1,162 research outputs found
Small-scale magnetic flux emergence in the quiet Sun
Small bipolar magnetic features are observed to appear in the interior of
individual granules in the quiet Sun, signaling the emergence of tiny magnetic
loops from the solar interior. We study the origin of those features as part of
the magnetoconvection process in the top layers of the convection zone. Two
quiet-Sun magnetoconvection models, calculated with the
radiation-magnetohydrodynamic (MHD) Bifrost code and with domain stretching
from the top layers of the convection zone to the corona, are analyzed. Using
3D visualization as well as a posteriori spectral synthesis of Stokes
parameters, we detect the repeated emergence of small magnetic elements in the
interior of granules, as in the observations. Additionally, we identify the
formation of organized horizontal magnetic sheets covering whole granules. Our
approach is twofold, calculating statistical properties of the system, like
joint probability density functions (JPDFs), and pursuing individual events via
visualization tools. We conclude that the small magnetic loops surfacing within
individual granules in the observations may originate from sites at or near the
downflows in the granular and mesogranular levels, probably in the first 1 or
1.5 Mm below the surface. We also document the creation of granule-covering
magnetic sheet-like structures through the sideways expansion of a small
subphotospheric magnetic concentration picked up, and pulled out of the
interior, by a nascent granule. The sheet-like structures we found in the
models may match the recent observations of Centeno et al. (2017).Comment: 9 pages, 5 figures, Published in The Astrophysical Journal Letter
Stabilization of the Kawahara-Kadomtsev-Petviashvili equation with time-delayed feedback
Results of stabilization for the higher order of the Kadomtsev-Petviashvili
equation are presented in this manuscript. Precisely, we prove with two
different approaches that under the presence of a damping mechanism and an
internal delay term (anti-damping) the solutions of the
Kawahara-Kadomtsev-Petviashvili equation are locally and globally exponentially
stable. The main novelty is that we present the optimal constant, as well as
the minimal time, that ensures that the energy associated with this system goes
to zero exponentially
Capital Fixity and Mobility in Response to the 2008-09 Crisis: Variegated Neoliberalism in Mexico and Turkey
The article examines the 2008-9 crisis responses in Mexico and Turkey as examples of variegated neoliberalism. The simultaneous interests of corporations and banks relative to the national fixing of capital and their mobility in the form of global investment heavily influenced each state authorityâs policy responses to the crisis at the expense of the interests of the poor, workers, and peasantry. Rather than pitching this as either evidence of persistent national differentiation or some Keynesian state resurgence, we argue from a historical materialist geographical framework that the responses of capital and state authorities in Mexico and Turkey actively constitute and reconstitute the global parameters of market regulatory design and neoliberal class rule through each stateâs distinct domestic policy formation and crisis management processes. While differing in specific content the form of Mexico and Turkeyâs state responses to the crisis ensured continuity in their foregoing neoliberal strategies of development and capital accumulation, most notably in the continued oppression of workers. That is, the prevailing strategy of accumulation continues to be variegated neoliberalism
Suppression of ferromagnetic ordering in doped manganites: Effects of the superexchange interaction
From a Monte Carlo study of the ferromagnetic Kondo lattice model for doped
manganites, including the antiferromagnetic superexchange interaction
(), we found that the ferromagnetic ordering was suppressed as
increased. The ferromagnetic transition temperature , as obtained from a
mean field fit to the calculated susceptibilities, was found to decrease
monotonically with increasing . Further, the suppression in
scales with the bandwidth narrowing induced by the antiferromagnetic
frustration originating from . From these results, we propose that the
change in the superexchange interaction strength between the electrons
of the Mn ions is one of the mechanisms responsible for the suppression in
observed in manganites of the type
(LaPr)CaMnO.Comment: 5 pages, 6 figures. To appear in PR
Observation of insulator-metal transition in EuNiO under high pressure
The charge transfer antiferromagnetic (T =220 K) insulator EuNiO
undergoes, at ambient pressure, a temperature-induced metal insulator MI
transition at T=463 K. We have investigated the effect of pressure (up
to p~20 GPa) on the electronic, magnetic and structural properties of
EuNiO using electrical resistance measurements, {151}^Eu nuclear
resonance scattering of synchrotron radiation and x-ray diffraction,
respectively. With increasing pressure we find at p =5.8 GPa a transition
from the insulating state to a metallic state, while the orthorhombic structure
remains unchanged up to 20 GPa. The results are explained in terms of a gradual
increase of the electronic bandwidth with increasing pressure, which results in
a closing of the charge transfer gap. It is further shown that the
pressure-induced metallic state exhibits magnetic order with a lowervalue of
T (T ~120 K at 9.4 GPa) which disappears between 9.4 and 14.4 GPa.Comment: 10 pages, 3 figure
Evaluation of physical and chemical soil properties under different management types in the south-western Colombian Andes
Aim of study: Evaluating the variability of physical and chemical soil properties under different soil uses in an experimental farmland of the southwestern Colombian Andes.Area of study: This research was conducted at the Botana Experimental Farm in the mountainous area of Nariño, at the south-western Colombia.Material and methods: nine soil variables were measured under six soil uses which included traditional agriculture, agroforestry systems, and a 67-year-old secondary forest that was used as a reference for comparisons with other soil uses. Data was analyzed through Principal Component Analysis and Duncanâs tests.Main results: organic carbon, cation exchange capacity, clay contents and base saturation were the variables with higher variability among soil uses. The secondary forest and an agroforestry system with alley-cropped wax laurel showed the best soil conditions, whilst pastures and monoculture potato crop plots showed the least desirable conditions for all variables.Research highlights: We found that soils under alley-crop with wax laurel presented the characteristics most similar to the secondary forest. Conversely, soils under alley-crop with alder resembled the soils under intensive management (pasture and potato monocrop); which is related to the inadequate management of this agroforestry systems, provoking that the woody component does not accomplish its goal when implemented.Keywords: soil; agroforestry systems; Andes; forest.Abbreviations used: ACAL, Alley cropping of Alder Trees, ACWL; Alley cropping of Wax Laurel; AFS, agroforestry systems; AWC, available water capacity; BD, Bulk Density; BS, Base saturation; CEC, Cation Exchange Capacity; CLA, Clay; CI, Confidence Intervals, INF, Infiltration; ANOVA, Analysis of Variance; OC, Soil Organic Carbon; PAST, Pasture; PCA, Principal Component Analysis; PC, Principal Component; POCR, Potato Crop; POR, Soil Porosity; SCAL, Scattered Alder Trees; SEFO, Secondary Forest; SU, soil uses; AU, Animal unit
H-alpha kinematics of S4G spiral galaxies-II. Data description and non-circular motions
We present a kinematical study of 29 spiral galaxies included in the Spitzer
Survey of Stellar Structure in Galaxies, using Halpha Fabry-Perot data obtained
with the Galaxy Halpha Fabry-Perot System instrument at the William Herschel
Telescope in La Palma, complemented with images in the R-band and in Halpha.
