6,340 research outputs found
Development of UHF radiometer
A wideband multifrequency UHF radiometer was initially developed to operate in the 500 to 710 MHz frequency range for the remote measurement of ocean water salinity. However, radio-frequency interference required a reconfiguration to operate in the single-frequency radio astronomy band of 608 to 614 MHz. Details of the radiometer development and testing are described. Flight testing over variable terrain provided a performance comparison of the UHF radiometer with an L-band radiometer for remote sensing of geophysical parameters. Although theoretically more sensitive, the UHF radiometer was found to be less desirable in practice than the L-band radiometer
Tuning the interactions of spin-polarized fermions using quasi-one-dimensional confinement
The behavior of ultracold atomic gases depends crucially on the two-body
scattering properties of these systems. We develop a multichannel scattering
theory for atom-atom collisions in quasi-one-dimensional (quasi-1D) geometries
such as atomic waveguides or highly elongated traps. We apply our general
framework to the low energy scattering of two spin-polarized fermions and show
that tightly-confined fermions have infinitely strong interactions at a
particular value of the 3D, free-space p-wave scattering volume. Moreover, we
describe a mapping of this strongly interacting system of two quasi-1D fermions
to a weakly interacting system of two 1D bosons.Comment: Submitted to Phys. Rev. Let
Quantum Monte Carlo study of quasi-one-dimensional Bose gases
We study the behavior of quasi-one-dimensional (quasi-1d) Bose gases by Monte
Carlo techniques, i.e., by the variational Monte Carlo, the diffusion Monte
Carlo, and the fixed-node diffusion Monte Carlo technique. Our calculations
confirm and extend our results of an earlier study [Astrakharchik et al.,
cond-mat/0308585]. We find that a quasi-1d Bose gas i) is well described by a
1d model Hamiltonian with contact interactions and renormalized coupling
constant; ii) reaches the Tonks-Girardeau regime for a critical value of the 3d
scattering length a_3d; iii) enters a unitary regime for |a_3d| -> infinity,
where the properties of the gas are independent of a_3d and are similar to
those of a 1d gas of hard-rods; and iv) becomes unstable against cluster
formation for a critical value of the 1d gas parameter. The accuracy and
implications of our results are discussed in detail.Comment: 15 pages, 9 figure
Form and function in hillslope hydrology : Characterization of subsurface ow based on response observations
Acknowledgements. We are grateful to Marcel Delock, Lisei Köhn, and Marvin Reich for their support during fieldwork, as well as Markus Morgner and Jean Francois Iffly for technical support, Britta Kattenstroth for hydrometeorological data acquisition and isotope sampling, and Barbara Herbstritt and Begoña Lorente Sistiaga for laboratory work. Laurent Pfister and Jean-Francois Iffly from the Luxembourg Institute of Science and Technology (LIST) are acknowledged for organizing the permissions for the experiments and providing discharge data for Weierbach 1 and Colpach. We also want to thank Frauke K. Barthold and the two anonymous reviewers, whose thorough remarks greatly helped to improve the manuscript. This study is part of DFG-funded CAOS project âFrom Catchments as Organised Systems to Models based on Dynamic Functional Unitsâ (FOR 1598). The article processing charges for this open-access publication were covered by a Research Centre of the Helmholtz Association.Peer reviewedPublisher PD
Form and function in hillslope hydrology : in situ imaging and characterization of flow-relevant structures
Thanks to Elly Karle and the Engler-BunteInstitute, KIT, for the IC measurements of bromide. We are grateful to Selina Baldauf, Marcel Delock, Razije Fiden, Barbara Herbstritt, Lisei Köhn, Jonas Lanz, Francois Nyobeu, Marvin Reich and Begona Lorente Sistiaga for their support in the lab and during fieldwork, as well as Markus Morgner and Jean Francois Iffly for technical support and Britta Kattenstroth for hydrometeorological data acquisition. Laurent Pfister and Jean-Francois Iffly from the Luxembourg Institute of Science and Technology (LIST) are acknowledged for organizing the permissions for the experiments. Moreover, we thank Markus Weiler (University of Freiburg) for his strong support during the planning of the hillslope experiment and the preparation of the manuscript. This study is part of the DFG-funded CAOS project âFrom Catchments as Organised Systems to Models based on Dynamic Functional Unitsâ (FOR 1598). The manuscript was substantially improved based on the critical and constructive comments of the anonymous reviewers, Christian Stamm and Alexander Zimmermann, and the editor Ross Woods during the open review process, which is highly appreciated.Peer reviewedPublisher PD
Quasi-one-dimensional Bose gases with large scattering length
Bose gases confined in highly-elongated harmonic traps are investigated over
a wide range of interaction strengths using quantum Monte Carlo techniques. We
find that the properties of a Bose gas under tight transverse confinement are
well reproduced by a 1d model Hamiltonian with contact interactions. We point
out the existence of a unitary regime, where the properties of the quasi-1d
Bose gas become independent of the actual value of the 3d scattering length. In
this unitary regime, the energy of the system is well described by a hard rod
equation of state. We investigate the stability of quasi-1d Bose gases with
positive and negative 3d scattering length.Comment: 5 pages, 3 figure
Tuning the structural and dynamical properties of a dipolar Bose-Einstein condensate: Ripples and instability islands
It is now well established that the stability of aligned dipolar Bose gases
can be tuned by varying the aspect ratio of the external harmonic confinement.
This paper extends this idea and demonstrates that a Gaussian barrier along the
strong confinement direction can be employed to tune both the structural
properties and the dynamical stability of an oblate dipolar Bose gas aligned
along the strong confinement direction. In particular, our theoretical
mean-field analysis predicts the existence of instability islands immersed in
otherwise stable regions of the phase diagram. Dynamical studies indicate that
these instability islands, which can be probed experimentally with present-day
technology, are associated with the going soft of a Bogoliubov--de Gennes
excitation frequency with radial breathing mode character. Furthermore, we find
dynamically stable ground state densities with ripple-like oscillations along
the radial direction. These structured ground states exist in the vicinity of a
dynamical radial roton-like instability.Comment: 9 pages, 11 figure
Three particles in an external trap: Nature of the complete J=0 spectrum
Three bosonic, spin-polarized atoms in a spherical oscillator potential
constitutes the simplest nontrivial Bose-Einstein condensate (BEC). The present
paper develops the tools needed to understand the nature of the complete J=0
energy spectrum for this prototype system, assuming a sum of two-body
potentials. The resulting spectrum is calculated as a function of the two-body
scattering length a_sc, which documents the evolution of certain many-body
levels that evolve from BEC-type to molecular-type as the scattering length is
decreased. Implications for the behavior of the condensate excited-state
spectrum and for condensate formation and decay are elucidated. The energy
levels evolve smoothly, even through the regime where the number of two-body
bound states N_b increases by 1, and a_{sc} switches from -infinity to
infinity. We point out the possibility of suppressing three-body recombination
by tuning the two-body scattering length to values that are larger than the
size of the condensate ground state. Comparisons with mean-field treatments are
presented
Belief heterogeneity and survival in incomplete markets
In complete markets economies (Sandroni [16]), or in economies with Pareto optimal outcomes (Blume and Easley [10]), the market selection hypothesis holds, as long as traders have identical discount factors. Traders who survive must have beliefs that merge with the truth. We show that in incomplete markets, regardless of tradersâ discount factors, the market selects for a range of beliefs, at least some of which do not merge with the truth. We also show that impatient traders with incorrect beliefs can survive and that these incorrect beliefs impact prices. These beliefs may be chosen so that they are far from the truth
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