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Abstracts
P4.4
Added mass of He II in experiments with oscillating quarts tuning
fork
I. Gritsenko, K. Klokol, S. Sokolov, and G. Sheshyn
ILTPE - B.Verkin Institute for Low Temperature Physics and Engineering of
the National Academy of Sciences of Ukraine
Using the method of quartz tuning fork the temperature and pressure dependences
of resonance frequency of the tuning fork, for T = 0.1 – 1.5 K and P = 1 – 24.8
atm, were measured and the amount of He II entrained by vibrating prong of
the fork (added mass) was determined in the laminar flow regime. Quartz tuning
forks with different resonance frequencies 6.65 kHz, 8.46 kHz, 12.1 kHz, 25.0 kHz,
33.6 kHz were studied. It was found that at T 1 K added mass per unit length of
the fork prong and added mass coefficient depends on frequency. In addition we
checked that, at T = 365 mK, the added mass changes with pressure according
to the density change of He II with pressure.
P4.5
Strong Coupling Effects and Shear Viscosity in an Ultracold Fermi
Gas
Daichi Kagamihara, Yoji Ohashi
Department of Physics, Faculty of Science and Technology, Keio University,
3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
We theoretically investigate the shear viscosity
η
, as well as the entropy density
s, in the normal state of an ultracold Fermi gas. Including pairing fluctuations
within the framework of a T-matrix approximation, we calculate these quantities
in the BCS-BEC crossover region. We evaluate the ratio
η
/s, to assess the lower
bound of this ratio, conjectured by Kovtun, Son, Starinets (KSS). In the crossover
region, this ratio is found to decrease with increasing the interaction strength, to
become very close to the KSS bound slightly in the BEC side at the superfluid
phase transition temperature.
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