16,993 research outputs found
Velocity, energy and helicity of vortex knots and unknots
In this paper we determine the velocity, the energy and estimate writhe and
twist helicity contributions of vortex filaments in the shape of torus knots
and unknots (toroidal and poloidal coils) in a perfect fluid. Calculations are
performed by numerical integration of the Biot-Savart law. Vortex complexity is
parametrized by the winding number , given by the ratio of the number of
meridian wraps to that of the longitudinal wraps. We find that for vortex
knots and toroidal coils move faster and carry more energy than a reference
vortex ring of same size and circulation, whereas for knots and poloidal
coils have approximately same speed and energy of the reference vortex ring.
Helicity is dominated by the writhe contribution. Finally, we confirm the
stabilizing effect of the Biot-Savart law for all knots and unknots tested,
that are found to be structurally stable over a distance of several diameters.
Our results also apply to quantized vortices in superfluid He.Comment: 17 pages, 8 figures, 2 table
Immature dendritic cells induce hyporesponsiveness to alloantigens in vitro and prolong mouse cardiac allograft survival
Density functional theory study of the nematic-isotropic transition in an hybrid cell
We have employed the Density Functional Theory formalism to investigate the
nematic-isotropic capillary transitions of a nematogen confined by walls that
favor antagonist orientations to the liquid crystal molecules (hybrid cell). We
analyse the behavior of the capillary transition as a function of the
fluid-substrate interactions and the pore width. In addition to the usual
capillary transition between isotropic-like to nematic-like states, we find
that this transition can be suppressed when one substrate is wet by the
isotropic phase and the other by the nematic phase. Under this condition the
system presents interface-like states which allow to continuously transform the
nematic-like phase to the isotropic-like phase without undergoing a phase
transition. Two different mechanisms for the disappearance of the capillary
transition are identified. When the director of the nematic-like state is
homogeneously planar-anchored with respect to the substrates, the capillary
transition ends up in a critical point. This scenario is analogous to the
observed in Ising models when confined in slit pores with opposing surface
fields which have critical wetting transitions. When the nematic-like state has
a linearly distorted director field, the capillary transition continuously
transforms in a transition between two nematic-like states.Comment: 31 pages, 10 figures, submitted to J. Chem. Phy
Perspectives on financial incentives to health service providers for increasing breast feeding and smoking quit rates during pregnancy: a mixed methods study
Objective: To explore the acceptability, mechanisms and consequences of provider incentives for smoking cessation and breast feeding as part of the Benefits of Incentives for Breastfeeding and Smoking cessation in pregnancy (BIBS) study.
Design: Cross-sectional survey and qualitative interviews.
Setting: Scotland and North West England.
Participants: Early years professionals: 497 survey respondents included 156 doctors; 197 health visitors/maternity staff; 144 other health staff. Qualitative interviews or focus groups were conducted with 68 pregnant/postnatal women/family members; 32 service providers; 22 experts/decision-makers; 63 conference attendees.
Methods: Early years professionals were surveyed via email about the acceptability of payments to local health services for reaching smoking cessation in pregnancy and breastfeeding targets. Agreement was measured on a 5-point scale using multivariable ordered logit models. A framework approach was used to analyse free-text survey responses and qualitative data.
Results: Health professional net agreement for provider incentives for smoking cessation targets was 52.9% (263/497); net disagreement was 28.6% (142/497). Health visitors/maternity staff were more likely than doctors to agree: OR 2.35 (95% CI 1.51 to 3.64; p<0.001). Net agreement for provider incentives for breastfeeding targets was 44.1% (219/497) and net disagreement was 38.6% (192/497). Agreement was more likely for women (compared with men): OR 1.81 (1.09 to 3.00; p=0.023) and health visitors/maternity staff (compared with doctors): OR 2.54 (95% CI 1.65 to 3.91; p<0.001). Key emergent themes were 'moral tensions around acceptability', 'need for incentives', 'goals', 'collective or divisive action' and 'monitoring and proof'. While provider incentives can focus action and resources, tensions around the impact on relationships raised concerns. Pressure, burden of proof, gaming, box-ticking bureaucracies and health inequalities were counterbalances to potential benefits.
Conclusions: Provider incentives are favoured by non-medical staff. Solutions which increase trust and collaboration towards shared goals, without negatively impacting on relationships or increasing bureaucracy are required
Fluid Mechanical and Electrical Fluctuation Forces in Colloids
Fluctuations in fluid velocity and fluctuations in electric fields may both
give rise to forces acting on small particles in colloidal suspensions. Such
forces in part determine the thermodynamic stability of the colloid. At the
classical statistical thermodynamic level, the fluid velocity and electric
field contributions to the forces are comparable in magnitude. When quantum
fluctuation effects are taken into account, the electric fluctuation induced
van der Waals forces dominate those induced by purely fluid mechanical motions.
The physical principles are applied in detail for the case of colloidal
particle attraction to the walls of the suspension container and more briefly
for the case of forces between colloidal particles.Comment: ReVTeX format, one *.eps figur
Active and passive multispectral scanner for earth resources applications: An advanced applications flight experiment
The development of an experimental airborne multispectral scanner to provide both active (laser illuminated) and passive (solar illuminated) data from a commonly registered surface scene is discussed. The system was constructed according to specifications derived in an initial programs design study. The system was installed in an aircraft and test flown to produce illustrative active and passive multi-spectral imagery. However, data was not collected nor analyzed for any specific application
Costimulatory molecule-deficient dendritic cell progenitors induce T cell hyporesponsiveness in vitro and prolong the survival of vascularized cardiac allografts
Donor pretreatment with FLT-3 ligand augments anti-donor CTL, NK and LAK cell activities within liver allografts and alters the pattern of intragraft apoptotic activity
Spectrum of turbulent Kelvin-waves cascade in superfluid helium
To explain the observed decay of superfluid turbulence at very low
temperature, it has been proposed that a cascade of Kelvin waves (analogous to
the classical Kolmogorov cascade) transfers kinetic energy to length scales
which are small enough that sound can be radiated away. We report results of
numerical simulations of the interaction of quantized vortex filaments. We
observe the development of the Kelvin-waves cascade, and compute the statistics
of the curvature, the amplitude spectrum (which we compare with competing
theories) and the fractal dimension.Comment: 32 pages, 22 figure
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