1,657 research outputs found
Broadband transverse susceptibility in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22
Producción CientíficaNoncollinear spin systems with magnetically induced ferroelectricity from changes in spiral magnetic ordering have attracted significant interest in recent research due to their remarkable magnetoelectric effects with promising applications. Single phase multiferroics are of great interest for these new multifunctional devices, being Y-type hexaferrites good candidates, and among them the ZnY compounds due to their ordered magnetic behaviour over room temperature. Polycrystalline Y type hexaferrites with composition Ba0.5Sr1.5Zn2Fe2O22 (BSZFO) were sintered in 1050 °C–1250 °C temperature range. Transverse susceptibility measurements carried out on these BSZFO samples in the temperature range 80–350 K with DC fields up to ± 5000 Oe reveal different behaviour depending on the sintering temperature. Sample sintered at 1250 °C is qualitatively different, suggesting a mixed Y and Z phase like CoY hexaferrites. Sintering at lower temperatures produce single phase Y-type, but the transverse susceptibility behaviour of the sample sintered at 1150 °C is shifted at temperatures 15 K higher. Regarding the DC field sweeps the observed behaviour is a peak that shifts to lower values with increasing temperature, and the samples corresponding to single Y phase exhibit several maxima and minima in the 250 K–330 K range at low DC applied field as a result of the magnetic field induced spin transitions in this compound.Ministerio de Ciencia, Innovación y Universidades; Agencia Estatal de Investigación with FEDER (MAT2016-80784-P
Reversible Graphene decoupling by NaCl photo-dissociation
We describe the reversible intercalation of Na under graphene on Ir(111) by
photo-dissociation of a previously adsorbed NaCl overlayer. After room
temperature evaporation, NaCl adsorbs on top of graphene forming a bilayer.
With a combination of electron diffraction and photoemission techniques we
demonstrate that the NaCl overlayer dissociates upon a short exposure to an
X-ray beam. As a result, chlorine desorbs while sodium intercalates under the
graphene, inducing an electronic decoupling from the underlying metal. Low
energy electron diffraction shows the disappearance of the moir\'e pattern when
Na intercalates between graphene and iridium. Analysis of the Na 2p core-level
by X-ray photoelectron spectroscopy shows a chemical change from NaCl to
metallic buried Na at the graphene/Ir interface. The intercalation-decoupling
process leads to a n-doped graphene due to the charge transfer from the Na, as
revealed by constant energy angle resolved X-ray photoemission maps. Moreover,
the process is reversible by a mild annealing of the samples without damaging
the graphene
The commons and anti-commons problems in the tourism economy
Countries specialised in tourism tend to face two problems with contradictory effects: the commons and the anti-commons, which lead to tourism over- and under-production, respectively. This paper develops a two-period model to analyse the joint effects of both problems on a small and remote tourism economy. Congestion and the complementariness between foreign transport and local tourism services are key features in this type of markets. As a result, direct selling and the presence of foreign tour-operators emerge as possible market arrangements with different implications in terms of welfare and public intervention. Four main results are obtained. First, in the direct selling situation the optimal policy depends on the relative importance of the problems. Second, the existence of tour-operators always leads to tourism over-production. Third, the presence of a single tour-operator does not solve the congestion problem. Lastly, the switch from several tour-operators to a single one is welfare reducing.commons, anti-commons, tourism, direct selling, tour-operators, optimal policy
High angular resolution near-infrared integral field observations of young star cluster complexes in NGC1365
This paper presents and examines new near-infrared integral field
observations of the three so-called 'embedded star clusters' located in the
nuclear region of NGC1365. Adaptive-optics- corrected K-band data cubes were
obtained with the ESO/VLT instrument SINFONI. The continuum in the K-band and
emission lines such as HeI, Bracket-gamma, and several H2 lines were mapped at
an achieved angular resolution of 0.2arcsec over a field of 3x3arcsec^2 around
each source. We find that the continuum emission of the sources is spatially
resolved. This means that they are indeed cluster complexes confined to regions
of about 50pc extension. We performed robust measurements of the equivalent
width of the CO absorption band at 2.3micro and of Bracket-gamma. For the main
mid-infrared bright sources, the data only allow us to determine an upper limit
to the equivalent width of the CO bands. Under the assumption of an
instantaneously formed standard initial mass function Starburst99 model, the
new measurements are found to be incompatible with previously published
mid-infrared line ratios. We show that an upper mass limit of 25 to 30 solar
masses, lower than the typically assumed 100solar masses, allows one to simply
remove this inconsistency. For such a model, the measurements are consistent
with ages in the range of 5.5Myr to 6.5Myr, implying masses in the range from 3
to 10 x 10^6 solar masses. We detect extended gas emission both in HII and H2.
