Makoto Takeo

Thermodynamic Conditions of the Test Gas in a Ballistic Compressor

The development of a free‐piston compressor at the University of Oregon is described. In order to characterize the thermodynamic conditions of the test gas in the ballistic compressor, a theoretical analysis of the pistons motion is made taking into account gas leakage, viscous friction, and heat losses. The values used for the radial clearance of the piston and the heat‐loss constant are chosen so that the computed peak pressure and minimum volume of the test gas agree with experiment. The predictions of this treatment are then compared with observed pressure and acceleration profiles which were taken using argon and helium as test gases over a range of peak test‐gas pressures from 476 to 1660 atm and are found to be in good agreement. The acceleration profile is found to be more sensitive than the pressure profile. It is evident that the compression process is nonadiabatic due to gas leakage around the piston and heat losses to the compressor walls.

The shift of iron emission lines produced by argon and helium

Abstract The shifts of all the strong emission lines of the neutral iron atom in hot compressed argon and helium (produced by a ballistic compressor) were measured in the region 2497–5900 A. Curves showing the shift vs. relative density (r.d.) are presented for 68 of these lines with argom and 14 with helium, over a range of r.d. from 28 to 104 at 3230°K for argon and from 36 to 108 at 3600°K for helium. For argon, the relative displacements of various spectral terms of FeI with different J, L, S or electron configurations are discussed. A decrease in red shift was observed at higher temperatures.

The shift of the emission lines of Cr and Ni produced by argon and helium

Abstract The shifts of all strong emission lines of neutral Cr and Ni in the wavelenght ranges of 3014–5328 A, and 3050–3619 A, respectively, with argon and of 3017–4651 A and 3369–3619 A, respectively, with helium have been measured. The temperatures and the relative densities (r.d.) of the gases at which observations were made are, respectively, 3230°K and 28–104 for Ar and 3600°K and 60–108 for He. The shift vs. r.d. relationship for 14 CrI lines and 11 NiI lines with argon, and 12 Cr lines and a single Ni line with helium, are tabulated. Some lines show a linear dependence of shift on r.d. and some behave linearly for low r.d. but quadratically for higher r.d. The general statements about the behavior of the relative shifts of spectral levels with respect to L and S values are the same as those for the FeI lines. The normal fine-structure levels (many multiplets of CrI) behave in their relative shifts oppositely to those of inverted levels (FeI), although the behavior depends on the more detailed structure of the levels.

Intensity analysis of the nature of Rb/Xe red satellite bands☆

Abstract Absorption intensities of the doublet lines, and their associated red satellite red satellite bands, for the first three members of the xenon perturbed rubidium principal series were analyzed in order to investigate the nature of the bands. From the intensity variation with xenon pressure, it is concluded that the bands are not due to molecular formation in the Rb electronic ground states. The ideas of molecule formation in the Rb electronic excited states were only partially confirmed. In transitions from the atomic states 2 P 3 2 and 2 P 1 2 to other states of quantization, the interatomic potential at small distances seems to be more complicated than the one customarily used in qualitative discussions on the production of bands.

The shift of some strong lines of Al, Ca, Cu, Mn, Mo, and Na in emission, produced by argon☆

Abstract The shift of the resonance lines of Ca, Cu, Mn, and Na and of AlI λ3082 and λ3944, CaII λ3933 and λ3968, and MoI λ3358 was measured in emission when perturbed by hot, dense argon at 3239°K (r.d. 35–100) in a ballistic compressor. Some of the results are compared with those previously obtained with static argon pressures.

Brownian motion of particles in concentrated suspensions

An intuitive treatment of Brownian motion is described, mainly based on the Langevin and generalized Smoluchowsky equation. It is assumed that spherical particles undergo Brownian forces as well as mutual hydrodynamic and intreparticle interactions when in thermal equilibrium. The velocity auto-correlation function summarizes the temporal behavior and the effects on the function due to Brownian forces and particle interactions are represented by parameters called a Brownian relaxation time, [tau]B, a hydrodynamic relaxation time, [tau]H, and an interaction relaxation time, [tau]I. The function is closely related to the mean square displacement of the particles. The mean square displacement is directly related to the average scattering of light from Brownian particles. The resulting effect is, in the frequency domain, the frequency broadening and, in the time domain, the intensity fluctuation. The latter is more suited in experimental observations of the temporal behavior of Brownian motion, although the detector size must be limited within the coherence area.

Formation of superhexagonal chromium hydride by exposure of chromium thin films to high-temperature, high-pressure hydrogen in a ballistic compressor

Abstract Single crystal, body-centered-cubic (bcc) Cr thin films were prepared by vacuum evaporation. These films were exposed to high-temperature (close to the melting point of Cr), high-pressure hydrogen gas in a ballistic compressor. Using a transmission electron microscope (TEM), second phase particles of superhexagonal (sh) structure, which have lattice constant a = 4.74 A and c/a = 1.88, are found in the films. The superhexagonal structure has a definite orientation relationship with the matrix: [021]sh t|[001]bcc and (2 1 2)sh t|( 11 0)bcc. It is quite stable in air and at room temperature, but decomposes to bcc Cr when heated or when bombarded by the electron beam in the TEM. Positive identification of hydrogen content was spectroscopically obtained by high-temperature vacuum extraction in a discharge tube. After vacuum extraction, the intensity of electron diffraction spots from the superhexagonal structure decreased.

Formation of iron hydride in iron foil exposed to a hot, dense gas mixture of argon and hydrogen

Abstract Pure iron foils were exposed to hot, dense argon-hydrogen mixtures for 1 ms in a ballistic compressor. The appearance of small particles, of size about 50 × 10 nm, was observed. They were oriented almost in the same direction to one another in the entanglement of dislocations. A resonant 15 N-p nuclear reaction was used to estimate the hydrogen concentration. This result and an electron diffraction pattern from the particle show that the particles are iron hydride, formed by the trapping of hydrogen atoms at octahedral sites with an Fe to H ratio of approximately 8-1.

Enhancement of Tc of Bi‐Sr‐Ca‐Cu‐O superconductor by rapid heating and cooling in a ballistic compressor

Exposure of the Bi‐Sr‐Ca‐Cu‐O superconductor to hot, dense argon in a ballistic compressor followed by rapid cooling enhances Tc of the superconductor. Similar increases of about 3 K were found for measurements on both pellets and thin films.

Effects of magnetic fields and flow applied to single electrodes on electrolytic cell potentials

The effects of a uniform magnetic field applied to one of the electrodes in a flow cell were investigated. It was found that the cell potential is either increased or decreased, depending on the relative orientations of the magnetic field, the electric field, and the flow. The change of the cell potential is directly proportional to the magnetic field strength and the flow velocity. The proportionality constant, however, depends on the relative orientation of the fields, contrary to expectation from magnetohydrodynamic theory on laminar flow. The orientation dependence is explained in terms of a turbulent boundary layer. The conductivity of this boundary layer is calculated.