20 research outputs found
Vortex Lattice Locking in Rotating Two-Component Bose-Einstein Condensates
The vortex density of a rotating superfluid, divided by its particle mass,
dictates the superfluid's angular velocity through the Feynman relation. To
find how the Feynman relation applies to superfluid mixtures, we investigate a
rotating two-component Bose-Einstein condensate, composed of bosons with
different masses. We find that in the case of sufficiently strong interspecies
attraction, the vortex lattices of the two condensates lock and rotate at the
drive frequency, while the superfluids themselves rotate at two different
velocities, whose ratio is the ratio between the particle mass of the two
species. In this paper, we characterize the vortex-locked state, establish its
regime of stability, and find that it surives within a disk smaller than a
critical radius, beyond which vortices become unbound, and the two Bose-gas
rings rotate together at the frequency of the external drive.Comment: 6 pages, 2 figure
Numerical exploration of a hexagonal string billiard
In this paper we are interested in the motion of a ball inside a billiard
table bounded by a particular smooth curve. This table belongs to a family of
billiards which can all be drawn by a common process: the so-called gardener's
string construction. The classical elliptical billiard is, of course, the
foremost member of this family. So it should come as no surprise that our
hexagonal string billiard shares many basic properties with the latter, but, on
the other hand, also exhibits some essential differences with it.
We have gathered numerical evidence against the Birkhoff-Poritsky conjecture.Comment: Preprint, 30 pages, 26 figure
Impact of eV-mass sterile neutrinos on neutrino-driven supernova outflows
Motivated by recent hints for sterile neutrinos from the reactor anomaly, we
study active-sterile conversions in a three-flavor scenario (2 active + 1
sterile families) for three different representative times during the
neutrino-cooling evolution of the proto-neutron star born in an
electron-capture supernova. In our "early model" (0.5 s post bounce), the
nu_e-nu_s MSW effect driven by Delta m^2=2.35 eV^2 is dominated by ordinary
matter and leads to a complete nu_e-nu_s swap with little or no trace of
collective flavor oscillations. In our "intermediate" (2.9 s p.b.) and "late
models" (6.5 s p.b.), neutrinos themselves significantly modify the nu_e-nu_s
matter effect, and, in particular in the late model, nu-nu refraction strongly
reduces the matter effect, largely suppressing the overall nu_e-nu_s MSW
conversion. This phenomenon has not been reported in previous studies of
active-sterile supernova neutrino oscillations. We always include the feedback
effect on the electron fraction Y_e due to neutrino oscillations. In all
examples, Y_e is reduced and therefore the presence of sterile neutrinos can
affect the conditions for heavy-element formation in the supernova ejecta, even
if probably not enabling the r-process in the investigated outflows of an
electron-capture supernova. The impact of neutrino-neutrino refraction is
strong but complicated, leaving open the possibility that with a more complete
treatment, or for other supernova models, active-sterile neutrino oscillations
could generate conditions suitable for the r-process.Comment: 23 pages, including 14 figures and 2 tables (minor changes in the
text). Matches published version in JCA
The dynamical Green's function and an exact optical potential for electron-molecule scattering including nuclear dynamics
We derive a rigorous optical potential for electron-molecule scattering
including the effects of nuclear dynamics by extending the common many-body
Green's function approach to optical potentials beyond the fixed-nuclei limit
for molecular targets. Our formalism treats the projectile electron and the
nuclear motion of the target molecule on the same footing whereby the dynamical
optical potential rigorously accounts for the complex many-body nature of the
scattering target. One central result of the present work is that the common
fixed-nuclei optical potential is a valid adiabatic approximation to the
dynamical optical potential even when projectile and nuclear motion are
(nonadiabatically) coupled as long as the scattering energy is well below the
electronic excitation thresholds of the target. For extremely low projectile
velocities, however, when the cross sections are most sensitive to the
scattering potential, we expect the influences of the nuclear dynamics on the
optical potential to become relevant. For these cases, a systematic way to
improve the adiabatic approximation to the dynamical optical potential is
presented that yields non-local operators with respect to the nuclear
coordinates.Comment: 22 pages, no figures, accepted for publ., Phys. Rev.
Determination of nutrient salts by automatic methods both in seawater and brackish water: the phosphate blank
9 páginas, 2 tablas, 2 figurasThe main inconvenience in determining nutrients in seawater by automatic methods is simply solved:
the preparation of a suitable blank which corrects the effect of the refractive index change on the recorded
signal. Two procedures are proposed, one physical (a simple equation to estimate the effect) and the other
chemical (removal of the dissolved phosphorus with ferric hydroxide).Support for this work came from CICYT (MAR88-0245 project) and
Conselleria de Pesca de la Xunta de GaliciaPeer reviewe