45 research outputs found
On the origin of the decrease in the torsional oscillator period of solid He4
A decrease in the rotational period observed in torsional oscillator
measurements was recently taken as a possible indication of a supersolid state
of helium. We reexamine this interpretation and note that the decrease in the
rotation period is also consistent with a solidification of a small liquid-like
component into a low-temperature glass. Such a solidification may occur by a
low-temperature quench of topological defects (e.g., grain boundaries or
dislocations) which we examined in an earlier work. The low-temperature glass
can account for not only a monotonic decrease in the rotation period as the
temperature is lowered but also explains the peak in the dissipation occurring
near the transition point. Unlike the non-classical rotational inertia
scenario, which depends on the supersolid fraction, the dependence of the
rotational period on external parameters, e.g., the oscillator velocity,
provides an alternate interpretation of the oscillator experiments. Future
experiments might explore this effect.Comment: 10 pages, 3 figures; to appear in Phys. Rev.
Human leukaemic cells. Determination of trace elements in nucleic acids and histones by neutron-activation analyses
Changes of the topological charge of vortices
We consider changes of the topological charge of vortices in quantum
mechanics by investigating analytical examples where the creation or
annihilation of vortices occurs. In classical hydrodynamics of non-viscous
fluids the Helmholtz-Kelvin theorem ensures that the velocity field circulation
is conserved. We discuss applicability of the theorem in the hydrodynamical
formulation of quantum mechanics showing that the assumptions of the theorem
may be broken in quantum evolution of the wavefunction leading to a change of
the topological charge.Comment: 5 pages, 2 figures, version accepted for publication in J. Phys.
Experiments on the twisted vortex state in superfluid 3He-B
We have performed measurements and numerical simulations on a bundle of
vortex lines which is expanding along a rotating column of initially
vortex-free 3He-B. Expanding vortices form a propagating front: Within the
front the superfluid is involved in rotation and behind the front the twisted
vortex state forms, which eventually relaxes to the equilibrium vortex state.
We have measured the magnitude of the twist and its relaxation rate as function
of temperature above 0.3Tc. We also demonstrate that the integrity of the
propagating vortex front results from axial superfluid flow, induced by the
twist.Comment: prepared for proceedings of the QFS2007 symposium in Kaza
NMR Experiments on Rotating Superfluid 3He-A : Evidence for Vorticity
Experiments on rotating superfluid 3He-A in an open cylindrical geometry show a change in the NMR line shape as a result of rotation: The amplitude of the peak decreases in proportion to f(T)g(Ω), where Ω is the angular velocity of rotation; at the same time the line broadens. Near Tc, f(T) is a linear function of 1−T/Tc. At small velocities g(Ω)∝Ω. These observations are consistent with the existence of vortices in rotating 3He-A.Peer reviewe
Physics of Neutron Star Crusts
The physics of neutron star crusts is vast, involving many different research
fields, from nuclear and condensed matter physics to general relativity. This
review summarizes the progress, which has been achieved over the last few
years, in modeling neutron star crusts, both at the microscopic and macroscopic
levels. The confrontation of these theoretical models with observations is also
briefly discussed.Comment: 182 pages, published version available at
<http://www.livingreviews.org/lrr-2008-10
Cryoirradiation in the nuclear IRT reactor of the Institute of Physics of the Academy of Sciences of the Georgian SSR
Entropy Difference of Native DNA Molecules and Its Nucleotides Random Mixtures at Low Temperatures
Observation of superfluidity in two- and one-dimensions
Even though there is no long-range-ordered state of a superfluid in dimensions lower than the three-dimension (3D) such as bulk ⁴He liquid, superfluidity has been observed for flat ⁴He films in 2D and recently for nanotubes of ⁴He in 1D by the torsional oscillator method. In the 2D state, in addition to the superfluid below the 2D Kosterlitz–Thouless transition temperature TKT, superfluidity is also observed in a normal fluid state above TKT, which depends strongly on the measurement frequency and the system size. In the 1D state of the nano-tubes, superfluidity is directly observed as a frequency shift in the torsional oscillator experiment. Some calcula-tions suggest a superfluidity of a 1D Bose fluid with a finite length, where thermal excitations of 2-phase winding play the main role for superfluid onset of each tube. Dynamics of the 1D superfluidity is also suggested by observing the dissipation in the torsional oscillator experiment