4,016 research outputs found
Preparation of Neutron-activated Xenon for Liquid Xenon Detector Calibration
We report the preparation of neutron-activated xenon for the calibration of
liquid xenon (LXe) detectors. Gamma rays from the decay of xenon metastable
states, produced by fast neutron activation, were detected and their activities
measured in a LXe scintillation detector. Following a five-day activation of
natural xenon gas with a Cf-252 (4 x 10^5 n/s) source, the activities of two
gamma ray lines at 164 keV and 236 keV, from Xe-131m and Xe-129m metastable
states, were measured at about 95 and 130 Bq/kg, respectively. We also observed
three additional lines at 35 keV, 100 keV and 275 keV, which decay away within
a few days. No long-lifetime activity was observed after the neutron
activation.Comment: to be published in NIM A, corrected typos in Table 1 and Fig.6 of the
previous versio
Piecewise linear transformation in diffusive flux discretization
To ensure the discrete maximum principle or solution positivity in finite
volume schemes, diffusive flux is sometimes discretized as a conical
combination of finite differences. Such a combination may be impossible to
construct along material discontinuities using only cell concentration values.
This is often resolved by introducing auxiliary node, edge, or face
concentration values that are explicitly interpolated from the surrounding cell
concentrations. We propose to discretize the diffusive flux after applying a
local piecewise linear coordinate transformation that effectively removes the
discontinuities. The resulting scheme does not need any auxiliary
concentrations and is therefore remarkably simpler, while being second-order
accurate under the assumption that the structure of the domain is locally
layered.Comment: 11 pages, 1 figures, preprint submitted to Journal of Computational
Physic
Exceptional Sequences of Line Bundles and Spherical Twists - a Toric Example
Exceptional sequences of line bundles on a smooth projective toric surface
are automatically full when they can be constructed via augmentation. By using
spherical twists, we give examples that there are also exceptional sequences
which can not be constructed this way but are nevertheless full.Comment: 12 pages, 3 figure
Three-body problem for ultracold atoms in quasi-one-dimensional traps
We study the three-body problem for both fermionic and bosonic cold atom
gases in a parabolic transverse trap of lengthscale . For this
quasi-one-dimensional (1D) problem, there is a two-body bound state (dimer) for
any sign of the 3D scattering length , and a confinement-induced scattering
resonance. The fermionic three-body problem is universal and characterized by
two atom-dimer scattering lengths, and . In the tightly bound
`dimer limit', , we find , and is linked
to the 3D atom-dimer scattering length. In the weakly bound `BCS limit',
, a connection to the Bethe Ansatz is established, which
allows for exact results. The full crossover is obtained numerically. The
bosonic three-body problem, however, is non-universal: and
depend both on and on a parameter related to the sharpness of
the resonance. Scattering solutions are qualitatively similar to fermionic
ones. We predict the existence of a single confinement-induced three-body bound
state (trimer) for bosons.Comment: 20 pages, 6 figures, accepted for publication in PRA, appendix on the
derivation of an integral formula for the Hurvitz zeta functio
On perturbations of Dirac operators with variable magnetic field of constant direction
We carry out the spectral analysis of matrix valued perturbations of
3-dimensional Dirac operators with variable magnetic field of constant
direction. Under suitable assumptions on the magnetic field and on the
pertubations, we obtain a limiting absorption principle, we prove the absence
of singular continuous spectrum in certain intervals and state properties of
the point spectrum. Various situations, for example when the magnetic field is
constant, periodic or diverging at infinity, are covered. The importance of an
internal-type operator (a 2-dimensional Dirac operator) is also revealed in our
study. The proofs rely on commutator methods.Comment: 12 page
Tunneling through a multigrain system: deducing the sample topology from the nonlinear conductance
We study a current transport through a system of a few grains connected with
tunneling links. The exact solution is given for an arbitrarily connected
double-grain system with a shared gate in the framework of the orthodox model.
The obtained result is generalized for multigrain systems with strongly
different tunneling resistances. We analyse the large-scale nonlinear
conductance and demonstrate how the sample topology can be unambiguously
deduced from the spectroscopy pattern (differential conductance versus
gate-bias plot). We present experimental data for a multigrain sample and
reconstruct the sample topology. A simple selection rule is formulated to
distinguish samples with spectral patterns free from spurious disturbance
caused by recharging of some grains nearby. As an example, we demonstrate
experimental data with additional peaks in the spectroscopy pattern, which can
not be attributed to coupling to additional grains. The described approach can
be used to judge the sample topology when it is not guaranteed by fabrication
and direct imaging is not possible.Comment: 13 pages (including 8 figures
Three Bosons in One Dimension with Short Range Interactions I: Zero Range Potentials
We consider the three-boson problem with -function interactions in
one spatial dimension. Three different approaches are used to calculate the
phase shifts, which we interpret in the context of the effective range
expansion, for the scattering of one free particle a off of a bound pair. We
first follow a procedure outlined by McGuire in order to obtain an analytic
expression for the desired S-matrix element. This result is then compared to a
variational calculation in the adiabatic hyperspherical representation, and to
a numerical solution to the momentum space Faddeev equations. We find excellent
agreement with the exact phase shifts, and comment on some of the important
features in the scattering and bound-state sectors. In particular, we find that
the 1+2 scattering length is divergent, marking the presence of a zero-energy
resonance which appears as a feature when the pair-wise interactions are
short-range. Finally, we consider the introduction of a three-body interaction,
and comment on the cutoff dependence of the coupling.Comment: 9 figures, 2 table
Renormalization of the Three-Body System with Short-Range Interactions
We discuss renormalization of the non-relativistic three-body problem with
short-range forces. The problem becomes non-perturbative at momenta of the
order of the inverse of the two-body scattering length, and an infinite number
of graphs must be summed. This summation leads to a cutoff dependence that does
not appear in any order in perturbation theory. We argue that this cutoff
dependence can be absorbed in a single three-body counterterm and compute the
running of the three-body force with the cutoff. We comment on relevance of
this result for the effective field theory program in nuclear and molecular
physics.Comment: 5 pages, RevTex, 4 PS figures included with epsf.sty, some clarifying
comments added, version to appear in Phys. Rev. Let
Mobility of thorium ions in liquid xenon
We present a measurement of the Th ion mobility in LXe at 163.0 K and
0.9 bar. The result obtained, 0.2400.011 (stat) 0.011 (syst)
cm/(kV-s), is compared with a popular model of ion transport.Comment: 6.5 pages,
Extracting current-induced spins: spin boundary conditions at narrow Hall contacts
We consider the possibility to extract spins that are generated by an
electric current in a two-dimensional electron gas with Rashba-Dresselhaus
spin-orbit interaction (R2DEG) in the Hall geometry. To this end, we discuss
boundary conditions for the spin accumulations between a spin-orbit coupled
region and contact without spin-orbit coupling, i.e. a normal two-dimensional
electron gas (2DEG). We demonstrate that in contrast to contacts that extend
along the whole sample, a spin accumulation can diffuse into the normal region
through finite contacts and detected by e.g. ferromagnets. For an
impedance-matched narrow contact the spin accumulation in the 2DEG is equal to
the current induced spin accumulation in the bulk of R2DEG up to a
geometry-dependent numerical factor.Comment: 18 pages, 7 figures, submitted to NJP focus issue on Spintronic
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