Spin-dependent acoustic response in the nonunitary A1 and A2 phases of superfluid 3He under high magnetic fields.

The transverse acoustic impedance of superfluid ^{3}He was measured in the A1 and A2 phases up to 13 T to investigate the surface states in nonunitary superfluids. The temperature dependence of the impedance was much larger in the A1 phase than in the A2 phase. This nonsymmetric behavior indicates that momentum exchange with walls for spin-down surface states is quite different from that for spin-up surface states. The spin-dependent response might be a reflection of an essential feature of the nonunitary states where gap amplitudes depend on spin states. Weak-coupling theories ignore any spin-dependent processes and do not account for the nonsymmetric behavior.

Magnetic response of odd-frequency s-wave Cooper pairs in a superfluid proximity system.

We investigate the magnetic response of a dirty-normal-Fermi-liquid-spin-triplet-superfluid proximity system consisting of liquid 3He and aerogel. In contrast to bulk superfluids, Pauli spin susceptibility in the proximity system exceeds its normal-state value locally around the interface. This enhanced Pauli paramagnetism originates from odd-frequency s-wave pairing arising due to spatial inhomogeneity. A characteristic observable signature of the paramagnetic effect can be found in the spin susceptibility temperature dependence.

Knudsen-to-hydrodynamic crossover in liquid 3He in a high-porosity aerogel.

We present a combined experimental and theoretical study of the drag force acting on a high porosity aerogel immersed in liquid (3)He and its effect on sound propagation. The drag force is characterized by the Knudsen number, which is defined as the ratio of the quasiparticle mean free path to the radius of an aerogel strand. Evidence of the Knudsen-hydrodynamic crossover is clearly demonstrated by a drastic change in the temperature dependence of ultrasound attenuation in 98% porosity aerogel. Our theoretical analysis shows that the frictional sound damping caused by the drag force is governed by distinct laws in the two regimes, providing excellent agreement with the experimental observation.

New anomaly in the transverse acoustic impedance of superfluid 3He-B with a wall coated by several layers of 4He.

We measured the transverse acoustic impedance of superfluid 3He-B with a wall coated by several layers of 4He. The coating is known to enhance the specularity in quasiparticle scattering by the wall. We found a new anomaly, a bump and a peak, in the temperature dependence of the transverse acoustic impedance. This agrees with a theoretical calculation using a partially specular wall boundary condition. The new anomaly is shown to arise from a change in the surface density of states by coating and the scattering of thermally occupied surface bound states to other states. The change is towards the density of states of Majorana cone in the specular limit.

Ultrasound attenuation of superfluid 3He in aerogel.

We have performed longitudinal ultrasound (9.5 MHz) attenuation measurements in the B phase of superfluid 3He in 98% porosity aerogel down to the zero temperature limit for a wide range of pressures at zero magnetic field. The absolute attenuation was determined by direct transmission of sound pulses. Compared to the bulk fluid, our results revealed a drastically different behavior in attenuation, which is consistent with theoretical accounts with gapless excitations and a collision drag effect.

Observation of surface Andreev bound States of superfluid 3He by transverse acoustic impedance measurements.

Complex transverse acoustic impedance of the superfluid (3)He-B was measured at the frequencies of 10 to 80 MHz at 17.0 bar by a cw bridge method. The observed temperature dependence was well explained by the quasiclassical theory with random S-matrix model for a diffusive surface. The temperature dependence was influenced by pair breaking and by quasiparticle density of states at the surface, which was drastically modified from the bulk one by the presence of surface Andreev bound states.

Transverse sound in liquid-3He-aerogel system.

Transverse sound in normal liquid 3He in aerogel is studied on the basis of the Landau transport equation taking into account the simultaneous oscillation of the aerogel. We show that the nature of transverse sound is strongly modified if aerogel is immersed in the liquid. Scattering of 3He quasiparticles by the aerogel molecules causes friction between the liquid and the aerogel, giving rise to coupled motion of the two systems. There exists a low-attenuation transverse sound mode in this coupled system. The high-temperature behavior of its attenuation alpha is given by alpha proportional, variant const+T-2, which is in contrast to alpha proportional, variant T in pure liquid 3He in the hydrodynamic regime.

Interleukin-4 induces expression of the CD45RA antigen on human thymocyte subpopulations.

Interleukin-4 (IL-4) is a multifunctional lymphokine which promotes the growth and/or maturation of multiple cell types. We have examined the ability of IL-4 to promote the phenotypic maturation of subsets of human thymocytes. When cultured in serum-free medium supplemented with recombinant IL-4, a subset of immature CD3-CD45RA- human thymocytes ceased to express the CD1 common thymocyte antigen and acquired phenotypic features characteristic of relatively mature thymocytes, such as high-density expression of the CD3 antigen and de novo expression of the CD45RA isoform of the common leukocyte antigen family. These changes, which were not seen in cells cultured in medium alone, occurred over an 8-9 day period and were accompanied by a significant increase in cell size. The CD45RA+ cells that derived from these immature CD3-CD45RA- precursors were mainly CD4-CD8- or CD8+ cells, and a significant proportion of these cells expressed the T cell receptor delta chain. IL-4 also increased expression of the CD45RA antigen on the more mature CD3+ thymocyte population. However, the CD45RA+ cells derived from IL-4 stimulated CD3+ thymocyte precursors expressed either the CD4 or the CD8 antigen, and virtually all expressed alpha/beta TCR chains. Studies of cell viability and cell growth indicated that these findings were due to direct changes in the phenotype of responsive cells rather than the growth or selective survival of a small number of mature thymocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of gamma-interferon and FK506 on resting B cell proliferation of New Zealand black/white F1 mice.

We examined the effects of gamma-interferon (gamma-IFN) and the new immunosuppressant FK506 on resting B cell proliferation of New Zealand black/white F1 hybrid (B/W F1) mice, an animal model of human systemic lupus erythematosus (SLE). gamma-IFN and FK506 inhibited in a dose-dependent manner both B cell proliferation and autoantibody production of resting B cells respectively. There was a synergistic interaction between gamma-IFN and FK506 in their inhibition and they did not exhibit cell cytotoxicity. This in vitro synergism of gamma-IFN and FK506 may have clinical application in that low doses of gamma-IFN and FK506 combinations may be effective to correct polyclonal B cell activation of patients with SLE.