4,504 research outputs found
How Can the United States Learn from Foreign Countries’ Transport and Use of Renewable Power?
Tuning the scattering length with an optically induced Feshbach resonance
We demonstrate optical tuning of the scattering length in a Bose-Einstein
condensate as predicted by Fedichev {\em et al.} [Phys. Rev. Lett. {\bf 77},
2913 (1996)]. In our experiment atoms in a Rb condensate are exposed to
laser light which is tuned close to the transition frequency to an excited
molecular state. By controlling the power and detuning of the laser beam we can
change the atomic scattering length over a wide range. In view of laser-driven
atomic losses we use Bragg spectroscopy as a fast method to measure the
scattering length of the atoms.Comment: submitted to PRL, 5 pages, 5 figure
Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms
We study elastic collisions in an optically trapped spin mixture of fermionic
lithium atoms in the presence of magnetic fields up to 1.5kG by measuring
evaporative loss. Our experiments confirm the expected magnetic tunability of
the scattering length by showing the main features of elastic scattering
according to recent calculations. We measure the zero crossing of the
scattering length that is associated with a predicted Feshbach resonance at
530(3)G. Beyond the resonance we observe the expected large cross section in
the triplet scattering regime
Phonon-induced rotation of the electronic nematic director in superconducting BiSe
The doped topological insulator , with
, becomes a nematic superconductor
below . The associated electronic nematic director is
described by an angle and is experimentally manifested in the
elliptical shape of the in-plane critical magnetic field . Because of
the threefold rotational symmetry of the lattice, is expected to align
with one of three high-symmetry directions corresponding to the in-plane
nearest-neighbor bonds, consistent with a -Potts nematic transition.
Here, we show that the nematic coupling to the acoustic phonons, which makes
the nematic correlation length tend to diverge along certain directions only,
can fundamentally alter this phenomenology in trigonal lattices. Compared to
hexagonal lattices, the former possesses a sixth independent elastic constant
due to the fact that the in-plane shear strain doublet
and the out-of-plane shear
strain doublet transform as the same
irreducible representation. We find that, when overcomes a threshold
value, which is expected to be the case in doped , the
nematic director unlocks from the high-symmetry directions due to the
competition between the quadratic phonon-mediated interaction and the cubic
nematic anharmonicity. This implies the breaking of the residual in-plane
twofold rotational symmetry (), resulting in a triclinic phase. We
discuss the implications of these findings to the structure of nematic domains
and to the shape of the in-plane in , and
to presence of nodes inside the superconducting state.Comment: 24 pages, 10 figure
Observation of the Pairing Gap in a Strongly Interacting Fermi Gas
We study fermionic pairing in an ultracold two-component gas of Li atoms
by observing an energy gap in the radio-frequency excitation spectra. With
control of the two-body interactions via a Feshbach resonance we demonstrate
the dependence of the pairing gap on coupling strength, temperature, and Fermi
energy. The appearance of an energy gap with moderate evaporative cooling
suggests that our full evaporation brings the strongly interacting system deep
into a superfluid state.Comment: 18 pages, 3 figure
SNAI transcription factors mediate epithelial--mesenchymal transition in lung fibrosis
Background: Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease characterised by accumulation of activated (myo)fibroblasts and excessive extracellular matrix deposition. The enhanced accumulation of (myo)fibroblasts may be attributed, in part, to the process of transforming growth factor \textgreekb1 (TGF\textgreekb1)-induced epithelial--mesenchymal transition (EMT), the phenotypic switching of epithelial to fibroblast-like cells. Although alveolar epithelial type II (ATII) cells have been shown to undergo EMT, the precise mediators and mechanisms remain to be resolved. The objective of this study is to investigate the role of SNAI transcription factors in the process of EMT and in IPF.Methods: Using quantitative reverse transcription-PCR (RT-PCR), immunofluorescence, immunohistochemistry, western blotting, as well as gain- and loss-of-function studies and functional assays, the role of SNAI1 and SNAI2 in TGF\textgreekb1-induced EMT in ATII cells in vitro was assessed; and the expression of SNAI transcription factors was analysed in experimental and human IPF in vivo.Results: TGF\textgreekb1 treatment increased the expression and nuclear accumulation of SNAI1 and SNAI2, in concert with induction of EMT in ATII cells. SNAI overexpression was sufficient to induce EMT, and small interfering RNA (siRNA)-mediated SNAI depletion attenuated TGF\textgreekb1-induced ATII cell migration and EMT. SNAI expression was elevated in experimental and human IPF and localised to hyperplastic ATII cells in vivo.Conclusions: The results demonstrate that TGF\textgreekb1-induced EMT in ATII cells is essentially controlled by the expression and nuclear translocation of SNAI transcription factors. Increased SNAI1 and SNAI2 expression in experimental and human IPF in vivo suggests that SNAI-mediated EMT may contribute to the fibroblast pool in idiopathic pulmonary fibrosis
NASA-KSC\u27S Earth Resources Benefits From Space Exploration
The purpose of this paper is to identify the nature and scope of earth resources activities at the Kennedy Space Center (KSC). Because of recent developments from space exploration, NASA and KSC have evolved an earth resources program which focuses on applied R&D activities of direct benefit to a variety of federal, state, and local users. The historical development of this program is traced, and several projects are identified with special emphasis on the use of sidelooking airborne radar in several Brevard County, Florida test areas
Dynamics of a strongly interacting Fermi gas: the radial quadrupole mode
We report on measurements of an elementary surface mode in an ultracold,
strongly interacting Fermi gas of 6Li atoms. The radial quadrupole mode allows
us to probe hydrodynamic behavior in the BEC-BCS crossover without being
influenced by changes in the equation of state. We examine frequency and
damping of this mode, along with its expansion dynamics. In the unitarity limit
and on the BEC side of the resonance, the observed frequencies agree with
standard hydrodynamic theory. However, on the BCS side of the crossover, a
striking down shift of the oscillation frequency is observed in the
hydrodynamic regime as a precursor to an abrupt transition to collisionless
behavior; this indicates coupling of the oscillation to fermionic pairs.Comment: 11 pages, 11 figures v2: minor change
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