Study on Flow Characteristics of Oil Viscosity Pump for Refrigerant Compressors

 Oil viscosity pumps are typically used for reciprocating compressors in household refrigerators to lubricate the compression mechanism. The oil viscosity pump is a simple structure in which a spiral groove is on the shaft surface. The lubricating oil supplied by this pump has a large influence on the performance and reliability, but the oil viscosity pump is designed based on the experience. We investigated the flow characteristics of the oil viscosity pump from theoretical and experimental study. We performed the study based on the assumption that the oil flow inside spiral groove was steady with two-dimensional viscous flow. As a result, we found that the pressure-flow rate (P-Q) characteristics has a linear relationship when the length of the spiral grooves, the rotational speed of the shaft, and the depth of the spiral grooves are in the limited area

Parity Transition of Spin-Singlet Superconductivity Using Sublattice Degrees of Freedom

縺（もつ）れ結晶で現れる多重超伝導状態の性質を解明. 京都大学プレスリリース. 2023-04-20.Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh₂As₂, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sublattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of multiple SC phases even under an interaction inducing spin-singlet superconductivity. CeRh₂As₂ is considered as the first example of multiple SC phases owing to this sublattice degree of freedom. However, microscopic information about the SC states has not yet been reported. In this study, we measured the SC spin susceptibility at two crystallographically inequivalent As sites using nuclear magnetic resonance for various magnetic fields. Our experimental results strongly indicate a spin-singlet state in both SC phases. In addition, the antiferromagnetic phase, which appears within the SC phase, only coexists with the LF SC phase; there is no sign of magnetic ordering in the HF SC phase. The present Letter reveals unique SC properties originating from the locally noncentrosymmetric characteristics

Low-temperature Magnetic Fluctuations Investigated by 125^{125}Te-NMR on the Uranium-based Superconductor UTe2_{2}

To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe$_{2}$, we measured the NMR Knight shift $K$ and the nuclear spin-lattice relaxation rate $1/T_{1}$ in $H \parallel a$ by $^{125}$Te-NMR on a $^{125}$Te-enriched single-crystal sample. $1/T_1T$ in $H \parallel a$ is much smaller than $1/T_1T$ in $H \parallel b$ and $c$, and magnetic fluctuations along each axis are derived from the $1/T_1T$ measured in $H$ parallel to all three crystalline axes. The magnetic fluctuations are almost identical at two Te sites and isotropic at high temperatures, but become anisotropic below 40 K, where heavy-fermion state is formed. The character of magnetic fluctuations in UTe$_2$ is discussed with the comparison to its static susceptibility and the results on other U-based superconductors. It is considered that the magnetic fluctuations probed with the NMR measurements are determined by the magnetic properties inside the two-leg ladder formed by U atoms, which are dominated by the $q_a$ = 0 ferromagnetic fluctuations.Comment: 10 pages, 6 figures

Large Reduction in the aa-axis Knight Shift on UTe2_2 with TcT_{\rm c} = 2.1 K

Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe$_2$ by using Knight-shift measurements for a magnetic field $H$ along all three crystalline axes. In the higher-quality sample, the SC transition temperature $T_{\rm c}$ is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR linewidth becomes narrower and is almost half of that in the previous sample with $T_{\rm c} \sim 1.6$ K when $H \parallel a$ and $c$. Although the Knight-shift behavior was not so different from the previous results for $H \parallel b$, and $c$, a large reduction in Knight shift along the $a$ axis was observed, in contrast with the previous $a$-axis Knight shift result. We discuss the origin of the difference between the previous and present results, and the possible SC state derived from the present results.Comment: 7 pages, 6 figures, including supplemental material