Tatsuro Shoda

Frequency modulation in shock wave-boundary layer interaction by repetitive-pulse laser energy deposition

Modulation of shock foot oscillation due to energy deposition by repetitive laser pulses in shock wave-boundary layer interaction over an axisymmetric nose-cylinder-flare model in Mach 1.92 flow was experimentally studied. From a series of 256 schlieren images, density oscillation spectra at each pixel were obtained. When laser pulses of approximately 7 mJ were deposited with a repetition frequency, fe, of 30 kHz or lower, the flare shock oscillation had a peak spectrum equivalent to the value of fe. However, with fe of 40 kHz–60 kHz, it experienced frequency modulation down to lower than 20 kHz.

On-chip enucleation of an oocyte by untethered microrobots

We propose a novel on-chip enucleation of an oocyte with zona pellucida by using a combination of untethered microrobots. To achieve enucleation within the closed space of a microfluidic chip, two microrobots, a microknife and a microgripper were integrated into the microfluidic chip. These microrobots were actuated by an external magnetic force produced by permanent magnets placed on the robotic stage. The tip of the microknife was designed by considering the biological geometric feature of an oocyte, i.e. the oocyte has a polar body in maturation stage II. Moreover, the microknife was fabricated by using grayscale lithography, which allows fabrication of three-dimensional microstructures. The microgripper has a gripping function that is independent of the driving mechanism. On-chip enucleation was demonstrated, and the enucleated oocytes are spherical, indicating that the cell membrane of the oocytes remained intact. To confirm successful enucleation using this method, we investigated the viability of oocytes after enucleation. The results show that the production rate, i.e. the ratio between the number of oocytes that reach the blastocyst stage and the number of bovine oocytes after nucleus transfer, is 100%. The technique will contribute to complex cell manipulation such as cell surgery in lab-on-a-chip devices.

On-chip enucleation of oocyte using untetherd micro-robot with gripping mechanism

We developed a highly functional untethered micro-robot that can manipulate cells with high gripping force in a micro-fluidic chip. The robot has gripping mechanism which is actuated by magnetic power. A permanent magnet is attached at the center of the gripping mechanism, and an electrical magnet controls the position of the magnet from the bottom of the micro-fluidic chip. The open-close accuracy of the gripper is about 3.0 μm. We succeeded in cutting of zona pelucida of oocyte and enucleation by using this micro-robot.

Effects of Negative Overpressure Phase of a Laser Breakdown-Induced Blast Wave on Impulse Characteristics

The behavior of a blast wave, in which an initial positive overpressure pulse is followed by a negative overpressure phase, has been investigated mainly by field test using such an explosive as trinitrotoluene (TNT) [1, 2]. The typical pressure history of a blast wave is shown in Fig. 1. The scaled distance Z, which is a function of released energy and distance from the blast wave source, characterizes the positive peak overpressure, Δp+; the duration of positive phase, t+; the negative peak pressure, Δp−; and the duration of negative phase, t−; these values are shown in Fig. 1. For a small Z, the effect of positive phase dominates because of the high Δp+ value. On the other hand, in the range of large Z, the Δp+ value becomes relatively smaller and the negative pressure phase becomes more important. However, it is difficult to evaluate the effect of the negative phase with high-accuracy method because the impulse imparted on an object is sensitive to its size, geometry, and location [3, 4]. Therefore, investigations on negative pressure phase are limited [4, 5] (Fig. 2).

Control of Unsteadiness in Shock Wave–Boundary Layer Interaction by Repetitive Laser Energy Deposition

Shock wave–boundary layer interaction (SWBLI) causes serious problems against realizing supersonic transport, such as flow unsteadiness which leads to degradation of engine performance, wing lift capacity and control surfaces effectiveness, and heat transfer and pressure loads which reduce the endurance of aircraft structures.

Shock Wave Boundary Layer Interaction Control using Repetitive-Pulse Laser Energy Depositions

Repetitive pulse laser energy deposition can modulate the shock wave oscillation frequency, which caused by shock wave and boundary layer interactions. Without energy deposition, the shock oscillation frequency is lower than 10 kHz. This frequency can be modulated to the repetition frequency of energy deposition. However, the oscillation frequency does not correspond to the energy deposition frequency when the frequency of the repetitive energy deposition become high enough to interact successive vortex rings. At 40 kHz energy deposition, the shock oscillation frequency is lower than 10 kHz, and the strong peak is observed at 1 kHz.