Biomedical subjects

Kentaro Nakamura

Publications and source records attributed to Kentaro Nakamura.

15 recordsLinked to original sources

PubMed2006

A miniature ultransonic pump using a bending disk transducer and a gap.

It is known that if a pipe end is faced at a vibrating surface in liquid with a small gap, liquid is suctioned into the pipe. As a miniature configuration, we introduce a bending disk transducer 30 mm in diameter using a ring-shaped PZT element. The disk vibrator is worked at the fundamental resonance frequency of 19 kHz of the bending mode. To optimize the pipe geometry, we experimentally investigated the effect of the outer diameter on the pump performance. As a result, the outer/inner diameter ratio of 3:2 is optimum for the gap smaller than 20 microm. We achieved the maximum pump pressure of 14.8 kPa and the maximum flow rate of 10 ml/min. using the prototype pump.

Journal Article↗

PubMed2006

A miniaturization of the multi-degree-of-freedom ultrasonic actuator using a small cylinder fixed on a substrate.

Multi-degree-of-freedom ultrasonic actuator has been studied for robot arms and multidimensional precision table and so on because of its simple structure, silent operation, and holding force. In this study, we aim to miniaturize multi-degree-of-freedom ultrasonic actuator for fabrication on a substrate. This actuator consists of a stainless steel cylinder and a PZT ring. The cylinder is fixed on a substrate and the PZT ring is glued to the substrate near the cylinder. The 1st longitudinal vibration and the 2nd bending vibration are simultaneously excited in the cylinder to make elliptical motion at the top of the cylinder and a ball rotor placed on the cylinder rotates because of the friction force. Length of the cylinder was decided so as to tune the resonance frequency of the 1st longitudinal vibration to the 2nd bending one. Actuator performances are evaluated experimentally using a 14 mm height and 7 mm diameter stainless steel cylinder with a 0.5 mm thickness PZT ring. The rotation about the cylinder axis is tested using the two orthogonal bending vibrations with 90 degrees phase difference. Also, the rotation about horizontal axes were investigated using the combination of the longitudinal vibration and one of two bending vibrations. We measured the rotation speed of a steel ball and obtained 15.8 rps using a 6 mm diameter ball rotor.

Journal Article↗

PubMed2006

A simple bidirectional linear microactuator for nanopositioning--the "Baltan" microactuator.

A new linear microactuator, using bulk PZT and electro-discharge-machined components, generates a sliding velocity and force of 100 mm/s and 12 mN, respectively, in either direction, and a peak velocity and force of 212 mm/s and 44 mN, respectively. Using a simple combination of two slightly different beams placed in contact with a slider, and vibrated at two different resonance frequencies, 508 and 522 kHz, by a specially designed, axially vibrating piezoelectric element, bidirectional linear motion was obtained. By simply reducing the length of the applied signal, the sliding distance was reduced to 90 nm +/- 2 nm, which could be improved with a variety of control methods. The design offers not only silent operation, slider clamping upon removal of power, and all of the other advantages of piezoelectric actuators, but also the potential to be further reduced in size to sub-mm3 for microrobotics and other applications.

Computer-Aided Design↗

PubMed2006

The full stomach test as a novel diagnostic technique for identifying patients at risk of Brugada syndrome.

INTRODUCTION: Autonomic modulation, particularly high vagal tone, plays an important role in the occurrence of ventricular tachyarrhythmias in the Brugada syndrome. Food intake modulates vagal activity. We assessed the usefulness of a novel diagnostic technique, the "full stomach test," for identifying a high-risk group in patients with a Brugada-type electrocardiogram (ECG). METHODS AND RESULTS: In 35 patients with a Brugada-type ECG, we assessed 12-lead ECGs before and after a large meal, a pilsicainide pharmacological test, spontaneous ST-segment change, late potentials by signal-averaged ECG, microvolt T-wave alternans, and four other ECG parameters. These patients were divided into two groups (i.e., high-risk group [n = 17] and indeterminate risk group [n = 18]). The full stomach test was defined as positive when augmentation of characteristic ECG abnormalities was observed after meals. Thirteen patients had a prior history of life-threatening events such as aborted sudden death and syncope, with a total of 30 episodes. These episodes had a circadian pattern, at night and after meals. The full stomach test was positive in 17 of the study patients (49%). A positive test outcome was characterized by a higher incidence of a history of life-threatening events than a negative test outcome (P = 0.015, odds ratio = 7.1). In comparison between the two groups, the incidence (82%) of positive outcomes in the high-risk group was significantly higher than that (17%) in the indeterminate risk group (P = 0.0002). CONCLUSIONS: Characteristic ECG changes diagnostic of Brugada syndrome are augmented by a large meal. These data are associated with a history of life-threatening events in Brugada syndrome.

