Search

A shape memory piezoelectric actuator can maintain a piezoelectric displacement without an operating voltage. It has two stable strain states at zero voltage: a poled state and a depoled state. The driving principle of the shape memory piezoelectric actuator is based on reorientation of the non-180 domains in the ferroelectric materials. In this study, a unimorph shape memory piezoelectric actuator with a soft lead zirconate titanate was fabricated. The fatigue and retention properties of this shape memory piezoelectric actuator were investigated. The fatigue behavior of the actuator in the early stages is considered to be closely related to the domain stabilization process. Continuous cycle fatigue tests revealed that the shape memory piezoelectric actuator continues to operate even after 106 cycles. Retention measurements revealed that the depoled state of the actuator was more stable than the poled state. The drift in the actuator displacement over one year was estimated to be less than 10% of the initial shape memory displacement. [ABSTRACT FROM AUTHOR]

Parasympathetic function is important in the induction and maintenance of sleep. We examined whether nocturnal vagal modulation of heart rate is related to the poor sleep quality commonly reported in chronic fatigue syndrome (CFS). Heart rate (HR, as R–R intervals) was continuously monitored during sleep in 20 patients with CFS and 20 matched control subjects. Questionnaires assessed demographic information, symptoms, functional impairment, and subjective sleep quality. CFS was associated with more sleep problems in general and poorer subjective sleep quality on the study night (all p < 0.003), and reports of repeated awakening during the night were 7 times more likely compared to healthy subjects ( p = 0.017). Time and frequency-domain parameters of HR variability during sleep were significantly lower in patients with CFS (all p < 0.006). Multiple regression analyses revealed that heart rate variability (HRV) parameters were the best predictors of subjective sleep measures. This study identified significant reductions in vagal modulation of heart rate during sleep in CFS. Low HRV strongly predicted sleep quality—suggesting a pervasive state of nocturnal sympathetic hypervigilance in CFS. [ABSTRACT FROM AUTHOR]

The fundamental study of a shape memory piezoelectric actuator was conducted, using operated with a pulsed voltage, so that low energy consumption and low voltage operation could be realized. To realize the shape memory operation of the piezoelectric actuator, an imprint electrical field was induced with a high electrical field of 3.5 kV/mm in a 150°C environment. The memory effect of the displacement and the permittivity of the shape memory piezoelectric actuator resulted from the asymmetric butterfly curve caused by the imprint electrical field. The actuator has two stable strain conditions and permittivity values that were dependent on the direction of polarization, imparting the shape memory effect and permittivity memory effect. Furthermore, self-sensing operation was realized by detection of the permittivity that corresponds to the position of the actuator. [ABSTRACT FROM AUTHOR]

In positioning applications, the drawbacks of piezoelectric actuators are hysteresis, nonlinearity and creep in piezoelectric displacement. Hence, a feedback control using a displacement sensor is usually essential for a precise positioning. Such displacement sensors hinder device miniaturization, necessitate a complicated configuration, and increase the manufacturing cost. In this study, a self-sensing control system using permittivity change detection was demonstrated. This system is based on the linear relationship between the permittivity and the piezoelectric displacement. This linear relationship was verified experimentally. And we examined the self-sensing positioning control using a real-time permittivity change detection system, and the non-linear piezoelectric property was successfully compensated. [ABSTRACT FROM AUTHOR]

Fundamental amplifying characteristics of 1.55-mum semiconductor optical amplifiers (SOAs) that contain multiquantum well (MQW) active layers with an optimized tensile strain or bulk active layers with various tensile strains were investigated. Both types of SOAs have their own merits and demerits. For device application in networks, driving current and wavelength in the low-polarization-sensitivity condition are very important, but they have not been clarified yet. The results of the present investigation clarify the driving current and wavelength characteristics of low-polarization-sensitivity SOAs with MQW and strained-bulk active layers. The low-polarization-sensitivity condition of SOAs with a strained-bulk active layer is shown to have a very wide range of driving current and wavelength for network-device application. These results, with other requirements taken into account, provide guidelines for choosing the type of SOA most suitable for a given application [ABSTRACT FROM PUBLISHER]

An efficient spotsize converter (SSC) is necessary for directly coupling an InP-based deep-ridge waveguide structure to a fiber. We have already proposed an SSC that uses a laterally buried taper, selectively grown over a thick cladding layer and an optimized deep-ridge-buried waveguide junction. The experimentally obtained converter loss was less than 2 dB, which is still large. Further optimization is possible by introducing a short taper waveguide for the deep-ridge-buried waveguide junctions and improving the taper shape by using a two-step linear taper with a short narrow waveguide. A simulation result shows that we can achieve a converter loss of less than 1 dB with a converter length of only 200 μm. [ABSTRACT FROM PUBLISHER]

