411 research outputs found
Conjunctions of Among Constraints
Many existing global constraints can be encoded as a conjunction of among
constraints. An among constraint holds if the number of the variables in its
scope whose value belongs to a prespecified set, which we call its range, is
within some given bounds. It is known that domain filtering algorithms can
benefit from reasoning about the interaction of among constraints so that
values can be filtered out taking into consideration several among constraints
simultaneously. The present pa- per embarks into a systematic investigation on
the circumstances under which it is possible to obtain efficient and complete
domain filtering algorithms for conjunctions of among constraints. We start by
observing that restrictions on both the scope and the range of the among
constraints are necessary to obtain meaningful results. Then, we derive a
domain flow-based filtering algorithm and present several applications. In
particular, it is shown that the algorithm unifies and generalizes several
previous existing results.Comment: 15 pages plus appendi
Bose-Einstein condensates in standing waves: The cubic nonlinear Schroedinger equation with a periodic potential
We present a new family of stationary solutions to the cubic nonlinear
Schroedinger equation with a Jacobian elliptic function potential. In the limit
of a sinusoidal potential our solutions model a dilute gas Bose-Einstein
condensate trapped in a standing light wave. Provided the ratio of the height
of the variations of the condensate to its DC offset is small enough, both
trivial phase and nontrivial phase solutions are shown to be stable. Numerical
simulations suggest such stationary states are experimentally observable.Comment: 4 pages, 4 figure
Stability of Repulsive Bose-Einstein Condensates in a Periodic Potential
The cubic nonlinear Schr\"odinger equation with repulsive nonlinearity and an
elliptic function potential models a quasi-one-dimensional repulsive dilute gas
Bose-Einstein condensate trapped in a standing light wave. New families of
stationary solutions are presented. Some of these solutions have neither an
analog in the linear Schr\"odinger equation nor in the integrable nonlinear
Schr\"odinger equation. Their stability is examined using analytic and
numerical methods. All trivial-phase stable solutions are deformations of the
ground state of the linear Schr\"odinger equation. Our results show that a
large number of condensed atoms is sufficient to form a stable, periodic
condensate. Physically, this implies stability of states near the Thomas-Fermi
limit.Comment: 12 pages, 17 figure
Stability of Attractive Bose-Einstein Condensates in a Periodic Potential
Using a standing light wave trap, a stable quasi-one-dimensional attractive
dilute-gas Bose-Einstein condensate can be realized. In a mean-field
approximation, this phenomenon is modeled by the cubic nonlinear Schr\"odinger
equation with attractive nonlinearity and an elliptic function potential of
which a standing light wave is a special case. New families of stationary
solutions are presented. Some of these solutions have neither an analog in the
linear Schr\"odinger equation nor in the integrable nonlinear Schr\"odinger
equation. Their stability is examined using analytic and numerical methods.
Trivial-phase solutions are experimentally stable provided they have nodes and
their density is localized in the troughs of the potential. Stable
time-periodic solutions are also examined.Comment: 12 pages, 18 figure
Stability of stationary states in the cubic nonlinear Schroedinger equation: applications to the Bose-Einstein condensate
The stability properties and perturbation-induced dynamics of the full set of
stationary states of the nonlinear Schroedinger equation are investigated
numerically in two physical contexts: periodic solutions on a ring and
confinement by a harmonic potential. Our comprehensive studies emphasize
physical interpretations useful to experimentalists. Perturbation by stochastic
white noise, phase engineering, and higher order nonlinearity are considered.
We treat both attractive and repulsive nonlinearity and illustrate the
soliton-train nature of the stationary states.Comment: 9 pages, 11 figure
Berry phases for the nonlocal Gross-Pitaevskii equation with a quadratic potential
A countable set of asymptotic space -- localized solutions is constructed by
the complex germ method in the adiabatic approximation for the nonstationary
Gross -- Pitaevskii equation with nonlocal nonlinearity and a quadratic
potential. The asymptotic parameter is 1/T, where is the adiabatic
evolution time.
A generalization of the Berry phase of the linear Schr\"odinger equation is
formulated for the Gross-Pitaevskii equation. For the solutions constructed,
the Berry phases are found in explicit form.Comment: 13 pages, no figure
Resurrection and redescription of Varestrongylus alces (Nematoda; Protostrongylidae), a lungworm of the Eurasian moose (Alces alces), with report on associated pathology
Varestrongylus alces, a lungworm in Eurasian moose from Europe has been considered a
junior synonym of Varestrongylus capreoli, in European roe deer, due to a poorly detailed
morphological description and the absence of a type-series.
