2,301 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
Dissipationless Phonon Hall Viscosity
We study the acoustic phonon response of crystals hosting a gapped
time-reversal symmetry breaking electronic state. The phonon effective action
can in general acquire a dissipationless "Hall" viscosity, which is determined
by the adiabatic Berry curvature of the electron wave function. This Hall
viscosity endows the system with a characteristic frequency, \omega_v; for
acoustic phonons of frequency \omega, it shifts the phonon spectrum by an
amount of order (\omega/\omega_v)^2 and it mixes the longitudinal and
transverse acoustic phonons with a relative amplitude ratio of \omega/\omega_v
and with a phase shift of +/- \pi/2, to lowest order in \omega/\omega_v. We
study several examples, including the integer quantum Hall states, the quantum
anomalous Hall state in Hg_{1-y}Mn_{y}Te quantum wells, and a mean-field model
for p_x + i p_y superconductors. We discuss situations in which the acoustic
phonon response is directly related to the gravitational response, for which
striking predictions have been made. When the electron-phonon system is viewed
as a whole, this provides an example where measurements of Goldstone modes may
serve as a probe of adiabatic curvature of the wave function of the gapped
sector of a system.Comment: 14 page
Modeling of the process of oilseed meat cooking in a multi-vat cooker during processing of oil raw materials
Вивчені й проаналізовані процеси, що відбуваються при жарінні м’ятки масличної сировини в кожному чані багаточанної жаровні. Розроблено їх математична модель, що враховує гідродинаміку первинної і вторинної циркуляції, енергію зв'язку вологи з матеріалом. Чисельні рішення моделі дозволять обґрунтувати технологічні режими жаріння і конструктивні параметри жаровні. Складено і проаналізовано тепловий баланс кондуктивного і конвектівного тепло-, масопереносу при сушінні м’ятк
Vortex states of rapidly rotating dilute Bose-Einstein condensates
We show that, in the Thomas-Fermi regime, the cores of vortices in rotating
dilute Bose-Einstein condensates adjust in radius as the rotation velocity,
, grows, thus precluding a phase transition associated with core
overlap at high vortex density. In both a harmonic trap and a rotating
hard-walled bucket, the core size approaches a limiting fraction of the
intervortex spacing. At large rotation speeds, a system confined in a bucket
develops, within Thomas-Fermi, a hole along the rotation axis, and eventually
makes a transition to a giant vortex state with all the vorticity contained in
the hole.Comment: 4 pages, 2 figures, RevTex4. Version as published; discussion
extended, some references added and update
Self-assembly of DNA-coded nanoclusters
We present a theoretical discussion of a self-assembly scheme which makes it
possible to use DNA to uniquely encode the composition and structure of micro-
and nanoparticle clusters. These anisotropic DNA-decorated clusters can be
further used as building blocks for hierarchical self-assembly of larger
structures. We address several important aspects of possible experimental
implementation of the proposed scheme: the competition between different types
of clusters in a solution, possible jamming in an unwanted configuration, and
the degeneracy due to symmetry with respect to particle permutations.Comment: v2, 4 pages, 7 figures, added journal re
Pinning and collective modes of a vortex lattice in a Bose-Einstein condensate
We consider the ground state of vortices in a rotating Bose-Einstein
condensate that is loaded in a corotating two-dimensional optical lattice. Due
to the competition between vortex interactions and their potential energy, the
vortices arrange themselves in various patterns, depending on the strength of
the optical potential and the vortex density. We outline a method to determine
the phase diagram for arbitrary vortex filling factor. Using this method, we
discuss several filling factors explicitly. For increasing strength of the
optical lattice, the system exhibits a transition from the unpinned hexagonal
lattice to a lattice structure where all the vortices are pinned by the optical
lattice. The geometry of this fully pinned vortex lattice depends on the
filling factor and is either square or triangular. For some filling factors
there is an intermediate half-pinned phase where only half of the vortices is
pinned. We also consider the case of a two-component Bose-Einstein condensate,
where the possible coexistence of the above-mentioned phases further enriches
the phase diagram. In addition, we calculate the dispersion of the low-lying
collective modes of the vortex lattice and find that, depending on the
structure of the ground state, they can be gapped or gapless. Moreover, in the
half-pinned and fully pinned phases, the collective mode dispersion is
anisotropic. Possible experiments to probe the collective mode spectrum, and in
particular the gap, are suggested.Comment: 29 pages, 4 figures, changes in section
Least-squares deconvolution based analysis of stellar spectra
In recent years, astronomical photometry has been revolutionised by space
missions such as MOST, CoRoT and Kepler. However, despite this progress,
high-quality spectroscopy is still required as well. Unfortunately,
high-resolution spectra can only be obtained using ground-based telescopes, and
since many interesting targets are rather faint, the spectra often have a
relatively low S/N. Consequently, we have developed an algorithm based on the
least-squares deconvolution profile, which allows to reconstruct an observed
spectrum, but with a higher S/N. We have successfully tested the method using
both synthetic and observed data, and in combination with several common
spectroscopic applications, such as e.g. the determination of atmospheric
parameter values, and frequency analysis and mode identification of stellar
pulsations.Comment: Proceedingspaper, 8 pages, 4 figures, appears in "Setting a New
Standard in the Analysis of Binary Stars", Eds K. Pavlovski, A. Tkachenko,
and G. Torres, EAS Publications Serie
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