5,248 research outputs found
Universality of weakly bound dimers and Efimov trimers close to Li-Cs Feshbach resonances
We study the interspecies scattering properties of ultracold Li-Cs mixtures
in their two energetically lowest spin channels in the magnetic field range
between 800 G and 1000 G. Close to two broad Feshbach resonances we create
weakly bound LiCs dimers by radio-frequency association and measure the
dependence of the binding energy on the external magnetic field strength. Based
on the binding energies and complementary atom loss spectroscopy of three other
Li-Cs s-wave Feshbach resonances we construct precise molecular singlet and
triplet electronic ground state potentials using a coupled-channels
calculation. We extract the Li-Cs interspecies scattering length as a function
of the external field and obtain almost a ten-fold improvement in the precision
of the values for the pole positions and widths of the s-wave Li-Cs Feshbach
resonances as compared to our previous work [Pires \textit{et al.}, Phys. Rev.
Lett. \textbf{112}, 250404 (2014)]. We discuss implications on the Efimov
scenario and the universal geometric scaling for LiCsCs trimers
Universal three-body recombination and Efimov resonances in an ultracold Li-Cs mixture
We study Efimov resonances via three-body loss in an ultracold two-component
gas of fermionic Li and bosonic Cs atoms close to a Feshbach
resonance at 843~G, extending results reported previously [Pires \textit{et
al.}, Phys. Rev. Lett. 112, 250404 (2014)] to temperatures around 120~nK. The
experimental scheme for reaching lower temperatures is based upon compensating
the gravity-induced spatial separation of the mass-imbalanced gases with
bichromatic optical dipole traps. We observe the first and second excited
Li-Cs-Cs Efimov resonance in the magnetic field dependence of the three-body
event rate constant, in good agreement with the universal zero-range theory at
finite temperature [Petrov and Werner, Phys. Rev. A 92, 022704 (2015)].
Deviations are found for the Efimov ground state, and the inelasticity
parameter is found to be significantly larger than those for
single-species systems
XMM-Newton observations of the low-luminosity cataclysmic variable V405 Pegasi
V405 Peg is a low-luminosity cataclysmic variable (CV) that was identified as
the optical counterpart of the bright, high-latitude ROSAT all-sky survey
source RBS1955. The system was suspected to belong to a largely undiscovered
population of hibernating CVs. Despite intensive optical follow-up its subclass
however remained undetermined.
We want to further classify V405 Peg and understand its role in the CV zoo
via its long-term behaviour, spectral properties, energy distribution and
accretion luminosity.
We perform a spectral and timing analysis of \textit{XMM-Newton} X-ray and
ultra-violet data. Archival WISE, HST, and Swift observations are used to
determine the spectral energy distribution and characterize the long-term
variability.
The X-ray spectrum is characterized by emission from a multi-temperature
plasma. No evidence for a luminous soft X-ray component was found. Orbital
phase-dependent X-ray photometric variability by occurred without
significant spectral changes. No further periodicity was significant in our
X-ray data. The average X-ray luminosity during the XMM-Newton observations was
L_X, bol simeq 5e30 erg/s but, based on the Swift observations, the
corresponding luminosity varied between 5e29 erg/s and 2e31 erg/son timescales
of years.
The CV subclass of this object remains elusive. The spectral and timing
properties show commonalities with both classes of magnetic and non-magnetic
CVs. The accretion luminosity is far below than that expected for a standard
accreting CV at the given orbital period. Objects like V405 Peg might represent
the tip of an iceberg and thus may be important contributors to the Galactic
Ridge X-ray Emission. If so they will be uncovered by future X-ray surveys,
e.g. with eROSITA.Comment: A&A, in pres
Collapse of an ecological network in Ancient Egypt
The dynamics of ecosystem collapse are fundamental to determining how and why
biological communities change through time, as well as the potential effects of
extinctions on ecosystems. Here we integrate depictions of mammals from
Egyptian antiquity with direct lines of paleontological and archeological
evidence to infer local extinctions and community dynamics over a 6000-year
span. The unprecedented temporal resolution of this data set enables
examination of how the tandem effects of human population growth and climate
change can disrupt mammalian communities. We show that the extinctions of
mammals in Egypt were nonrandom, and that destabilizing changes in community
composition coincided with abrupt aridification events and the attendant
collapses of some complex societies. We also show that the roles of species in
a community can change over time, and that persistence is predicted by measures
of species sensitivity, a function of local dynamic stability. Our study is the
first high-resolution analysis of the ecological impacts of environmental
change on predator-prey networks over millennial timescales, and sheds light on
the historical events that have shaped modern animal communities
Recurrent focal myositis: a rare inflammatory myopathy
Focal myositis is an acute and localized muscle inflammation of unknown aetiology. The clinical diagnosis is often difficult to obtain, since it can be confused with infections, vascular thrombosis or muscle tumours such as sarcomas. This leads to a significant delay in the diagnosis, resulting in the administration of inappropriate and potentially harmful treatments. We report here a case of recurrent focal myositis in a woman where the diagnosis was only obtained after 6 years, despite multiple hospital admissions. This case reinforces the importance of clinical knowledge and experience to tackle challenging medical scenario
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