530 research outputs found
Pairing based cooling of Fermi gases
We propose a pairing-based method for cooling an atomic Fermi gas. A three
component (labels 1, 2, 3) mixture of Fermions is considered where the
components 1 and 2 interact and, for instance, form pairs whereas the component
3 is in the normal state. For cooling, the components 2 and 3 are coupled by an
electromagnetic field. Since the quasiparticle distributions in the paired and
in the normal states are different, the coupling leads to cooling of the normal
state even when initially (notation ).
The cooling efficiency is given by the pairing energy and by the linewidth of
the coupling field. No superfluidity is required: any type of pairing, or other
phenomenon that produces a suitable spectral density, is sufficient. In
principle, the paired state could be cooled as well but this requires
. The method has a conceptual analogy to cooling based on
superconductor -- normal metal (SN) tunneling junctions. Main differences arise
from the exact momentum conservation in the case of the field-matter coupling
vs. non-conservation of momentum in the solid state tunneling process.
Moreover, the role of processes that relax the energy conservation requirement
in the tunneling, e.g. thermal fluctuations of an external reservoir, is now
played by the linewidth of the field. The proposed method should be
experimentally feasible due to its close connection to RF-spectroscopy of
ultracold gases which is already in use.Comment: Journal version 4 pages, 4 figure
Bakhtiari, Leskinen and Torma Reply
This is a Reply to: Comment on "Spectral Signatures of the
Fulde-Ferrell-Larkin-Ovchinnikov Order Parameter in One-Dimensional Optical
Lattices" R. A. Molina J. Dukelksy, and P. Schmitteckert, Phys. Rev. Lett. 102,
168901 (2009)Comment: 1 page, published versio
Detection of aphid migrations in Finland
Our insect immigration warning system was built on the atmospheric dispersion model that has been used in predicting long-range transport of airborne pollen. We observed immigrations with a trap network consisting of rotating tow-nets, yellow sticky traps, and suction traps.
Based on our studies the aphids can be detected with radars when they occur in large numbers
Spin-asymmetric Josephson effect
The Josephson effect is a manifestation of the macroscopic phase coherence of
superconductors and superfluids. We propose that with ultracold Fermi gases one
can realise a spin-asymmetric Josephson effect in which the two spin components
of a Cooper pair are driven asymmetrically - corresponding to driving a
Josephson junction of two superconductors with different voltages V_\uparrow
and V_\downarrow for spin up and down electrons, respectively. We predict that
the spin up and down components oscillate at the same frequency but with
different amplitudes. Our results reveal that the standard description of the
Josephson effect in terms of bosonic pair tunnelling is insufficient. We
provide an intuitive interpretation of the Josephson effect as interference in
Rabi oscillations of pairs and single particles, the latter causing the
asymmetry.Comment: Article: 4 pages, 3 figures. Supplementary material: 12 pages, 7
figure
Integrating Historical Person Registers as Linked Open Data in the WarSampo Knowledge Graph
Semantic data integration from heterogeneous, distributed data silos enables Digital Humanities research and application development employing a larger, mutually enriched and interlinked knowledge graph. However, data integration is challenging, involving aligning the data models and reconciling the concepts and named entities, such as persons and places. This paper presents a record linkage process to reconcile person references in different military historical person registers with structured metadata. The information about persons is aggregated into a single knowledge graph. The process was applied to reconcile three person registers of the popular semantic portal "WarSampo -- Finnish World War 2 on the Semantic Web". The registers contain detailed information about some 100,000 people and are individually maintained by domain experts. Thus, the integration process needs to be automatic and adaptable to changes in the registers. An evaluation of the record linkage results is promising and provides some insight into military person register reconciliation in general.Peer reviewe
Cooper-pair resonances and subgap Coulomb blockade in a superconducting single-electron transistor
We have fabricated and measured superconducting single-electron transistors
with Al leads and Nb islands. At bias voltages below the gap of Nb we observe
clear signatures of resonant tunneling of Cooper pairs, and of Coulomb blockade
of the subgap currents due to linewidth broadening of the energy levels in the
superconducting density of states of Nb. The experimental results are in good
agreement with numerical simulations.Comment: 4 pages, 3 figure
Spectral signatures of the Fulde-Ferrell-Larkin-Ovchinnikov order parameter in one-dimensional optical lattices
We address an imbalanced two-component atomic Fermi gas restricted by a
one-dimensional (1D) optical lattice and an external harmonic potential, within
the mean-field Bogoliubov-de Gennes (BdG) formalism. We show that
characteristic features of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state
are visible in the RF-spectra and in the momentum resolved photoemission
spectra of the gas. Specially, Andreev states or mid-gap states can be clearly
resolved, which gives a direct experimentally observable signature of the
oscillating order parameter.Comment: published versio
Metabarcoding successfully tracks temporal changes in eukaryotic communities in coastal sediments
Metabarcoding is a method that combines high-throughput DNA sequencing and DNA-based identification. Previously, this method has been successfully used to target spatial variation of eukaryote communities in marine sediments, however, the temporal changes in these communities remain understudied. Here, we follow the temporal changes of the eukaryote communities in Baltic Sea surface sediments collected from two coastal localities during three seasons of two consecutive years. Our study reveals that the structure of the sediment eukaryotic ecosystem was primarily driven by annual and seasonal changes in prevailing environmental conditions, whereas spatial variation was a less significant factor in explaining the variance in eukaryotic communities over time. Therefore, our data suggests that shifts in regional climate regime or large-scale changes in the environment are the overdriving factors in shaping the coastal eukaryotic sediment ecosystems rather than small-scale changes in local environmental conditions or heterogeneity in ecosystem structure. More studies targeting temporal changes are needed to further understand the long-term trends in ecosystem stability and response to climate change. Furthermore, this work contributes to the recent efforts in developing metabarcoding applications for environmental biomonitoring, proving a comprehensive option for traditional monitoring approaches.Peer reviewe
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