1,625 research outputs found
Tkachenko modes as sources of quasiperiodic pulsar spin variations
We study the long wavelength shear modes (Tkachenko waves) of triangular
lattices of singly quantized vortices in neutron star interiors taking into
account the mutual friction between the superfluid and the normal fluid and the
shear viscosity of the normal fluid. The set of Tkachenko modes that propagate
in the plane orthogonal to the spin vector are weakly damped if the coupling
between the superfluid and normal fluid is small. In strong coupling, their
oscillation frequencies are lower and are undamped for small and moderate shear
viscosities. The periods of these modes are consistent with the observed
~100-1000 day variations in spin of PSR 1828-11.Comment: 7 pages, 3 figures, uses RevTex, v2: added discussion/references,
matches published versio
Rapidly rotating Bose-Einstein condensates in anharmonic potentials
Rapidly rotating Bose-Einstein condensates confined in anharmonic traps can
exhibit a rich variety of vortex phases, including a vortex lattice, a vortex
lattice with a hole, and a giant vortex. Using an augmented Thomas-Fermi
variational approach to determine the ground state of the condensate in the
rotating frame -- valid for sufficiently strongly interacting condensates -- we
determine the transitions between these three phases for a
quadratic-plus-quartic confining potential. Combining the present results with
previous numerical simulations of small rotating condensates in such anharmonic
potentials, we delineate the general structure of the zero temperature phase
diagram.Comment: 5 pages, 5 figure
Coulomb Charging Effects in an Open Quantum Dot
Low-temperature transport properties of a lateral quantum dot formed by
overlaying finger gates in a clean one-dimensional channel are investigated.
Continuous and periodic oscillations superimposed upon ballistic conductance
steps are observed, when the conductance G of the dot changes within a wide
range 0<G<6e^2/h. Calculations of the electrostatics confirm that the measured
periodic conductance oscillations correspond to successive change of the total
charge of the dot by . By modelling the transport it is shown that the
progression of the Coulomb oscillations into the region G>2e^2/h may be due to
suppression of inter-1D-subband scattering. Fully transmitted subbands
contribute to coherent background of conductance, while sequential tunneling
via weakly transmitted subbands leads to Coulomb charging of the dot.Comment: 12 pages, RevTeX, 15 eps figures included, submitted to Phys. Rev.
Effects of Sequence Disorder on DNA Looping and Cyclization
Effects of sequence disorder on looping and cyclization of the
double-stranded DNA are studied theoretically. Both random intrinsic curvature
and inhomogeneous bending rigidity are found to result in a remarkably wide
distribution of cyclization probabilities. For short DNA segments, the range of
the distribution reaches several orders of magnitude for even completely random
sequences. The ensemble averaged values of the cyclization probability are also
calculated, and the connection to the recent experiments is discussed.Comment: 8 pages, 4 figures, LaTeX; accepted to Physical Review E; v2: a
substantially revised version; v3: references added, conclusions expanded,
minor editorial corrections to the text; v4: a substantially revised and
expanded version (total number of pages doubled); v5: new Figure 4, captions
expanded, minor editorial improvements to the tex
Tkachenko oscillations and the compressibility of a rotating Bose gas
The elastic oscillations of the vortex lattice of a cold Bose gas (Tkachenko
modes) are shown to play a crucial role in the saturation of the
compressibility sum rule, as a consequence of the hybridization with the
longitudinal degrees of freedom. The presence of the vortex lattice is
responsible for a behavior of the static structure factor at small
wavevectors , which implies the absence of long range order in 2D
configurations at zero temperature. Sum rules are used to calculate the
Tkachenko frequency in the presence of harmonic trapping. Results are derived
in the Thomas-Fermi regime and compared with experiments as well as with
previous theoretical estimates.Comment: 4 pages, 2 figure
Dynamic ion structure factor of warm dense matter
The dynamics of the ion structure in warm dense matter is determined by molecular dynamics simulations using an effective ion-ion potential. This potential is obtained from ab initio simulations and has a strong short-range repulsion added to a screened Coulomb potential. Models based on static or dynamic local field corrections are found to be insufficient to describe the data. An extended Mermin approach, a hydrodynamic model, and the method of moments with local constraints are capable of reproducing the numerical results but have rather limited predictive powers as they all need some numerical data as input. The method of moments is found to be the most promising
Influence of equation of state on interpretation of electrical conductivity measurements in strongly coupled tungsten plasma
We study the influence of equation-of-state (EOS) model on the interpretation
of electrical conductivity measurements in strongly coupled plasma of tungsten
by Korobenko et al. (2002 Plasma Physics Reports 28(12) 1008--1016). Three
different semiempirical EOS models for tungsten are used. Discrepancies in
obtained thermodynamic parameters and specific resistivity values as compared
with calculation results of Korobenko et al. are analysed.Comment: 11 pages, 5 Postscript figures, accepted for publication in J. Phys.
A: Math. Ge
Precompact noncompact reflexive abelian groups
We present a series of examples of precompact, noncompact, reflexive
topological Abelian groups. Some of them are pseudocompact or even countably
compact, but we show that there exist precompact non-pseudocompact reflexive
groups as well. It is also proved that every pseudocompact Abelian group is a
quotient of a reflexive pseudocompact group with respect to a closed reflexive
pseudocompact subgroup
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