Koji Teshima

Characteristics of Pulsed Molecular Beams from an Electromagnetic Valve

Pulsed molecular beams of about 5 msec duration of room temperature argon from an electromagnetic valve are examined, and their intensities, conditions for the optimum nozzle-skimmer distances and source pressures, with a flat beam intensity, and their speed ratios were measured. The optimum conditions were obtained for the Knudsen number based on the skimmer orifice Kns=2–6. The dependence of the beam intensity for the optimum conditions on the source pressure agrees very well with a modified expression given here based on the sudden freezing model. The attainable speed ratios agree with the semi-empirical relation of Anderson and Fenn.

Biomechanical effects of shock waves onEscherichia coli and λphage DNA

Escherichia coli (recombinant cells) and λphage DNA in suspension liquid were exposed to pressure pulses of about 20μs duration and amplitude of up to 14 MPa. These pulses were generated by a diaphragmless shock tube. The destruction of cells was monitored by the assay of phenylalanine dehydrogenase leaking from the recombinant cells and was found to increase remarkably at the peak pressure of higher than 12 MPa. A probability relation for the cell destruction expressed as a function of pressure was proposed. It is most likely that there exists a threshold pressure for the cell destruction. Fragmentation effects of shock waves on λphage DNA were analyzed by electrophoresis. They were enhanced by increasing the shock wave strength and the number of shots. Probability for the DNA fragmentation as a function of pressure and molecular size was estimated with HPLC. The larger size of the DNA was more easily fragmented. A threshold pressure does not seem to exist for the DNA fragmentation.

Two‐dimensional focusing of a supersonic free jet by a rectangular orifice

Supersonic free jets issuing from rectangular orifices have been observed by using a laser‐induced fluorescence technique. Anisotropy of expansion in two directions, the orifice length (z) and width (y), apparently occurs in the jet structure at a large pressure ratio (between reservoir and vacuum chambers); the jet spreads in the y direction whereas it converges in the z direction. This effect is enhanced by interaction of lateral shocks from both ends of the orifice when a small aspect ratio orifice is used. Under a flow condition whereby the shocks reflect normally on the axis, the jet becomes very thin in the z direction.

Destruction of mouse lymphoma cells with high pressure pulses generated by a diaphragmless shock tube

A high pressure pulse, which was produced by a shock tube, was hit repeatedly on a pellet of mouse EL-4 T-lymphoma cells packed in a small test tube which was filled up with culture medium. The pressure pulse measured at the conical bottom of the tube had about 30 μs width and up to 8.4 MPa height depending on the driver gas pressure of the shock tube. The lymphoma cells began to be destroyed by hitting with 100 pulses having a peak pressure around 3 MPa. The fraction of dead cells in the tube exposed to the shock wave of 100 pulses rose exponentially as the peak pressure was increased from 3 MPa to 8 MPa. The fraction of dead cells at 6.0 MPa of the peak pressure was around 10%. However, proliferative function of the cells survived after exposure to 6.0 MPa-peak-pressure pulses seemed intact because the cells which survived the exposure proliferated as well as the nonexposed control cells.

DSMC calculation of supersonic expansion at a very large pressure ratio

Supersonic expansion of room temperature argon from a sonic orifice at a very large pressure ratio up to 16000 for different stagnation Knudsen numbers, 2×10−3 and 4×10−4 is simulated by the DSMC method. In order to calculate a large flowfield different sized cells and a different time-step scheme were adopted. It was shown that the effects of rarefaction and background gas to the jet size can be evaluated using a rarefaction parameter or a local Knudsen number. The calculation was also made for the expansion to a vacuum for a wide range of the stagnation Knudsen number, 4×10−4–0.1. The terminal parallel temperature dependence to the stagnation Knudsen number agrees well with the sudden freezing model.

DSMC Calculation of supersonic free jets from an orifice with convex and concave corners

Supersonic free jets from an orifice with convex and concave corners are investigated in three-dimensional field by the DSMC method. The plumes develop faster from the concave corners of a hexagram orifice with symmetric cross section than those from the convex corners. The mechanism of the development is revealed through the observation of velocity vectors right behind the orifice. The directions of flow are also investigated in various cross sections of a jet. There is a complicated flow-field and several circulations of flow are observed. The variation of cross section of a star-shaped jet along the jet axis changes with the ratio of a stagnation pressure to a background pressure. In an asymmetric orifice, a plume from a concave corner is inclined to an adjacent plume and they are merged into a bigger plume.

Translational Nonequilibrium in a Free Jet Expansion of a Binary Gas Mixture

Frozen parallel temperatures and frozen velocities of each species in the free jet expansions of helium-argon, helium-neon and neon-argon gas mixtures have been measured by a molecular beam time- of-f light method in the range of P0d=l–2 Torr cm, where P0 is the source pressure and d the orifice diameter. We have obtained that the frozen temperature of the heavy species is higher than that of the light species and that the ratio of the frozen temperature of the heavy species to that of the light species increases with increasing their mass ratio. We have also made the numerical calculation for the source flow expansion of the binary mixture using an ellipsoidal velocity distribution function. The calculations have been made for a rather larger value of P0d compared with the present experiments, but the results are qualitatively in good agreement with the present experiments in the dependency of the frozen temperature of each species on the mole fraction of the heavy species and on the mass ratio.

Thermal Boundary Layer Effects on Mass Sampling from a Shock Tube

Abstract : A shock heated molecular beam (SHMB) is useful for study of the molecular reaction dynamics especially those including internally excited molecules. A time-of-flight (TOF) method to analyze the velocity distribution of the beam molecules can be used to determine their internal states by using the energy conservation and has been used for the conventional molecular beams.

Shock waves generated by an opposing jet

The shock waves generated by a sonic nose jet exhausting counter to a supersonic free stream of a Mach number 3 were visualized by means of a laser induced fluorescence method. The experiments were conducted for various values of the ratio of opposing jet total pressure to free stream total pressure. The ratio of a jet exit diameter to a body diameter was taken to be 0.2 and 0.4. The results show that the shock waves generated by the opposing jet are significantly affected not only by the ratio of jet total pressure to free stream total pressure but also by the ratio of the jet exit diameter to the body diameter. It was also observed that at low pressure ratios, there exists unstable flow regime. Simple analysis is applied to the prediction of the position of a free stream shock and a Mach disc, and compared with the experimental result. The comparisons show good agreement.

High-Frequency Generation of High-Pressure Pulses Using a Diaphragmless Shock Tube

We have developed a high-pressure pulse generator at a high repetitive rate by combining a diaphragmless shock tube with shock strengthening by area convergence. The diaphragmless shock tube generates shock waves with Mach numbers of up to 2 traveling in the tube at atmospheric pressure. The shock waves are accelerated by reducing the cross sectional area of the tube. The maximum pressure at the tube end, where the cross sectional area was reduced to 1/64 from the original, exceeded 10MPa and the pulse width was about 25 μ sec. These pressure pulses were generated at a rate of one pulse per several seconds. The facility was used to study biomechanical and biological effects of high-pressure pulses on microorganisms and DNA.