1,112 research outputs found
Modelling vortex-vortex and vortex-boundary interaction
The motion of two-dimensional inviscid, incompressible fluid with regions of constant vorticity
is studied for three classes of geophysically motivated problem. First, equilibria consisting of point
vortices located near a vorticity interface generated by a shear flow are found analytically in the
linear (small-amplitude) limit and then numerically for the fully nonlinear problem. The equilibria
considered are mainly periodic in nature and it is found that an array of equilibrium shapes exist.
Numerical equilibria agree well with those predicted by linear theory when the amplitude of the
waves at the interface is small.
The next problem considered is the time-dependent interaction of a point vortex with a single
vorticity jump separating regions of opposite signed vorticity on the surface of a sphere. Initially,
small amplitude interfacial waves are generated where linear theory is applicable. It is found that a
point vortex in a region of same signed vorticity initially moves away from the interface and a point
vortex in a region of opposite signed vortex moves towards it. Configurations with weak vortices
sufficiently far from the interface then undergo meridional oscillation whilst precessing about the
sphere. A vortex at a pole in a region of same sign vorticity is a stable equilibrium whereas in
a region of opposite-signed vorticity it is an unstable equilibrium. Numerical computations using
contour dynamics confirm these results and nonlinear cases are examined.
Finally, techniques based on conformal mapping and the numerical method of contour dynamics
are presented for computing the motion of a finite area patch of constant vorticity on a sphere and
on the surface of a cylinder in the presence of impenetrable boundaries. Several examples of impenetrable
boundaries are considered including a spherical cap, longitudinal wedge, half-longitudinal
wedge, and a thin barrier with one and two gaps in the case of the sphere, and a thin island and
‘picket’ fence in the case of the cylinder. Finite area patch motion is compared to exact point vortex
trajectories and good agreement is found between the point vortex trajectories and the centroid
motion of finite area patches when the patch remains close to circular. More exotic motion of the
finite area patches on the sphere, particularly in the thin barrier case, is then examined. In the case
when background flow owing to a dipole located on the barrier is present, the vortex path is pushed
close to one of the barrier edges, leading to vortex shedding and possible splitting and, in certain
cases, to a quasi-steady trapped vortex. A family of vortex equilibria bounded between the gap in
the thin barrier on a sphere is also computed
A comparison of structured and unstructured navigation through a CBT package
The advent of hypertext has opened up new possibilities in computer-based training. The design of courseware without any predetermined structure could make the designer's task easier, and allow greater flexibility for the trainee to structure the learning environment to suit their own learning style, This investigation was concerned with the exploration of performance differences in structured and unstructured training environments. In the structured condition, subjects encountered presequenced training and practice modules. For the unstructured condition, subjects determined their own sequence of modules. It was proposed that performance may be better in the unstructured condition. The findings indicate that this depends upon individual differences in cognitive style, some styles seemingly better at exploiting the unstructured learning environment than others
Genome-wide association study identifies common and low-frequency variants at the AMHgene locus that strongly predict serum AMH levels in males
Anti-Müllerian hormone (AMH) is an essential messenger of sexual differentiation in the foetus and is an emerging biomarker of postnatal reproductive function in females. Due to a paucity of adequately sized studies, the genetic determinants of circulating AMH levels are poorly characterized. In samples from 2815 adolescents aged 15 from the ALSPAC study, we performed the first genome-wide association study of serum AMH levels across a set of ∼9 M ‘1000 Genomes Reference Panel’ imputed genetic variants. Genetic variants at the AMH protein-coding gene showed considerable allelic heterogeneity, with both common variants [rs4807216 (PMale = 2 × 10−49, Beta: ∼0.9 SDs per allele), rs8112524 (PMale = 3 × 10−8, Beta: ∼0.25)] and low-frequency variants [rs2385821 (PMale = 6 × 10−31, Beta: ∼1.2, frequency 3.6%)] independently associated with apparently large effect sizes in males, but not females. For all three SNPs, we highlight mechanistic links to AMH gene function and demonstrate highly significant sex interactions (PHet 0.0003–6.3 × 10−12), culminating in contrasting estimates of trait variance explained (24.5% in males versus 0.8% in females). Using these SNPs as a genetic proxy for AMH levels, we found no evidence in additional datasets to support a biological role for AMH in complex traits and diseases in men
Entwined Pairs and Schroedinger 's Equation
We show that a point particle moving in space-time on entwined-pair paths
generates Schroedinger's equation in a static potential in the appropriate
continuum linit. This provides a new realist context for the Schroedinger
equation within the domain of classical stochastic processes. It also suggests
