Engineering topics

Kohama, Y.

Publications and source records attributed to Kohama, Y..

3 records

DOE OSTI2023

Radio frequency electrical resistance measurement under destructive pulsed magnetic fields

We developed a resistance measurement using radio frequency reflection to investigate the electrical transport characteristics under destructive pulsed magnetic fields above 100 T. A sample stage consisting of a homemade flexible printed circuit reduced the noise caused by the induced voltage from the pulsed magnetic fields, improving the accuracy of the measurements of the reflected waves. From the obtained reflectance data, the absolute value of the magnetoresistance was successfully determined by analyzing the phase with admittance charts. In conclusion, these developments enable more accurate and comprehensive measurements of electrical resistance in pulsed magnetic fields.

47 OTHER INSTRUMENTATION↗

DOE OSTI2019

Unconventional field-induced spin gap in an S = 1/2 chiral staggered chain

We investigate the low-temperature magnetic properties of the molecule-based chiral spin chain [Cu(pym)(H 2 O) 4 ]SiF 6 ·H 2 O (pym = pyrimidine). Electron-spin resonance, magnetometry and heat capacity measurements reveal the presence of staggered g tensors, a rich low-temperature excitation spectrum, a staggered susceptibility and a spin gap that opens on the application of a magnetic field. These phenomena are reminiscent of those previously observed in non-chiral staggered chains, which are explicable within the sine-Gordon quantum-field theory. In the present case, however, the size of the gap and its measured linear field dependence do not fit with the sine-Gordon model as it stands. We propose that the differences arise due to additional terms in the Hamiltonian resulting from the chiral structure of [Cu(pym)(H 2 O)4]SiF 6 ·H 2 O, particularly a uniform Dzyaloshinskii-Moriya coupling and a four-fold periodic staggered field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1991

A new parameter for predicting crossflow instability

Instability of boundary-layer over a concave wall and a rotating disk which were thought to be essentially different in instability sources, are compared in order to investigate whether or not a single crossflow parameter can be defined. Using a newly defined crossflow parameter, prediction was attempted on a yawed cylinder boundary-layer transition. By comparing the calculation with experiment, it was found out that this parameter can document fairly well the onset condition of the crossflow instability.

Kohama, Y.↗