Adult↗

PubMed2005

Orally tolerized T cells can form conjugates with APCs but are defective in immunological synapse formation.

Oral tolerance is systemic immune hyporesponsiveness induced by the oral administration of soluble Ags. Hyporesponsiveness of Ag-specific CD4 T cells is responsible for this phenomenon. However, the molecular mechanisms underlying the hyporesponsive state of these T cells are not fully understood. In the present study, we investigated the ability of orally tolerized T cells to form conjugates with Ag-bearing APCs and to translocate TCR, protein kinase C-theta (PKC-theta), and lipid rafts into the interface between T cells and APCs. Orally tolerized T cells were prepared from the spleens of OVA-fed DO11.10 mice. Interestingly, the orally tolerized T cells did not show any impairment in the formation of conjugates with APCs. The conjugates were formed in a LFA-1-dependent manner. Upon antigenic stimulation, the tolerized T cells could indeed activate Rap1, which is critical for LFA-1 activation and thus cell adhesion. However, orally tolerized T cells showed defects in the translocation of TCR, PKC-theta, and lipid rafts into the interface between T cells and APCs. Translocation of TCR and PKC-theta to lipid raft fractions upon antigenic stimulation was also impaired in the tolerized T cells. Ag-induced activation of Vav, Rac1, and cdc42, which are essential for immunological synapse and raft aggregation, were down-regulated in orally tolerized T cells. These results demonstrate that orally tolerized T cells can respond to specific Ags in terms of conjugate formation but not with appropriate immunological synapse formation. This may account for the hyporesponsive state of orally tolerized T cells.

Administration, Oral↗

PubMed2005

A traveling-wave, modified ring linear piezoelectric microactuator with enclosed piezoelectric elements--the "scream" actuator.

A 1.8 cc silent bidirectional traveling-wave, self-moving linear microactuator is shown to be capable of generating a sliding velocity of 0.22 m/s and sliding force of 1.1 N. Through the use of computational analysis in the actuator's design, the vibration characteristics were improved in order to obtain a better actuator. The generation of a radial traveling wave about the circumference of the actuator, akin to a ring, is shown to exist despite the unusual shape, and the presence of traveling wave motion along the output face also is shown to exist. By using short-time sinusoidal signals, slider displacements as small as 82 nm were obtained from the actuator, and by using direct current (DC) input, displacements of up to +/-107 nm were obtained, suggesting a way to obtain subnanometer positioning accuracy over arbitrary sliding distances. By reversing the phase between the paired driving signals, the direction of motion was reversed at up to 300 Hz; the slider displacement and velocity was found to be inversely proportional to the phase-reversal rate, and the slider's peak velocity and maximum thrust force were directly proportional to the phase between the driving signals. The output force and velocity of the actuator was fairly insensitive to the input frequency, giving measurable motion between 132.5 and 141.5 kHz, but was sensitive to the input voltage, requiring at least 38 V input for operation, and was approximately quadratically dependent on the applied preload centered about 2.25 N.

Journal Article↗

PubMed2005

An ultrasonic linear motor using ridge-mode traveling waves.

A new type of ultrasonic linear motor is presented using traveling waves excited along a ridge atop a substrate. The ridge cross section was designed to permit only the fundamental mode to be excited during operation of the motor, with a Langevin transducer used as the source of vibration in this study. The ridge waveguide was first made of lossy media to avoid reflecting vibration energy back toward the vibration source, forming a traveling wave. A 5-mm-wide, 15-mm-tall rectangular acrylic ridge was used to move a slider placed upon it toward the vibration source, in opposition to the direction of the traveling wave transmitted along the waveguide ridge. Using a low-loss 3 x 6-mm aluminum rectangular ridge combined with a damper clamped onto the far end of the waveguide, similar results were obtained. To obtain bidirectional operation, the damper was replaced with a second Langevin transducer, giving a pair of transducers located perpendicularly to the ends of the ridge and driven with an appropriate phase difference. The moving direction of the slider was reversed by shifting this phase difference by about 180 degrees. With this simple configuration, it may soon be possible to fabricate a linear micromotor system on a silicon substrate or other semiconductor wafer adjacent to other electronic and optoelectronic devices.

