2,110 research outputs found
Structure of a mycobacterial polysaccharide-fatty acyl-CoA complex: nuclear magnetic resonance studies.
Simple Ginzburg-Landau Theory for Vortices in a Crystal Lattice
We study the Ginzburg-Landau model with a nonlocal quartic term as a simple
phenomenological model for superconductors in the presence of coupling between
the vortex lattice and the underlying crystal lattice. In mean-field theory,
our model is consistent with a general oblique vortex lattice ranging from a
triangular lattice to a square lattice. This simple formulation enables us to
study the effect of thermal fluctuations in the vortex liquid regime. We
calculate the structure factor of the vortex liquid nonperturbatively and find
Bragg-like peaks with four-fold symmetry appearing in the structure factor even
though there is only a short-range crystalline order.Comment: Revised version with new title and additional results for the vortex
liquid regime, to be published in Phys. Rev. Lett. 5 pages RevTeX, 1 figure
include
Vortex Structure in Superconducting Stripe States
The vortex structure in superconducting stripe states is studied according to
the Bogoliubov-de Gennes theory on the two-dimensional Hubbard model with
nearest-neighbor sites pairing interaction. The vortex is trapped at the
outside region of the stripe line, where the superconductivity is weak. The
superconducting coherence length along the stripe direction becomes long. There
are no eminent low-energy electronic states even near the vortex core. These
characters resemble the Josephson vortex in layered superconductors under a
parallel field.Comment: LaTeX 5 pages (using jpsj macros) with 3 figure
A coordinated optical and X-ray spectroscopic campaign on HD179949: searching for planet-induced chromospheric and coronal activity
HD179949 is an F8V star, orbited by a close-in giant planet with a period of
~3 days. Previous studies suggested that the planet enhances the magnetic
activity of the parent star, producing a chromospheric hot spot which rotates
in phase with the planet orbit. However, this phenomenon is intermittent since
it was observed in several but not all seasons. A long-term monitoring of the
magnetic activity of HD179949 is required to study the amplitude and time
scales of star-planet interactions. In 2009 we performed a simultaneous optical
and X-ray spectroscopic campaign to monitor the magnetic activity of HD179949
during ~5 orbital periods and ~2 stellar rotations. We analyzed the CaII H&K
lines as a proxy for chromospheric activity, and we studied the X-ray emission
in search of flux modulations and to determine basic properties of the coronal
plasma. A detailed analysis of the flux in the cores of the CaII H&K lines and
a similar study of the X-ray photometry shows evidence of source variability,
including one flare. The analysis of the the time series of chromospheric data
indicates a modulation with a ~11 days period, compatible with the stellar
rotation period at high latitudes. Instead, the X-ray light curve suggests a
signal with a period of ~4 days, consistent with the presence of two active
regions on opposite hemispheres. The observed variability can be explained,
most likely, as due to rotational modulation and to intrinsic evolution of
chromospheric and coronal activity. There is no clear signature related to the
orbital motion of the planet, but the possibility that just a fraction of the
chromospheric and coronal variability is modulated with the orbital period of
the planet, or the stellar-planet beat period, cannot be excluded. We conclude
that any effect due to the presence of the planet is difficult to disentangle
When will I get my paper back? A replication study of publication timelines for health professions education research.
INTRODUCTION: Biomedical researchers have lamented the lengthy timelines from manuscript submission to publication and highlighted potential detrimental effects on scientific progress and scientists\u27 careers. In 2015, Himmelstein identified the mean time from manuscript submission to acceptance in biomedicine as approximately 100 days. The length of publication timelines in health professions education (HPE) is currently unknown.
METHODS: This study replicates Himmelstein\u27s work with a sample of 14 HPE journals published between 2008-2018. Using PubMed, 19,182 article citations were retrieved. Open metadata for each were downloaded, including the date the article was received by the journal, date the authors resubmitted revisions, date the journal accepted the article, and date of entry into PubMed. Journals without publication history metadata were excluded.
