5,371 research outputs found
Dynamics in the deep Canada Basin, Arctic Ocean, inferred by thermistor chain time series
Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 37 (2007): 1066â1076, doi:10.1175/JPO3032.1.A 50-day time series of high-resolution temperature in the deepest layers of the Canada Basin in the Arctic Ocean indicates that the deep Canada Basin is a dynamically active environment, not the quiet, stable basin often assumed. Vertical motions at the near-inertial (tidal) frequency have amplitudes of 10â 20 m. These vertical displacements are surprisingly large considering the downward near-inertial internal wave energy flux typically observed in the Canada Basin. In addition to motion in the internal-wave frequency band, the measurements indicate distinctive subinertial temperature fluctuations, possibly due to intrusions of new water masses
Self-localized impurities embedded in a one dimensional Bose-Einstein condensate and their quantum fluctuations
We consider the self-localization of neutral impurity atoms in a
Bose-Einstein condensate in a 1D model. Within the strong coupling approach, we
show that the self-localized state exhibits parametric soliton behavior. The
corresponding stationary states are analogous to the solitons of non-linear
optics and to the solitonic solutions of the Schroedinger-Newton equation
(which appears in models that consider the connection between quantum mechanics
and gravitation). In addition, we present a Bogoliubov-de-Gennes formalism to
describe the quantum fluctuations around the product state of the strong
coupling description. Our fluctuation calculations yield the excitation
spectrum and reveal considerable corrections to the strong coupling
description. The knowledge of the spectrum allows a spectroscopic detection of
the impurity self-localization phenomenon.Comment: 7 pages, 5 figure
Radium single-ion optical clock
We explore the potential of the electric quadrupole transitions
7s\,^2S_{1/2} - 6d\,^2D_{3/2}, 6d\,^2D_{5/2} in radium isotopes as
single-ion optical frequency standards. The frequency shifts of the clock
transitions due to external fields and the corresponding uncertainties are
calculated. Several competitive Ra candidates with 223 - 229 are
identified. In particular, we show that the transition
7s\,^2S_{1/2}\,(F=2,m_F=0) - 6d\,^2D_{3/2}\,(F=0,m_F=0) at 828 nm in
Ra, with no linear Zeeman and electric quadrupole shifts, stands
out as a relatively simple case, which could be exploited as a compact, robust,
and low-cost atomic clock operating at a fractional frequency uncertainty of
. With more experimental effort, the Ra clocks
could be pushed to a projected performance reaching the level.Comment: 20 pages, 1 figur
Small polarons in dilute gas Bose-Einstein condensates
A neutral impurity atom immersed in a dilute Bose-Einstein condensate (BEC)
can have a bound ground state in which the impurity is self-localized. In this
small polaron-like state, the impurity distorts the density of the surrounding
BEC, thereby creating the self-trapping potential minimum. We describe the
self-localization in a strong coupling approach
BRDFs acquired by directional radiative measurements during EAGLE and AGRISAR
Radiation is the driving force for all processes and interactions between earth surface and atmosphere. The amount of
measured radiation reflected by vegetation depends on its structure, the viewing angle and the solar angle. This angular
dependence is usually expressed in the Bi-directional Reflectance Distribution Function (BRDF). This BRDF is not
only different for different types of vegetation, but also different for different stages of the growth. The BRDF therefore
has to be measured at ground level before any satellite imagery can be used the calculate surface-atmosphere
interaction. The objective of this research is to acquire the BRDFs for agricultural crop types.
A goniometric system is used to acquire the BRDFs. This is a mechanical device capable of a complete hemispherical
rotation. The radiative directional measurements are performed with different sensors that can be attached to this
system. The BRDFs are calculated from the measured radiation.
In the periods 10 June - 18 June 2006 and 2 July - 10 July 2006 directional radiative measurements were performed at
three sites: Speulderbos site, in the Netherlands, the Cabauw site, in the Netherlands, and an agricultural test site in
Goermin, Germany. The measurements were performed over eight different crops: forest, grass, pine tree, corn, wheat,
sugar beat and barley. The sensors covered the spectrum from the optical to the thermal domain. The measured radiance
is used to calculate the BRDFs or directional thermal signature.
This contribution describes the measurements and calculation of the BRDFs of forest, grassland, young corn, mature
corn, wheat, sugar beat and barley during the EAGLE2006 and AGRISAR 2006 fieldcampaigns. Optical BRDF have
been acquired for all crops except barley. Thermal angular signatures are acquired for all the crop
Renormalization of One-Pion Exchange and Power Counting
The renormalization of the chiral nuclear interactions is studied. In leading
order, the cutoff dependence is related to the singular tensor interaction of
the one-pion exchange potential. In S waves and in higher partial waves where
the tensor force is repulsive this cutoff dependence can be absorbed by
counterterms expected at that order. In the other partial waves additional
contact interactions are necessary. The implications of this finding for the
effective-field-theory program in nuclear physics are discussed.Comment: 19 pages, 18 figure
Why we interact : on the functional role of the striatum in the subjective experience of social interaction
Acknowledgments We thank Neil Macrae and Axel Cleeremans for comments on earlier versions of this manuscript. Furthermore, we are grateful to DorothĂ© Krug and Barbara Elghahwagi for their assistance in data acquisition. This study was supported by a grant of the Köln Fortune Program of the Medical Faculty at the University of Cologne to L.S. and by a grant âOther Mindsâ of the German Ministry of Research and Education to K.V.Peer reviewedPreprin
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