18,228 research outputs found
Photoproduction off the nucleon revisited: Evidence for a narrow N(1688) resonance?
Revised analysis of beam asymmetry for the photoproduction on
the free proton reveals a structure at GeV. Fit of the
experimental data based on the E429 solution of the SAID partial wave analysis
suggests a narrow ( MeV) resonance. Possible candidates are
, or resonances. The result is considered in
conjunction with the recent evidence for a bump-like structure at GeV in the quasi-free photoproduction on the neutron.Comment: Contribution to the Workshop on the Physics of the Excited Nucleons
NSTAR2007, Bonn, Germany, Sept. 5 - 8 2007. To be published in Eur.Phys.J.
Magnetoelastic coupling and charge correlation lengths in a twin domain of Ba(FeCo)As (): A high-resolution X-ray diffraction study
The interplay between structure, magnetism and superconductivity in single
crystal Ba(FeCo)As (x=0.047) has been studied using
high-resolution X-ray diffraction by monitoring charge Bragg reflections in
each twin domain separately. The emergence of the superconducting state is
correlated with the suppression of the orthorhombic distortion around
\emph{T}, exhibiting competition between orthorhombicity and
superconductivity. Above \emph{T}, the in-plane charge correlation
length increases with the decrease of temperature, possibly induced by nematic
fluctuations in the paramagnetic tetragonal phase. Upon cooling, anomalies in
the in-plane charge correlation lengths along () and axes
() are observed at \emph{T} and also at
\emph{T} indicative of strong magnetoelastic coupling. The
in-plane charge correlation lengths are found to exhibit anisotropic behavior
along and perpendicular to the in-plane component of stripe-type AFM wave
vector (101) below around \emph{T}. The temperature
dependence of the out-of-plane charge correlation length shows a single anomaly
at \emph{T}, reflecting the connection between Fe-As distance and
Fe local moment. The origin of the anisotropic in-plane charge correlation
lengths and is discussed on the basis of the antiphase
magnetic domains and their dynamic fluctuations.Comment: 7 pages, 6 figures, 34 references, submitted for publication in
Physical Review
Large magnetic penetration depth and thermal fluctuations in a Ca(PtAs)[(FePt)As] (x=0.097) single crystal
We have measured the temperature dependence of the absolute value of the
magnetic penetration depth in a
Ca(PtAs)[(FePt)As] (x=0.097)
single crystal using a low-temperature magnetic force microscope (MFM). We
obtain (0)1000 nm via extrapolating the data to .
This large and pronounced anisotropy in this system are responsible
for large thermal fluctuations and the presence of a liquid vortex phase in
this low-temperature superconductor with critical temperature of 11 K,
consistent with the interpretation of the electrical transport data. The
superconducting parameters obtained from and coherence length
place this compound in the extreme type \MakeUppercase{\romannumeral 2} regime.
Meissner responses (via MFM) at different locations across the sample are
similar to each other, indicating good homogeneity of the superconducting state
on a sub-micron scale
Discovery of a rapid, luminous nova in NGC 300 by the KMTNet Supernova Program
We present the discovery of a rapidly evolving transient by the Korean
Microlensing Telescope Network Supernova Program (KSP). KSP is a novel
high-cadence supernova survey that offers deep ( mag in bands)
nearly continuous wide-field monitoring for the discovery of early and/or fast
optical transients. KSP-OT-201509a, reported here, was discovered on 2015
September 27 during the KSP commissioning run in the direction of the nearby
galaxy NGC~300, and stayed above detection limit for 22 days. We use our
light-curves to constrain the ascent rate, mag day in
, decay time scale, days, and peak absolute magnitude,
mag. We also find evidence for a short-lived
pre-maximum halt in all bands. The peak luminosity and lightcurve evolution
make KSP-OT-201509a consistent with a bright, rapidly decaying nova outburst.
We discuss constraints on the nature of the progenitor and its environment
using archival HST/ACS images and conclude with a broad discussion on the
nature of the system.Comment: 7 pages in aastex6 two-column format, 4 figures; accepted in Ap
Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag+ ion
New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag+ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu2+, and Hg2+ quench both the monomer and excimer emission of pyrene acutely. The 1H NMR results indicated that Ag+ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene
Unconventional pairing in the iron arsenide superconductors
We use magnetic long range order as a tool to probe the Cooper pair wave
function in the iron arsenide superconductors. We show theoretically that
antiferromagnetism and superconductivity can coexist in these materials only if
Cooper pairs form an unconventional, sign-changing state. The observation of
coexistence in Ba(FeCo)As then demonstrates
unconventional pairing in this material. The detailed agreement between theory
and neutron diffraction experiments, in particular for the unusual behavior of
the magnetic order below , demonstrates the robustness of our
conclusions. Our findings strongly suggest that superconductivity is
unconventional in all members of the iron arsenide family.Comment: 3 figures and 4 pages; final version as published
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