430 research outputs found
Theta 13 Determination with Nuclear Reactors
Recently there has been a lot of interest around the world in the use of
nuclear reactors to measure theta 13, the last undetermined angle in the
3-neutrino mixing scenario. In this paper the motivations for theta 13
measurement using short baseline nuclear reactor experiments are discussed. The
features of such an experiment are described in the context of Double Chooz,
which is a new project planned to start data-taking in 2008, and to reach a
sensitivity of sinsq(2 theta 13) < 0.03.Comment: Submission for XXXIXth Rencontres de Moriond, Electroweak
Interactions and Unified Theories, held in La Thuile, Italy, March 2004 (9
pages 4 figures
Sensitivity of seismically cued antineutrino detectors to nuclear explosions
We evaluate the sensitivity of large, gadolinium-doped water detectors to
antineutrinos released by nuclear fission explosions, using updated signal and
background models and taking advantage of the capacity for seismic observations
to provide an analysis trigger. Under certain realistic conditions, the
antineutrino signature of a 250-kiloton pure fission explosion could be
identified several hundred kilometers away in a detector about the size of the
largest module currently proposed for a basic physics experiment. In principle,
such an observation could provide rapid confirmation that the seismic signal
coincided with a fission event, possibly useful for international monitoring of
nuclear weapon tests. We discuss the limited potential for seismically cued
antineutrino observations to constrain fission yield, differentiate pure
fission from fusion-enhanced weapon tests, indicate that the seismic evidence
of an explosion had been intentionally masked, or verify the absence of
explosive testing in a targeted area. We conclude that advances in seismic
monitoring and neutrino physics have made the detection of explosion-derived
antineutrinos more conceivable than previously asserted, but the size and cost
of sufficiently sensitive detectors continue to limit applications
Liquid droplets on a free-standing glassy membrane: deformation through the glass transition
In this study, micro-droplets are placed on thin, glassy, free-standing films
where the Laplace pressure of the droplet deforms the free-standing film,
creating a bulge. The film's tension is modulated by changing temperature
continuously from well below the glass transition into the melt state of the
film. The contact angle of the liquid droplet with the planar film as well as
the angle of the bulge with the film are measured and found to be consistent
with the contact angles predicted by a force balance at the contact line.Comment: 6 pages, 5 figure
Snap-off production of monodisperse droplets
We introduce a novel technique to produce monodisperse droplets through the
snap-off mechanism. The methodology is simple, versatile, and requires no
specialized or expensive components. The droplets produced have polydispersity
<1% and can be as small as 2.5 m radius. A convenient feature is that the
droplet size is constant over a 100-fold change in flow rate, while at higher
flows the droplet size can be continuously adjusted.Comment: to be published in Eur. Phys. J. E as a "Tips and Tricks" articl
Capillary leveling of stepped films with inhomogeneous molecular mobility
A homogeneous thin polymer film with a stepped height profile levels due to
the presence of Laplace pressure gradients. Here we report on studies of
polymeric samples with precisely controlled, spatially inhomogeneous molecular
weight distributions. The viscosity of a polymer melt strongly depends on the
chain length distribution; thus, we learn about thin-film hydrodynamics with
viscosity gradients. These gradients are achieved by stacking two films with
different molecular weights atop one another. After a sufficient time these
samples can be well described as having one dimensional viscosity gradients in
the plane of the film, with a uniform viscosity normal to the film. We develop
a hydrodynamic model that accurately predicts the shape of the experimentally
observed self-similar profiles. The model allows for the extraction of a
capillary velocity, the ratio of the surface tension and the viscosity, in the
system. The results are in excellent agreement with capillary velocity
measurements of uniform mono- and bi-disperse stepped films and are consistent
with bulk polymer rheology.Comment: Accepted for publication in Soft Matter, Themed Issue on "The
Geometry and Topology of Soft Materials
Self-Similarity and Energy Dissipation in Stepped Polymer Films
The surface of a thin liquid film with nonconstant curvature is unstable, as
the Laplace pressure drives a flow mediated by viscosity. We present the
results of experiments on one of the simplest variable curvature surfaces: a
stepped polymer film. Height profiles are measured as a function of time for a
variety of molecular weights. The evolution of the profiles is shown to be
self-similar. This self-similarity offers a precise measurement of the
capillary velocity by comparison with numerical solutions of the thin film
equation. We also derive a master expression for the time dependence of the
excess free energy as a function of the material properties and film geometry.
The experiment and theory are in excellent agreement and indicate the
effectiveness of stepped polymer films to elucidate nanoscale rheological
properties.Comment: 5 pages, 4 figures, article accepted for publication in Physical
Review Letter
Approach to universal self-similar attractor for the levelling of thin liquid films
We compare the capillary levelling of a random surface perturbation on a thin
polystyrene film with a theoretical study on the two-dimensional
capillary-driven thin film equation. Using atomic force microscopy, we follow
the time evolution of samples prepared with different initial perturbations of
the free surface. In particular, we show that the surface profiles present long
term self-similarity, and furthermore, that they converge to a universal
self-similar attractor that only depends on the volume of the perturbation,
consistent with the theory. Finally, we look at the convergence time for the
different samples and find very good agreement with the analytical predictions.Comment: 7 pages, 5 figure
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