Journal Article↗

PubMed2005

A norovirus protease structure provides insights into active and substrate binding site integrity.

Norovirus 3C-like proteases are crucial to proteolytic processing of norovirus polyproteins. We determined the crystal structure of the 3C-like protease from Chiba virus, a norovirus, at 2.8-A resolution. An active site including Cys139 and His30 is present, as is a hydrogen bond network that stabilizes the active site conformation. In the oxyanion hole backbone, a structural difference was observed probably upon substrate binding. A peptide substrate/enzyme model shows that several interactions between the two components are critical for substrate binding and that the S1 and S2 sites appropriately accommodate the substrate P1 and P2 residues, respectively. Knowledge of the structure and a previous mutagenesis study allow us to correlate proteolysis and structure.

3C Viral Proteases↗

PubMed2005

[Clinical evaluation of 3D delayed-enhancement MRI using parallel imaging in the assessment of myocardial viability].

This study aimed to evaluate the efficacy of breath-hold three-dimensional (3D)delayed-enhancement MRI using parallel imaging in terms of the effect of parallel imaging on the image quality and visualization of myocardial infarction. Twenty-two patients (17 men and 5 women) with suspected myocardial infarction underwent breath-hold 3D late-enhanced viability examination at least 30 days after occurrence. All patients underwent a Tl-scintigraphy examination. First, 10 patients were examined without applying parallel imaging, then the next 12 patients were studied using parallel imaging. All 3D late-enhanced images at the short axis were acquired 10, 15, and 20 min after an injection of contrast agent, and both the long axis and the four-chamber views were acquired after 15 min. In quantitative analysis, the late-enhanced myocardial images at 10, 15, and 20 min showed higher contrast-to-noise ratios (CNR) in parallel imaging than those with no parallel imaging. During the time-intensity curve of the myocardium, no significant change was observed at 10 or 15 min; however, marked signal reduction was observed at 20 min. In diagnostic evaluation, images obtained with parallel imaging were superior to those without parallel imaging. In general, the application of parallel imaging reduces acquisition time with an expense of reduction in SNR. However, the breath-hold 3D late-enhanced images with parallel imaging showed no apparent SNR reduction. Furthermore, parallel imaging provided clear edge definition between the infarction and the normal region. The reduction of acquisition time with parallel imaging may be less susceptible to fast cardiac motion. In conclusion, breath-hold 3D delayed-enhancement MRI using parallel imaging was highly evaluated in our study and may show promise in clinical application.

Aged↗

PubMed2004

A torsional transducer through in-plane shearing of paired planar piezoelectric elements.

A torsional microtransducer for high-power applications was developed using standard bulk lead zirconium titantate (PZT) placed upon a small rectangular prism made from phosphor bronze, with a tapered conical end serving as a horn and a machined interior to improve the actuator's response. Torsion was obtained from a prototype at the design frequency of 192 kHz as well as over a wide range of frequencies from 136 kHz to 1.02 MHz. Torsional vibration velocities of 335 mm/s at 192 kHz were measured at 27.3 V(RMS) on the 1.5-mm diameter output tip, amounting to 25,600 degree/s vibration velocity along the outer circumference of the tip. At 1.02 MHz, a torsional vibration velocity of 1750 mm/s (134,000 degree/s) at 17.8 V(RMS) was obtained through use of the thickness mode of the PZT elements. Using the design described in this study, high-power torsional transducers with diameters of 5 mm and below are now possible.

Journal Article↗

PubMed2004

[Reliability of students' evaluations of university teaching: an analysis of four-facet data by a generalized model and structural equation modeling].

In our study, we examined the reliability of students' evaluation of university teaching. First, we analyzed four-facet data (teacher x rater x viewpoint x order) by the generalizability theory approach, and estimated the variance components for the facets as a G study. Then, we evaluated the reliability from the point of view of the generalizability coefficient (a reliability-like coefficient that is used when a decision concerns the relative ordering of individuals) and the index of dependability (an index that is used when a decision focuses on the absolute level of an individual's performance independent of others' performance), and examined how those indices change as the number of raters and viewpoints are changed. With these analyses we found conditions needed to maintain sufficient reliability of the evaluation for various situations. We also introduced a new method to evaluate the reliability at each level of facet by using structural equation modeling. By this method, one can examine the reliability of students' evaluation of university teaching more specifically.

