2,030 research outputs found
Direct Observation of Site-specific Valence Electronic Structure at Interface: SiO2/Si Interface
Atom specific valence electronic structures at interface are elucidated
successfully using soft x-ray absorption and emission spectroscopy. In order to
demonstrate the versatility of this method, we investigated SiO2/Si interface
as a prototype and directly observed valence electronic states projected at the
particular atoms of the SiO2/Si interface; local electronic structure strongly
depends on the chemical states of each atom. In addition we compared the
experimental results with first-principle calculations, which quantitatively
revealed the interfacial properties in atomic-scale.Comment: 4 pages, 3 figure
Interference scheme to measure light-induced nonlinearities in Bose-Einstein condensates
Light-induced nonlinear terms in the Gross-Pitaevskii equation arise from the
stimulated coherent exchange of photons between two atoms. For atoms in an
optical dipole trap this effect depends on the spatial profile of the trapping
laser beam. Two different laser beams can induce the same trapping potential
but very different nonlinearities. We propose a scheme to measure light-induced
nonlinearities which is based on this observation.Comment: 2 figure
Spatial coherence and density correlations of trapped Bose gases
We study first and second order coherence of trapped dilute Bose gases using
appropriate correlation functions. Special attention is given to the discussion
of second order or density correlations. Except for a small region around the
surface of a Bose-Einstein condensate the correlations can be accurately
described as those of a locally homogeneous gas with a spatially varying
chemical potential. The degrees of first and second order coherence are
therefore functions of temperature, chemical potential, and position. The
second order correlation function is governed both by the tendency of bosonic
atoms to cluster and by a strong repulsion at small distances due to atomic
interactions. In present experiments both effects are of comparable magnitude.
Below the critical temperature the range of the bosonic correlation is affected
by the presence of collective quasi-particle excitations. The results of some
recent experiments on second and third order coherence are discussed. It is
shown that the relation between the measured quantities and the correlation
functions is much weaker than previously assumed.Comment: RevTeX, 25 pages with 7 Postscript figure
Bleeding-Related Hospital Admissions and 30-Day Re-Admissions in Patients with Nonvalvular Atrial Fibrillation Treated with Dabigatran versus Warfarin
Observation of Caustics in the Trajectories of Cold Atoms in a Linear Magnetic Potential
We have studied the spatial and temporal dynamics of a cold atom cloud in the
conservative force field of a ferromagnetic guide, after laser cooling has been
switched off suddenly. We observe outgoing 'waves' that correspond to caustics
of individual trajectories of trapped atoms. This provides detailed information
on the magnetic field, the energy distribution and the spin states.Comment: 21 pages, incl. 12 figure
Quasi-continuous atom laser in the presence of gravity
We analyse the extraction of a coherent atomic beam from a trapped
Bose-Einstein condensate using a rf transition to a non-trapping state at T=0
K. Our quantum treatment fully takes gravity into account but neglects all
interactions in the free falling beam. We obtain an analytical expression of
the output rate and of the wave function of the extracted beam, i.e. the output
mode of the ``atom laser''. Our model reproduces satisfactorily experimental
data without any adjustable parameter.Comment: 4 pages, 2 figure
Generic model of an atom laser
We present a generic model of an atom laser by including a pump and loss term
in the Gross-Pitaevskii equation. We show that there exists a threshold for the
pump above which the mean matter field assumes a non-vanishing value in
steady-state. We study the transient regime of this atom laser and find
oscillations around the stationary solution even in the presence of a loss
term. These oscillations are damped away when we introduce a position dependent
loss term. For this case we present a modified Thomas-Fermi solution that takes
into account the pump and loss. Our generic model of an atom laser is analogous
to the semi-classical theory of the laser.Comment: 15 pages, including 5 figures, submitted to Phys. Rev. A, revised
manuscript, file also available at
http://www.physik.uni-ulm.de/quan/users/kne
Phase resolution limit in macroscopic interference between Bose-Einstein condensates
We study the competition between phase definition and quantum phase
fluctuations in interference experiments between independently formed Bose
condensates. While phase-sensitive detection of atoms makes the phase
progressively better defined, interactions tend to randomize it faster as the
uncertainty in the relative particle number grows. A steady state is reached
when the two effects cancel each other. Then the phase resolution saturates to
a value that grows with the ratio between the interaction strength and the atom
detection rate, and the average phase and number begin to fluctuate
classically. We discuss how our study applies to both recently performed and
possible future experiments.Comment: 4 pages, 5 figure
Presynaptic actions of 4-Aminopyridine and γ-aminobutyric acid on rat sympathetic ganglia in vitro
Responses to bath-applications of 4-aminopyridine (4-AP) and -aminobutyric acid (GABA) were recorded intracellularly from neurones in the rat isolated superior cervical ganglion.
4-aminopyridine (0.1–1.0 mmol/l) usually induced spontaneous action potentials and excitatory postsynaptic potentials (EPSPs), which were blocked by hexamethonium. Membrane potential was unchanged; spike duration was slightly increased. Vagus nerve B-and C-fibre potentials were prolonged.
In 4-AP solution (0.1–0.3 mmol/l), GABA (0.1 mmol/l), 3-aminopropanesulphonic acid or muscimol evoked bursts of spikes and EPSPs in addition to a neuronal depolarization. These bursts, which were not elicited by glycine, glutamate, taurine or (±)-baclofen, were completely antagonised by hexamethonium, tetrodotoxin or bicuculline methochloride.
It is concluded that: (a) 4-AP has a potent presynaptic action on sympathetic ganglia; (b) presynaptic actions of GABA can be recorded postsynaptically in the presence of 4-AP; and (c) the presynaptic GABA-receptors revealed in this condition are similar to those on the postsynaptic membrane
Genetic variation at MECOM, TERT, JAK2 and HBS1L-MYB predisposes to myeloproliferative neoplasms
Clonal proliferation in myeloproliferative neoplasms (MPN) is driven by somatic mutations in JAK2, CALR or MPL, but the contribution of inherited factors is poorly characterized. Using a three-stage genome-wide association study of 3,437 MPN cases and 10,083 controls, we identify two SNPs with genome-wide significance in JAK2V617F-negative MPN: rs12339666 (JAK2; meta-analysis P=1.27 × 10−10) and rs2201862 (MECOM; meta-analysis P=1.96 × 10−9). Two additional SNPs, rs2736100 (TERT) and rs9376092 (HBS1L/MYB), achieve genome-wide significance when including JAK2V617F-positive cases. rs9376092 has a stronger effect in JAK2V617F-negative cases with CALR and/or MPL mutations (Breslow–Day P=4.5 × 10−7), whereas in JAK2V617F-positive cases rs9376092 associates with essential thrombocythemia (ET) rather than polycythemia vera (allelic χ2 P=7.3 × 10−7). Reduced MYB expression, previously linked to development of an ET-like disease in model systems, associates with rs9376092 in normal myeloid cells. These findings demonstrate that multiple germline variants predispose to MPN and link constitutional differences in MYB expression to disease phenotype
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