instead of the Japan's Feed-in Tariff with subsidy, net-metering without subsidy is enough for keeping almost the same internal rate of return of residential PV systems for new and existing houses. This paper will be helpful to cost-effective R&D planning by a modeling and simulation approach.
Wind energy technologies have evolved dramatically over the past years. In particular, floating offshore wind turbines have attracted interest. In the case of a floating concept, the platform motions induced by both the wind and wave conditions must be mitigated by an advanced control method. In this paper, we propose blade pitch angle control for floating offshore wind turbines using model predictive control (MPC) integrating wind disturbance preview to reduce the platform pitch fluctuations and to regulate the generator power.
To design airfoils for novel airplanes, new knowledge of aerodynamics is required. Modified Parametric SECtion (modified PARSEC) airfoil representation is one of the promising methods for automated airfoil/wing design. In this paper, this method is applied to airfoil design exploration by means of a Kriging model based genetic algorithm (GA) to obtain an optimal airfoil for consideration in the development of a Martian airplane. In this study, an airfoil that can obtain a sufficient glide ratio is considered. The objective function is to maximize the maximum lift-to-drag ratio. To extract the knowledge from solutions, the self-organizing map map (SOM) is also applied. According to the exploration result, several solutions which carry out high aerodynamic performances could be found out. In addition, design knowledges on the low Reynolds number airfoil could be extracted efficiently by SOM. SOM's results suggest that the airfoil with and higher camber at the trailing edge is more suitable for a Martian airplane.
As vehicle driving is heavily influenced by road surface conditions, it is essential for ensuring traffic safety in winter season to properly detect the condition. Therefore, various methods such as laser radar and near-infrared detector to detect road surface conditions have been proposed. However, these methods have not been widely applied for detecting the condition of public highways because of the high deployment costs. Though on the other hand, a method using visible camera does not require expensive equipment, has been applied mainly for daytime use due to the problems of light sources. This paper proposes the method using videos acquired through an existing CCTV camera for road monitoring in order to detect road surface conditions in winter season both during daytime and nighttime. Texture features based on an RGB histogram and a support vector machine are used in this method for detecting the condition of divided into blocks. It was concluded that the method can effectively detect dry, wet and snowy conditions.
The visualization of the Pareto optimal solution set is one of important issues of the multi-objective optimization. The Pareto optimal solution visualization method using the self-organizing maps is one of promising visualization methods. This method has two shortcomings. One is that the map size has to be determined in advance. The other is that infeasible solutions can appear in the learnt maps. This paper proposes a new visualization technique using the growing hierarchical SOM (GHSOM), which is expected to solve foregoing shortcomings. This paper also proposes to introduce a symmetric transformation of maps into the learning algorithm in order to obtain easily viewable unified map. The effectiveness of the proposed method is confirmed through several numerical experiments.
In recent years, technological developments of electronic circuit have made it possible to detect odors. There has been considerable interest in odor sensors in various fields. In our research, we utilize quartz crystal microbalance sensors as odor sensors because they are inexpensive and have similar properties of human nose. Although an odor is measured by combining a lot of Quartz Crystal Microbalance sensors having different performances for odor detection, it is difficult to detect the specific odor that we want. Additionally, the detection of mixed odor is more difficult since the data of mixed odor is imbalance in practice. To solve this problem, in this paper, we propose a new odor detecting algorithm for imbalanced data improving support vector machine. The characteristic point of the proposed method is it enables us to compensate hyperplane for support vector machine by improving penalty term of it. From the experimental results with some datasets, we achieved that our proposed method allowed us to classify imbalanced data better than support vector machine and we confirmed it was feasible and effective for odor detection.
In this article, we describe development and utilization of a multi layout generation system for online document. Recently, generally in engineering universities, lecture slides like PDF documents are distributed at the online in almost all classrooms by utilizing ICT. Most teachers provide PDF documents which are designed using precise but specific layout. But, as they say, ‘everyone has his own taste'. Therefore, our aim is to develop a system that automatically generates any PDF documents on the various layouts from original PDF documents which teachers created. By utilizing our proposed system, we can reduce the burden on teachers, and it is possible to provide PDF documents suitable for each student.
This letter describes sheet-type robot, which can change its shape from a planar sheet to three dimensional structure, move omni-directionally and have transporting capacity. Although many researches on transformable robots are reported, the transformation capability is limited and the structure is complex. A sheet-type robot has a potential to be miniaturized due to its features and to become several complex structures like Origami, a Japanese art work. We achieved three dimensional structure from a sheet-type robot and could confirm its potential.