3,128 research outputs found
The Reactivity of MgB2 with Common Substrate and Electronic Materials
The reactivity of MgB2 with powdered forms of common substrate and electronic
materials is reported. Reaction temperatures between 600 C and 800 C,
encompassing the range commonly employed in thin-film fabrication, were
studied. The materials tested for reactivity were ZrO2, yttria stabilized
zirconia (YSZ), MgO, Al2O3, SiO2, SrTiO3, TiN, TaN, AlN, Si, and SiC. At 600 C,
MgB2 reacted only with SiO2 and Si. At 800 C, however, reactions were observed
for MgB2 with Al2O3, SiO2, Si, SiC, and SrTiO3. The Tc of MgB2 decreased in the
reactions with SiC and Al2O3.Comment: 5 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
Lone Pair Effect, Structural Distortions and Potential for Superconductivity in Tl Perovskites
Drawing the analogy to BaBiO3, we investigate via ab-initio electronic
structure calculations potential new superconductors of the type ATlX3 with A =
Rb, Cs and X = F, Cl, and Br, with a particular emphasis on RbTlCl3. Based on
chemical reasoning, supported by the calculations, we show that Tl-based
perovskites have structural and charge instabilities driven by the lone pair
effect, similar to the case of BaBiO3, effectively becoming A2Tl1+Tl3+X6. We
find that upon hole doping of RbTlCl3, structures without Tl1+, Tl3+ charge
disproportionation become more stable, although the ideal cubic perovskite,
often viewed as the best host for superconductivity, should not be the most
stable phase in the system. The known superconductor (Sr,K)BiO3 and hole doped
RbTlCl3, predicted to be most stable in the same tetragonal structure, display
highly analogous calculated electronic band structures.Comment: 5 pages, 5 figure
(13)C NMR investigation of the superconductor MgCNi_3 up to 800K
We report (13)C NMR characterization of the new superconductor MgCNi_3 (He et
al., Nature (411), 54 (2001)). We found that both the uniform spin
susceptibility and the spin fluctuations show a strong enhancement with
decreasing temperature, and saturate below ~50K and ~20K respectively. The
nuclear spin-lattice relaxation rate 1/(13)T_1T exhibits typical behaviour for
isotropic s-wave superconductivity with a coherence peak below Tc=7.0K that
grows with decreasing magnetic field.Comment: Accepted for publication in Physical Review Letter
Therapeutic approaches with intravitreal injections in geographic atrophy secondary to age-related macular degeneration: current drugs and potential molecules
The present review focuses on recent clinical trials that analyze the efficacy of
intravitreal therapeutic agents for the treatment of dry age-related macular degeneration (AMD),
such as neuroprotective drugs, and complement inhibitors, also called immunomodulatory or
anti-inflammatory agents. A systematic literature search was performed to identify randomized
controlled trials published prior to January 2019. Patients affected by dry AMD treated with
intravitreal therapeutic agents were included. Changes in the correct visual acuity and reduction in
geographic atrophy progression were evaluated. Several new drugs have shown promising results,
including those targeting the complement cascade and neuroprotective agents. The potential action
of the two groups of drugs is to block complement cascade upregulation of immunomodulating
agents, and to prevent the degeneration and apoptosis of ganglion cells for the neuroprotectors,
respectively. Our analysis indicates that finding treatments for dry AMD will require continued
collaboration among researchers to identify additional molecular targets and to fully interrogate the
utility of pluripotent stem cells for personalized therapy
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
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