6,931 research outputs found
First results of the CERN Resonant WISP Search (CROWS)
The CERN Resonant WISP Search (CROWS) probes the existence of Weakly
Interacting Sub-eV Particles (WISPs) like axions or hidden sector photons. It
is based on the principle of an optical light shining through the wall
experiment, adapted to microwaves. Critical aspects of the experiment are
electromagnetic shielding, design and operation of low loss cavity resonators
and the detection of weak sinusoidal microwave signals. Lower bounds were set
on the coupling constant GeV for axion like
particles with a mass of eV. For hidden sector photons, lower
bounds were set for the coupling constant at a mass
of eV. For the latter we were probing a previously
unexplored region in the parameter space
Continuous loading of an electrostatic trap for polar molecules
A continuously operated electrostatic trap for polar molecules is
demonstrated. The trap has a volume of ~0.6 cm^3 and holds molecules with a
positive Stark shift. With deuterated ammonia from a quadrupole velocity
filter, a trap density of ~10^8/cm^3 is achieved with an average lifetime of
130 ms and a motional temperature of ~300 mK. The trap offers good starting
conditions for high-precision measurements, and can be used as a first stage in
cooling schemes for molecules and as a "reaction vessel" in cold chemistry.Comment: 4 pages, 3 figures v2: several small improvements, new intr
Effects of angular shift transformations between movements and their visual feedback on coordination in unimanual circling
Tool actions are characterized by a transformation between movements and their resulting consequences in the environment. This transformation has to be taken into account when tool actions are planned and executed. We investigated how angular shift transformations between circling movements and their visual feedback affect the coordination of this feedback with visual events in the environment. We used a task that required participants to coordinate the visual feedback of a circular hand movement (presented on the right side of a screen) with a circling stimulus (presented on the left side of a screen). Four stimulus-visual feedback relations were instructed: same or different rotations of stimulus and visual feedback, either in same or different y-directions. Visual speed was varied in three levels (0.8, 1, and 1.2 Hz). The movement-visual feedback relation was manipulated using eight angular shifts: (-180, -135, -90, -45, 0, 45, 90, and 135°). Participants were not able to perform the different rotation/different y-direction pattern, but instead fell into the different rotation/same y-direction pattern. The different rotation/same y-direction pattern and the same rotation/same y-direction pattern were performed equally well, performance was worse in the same rotation/different y-direction pattern. Best performance was observed with angular shifts 0 and -45° and performance declined with larger angular shifts. Further, performance was better with negative angular shifts than with positive angular shifts. Participants did not fully take the angular shift transformation into account: when the angular shifts were negative the visual feedback was more in advance, and when angular shifts were positive the visual feedback was less in advance of the stimulus than in 0° angular shift. In conclusion, the presence and the magnitude of angular shift transformations affect performance. Internal models do not fully take the shift transformation into account
Flow correlated percolation during vascular network formation in tumors
A theoretical model based on the molecular interactions between a growing
tumor and a dynamically evolving blood vessel network describes the
transformation of the regular vasculature in normal tissues into a highly
inhomogeneous tumor specific capillary network. The emerging morphology,
characterized by the compartmentalization of the tumor into several regions
differing in vessel density, diameter and necrosis, is in accordance with
experimental data for human melanoma. Vessel collapse due to a combination of
severely reduced blood flow and solid stress exerted by the tumor, leads to a
correlated percolation process that is driven towards criticality by the
mechanism of hydrodynamic vessel stabilization.Comment: 4 pages, 3 figures (higher resolution at
http://www.uni-saarland.de/fak7/rieger/HOMEPAGE/flow.eps
Trapping of Neutral Rubidium with a Macroscopic Three-Phase Electric Trap
We trap neutral ground-state rubidium atoms in a macroscopic trap based on
purely electric fields. For this, three electrostatic field configurations are
alternated in a periodic manner. The rubidium is precooled in a magneto-optical
trap, transferred into a magnetic trap and then translated into the electric
trap. The electric trap consists of six rod-shaped electrodes in cubic
arrangement, giving ample optical access. Up to 10^5 atoms have been trapped
with an initial temperature of around 20 microkelvin in the three-phase
electric trap. The observations are in good agreement with detailed numerical
simulations.Comment: 4 pages, 4 figure
Random quantum magnets with long-range correlated disorder: Enhancement of critical and Griffiths-McCoy singularities
We study the effect of spatial correlations in the quenched disorder on
random quantum magnets at and near a quantum critical point. In the random
transverse field Ising systems disorder correlations that decay algebraically
with an exponent rho change the universality class of the transition for small
enough rho and the off-critical Griffiths-McCoy singularities are enhanced. We
present exact results for 1d utilizing a mapping to fractional Brownian motion
and generalize the predictions for the critical exponents and the generalized
dynamical exponent in the Griffiths phase to d>=2.Comment: 4 pages RevTeX, 1 eps-figure include
Density Profiles in Random Quantum Spin Chains
We consider random transverse-field Ising spin chains and study the
magnetization and the energy-density profiles by numerically exact calculations
in rather large finite systems (). Using different boundary
conditions (free, fixed and mixed) the numerical data collapse to scaling
functions, which are very accurately described by simple analytic expressions.