We argue that the central cluster complexes are the sources of excitation for
the whole nebulae, through ionisation and shock heating. We detect a blue wing
on the Bracket-gamma emission profile, suggesting the existence of gas outflows
centred on the cluster complexes. We do not find any evidence for the presence
of a lower mass cluster population, which would fill up a 'traditional' power
law cluster mass function.Comment: 15 pages, 10 figures, accepted for publication in A&
Broadband transverse susceptibility in multiferroic Y-type hexaferrite BaSrCoFeO
Single phase multiferroics in which ordered magnetic and ferroelectricity
coexist, are of great interest for new multifunctional devices, and among them
Y-type hexaferrites are good candidates. Transverse susceptibility
measurements, which have been proved to be a versatile tool to study singular
properties of bulk and nanoparticle magnetic systems, have been carried out
with a broadband system on polycrystalline Y type hexaferrites with composition
BaSrCoFeO, optimal to exhibit multiferroic
properties. In the temperature range 80-350 K transverse susceptibility
measurements with DC fields up to 5000 Oe reveal different behaviour
depending on the sintering temperature. The thermal evolution of the anisotropy
field peak exhibit four regions with different slopes: positive in 80-130 K,
negative in 130-200 K, constant in 200-280 K and negative in 280-350 K, which
can be considered a signature of spin transitions in this compound.Comment: arXiv admin note: substantial text overlap with arXiv:2401.1614
Constraint on the time variation of the fine-structure constant with the SDSS-III/BOSS DR12 quasar sample
From the Sloan Digital Sky Survey (SDSS) Data Release 12, which covers the
full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate
the possible variation of the fine-structure constant over cosmological
time-scales. We analyse the largest quasar sample considered so far in the
literature, which contains 13175 spectra (10363 from SDSS-III/BOSS DR12 + 2812
from SDSS-II DR7) with redshift 1. We apply the emission-line method on
the [O III] doublet (4960, 5008 A) and obtain for the relative variation of the fine-structure
constant. We also investigate the possible sources of systematics:
misidentification of the lines, sky OH lines, H and broad line
contamination, Gaussian and Voigt fitting profiles, optimal wavelength range
for the Gaussian fits, chosen polynomial order for the continuum spectrum,
signal-to-noise ratio and good quality of the fits. The uncertainty of the
measurement is dominated by the sky subtraction. The results presented in this
work, being systematics limited, have sufficient statistics to constrain
robustly the variation of the fine-structure constant in redshift bins ( 0.06) over the last 7.9 Gyr. In addition, we study the [Ne III]
doublet (3870, 3969 A) present in 462 quasar spectra and discuss the systematic
effects on using these emission lines to constrain the fine-structure constant
variation. Better constraints on (10) using
the emission-line method would be possible with high-resolution spectroscopy
and large galaxy/qso surveys.Comment: 16 pages, 16 figures. Version published in MNRAS. Analysis enlarged,
public catalogue now availabl
Explaining High Economic Growth in Small Tourism Countries with a Dynamic General Equilibrium Model
This paper shows that tourism specialisation can help to explain the observed high growth rates of small countries. For this purpose, two models of growth and trade are constructed to represent the trade relations between two countries. One of the countries is large, rich, has an own source of sustained growth and produces a tradable capital good. The other is a small poor economy, which does not have an own engine of growth and produces tradable tourism services. The poor country exports tourism services to and imports capital goods from the rich economy. In one model tourism is a luxury good, while in the other the expenditure elasticity of tourism imports is unitary. Two main results are obtained. In the long run, the tourism country overcomes decreasing returns and permanently grows because its terms of trade continuously improve. Since the tourism sector is relatively less productive than the capital good sector, tourism services become relatively scarcer and hence more expensive than the capital good. Moreover, along the transition the growth rate of the tourism economy holds well above the one of the rich country for a long time. The growth rate differential between countries is particularly high when tourism is a luxury good. In this case, there is a faster increase in the tourism demand. As a result, investment of the small economy is boosted and its terms of trade highly improve
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