In a lightwave circuit using a strongly confined waveguide, higher order leaky modes must be suppressed to obtain ideal characteristics, especially in arrayed waveguide gratings (AWGs). Propagation loss for higher order leaky modes in InP-based deep-ridge waveguides was investigated by simulation and experiment. A highly sensitive loss measurement method based on optical low-coherence reflectometry was used to determine the loss, and the relationship between the loss for the higher order mode and AWG crosstalk was investigated. Optimizing the deep-ridge waveguide parameters, especially the core thickness, the refractive index of the core, and the etch depth under the core, significantly reduced the propagation loss for the higher order leaky mode. The effective elimination of the higher order modes will enable fabrication of low-crosstalk AWG routers. [ABSTRACT FROM PUBLISHER]

We propose a high-gain semiconductor optical amplifier with an integrated bent spot-size converter (BEND SS-SOA). A straight active waveguide enables us to use a pn-buried heterostructure (pn-BH) with a high current-blocking effect and uniform characteristics. We can optimize a bent spot-size converter waveguide to provide low optical feedback from the facets and high-coupling efficiency to a flat-end optical fiber with low radiation loss due to the bend. The devices we fabricated achieve a high fiber-to-fiber gain of 18 dB with a coupling efficiency of -3.5 dB, and we have demonstrated a four-channel array with uniform characteristics [ABSTRACT FROM PUBLISHER]

Attempts to determine whether class II transactivator (CIITA) is responsible for the impaired up-regulation of major histocompatibility complex II molecules. Evaluation of the surface marker expression on thymic epithelial cells; Relationship between CIITA and the phenotypic characteristics of lymphocytes; Characteristics of thymoma.

This paper investigates the effectiveness of multiple indium atomic planes in reducing the dislocation density in GaAs epitaxial layers grown by metalorganic molecular beam epitaxy on GaAs-coated Si substrates prepared by metalorganic chemical vapor deposition. In situ reflection high-energy electron diffraction patterns show that, during the growth of multiple indium atomic-plane structures, two-dimensional growth takes place. Cross-sectional transmission electron microscope observation shows that InAs sublayers are commensurate; hence the critical thickness of the InAs layer in this structure is more than one-monolayer. Cathodoluminescence examination indicates that the defect density decreases as the number (<60) of indium atomic planes increases. This new structure is more effective in dislocation reduction than conventional InGaAs/GaAs strained-layer superlattices. [ABSTRACT FROM AUTHOR]

We will discuss an expected utility of rewards which are generated by Markov decision processes. This is applied to the optimal stopping problem with a utility treatment. Also a combined model of the decision processes and the stopping problem, called a stopped Markov decision, is considered under the utility. [ABSTRACT FROM AUTHOR]

Stiffness of the vocal fold is a significant factor in determining mucosal wave propagation and in the control of the fundamental frequency of phonation. We measured pliability of the vocal fold mucosa in an in vivo canine model as an index of stiffness while the histological layer-by-layer structure of the vocal fold was not disrupted. The point 1 mm below the free edge showed a maximal pliability that gradually diminished toward the tracheal side and reached a minimum. When the thyroarytenoid (TA) muscle contracted, pliability of the mucosa was significantly increased (P < 0.001). Mucosal pliability of the excised larynx was significantly increased compared with that in vivo (P < 0.001). The point of minimal pliability in the absence of TA muscle contraction did not shift after excision of the larynx, while TA muscle contraction caused a downward shift of the point of minimal pliability. Mucosal pliability can thus be used to quantitatively assess the effects of TA muscle contraction on stiffness of the vocal fold mucosa. [ABSTRACT FROM AUTHOR]

Current and wavelength characteristics for 1.55-μm semiconductor optical amplifiers (SOAs) containing bulk active layers with various tensile strains were investigated. The strain dependence of the gain-difference between the TE-mode and TM-mode (ΔGTE-TM ) was almost linear having a waveguide-width over 0.8-1.5 μm. A -0.12% tensile-strained bulk SOA had very low ΔGTE-TM of less than 0.8 dB for driving current ranging from 0 to 120 mA. The low-polarization-sensitive condition of SOAs with strained-bulk active layers was shown to yield very wide range in driving current and wavelength for network device applications [ABSTRACT FROM PUBLISHER]

A periodic multi/demultiplexer that has a square spectrum response with a 200-GHz free spectrum range was fabricated using a modified Mach-Zehnder interferometer with MMI couplers, a delay line, and a ring resonator. A large enhancement of the FSR is obtained by using a deep ridge waveguide. The transmission bandwidths of 1 dB down and -15-dB rejection are about 75 GHz and over 50 GHz, respectively [ABSTRACT FROM PUBLISHER]

Demonstrates low-threshold operation of optically pumped hemispherical InGaAs single-quantum-well lasers. Calculation of the spontaneous emission modification; Impact of enhanced spontaneous emission coupling efficiency on lasing threshold; Potential of carrier confinement for low threshold lasers.

Eight-channel wavelength-division-multiplexed (WDM) channel selectors were fabricated based on an monolithic integration of two arrayed-waveguide gratings and a semiconductor optical amplifier array on InP substrates. A compact device size of 5.2×3.6 mm2 was achieved with a combination of deep-ridge waveguides and buried waveguides. The device can select an arbitrary signal from a WDM signal with a low crosstalk of less than -40 dB, and fiber-to-fiber zero insertion loss operations were also achieved [ABSTRACT FROM PUBLISHER]