2,118 research outputs found
Magnetic behaviour of PrPd2B2C
We have synthesized a new quaternary borocarbide PrPdBC and
measured its magnetization, electrical resistivity and specific heat. The
compound crystallizes in the LuNiBC-type tetragonal structure
(space group {\it I4/mmm}). Above 100 K the magnetic susceptibility follows
Curie-Weiss behavior with effective moment = 3.60 , which
is very close to the value expected for Pr ions. We do not find evidence
for magnetic or superconducting transition down to 0.5 K. Specific heat
exhibits a broad Schottky type anomaly with a peak at 24 K, very likely related
to crystal electric field (CEF) excitation. The magnetic properties suggest the
presence of a singlet CEF ground state leading to a Van-Vleck paramagnetic
ground state.Comment: 2 pages, 2 figure
Evolution of magnetic fluctuations through the Fe-induced paramagnetic to ferromagnetic transition in CrB
In itinerant ferromagnets, the quenched disorder is predicted to dramatically
affect the ferromagnetic to paramagnetic quantum phase transition driven by
external control parameters at zero temperature. Here we report a study on
Fe-doped CrB, which, starting from the paramagnetic parent, orders
ferromagnetically for Fe-doping concentrations larger than \%. In parent CrB, B nuclear magnetic resonance data reveal
the presence of both ferromagnetic and antiferromagnetic fluctuations. The
latter are suppressed with Fe-doping, before the ferromagnetic ones finally
prevail for . Indications for non-Fermi liquid behavior, usually
associated with the proximity of a quantum critical point, were found for all
samples, including undoped CrB. The sharpness of the ferromagnetic-like
transition changes on moving away from , indicating significant
changes in the nature of the magnetic transitions in the vicinity of the
quantum critical point. Our data provide constraints for understanding quantum
phase transitions in itinerant ferromagnets in the limit of weak quenched
disorder.Comment: 8 pages, 7 figure
Insights on star formation histories and physical properties of Herschel-detected galaxies
We test the impact of using variable star forming histories (SFHs) and the
use of the IR luminosity (LIR) as a constrain on the physical parameters of
high redshift dusty star-forming galaxies. We explore in particular the stellar
properties of galaxies in relation with their location on the SFR-M* diagram.
We perform SED fitting of the UV-NIR and FIR emissions of a large sample of
GOODS-Herschel galaxies, for which rich multi-wavelength observations are
available. We test different SFHs and imposing energy conservation in the SED
fitting process, to face issues like the age-extinction degeneracy and produce
SEDs consistent with observations. Our models work well for the majority of the
sample, with the notable exception of the high LIR end, for which we have
indications that our simple energy conservation approach cannot hold true. We
find trends in the SFHs fitting our sources depending on stellar mass M* and z.
Trends also emerge in the characteristic timescales of the SED models depending
on the location on the SFR-M* diagram. We show that whilst using the same
available observational data, we can produce galaxies less star-forming than
usually inferred, if we allow declining SFHs, while properly reproducing their
observables. These sources can be post-starbursts undergoing quenching, and
their SFRs are potentially overestimated if inferred from their LIR. Fitting
without the IR constrain leads to a strong preference for declining SFHs, while
its inclusion increases the preference of rising SFHs, more so at high z, in
tentative agreement with the cosmic star formation history. Keeping in mind
that the sample is biased towards high LIR, the evolution shaped by our model
appears as both bursty (initially) and steady-lasting (later on). The global
SFH of the sample follows the cosmic SFH with a small scatter, and is
compatible with the "downsizing" scenario of galaxy evolution.Comment: 28 pages, 26 figures, one appendix, Accepted for publication in
Astronomy & Astrophysic
Superconductivity in Dense Wires
becomes superconducting just below 40 K. Whereas porous
polycrystalline samples of can be synthesized from boron powders, in
this letter we demonstrate that dense wires of can be prepared by
exposing boron filaments to vapor. The resulting wires have a diameter of
160 , are better than 80% dense and manifest the full shielding in the superconducting state. Temperature-dependent
resistivity measurements indicate that is a highly conducting metal in
the normal state with = 0.38 -. Using this value, an
electronic mean free path, can be estimated, indicating
that wires are well within the clean limit. , , and
data indicate that manifests comparable or better superconducting
properties in dense wire form than it manifests as a sintered pellet.Comment: Figures' layout fixe
Management of patients with Graves' disease and orbital involvement: role of spectral domain optical coherence tomography
PURPOSE:
To investigate the role of choroidal thickness evaluation with spectral domain optical coherence tomography (SDOCT) and enhanced depth imaging (EDI) technique in the management of patients with Graves' disease and orbitopathy (GO).
METHODS:
Thirty-six eyes of 18 patients with GO and 36 eyes of 18 age-matched control subjects were included in this retrospective observational study. All the subjects underwent a complete ophthalmological evaluation, including clinical activity score (CAS) and exophthalmometry. The SDOCT images of the choroid were obtained by EDI modality.
RESULTS:
Choroidal thickness was significantly increased in GO than in control eyes (p < 0.01). A significant correlation was found between choroidal thickness and CAS, proptosis, and the duration of disease (p < 0.05).
CONCLUSION:
This study shows that choroidal thickness, evaluated with EDI-OCT, is significantly increased in patients with GO and correlates with the activity of the disease, proptosis, and duration of the disease. The choroidal thickening may reflect the ocular hemodynamic changes, and enhanced depth imaging optical coherence tomography may be a useful tool for the evaluation of orbital congestion and management of patients with Graves' disease and orbital involvement
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