The average magnetization profiles satisfy the Fisher-de Gennes scaling
conjecture and the corresponding scaling functions are indistinguishable from
those predicted by conformal invariance.Comment: 4 pages RevTeX, 4 eps-figures include
Off-Equilibrium Dynamics in Finite-Dimensional Spin Glass Models
The low temperature dynamics of the two- and three-dimensional Ising spin
glass model with Gaussian couplings is investigated via extensive Monte Carlo
simulations. We find an algebraic decay of the remanent magnetization. For the
autocorrelation function a typical
aging scenario with a scaling is established. Investigating spatial
correlations we find an algebraic growth law of
the average domain size. The spatial correlation function scales with . The sensitivity of the
correlations in the spin glass phase with respect to temperature changes is
examined by calculating a time dependent overlap length. In the two dimensional
model we examine domain growth with a new method: First we determine the exact
ground states of the various samples (of system sizes up to )
and then we calculate the correlations between this state and the states
generated during a Monte Carlo simulation.Comment: 38 pages, RevTeX, 14 postscript figure
Small catchment runoff sensitivity to station density and spatial interpolation: Hydrological modeling of heavy rainfall using a dense rain Gauge network
Precipitation is the most important input to hydrological models, and its spatial variability can strongly influence modeled runoff. The highly dense station network WegenerNet (0.5 stations per km2) in southeastern Austria offers the opportunity to study the sensitivity of modeled runoff to precipitation input. We performed a large set of runoff simulations (WaSiM model) using 16 subnetworks with varying station densities and two interpolation schemes (inverse distance weighting, Thiessen polygons). Six representative heavy precipitation events were analyzed, placing a focus on small subcatchments (10–30 km2) and different event durations. We found that the modeling performance generally improved when the station density was increased up to a certain resolution: a mean nearest neighbor distance of around 6 km for long-duration events and about 2.5 km for short-duration events. However, this is not always true for small subcatchments. The sufficient station density is clearly dependent on the catchment area, event type, and station distribution. When the network is very dense (mean distance < 1.7 km), any reasonable interpolation choice is suitable. Overall, the station density is much more important than the interpolation scheme. Our findings highlight the need to study extreme precipitation characteristics in combination with runoff modeling to decompose precipitation uncertainties more comprehensively
Water vapor at a translational temperature of one kelvin
We report the creation of a confined slow beam of heavy-water (D2O) molecules
with a translational temperature around 1 kelvin. This is achieved by filtering
slow D2O from a thermal ensemble with inhomogeneous static electric fields
exploiting the quadratic Stark shift of D2O. All previous demonstrations of
electric field manipulation of cold dipolar molecules rely on a predominantly
linear Stark shift. Further, on the basis of elementary molecular properties
and our filtering technique we argue that our D2O beam contains molecules in
only a few ro-vibrational states.Comment: 4 pages, 4 figures, 1 tabl
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