2,891 research outputs found
Effect of a polymer additive on heat transport in turbulent Rayleigh-B\'enard convection
Measurements of heat transport, as expressed by the Nusselt number , are
reported for turbulent Rayleigh-B\'enard convection of water containing up to
120 ppm by weight of poly-[ethylene oxide] with a molecular weight of
g/mole. Over the Rayleigh number range 5\times 10^9 \alt Ra
\alt 7 \times 10^{10} is smaller than it is for pure water by up to 10%.Comment: 3 pages, 2 figure
Quantum Decoherence of Photons in the Presence of Hidden U(1)s
Many extensions of the standard model predict the existence of hidden sectors
that may contain unbroken abelian gauge groups. We argue that in the presence
of quantum decoherence photons may convert into hidden photons on sufficiently
long time scales and show that this effect is strongly constrained by CMB and
supernova data. In particular, Planck-scale suppressed decoherence scales D ~
E^2/M_Pl (characteristic for non-critical string theories) are incompatible
with the presence of even a single hidden U(1). The corresponding bounds on the
decoherence scale are four orders of magnitude stronger than analogous bounds
derived from solar and reactor neutrino data and complement other bounds
derived from atmospheric neutrino data.Comment: 8 pages, 9 figure
Exotic Neutrino Interactions in Cosmic Rays
The spectrum of extra-galactic cosmic rays (CRs) is expected to follow the Greisen-Zatsepin-Kuzmin (GZK) cutoff at about 5x10^10 GeV which results from energy losses of charged nuclei in the cosmic microwave background. So far the confrontation of this feature with CR data is inconclusive. In the absence of close-by sources a power-law continuation of the spectrum might signal the contribution of new physics. We have investigated the statistical significance of a model where exotic interactions of cosmogenic neutrinos are the origin of super-GZK events. A strong neutrino-nucleon interaction is favored by CR data, even if we account for a systematic shift in energy calibration
Competition between Spiral-Defect Chaos and Rolls in Rayleigh-Benard Convection
We present experimental results for pattern formation in Rayleigh-Benard
convection of a fluid with a Prandtl number, Pr~ 4. We find that the
spiral-defect-chaos (SDC) attractor which exists for Pr~1 has become unstable.
Gradually increasing the temperature difference from below to well above its
critical value no longer leads to SDC. A sudden jump of temperature difference
from below to above onset causes convection to grow from thermal fluctuations
and does yield SDC. However, the SDC is a transient; it coarsens and forms a
single cell-filling spiral which then drifts toward the cell wall and
disappears.Comment: 9 pages(RevTeX), 5 jpg figures, To appear as Rapid Communication in
PR
Rayleigh-B\'{e}nard convection in a homeotropically aligned nematic liquid crystal
We report experimental results for convection near onset in a thin layer of a
homeotropically aligned nematic liquid crystal heated from below as a function
of the temperature difference and the applied vertical magnetic
field and compare them with theoretical calculations. The experiments cover
the field range 8 \alt h \equiv H/ H_{F} \alt 80 ( is the
Fr\'eedericksz field). For less than a codimension-two field the bifurcation is subcritical and oscillatory, with travelling- and
standing-wave transients. Beyond the bifurcation is stationary and
subcritical until a tricritical field is reached, beyond which it
is supercritical. The bifurcation sequence as a function of found in the
experiment confirms the qualitative aspects of the theoretical predictions.
However, the value of is about 10% higher than the predicted value and
the results for are systematically below the theory by about 2% at small
and by as much as 7% near . At , is continuous within
the experimental resolution whereas the theory indicates a 7% discontinuity.
The theoretical tricritical field is somewhat below the
experimental one. The fully developed flow above for is
chaotic. For the subcritical stationary bifurcation also
leads to a chaotic state. The chaotic states persist upon reducing the Rayleigh
number below , i.e. the bifurcation is hysteretic. Above the tricritical
field , we find a bifurcation to a time independent pattern which within
our resolution is non-hysteretic.Comment: 15 pages incl. 23 eps figure
- …