181 research outputs found
Measurement of the hyperfine structure of the S1/2-D5/2 transition in 43Ca+
The hyperfine structure of the S1/2-D5/2 quadrupole transition at 729 nm in
43Ca+ has been investigated by laser spectroscopy using a single trapped 43Ca+
ion. We determine the hyperfine structure constants of the metastable level as
A=-3.8931(2) MHz and B=-4.241(4) MHz. The isotope shift of the transition with
respect to 40Ca+ was measured to be 4134.713(5) MHz. We demonstrate the
existence of transitions that become independent of the first-order Zeeman
shift at non-zero low magnetic fields. These transitions might be better suited
for building a frequency standard than the well-known 'clock transitions'
between m=0 levels at zero magnetic field.Comment: corrected for sign errors in the hyperfine constants. No corrections
to were made to the data analysi
Quasiparticle spin susceptibility in heavy-fermion superconductors : An NMR study compared with specific heat results
Quasi-particle spin susceptibility () for various heavy-fermion
(HF) superconductors are discussed on the basis of the experimental results of
electronic specific heat (), NMR Knight shift () and NMR
relaxation rate () within the framework of the Fermi liquid model for a
Kramers doublet crystal electric field (CEF) ground state.
is calculated from the enhanced Sommerfeld coefficient and
from the quasi-particle Korringa relation
via the relation of
where is the hyperfine
coupling constant, the Abogadoro's number and the Bohr magneton.
For the even-parity (spin-singlet) superconductors CeCuSi, CeCoIn
and UPdAl, the fractional decrease in the Knight shift, , below the superconducting transition temperature () is due to
the decrease of the spin susceptibility of heavy quasi-particle estimated
consistently from and . This result
allows us to conclude that the heavy quasi-particles form the spin-singlet
Cooper pairs in CeCuSi, CeCoIn and UPdAl. On the other
hand, no reduction in the Knight shift is observed in UPt and
UNiAl, nevertheless the estimated values of and
are large enough to be probed experimentally. The odd-parity
superconductivity is therefore concluded in these compounds. The NMR result
provides a convincing way to classify the HF superconductors into either even-
or odd- parity paring together with the identification for the gap structure,
as long as the system has Kramers degeneracy.Comment: 11 pages, 3 tables, 5 figures, RevTex4(LaTex2e
Elevated surface chlorophyll associated with natural oil seeps in the Gulf of Mexico
Natural hydrocarbon seeps occur on the sea floor along continental margins, and account for up to 47% of the oil released into the oceans. Hydrocarbon seeps are known to support local benthic productivity, but little is known about their impact on photosynthetic organisms in the overlying water column. Here we present observations with high temporal and spatial resolution of chlorophyll concentrations in the northern Gulf of Mexico using in situ and shipboard flow-through fluorescence measurements from May to July 2012, as well as an analysis of ocean-colour satellite images from 1997 to 2007. All three methods reveal elevated chlorophyll concentrations in waters influenced by natural hydrocarbon seeps. Temperature and nutrient profiles above seep sites suggest that nutrient-rich water upwells from depth, which may facilitate phytoplankton growth and thus support the higher chlorophyll concentrations observed. Because upwelling occurs at natural seep locations around the world, we conclude that offshore hydrocarbon seeps, and perhaps other types of deep ocean vents and seeps at depths exceeding 1,000 m, may influence biogeochemistry and productivity of the overlying water column
Serial Section Scanning Electron Microscopy (S(3)EM) on Silicon Wafers for Ultra-Structural Volume Imaging of Cells and Tissues.
High resolution, three-dimensional (3D) representations of cellular ultrastructure are essential for structure function studies in all areas of cell biology. While limited subcellular volumes have been routinely examined using serial section transmission electron microscopy (ssTEM), complete ultrastructural reconstructions of large volumes, entire cells or even tissue are difficult to achieve using ssTEM. Here, we introduce a novel approach combining serial sectioning of tissue with scanning electron microscopy (SEM) using a conductive silicon wafer as a support. Ribbons containing hundreds of 35 nm thick sections can be generated and imaged on the wafer at a lateral pixel resolution of 3.7 nm by recording the backscattered electrons with the in-lens detector of the SEM. The resulting electron micrographs are qualitatively comparable to those obtained by conventional TEM. S 3 EM images of the same region of interest in consecutive sections can be used for 3D reconstructions of large structures. We demonstrate the potential of this approach by reconstructing a 31.7 mm 3 volume of a calyx of Held presynaptic terminal. The approach introduced here, Serial Section SEM (S 3 EM), for the first time provides the possibility to obtain 3D ultrastructure of large volumes with high resolution and to selectively and repetitively home in on structures of interest. S 3 EM accelerates process duration, is amenable to full automation and can be implemented wit
SQUIDs in biomagnetism : A roadmap towards improved healthcare
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 686865.Peer reviewedPublisher PD
- …