2,405 research outputs found
Hexagons become second if symmetry is broken
Pattern formation on the free surface of a magnetic fluid subjected to a
magnetic field is investigated experimentally. By tilting the magnetic field
the symmetry can be broken in a controllable manner. When increasing the
amplitude of the tilted field, the flat surface gives way to liquid ridges. A
further increase results in a hysteretic transition to a pattern of stretched
hexagons. The instabilities are detected by means of a linear array of magnetic
hall sensors and compared with theoretical predictions.Comment: accepted for publication by Physical Review E/Rapid Communicatio
Cognitive Information Processing
Contains reports on four research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA28-043-AMC-02536(E)National Institutes of Health (Grant 1 PO1 GM-14940-01
HITRAP: A facility at GSI for highly charged ions
An overview and status report of the new trapping facility for highly charged
ions at the Gesellschaft fuer Schwerionenforschung is presented. The
construction of this facility started in 2005 and is expected to be completed
in 2008. Once operational, highly charged ions will be loaded from the
experimental storage ring ESR into the HITRAP facility, where they are
decelerated and cooled. The kinetic energy of the initially fast ions is
reduced by more than fourteen orders of magnitude and their thermal energy is
cooled to cryogenic temperatures. The cold ions are then delivered to a broad
range of atomic physics experiments.Comment: 8 pages, 11 figure
Hydrological impacts of climate change at catchment scale : a case study in the Grand-Duchy of Luxembourg
As a consequence of an increase of days with westerly atmospheric fluxes, bringing humid air masses from the Atlantic Ocean to Western Europe, important changes in the annual and seasonal distribution of rainfall have been observed over the past 150 years. Annual rainfall totals observed during the second half of the 19th century were less important than those observed during the second half of the 20th century. Moreover, during the past 50 years winter rainfall totals have significantly increased, while summer rainfall totals have been decreasing. Streamflow observations through the second half of the 20th century have shown a significant increase of winter maximum daily streamflow, in reaction to the winter rainfall increase. The modelling of the streamflow under the 19th century climatological conditions suggests that since then, the number of winter flood days has increased, while the occurrence of summer flood days has decreased. Moreover, high floods appear to have been more frequent in the second half of the 20th century
Rigorous Probabilistic Analysis of Equilibrium Crystal Shapes
The rigorous microscopic theory of equilibrium crystal shapes has made
enormous progress during the last decade. We review here the main results which
have been obtained, both in two and higher dimensions. In particular, we
describe how the phenomenological Wulff and Winterbottom constructions can be
derived from the microscopic description provided by the equilibrium
statistical mechanics of lattice gases. We focus on the main conceptual issues
and describe the central ideas of the existing approaches.Comment: To appear in the March 2000 special issue of Journal of Mathematical
Physics on Probabilistic Methods in Statistical Physic
Random Cluster Models on the Triangular Lattice
We study percolation and the random cluster model on the triangular lattice
with 3-body interactions. Starting with percolation, we generalize the
star--triangle transformation: We introduce a new parameter (the 3-body term)
and identify configurations on the triangles solely by their connectivity. In
this new setup, necessary and sufficient conditions are found for positive
correlations and this is used to establish regions of percolation and
non-percolation. Next we apply this set of ideas to the random cluster
model: We derive duality relations for the suitable random cluster measures,
prove necessary and sufficient conditions for them to have positive
correlations, and finally prove some rigorous theorems concerning phase
transitions.Comment: 24 pages, 1 figur
A Finite-Volume Version of Aizenman-Higuchi Theorem for the 2d Ising Model
In the late 1970s, in two celebrated papers, Aizenman and Higuchi
independently established that all infinite-volume Gibbs measures of the
two-dimensional ferromagnetic nearest-neighbor Ising model are convex
combinations of the two pure phases. We present here a new approach to this
result, with a number of advantages: (i) We obtain an optimal finite-volume,
quantitative analogue (implying the classical claim); (ii) the scheme of our
proof seems more natural and provides a better picture of the underlying
phenomenon; (iii) this new approach might be applicable to systems for which
the classical method fails.Comment: A couple of typos corrected. To appear in Probab. Theory Relat.
Field
Evaluating model performance of an ensemble-based chemical data assimilation system during INTEX-B field mission
We present a global chemical data assimilation system using a global atmosphere model, the Community Atmosphere Model (CAM3) with simplified chemistry and the Data Assimilation Research Testbed (DART) assimilation package. DART is a community software facility for assimilation studies using the ensemble Kalman filter approach. Here, we apply the assimilation system to constrain global tropospheric carbon monoxide (CO) by assimilating meteorological observations of temperature and horizontal wind velocity and satellite CO retrievals from the Measurement of Pollution in the Troposphere (MOPITT) satellite instrument. We verify the system performance using independent CO observations taken on board the NSF/NCAR C-130 and NASA DC-8 aircrafts during the April 2006 part of the Intercontinental Chemical Transport Experiment (INTEX-B). Our evaluations show that MOPITT data assimilation provides significant improvements in terms of capturing the observed CO variability relative to no MOPITT assimilation (i.e. the correlation improves from 0.62 to 0.71, significant at 99% confidence). The assimilation provides evidence of median CO loading of about 150 ppbv at 700 hPa over the NE Pacific during April 2006. This is marginally higher than the modeled CO with no MOPITT assimilation (~140 ppbv). Our ensemble-based estimates of model uncertainty also show model overprediction over the source region (i.e. China) and underprediction over the NE Pacific, suggesting model errors that cannot be readily explained by emissions alone. These results have important implications for improving regional chemical forecasts and for inverse modeling of CO sources and further demonstrate the utility of the assimilation system in comparing non-coincident measurements, e.g. comparing satellite retrievals of CO with in-situ aircraft measurements
The CRESST II Dark Matter Search
Direct Dark Matter detection with cryodetectors is briefly discussed, with
particular mention of the possibility of the identification of the recoil
nucleus. Preliminary results from the CREEST II Dark Matter search, with 730
kg-days of data, are presented. Major backgrounds and methods of identifying
and dealing with them are indicated.Comment: Talk at DSU workshop, ITP Beijing, Oct. 2011. 9 figures, 2 table
- …