RESULTS: Publication history data were available for 55% (n = 8) of the journals sampled. The publication histories of 4,735 (25%) articles were analyzed. Mean time from: (1) author submission to journal acceptance was 180.93 days (SD = 103.89), (2) author submission to posting on PubMed was 263.55 days (SD = 157.61), and (3) journal acceptance to posting on PubMed was 83.15 days (SD = 135.72).
DISCUSSION: This study presents publication metadata for journals that openly provide it-a first step towards understanding publication timelines in HPE. Findings confirm the replicability of the original study, and the limited data suggest that, in comparison to biomedical scientists broadly, medical educators may experience longer wait times for article acceptance and publication. Reasons for these delays are currently unknown and deserve further study; such work would be facilitated by increased public access to journal metadata
Theory of equilibrium flux lattices in unconventional superconductors
We investigate equilibrium flux lattice structures in superconductors with
unconventional order parameters, such as high- cuprates, using a
generalized London model with non-local electrodynamics derived from a simple
microscopic model. We find a rich phase diagram containing triangular, centered
rectangular and square lattices with various orientations to the ionic lattice,
as a function of magnetic field and temperature.Comment: 4 pages, RevTeX, 2 PostScript figures included [The version to appear
in PRL. Stylistic changes in the text, a brief discussion of new results
involving the non-linear Meissner effect in the vortex lattice added.
Expansion of the Vortex Cores in YBa2Cu3O6.95 at Low Magnetic Fields
Muon spin rotation spectroscopy has been used to measure the effective size
of the vortex cores in optimally doped YBa2Cu3O6.95 as a function of
temperature and magnetic field deep in the superconducting state. While the
core size at H=2T is close to 20 angstroms and consistent with that measured by
STM at 6T, we find a striking increase in the core size at lower magnetic
fields, where it approaches an extraordinarily large value of about 100
angstroms. This suggests that the average value of the superconducting
coherence length in cuprate superconductors may be larger than previously
thought at low magnetic fields.Comment: 9 pages, 4 figures, 1 text fil
Field Induced Reduction of the Low Temperature Superfluid Density in YBa2Cu3O6.95
A novel high magnetic field (8 T) spectrometer for muon spin rotation has
been used to measure the temperature dependence of the in-plane magnetic
penetration depth in YBa2Cu3O6.95. At low H and low T, the penetration depth
exhibits the characteristic linear T dependence associated with the energy gap
of a d_x^2-y^2-wave superconductor. However, at higher fields the penetration
depth is essentially temperature independent at low T. We discuss possible
interpretations of this surprising new feature in the low-energy excitation
spectrum.Comment: 8 pages, 4 figures, 1 RevTex file and 4 postscript figure
Low Temperature Behavior of the Vortex Lattice in Unconventional Superconductors
We study the effect of the superconducting gap nodes on the vortex lattice
properties of high temperature superconductors at very low temperatures. The
nonlinear, nonlocal and nonanalytic nature of this effect is shown to have
measurable consequences for the vortex lattice geometry and the effective
penetration depth in the mixed state as measured by muon-spin-rotation
experiments.Comment: 3 figures and extensive discussion added, Version to appear in
September 1 issue of PR
Coordinated X-ray and Optical observations of Star-Planet Interaction in HD 17156
The large number of close-in Jupiter-size exoplanets prompts the question
whether star-planet interaction (SPI) effects can be detected. We focused our
attention on the system HD 17156, having a Jupiter-mass planet in a very
eccentric orbit. Here we present results of the XMM-Newton observations and of
a five months coordinated optical campaign with the HARPS-N spectrograph. We
observed HD 17156 with XMM-Newton when the planet was approaching the apoastron
and then at the following periastron passage, quasi simultaneously with
HARPS-N. We obtained a clear () X-ray detection only at the
periastron visit, accompanied by a significant increase of the
chromospheric index. We discuss two possible scenarios for the activity
enhancement: magnetic reconnection and flaring or accretion onto the star of
material tidally stripped from the planet. In any case, this is possibly the
first evidence of a magnetic SPI effect caught in action
- …