that self-quantizing systems may provide considerable insight into conventional
quantum mechanics.Comment: 16 pg. 1 fi
Effect of herbicides on growth and nitrogen fixation potential (ARA) of field pea and lentil
Non-Peer Reviewe
Sociodemographic and Clinical Predictors of Prescription Opioid Use in a Longitudinal Community-Based Cohort Study of Middle-Aged and Older Adults
Objectives: Identifying factors associated with opioid use in middle-aged and older adults is a fundamental step in the mitigation of potentially unnecessary opioid consumption and opioid-related harms. Methods: Using longitudinal data on a community-based cohort of adults aged 50–90 years residing in Johnston County, North Carolina, we examined sociodemographic and clinical factors in non-opioid users (n = 786) at baseline (2006–2010) as predictors of opioid use at follow-up (2013–2015). Variables included age, sex, race, obesity, educational attainment, employment status, household poverty rate, marital status, depressive symptoms, social support, pain catastrophizing, pain sensitivity, insurance status, polypharmacy, and smoking status. Results: At follow-up, 13% of participants were using prescription opioids. In the multivariable model, high pain catastrophizing (adjusted odds ratio; 95% confidence interval = 2.14; 1.33–3.46), polypharmacy (2.08; 1.23–3.53), and history of depressive symptoms (2.00; 1.19–3.38) were independent markers of opioid use. Discussion: Findings support the assessment of these modifiable factors during clinical encounters in patients ≥ 50 years old with chronic pain
Critical points in edge tunneling between generic FQH states
A general description of weak and strong tunneling fixed points is developed
in the chiral-Luttinger-liquid model of quantum Hall edge states. Tunneling
fixed points are a subset of `termination' fixed points, which describe
boundary conditions on a multicomponent edge. The requirement of unitary time
evolution at the boundary gives a nontrivial consistency condition for possible
low-energy boundary conditions. The effect of interactions and random hopping
on fixed points is studied through a perturbative RG approach which generalizes
the Giamarchi-Schulz RG for disordered Luttinger liquids to broken left-right
symmetry and multiple modes. The allowed termination points of a multicomponent
edge are classified by a B-matrix with rational matrix elements. We apply our
approach to a number of examples, such as tunneling between a quantum Hall edge
and a superconductor and tunneling between two quantum Hall edges in the
presence of interactions. Interactions are shown to induce a continuous
renormalization of effective tunneling charge for the integrable case of
tunneling between two Laughlin states. The correlation functions of
electronlike operators across a junction are found from the B matrix using a
simple image-charge description, along with the induced lattice of boundary
operators. Many of the results obtained are also relevant to ordinary Luttinger
liquids.Comment: 23 pages, 6 figures. Xiao-Gang Wen: http://dao.mit.edu/~we
Formation of Small-Scale Condensations in the Molecular Clouds via Thermal Instability
A systematic study of the linear thermal instability of a self-gravitating
magnetic molecular cloud is carried out for the case when the unperturbed
background is subject to local expansion or contraction. We consider the
ambipolar diffusion, or ion-neutral friction on the perturbed states. In this
way, we obtain a non-dimensional characteristic equation that reduces to the
prior characteristic equation in the non-gravitating stationary background. By
parametric manipulation of this characteristic equation, we conclude that there
are, not only oblate condensation forming solutions, but also prolate solutions
according to local expansion or contraction of the background. We obtain the
conditions for existence of the Field lengths that thermal instability in the
molecular clouds can occur. If these conditions establish, small-scale
condensations in the form of spherical, oblate, or prolate may be produced via
thermal instability.Comment: 16 page, accepted by Ap&S
Generation Gap and the Impact of the Web on Goods Quality Perceptions
This study explores how age and general online shopping experience affect consumer perceptions on product quality uncertainty. Using the survey data collected from 549 consumers, we investigated how they perceive the uncertainty of product quality on six search, experience and credence goods. The ANOVA results show that age and the Web shopping experience of consumers are significant factors. A generation gap is indeed seen for all but one experience good. Web shopping experience is not a significant factor for search goods but is for experience and credence goods. There is an interaction effect between age and Web shopping experience for one credence good. Implications of these results are discussed
A Study of the Residual 39Ar Content in Argon from Underground Sources
The discovery of argon from underground sources with significantly less 39Ar
than atmospheric argon was an important step in the development of
direct-detection dark matter experiments using argon as the active target. We
report on the design and operation of a low background detector with a single
phase liquid argon target that was built to study the 39Ar content of the
underground argon. Underground argon from the Kinder Morgan CO2 plant in
Cortez, Colorado was determined to have less than 0.65% of the 39Ar activity in
atmospheric argon.Comment: 21 pages, 10 figure
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