The primary goal is to study the evolution and properties of the main
structural components of galaxies through the kinematical analysis of the FP
data, complemented with studies of morphology, star formation and mass
distribution. In this paper we describe how the FP data have been obtained,
processed and analysed. We present the resulting moment maps, rotation curves,
velocity model maps and residual maps. Images are available in FITS format
through the NASA/IPAC Extragalactic Database and the Centre de Donn\'ees
Stellaires. With these data products we study the non-circular motions, in
particular those found along the bars and spiral arms. The data indicate that
the amplitude of the non-circular motions created by the bar does not correlate
with the bar strength indicators. The amplitude of those non-circular motions
in the spiral arms does not correlate with either arm class or star formation
rate along the spiral arms. This implies that the presence and the magnitude of
the streaming motions in the arms is a local phenomenon.Comment: 23 pages, 14 figures, without appendices, accepted to be published in
MNRA
Above-bandgap ordinary optical properties of GaSe single crystal
We report above-bandgap ordinary optical properties of Δ-phase GaSe single crystal. Reference-quality pseudodielectric function ăΔ(E)ă = ăΔ1(E)ă+iăΔ2(E)ă and pseudorefractive index ăN(E)ă = ăn(E)ă+iăk(E)ă spectra were measured by spectroscopic ellipsometry from 0.73âtoâ6.45âeV at room temperature for the light polarization perpendicular to the optic axis (mathâ„math). The ăΔă spectrum exhibited several interband-transition critical-point structures. Analysis of second-energy derivatives calculated numerically from the measured data yielded the critical-point energy [email protected]
Slow dynamics of the contact process on complex networks
The Contact Process has been studied on complex networks exhibiting different
kinds of quenched disorder. Numerical evidence is found for Griffiths phases and other
rare region effects, in ErdËos RĂ©nyi networks, leading rather generically to anomalously
slow (algebraic, logarithmic,...) relaxation. More surprisingly, it turns out that Griffiths
phases can also emerge in the absence of quenched disorder, as a consequence of sole
topological heterogeneity in networks with finite topological dimension. In case of scalefree
networks, exhibiting infinite topological dimension, slow dynamics can be observed
on tree-like structures and a superimposed weight pattern. In the infinite size limit the
correlated subspaces of vertices seem to cause a smeared phase transition. These results
have a broad spectrum of implications for propagation phenomena and other dynamical
process on networks and are relevant for the analysis of both models and empirical data
Are anti-ganglioside antibodies detectable in serum from patients with critical illness myopathy and polyneuropathy?
Introduction: Critical illness myopathy (CIM) and polyneuropathy (CIP) are the most common cause of acquired weakness in intensive care units (ICU). However, its exact pathogenesis remains unclear. Abnormal excitability of muscle due to a sodium channelopathy is one of the mechanisms proposed. The aim of this study is to test for the presence of anti-ganglioside antibodies in serum from patients with CIM or both combined CIM/CIP, since there is evidence that they can cause reversible dysfunction of voltage-gated sodium channels.Methods: In a prospective way, we studied 35 patients admitted in ICU by weekly EMG. When positive spontaneous activity (PSA) was detected, a muscle biopsy was performed. Twenty patients met criteria of CIM; five of them also developed overlapping CIP. We did not detect any kind of abnormality in 10 patients during the follow up period. Sera were analyzed for the presence of anti-ganglioside antibodies (Ganglioside-profile 2 Euroline, Euroimmun). Results: Overall, positive reactivity against anti-GT1b was found in one patient with CIM, representing 2.8% (1/35) of the total sample.Conclusion: Reduced percentage of patients affected of CIM or CIM/CIP exhibits positive reactive against anti-ganglioside antibodies. Thus, it could be suggested they do not play a primary role in their pathogenesis. Key words: Critical illness myopathy, critical illness polineuropathy, difficult weaning, channelopathy, muscle fiber inexcitability, anti-ganglioside antibodies  DOI: http://dx.doi.org/10.17268/rmt.2020.v15i01.0
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