Adult↗

PubMed2004

An ultrasonic motor driven by the phase-velocity difference between two traveling waves.

This paper presents a new ultrasonic motor in which the rotor rotation speed is locked by the phase-velocity difference between the two traveling waves propagating on the stator and the rotor. First, the unique construction to excite two traveling waves both in the stator and the rotor is described. Then, the operation principle of the present motor is revealed by our careful experiments. Dynamics of the two traveling waves are measured by an in-plane laser Doppler vibrometer under various conditions, as well as the motor performances. Our experiments show that the rotation speed of the motor is equal to the phase-velocity difference between the two traveling waves on the contact surfaces of rotor and stator. It is confirmed that the rotor rotates so as to cancel the phase-velocity difference between the traveling vibrations along the circumferences of the rotor and stator. If the load does not exceed the maximum torque that is determined by the vibration amplitude, the rotation speed is subject only to the phase-velocity difference.

Journal Article↗

PubMed2003

Stability analysis of an acoustically levitated disk.

In this paper, a model is developed for the stability analysis of an acoustically levitated disk on the basis of analyzing eddy acoustic streaming and acoustic viscous stress. In the model, the effect of the acoustic streaming outside the boundary layer that is on the surface of the levitated disk is properly taken into account. Also, the calculation of sound field and acoustic viscous stress is limited to the range that has a dominant effect on the stability. By this method, we obtain a quite accurate solution of the stability coefficient. For the small horizontal shift of a large levitated disk, the model is verified by the good agreement between the experimental and theoretical results. By means of this model and relevant experiments, some factors that affect the stability of the levitated disk are investigated, and useful guidelines for design and application are obtained. It is found that the range from the edge to the outermost nodal circle of the disk-shaped vibrator has a large effect on the stability of the levitated disk. To stabilize the levitated disk by acoustic viscous force, the distance between the edge and the outermost nodal circle of the vibrator must be larger than a critical value, which is determined by the driving frequency and the sound velocity of the fluid between the levitated disk and the vibrator. When this condition is satisfied, increasing the distance between the edge and the outermost nodal circle leads to a decrease in the stability. It is also found that the property of the fluid between the levitated disk and the vibrator has a large effect on the stability. It is easier to stabilize the levitated disk in steam than in air, but more difficult to do so in carbon dioxide and hydrogen. In addition, theoretical results show that increasing the weight per unit area of the levitated object increases the stability for a given vibrator velocity. The distribution of the acoustic viscous stress and the dependence of the stability coefficient and the holding force on the horizontal shift of the levitated disk, which are obtained by this study, also are useful to a better understanding of the stability of the levitated disk.

Journal Article↗

PubMed2003

A single-element tuning fork piezoelectric linear actuator.

This paper describes the design of a piezoelectric tuning-fork, dual-mode motor. The motor uses a single multilayer piezoelectric element in combination with tuning fork and shearing motion to form an actuator using a single drive signal. Finite-element analysis was used in the design of the motor, and the process is described along with the selection of the device's materials and its performance. Swaging was used to mount the multilayer piezoelectric element within the stator. Prototypes of the 25-mm long bidirectional actuator achieved a maximum linear no-load speed of 16.5 cm/s, a maximum linear force of 1.86 N, and maximum efficiency of 18.9%.

Journal Article↗

PubMed2002

Numerical analysis of the hybrid transducer ultrasonic motor: comparison of characteristics calculated by transmission-line and lumped-element models.

In this paper, a hybrid transducer ultrasonic motor is numerically analyzed by using two equivalent electrical circuit models. A transmission-line model for the torsional vibration in the stator, which can model any torsional vibration mode and their combinations, was introduced and compared with a lumped-element model, which modeled the fundamental torsional resonance mode in the stator. The calculation result by using the transmission-line model demonstrated that the second harmonic torsional vibration increased either with the static spring force by which the rotor was pressed to the stator or with the load torque placed on the rotor. The difference in the calculated motor performance between the two models appeared when the second harmonic torsional vibration became large at a sufficient static spring force.

Transducers↗