Methods
Specimens used in the redescription were collected from lesions in the lungs of Eurasian
moose, from Vestby, Norway. Specimens were described based on comparative morphology
and integrated approaches. Molecular identification was based on PCR, cloning and
sequencing of the ITS-2 region of the nuclear ribosomal DNA. Phylogenetic analysis
compared V. alces ITS-2 sequences to these of other Varestrongylus species and other
protostrongylids.
Results
Varestrongylus alces is resurrected for protostrongylid nematodes of Eurasian moose from
Europe. Varestrongylus alces causes firm nodular lesions that are clearly differentiated from
the adjacent lung tissue. Histologically, lesions are restricted to the parenchyma with adult,
egg and larval parasites surrounded by multinucleated giant cells, macrophages, eosinophilic
granulocytes, lymphocytes. The species is valid and distinct from others referred to
Varestrongylus, and should be separated from V. capreoli. Morphologically, V. alces can be
distinguished from other species by characters in the males that include a distally bifurcated
gubernaculum, arched denticulate crura, spicules that are equal in length and relatively short,
and a dorsal ray that is elongate and bifurcated. Females have a well-developed provagina,
and are very similar to those of V. capreoli. Morphometrics of first-stage larvae largely
overlap with those of other Varestrongylus. Sequences of the ITS-2 region strongly support
mutual independence of V. alces, V. cf. capreoli, and the yet undescribed species of
Varestrongylus from North American ungulates. These three taxa form a well-supported
crown-clade as the putative sister of V. alpenae. The association of V. alces and Alces or its
ancestors is discussed in light of host and parasite phylogeny and host historical
biogeography.
Varestrongylus alces is a valid species, and should be considered distinct from V. capreoli.
Phylogenetic relationships among Varestrongylus spp. from Eurasia and North America are
complex and consistent with faunal assembly involving recurrent events of geographic
expansion, host switching and subsequent speciation.
Cervidae, Cryptic species, Historical biogeography, ITS-2, Metastrongyloidea, Parasite
biodiversity, Varestrongylinae, Varestrongylus capreoli, Verminous pneumoniapublishedVersio
Density Changes in Low Pressure Gas Targets for Electron Scattering Experiments
A system of modular sealed gas target cells has been developed for use in
electron scattering experiments at the Thomas Jefferson National Accelerator
Facility (Jefferson Lab). This system was initially developed to complete the
MARATHON experiment which required, among other species, tritium as a target
material. Thus far, the cells have been loaded with the gas species 3H, 3He,
2H, 1H and 40Ar and operated in nominal beam currents of up to 22.5 uA in
Jefferson Lab's Hall A. While the gas density of the cells at the time of
loading is known, the density of each gas varies uniquely when heated by the
electron beam. To extract experimental cross sections using these cells,
density dependence on beam current of each target fluid must be determined. In
this study, data from measurements with several beam currents within the range
of 2.5 to 22.5 uA on each target fluid are presented. Additionally, expressions
for the beam current dependent fluid density of each target are developed.Comment: 8 pages, 12 figures, 4 table
The CLAS12 Backward Angle Neutron Detector (BAND)
The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted
at backward angles of to , with momenta between
and MeV/c. It is positioned 3 meters upstream of the target, consists of
rows and layers of cm by cm scintillator bars, and read
out on both ends by PMTs to measure time and energy deposition in the
scintillator layers. Between the target and BAND there is a 2 cm thick lead
wall followed by a 2 cm veto layer to suppress gammas and reject charged
particles. This paper discusses the component-selection tests and the detector
assembly. Timing calibrations (including offsets and time-walk) were performed
using a novel pulsed-laser calibration system, resulting in time resolutions
better than ps (150 ps) for energy depositions above 2 MeVee (5 MeVee).
Cosmic rays and a variety of radioactive sources were used to calibration the
energy response of the detector. Scintillator bar attenuation lengths were
measured. The time resolution results in a neutron momentum reconstruction
resolution, \% for neutron momentum MeV/c.
Final performance of the BAND with CLAS12 is shown, including electron-neutral
particle timing spectra and a discussion of the off-time neutral contamination
as a function of energy deposition threshold.Comment: 17 pages, 25 figures, 3 tables. Accepted for publication in NIM-
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