118 research outputs found
Inadequate Protection: Examining the Due Process Rights of Individuals in Child Abuse and Neglect Registries
This Article seeks to advance due process protections for people included in state child abuse and neglect registries. Between states, there are differences in the types of cases included in the state registry and the process required to be placed on or removed from the registry. To obtain judicial due process review, a plaintiff must demonstrate that a protected liberty or property interest is at stake. When federal courts have evaluated the individual liberty interest(s) implicated by placement on state child abuse and neglect registries, they have so far only found such an interest when the plaintiff’s employment opportunities were clearly affected. We identify a more principled method by which courts should evaluate challenges to state child abuse and neglect registries. Our proposed method would root the analysis in the core constitutional right of family integrity. We then go on to identify ways in which states could structure their child abuse and neglect registries to better comport with due process requirements
Vortex Waves in a Cloud of Bose Einstein - Condensed, Trapped Alkali - Metal Atoms
We consider the vortex state solution for a rotating cloud of trapped, Bose
Einstein - condensed alkali atoms and study finite temperature effects. We find
that thermally excited vortex waves can distort the vortex state significantly,
even at the very low temperatures relevant to the experiments.Comment: to appear in Phys. Rev.
Identification of Kelvin waves: numerical challenges
Kelvin waves are expected to play an essential role in the energy dissipation
for quantized vortices. However, the identification of these helical
distortions is not straightforward, especially in case of vortex tangle. Here
we review several numerical methods that have been used to identify Kelvin
waves within the vortex filament model. We test their validity using several
examples and estimate whether these methods are accurate enough to verify the
correct Kelvin spectrum. We also illustrate how the correlation dimension is
related to different Kelvin spectra and remind that the 3D energy spectrum E(k)
takes the form 1/k in the high-k region, even in the presence of Kelvin waves.Comment: 6 pages, 5 figures. The final publication is available at
http://www.springerlink.co
Instability of Superfluid Flow in the Neutron Star Inner Crust
Pinning of superfluid vortices to the nuclear lattice of the inner crust of a
neutron star supports a velocity difference between the superfluid and the
solid as the star spins down. Under the Magnus force that arises on the vortex
lattice, vortices undergo {\em vortex creep} through thermal activation or
quantum tunneling. We examine the hydrodynamic stability of this situation.
Vortex creep introduces two low-frequency modes, one of which is unstable above
a critical wavenumber for any non-zero flow velocity of the superfluid with
respect to the solid. For typical pinning parameters of the inner crust, the
superfluid flow is unstable over length scales \lap 10 m and over timescales
as fast as months. The vortex lattice could degenerate into a tangle, and the
superfluid flow could become turbulent. Unexpectedly large dissipation would
suppress this instability.Comment: 9 pages. Final journal versio
Instability of vortex array and transitions to turbulent states in rotating helium II
We consider superfluid helium inside a container which rotates at constant
angular velocity and investigate numerically the stability of the array of
quantized vortices in the presence of an imposed axial counterflow. This
problem was studied experimentally by Swanson {\it et al.}, who reported
evidence of instabilities at increasing axial flow but were not able to explain
their nature. We find that Kelvin waves on individual vortices become unstable
and grow in amplitude, until the amplitude of the waves becomes large enough
that vortex reconnections take place and the vortex array is destabilized. The
eventual nonlinear saturation of the instability consists of a turbulent tangle
of quantized vortices which is strongly polarized. The computed results compare
well with the experiments. Finally we suggest a theoretical explanation for the
second instability which was observed at higher values of the axial flow
Hydromagnetic waves in a superfluid neutron star with strong vortex pinning
Neutron-star cores may be hosts of a unique mixture of a neutron superfluid
and a proton superconductor. Compelling theoretical arguments have been
presented over the years that if the proton superconductor is of type II, than
the superconductor fluxtubes and superfluid vortices should be strongly coupled
and hence the vortices should be pinned to the proton-electron plasma in the
core. We explore the effect of this pinning on the hydromagnetic waves in the
core, and discuss 2 astrophysical applications of our results: 1. We show that
even in the case of strong pinning, the core Alfven waves thought to be
responsible for the low-frequency magnetar quasi-periodic oscillations (QPO)
are not significantly mass-loaded by the neutrons. The decoupling of about 0.95
of the core mass from the Alfven waves is in fact required in order to explain
the QPO frequencies, for simple magnetic geometries and for magnetic fields not
greater than 10^{15} Gauss. 2. We show that in the case of strong vortex
pinning, hydromagnetic stresses exert stabilizing influence on the Glaberson
instability, which has recently been proposed as a potential source of
superfluid turbulence in neutron stars.Comment: 10 pages, significantly improved and accepted to MNRAS. Old results
unchanged, additional new result: robust theoretical upper limit on the fast
precession angl
Quantum hydrodynamics
Quantum hydrodynamics in superfluid helium and atomic Bose-Einstein
condensates (BECs) has been recently one of the most important topics in low
temperature physics. In these systems, a macroscopic wave function appears
because of Bose-Einstein condensation, which creates quantized vortices.
Turbulence consisting of quantized vortices is called quantum turbulence (QT).
The study of quantized vortices and QT has increased in intensity for two
reasons. The first is that recent studies of QT are considerably advanced over
older studies, which were chiefly limited to thermal counterflow in 4He, which
has no analogue with classical traditional turbulence, whereas new studies on
QT are focused on a comparison between QT and classical turbulence. The second
reason is the realization of atomic BECs in 1995, for which modern optical
techniques enable the direct control and visualization of the condensate and
can even change the interaction; such direct control is impossible in other
quantum condensates like superfluid helium and superconductors. Our group has
made many important theoretical and numerical contributions to the field of
quantum hydrodynamics of both superfluid helium and atomic BECs. In this
article, we review some of the important topics in detail. The topics of
quantum hydrodynamics are diverse, so we have not attempted to cover all these
topics in this article. We also ensure that the scope of this article does not
overlap with our recent review article (arXiv:1004.5458), "Quantized vortices
in superfluid helium and atomic Bose--Einstein condensates", and other review
articles.Comment: 102 pages, 29 figures, 1 tabl
Rotating inclined cylinder and the effect of the tilt angle on vortices
We study numerically some possible vortex configurations in a rotating
cylinder that is tilted with respect to the rotation axis and where different
numbers of vortices can be present at given rotation velocity. In a long
cylinder at small tilt angles the vortices tend to align along the cylinder
axis and not along the rotation axis. We also show that the axial flow along
the cylinder axis, caused by the tilt, will result in the Ostermeier-Glaberson
instability above some critical tilt angle. When the vortices become unstable
the final state often appears to be a dynamical steady state, which may contain
turbulent regions where new vortices are constantly created. These new vortices
push other vortices in regions with laminar flow towards the top and bottom
ends of the cylinder where they finally annihilate. Experimentally the inclined
cylinder could be a convenient environment to create long lasting turbulence
with a polarization which can be adjusted with the tilt angle.Comment: 10 pages, 10 figure
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