18,728 research outputs found
Persistence of the valence bond glass state in the double perovskites Ba2-xSrxYMoO6
Peer reviewedPublisher PD
Passivity-based harmonic control through series/parallel damping of an H-bridge rectifier
Nowadays the H-bridge is one of the preferred solutions to connect DC loads or distributed sources to the single-phase grid. The control aims are: sinusoidal grid current with unity power factor and optimal DC voltage regulation capability. These objectives should be satisfied, regardless the conditions of the grid, the DC load/source and the converter nonlinearities. In this paper a passivity-based approach is thoroughly investigated proposing a damping-based solution for the error dynamics. Practical experiments with a real converter validate the analysis.
Valence bond glass on an fcc lattice in the double perovskite Ba2YMoO6
Peer reviewedPublisher PD
Deuteron Magnetic Quadrupole Moment From Chiral Effective Field Theory
We calculate the magnetic quadrupole moment (MQM) of the deuteron at leading
order in the systematic expansion provided by chiral effective field theory. We
take into account parity and time-reversal violation which, at the quark-gluon
level, results from the QCD vacuum angle and dimension-six operators that
originate from physics beyond the Standard Model. We show that the deuteron MQM
can be expressed in terms of five low-energy constants that appear in the
parity- and time-reversal-violating nuclear potential and electromagnetic
current, four of which also contribute to the electric dipole moments of light
nuclei. We conclude that the deuteron MQM has an enhanced sensitivity to the
QCD vacuum angle and that its measurement would be complementary to the
proposed measurements of light-nuclear EDMs
Chiral separation by enantioselective liquid–liquid extraction
The literature on enantioselective liquid–liquid extraction (ELLE) spans more than half a century of research. Nonetheless, a comprehensive overview has not appeared during the past few decades. Enantioselective liquid–liquid extraction is a technology of interest for a wide range of chemists and chemical engineers in the fields of fine chemicals, pharmaceuticals, agrochemicals, fragrances and foods. In this review the principles and advances of resolution through enantioselective liquid–liquid extraction are discussed, starting with an introduction on the principles of enantioselective liquid–liquid extraction including host–guest chemistry, extraction and phase transfer mechanisms, and multistage liquid–liquid extraction processing. Then the literature on enantioselective liquid–liquid extraction systems is reviewed, structured on extractant classes. The following extractant classes are considered: crown ether based extractants, metal complexes and metalloids, extractants based on tartrates, and a final section with all other types of chiral extractants.
Unraveling models of CP violation through electric dipole moments of light nuclei
We show that the proposed measurements of the electric dipole moments of
light nuclei in storage rings would put strong constraints on models of
flavor-diagonal CP violation. Our analysis is exemplified by a comparison of
the Standard Model including the QCD theta term, the minimal left-right
symmetric model, a specific version of the so-called aligned two-Higgs doublet
model, and briefly the minimal supersymmetric extension of the Standard Model.
By using effective field theory techniques we demonstrate to what extend
measurements of the electric dipole moments of the nucleons, the deuteron, and
helion could discriminate between these scenarios. We discuss how measurements
of electric dipole moments of other systems relate to the light-nuclear
measurements.Comment: Published versio
The evolved circumbinary disk of AC Her: a radiative transfer, interferometric and mineralogical study
We aim to constrain the structure of the circumstellar material around the
post-AGB binary and RV Tauri pulsator AC Her. We want to constrain the spatial
distribution of the amorphous as well as of the crystalline dust. We present
very high-quality mid-IR interferometric data that were obtained with
MIDI/VLTI. We analyse the MIDI data and the full SED, using the MCMax radiative
transfer code, to find a good structure model of AC Her's circumbinary disk. We
include a grain size distribution and midplane settling of dust
self-consistently. The spatial distribution of crystalline forsterite in the
disk is investigated with the mid-IR features, the 69~m band and the
11.3~m signatures in the interferometric data. All the data are well
fitted. The inclination and position angle of the disk are well determined at
i=50+-8 and PA=305+-10. We firmly establish that the inner disk radius is about
an order of magnitude larger than the dust sublimation radius. Significant
grain growth has occurred, with mm-sized grains being settled to the midplane
of the disk. A large dust mass is needed to fit the sub-mm fluxes. By assuming
{\alpha}=0.01, a good fit is obtained with a small grain size power law index
of 3.25, combined with a small gas/dust ratio <10. The resulting gas mass is
compatible with recent estimates employing direct gas diagnostics. The spatial
distribution of the forsterite is different from the amorphous dust, as more
warm forsterite is needed in the surface layers of the inner disk. The disk in
AC Her is very evolved, with its small gas/dust ratio and large inner hole.
Mid-IR interferometry offers unique constraints, complementary to mid-IR
features, for studying the mineralogy in disks. A better uv coverage is needed
to constrain in detail the distribution of the crystalline forsterite in AC
Her, but we find strong similarities with the protoplanetary disk HD100546.Comment: update with final version published in A&
Clustering and light profiles of galaxies in the environment of 20 Ultra Steep Spectrum Radio sources
We have analyzed galaxy properties in the neighborhood of 20 Ultra-Steep
Spectrum Radio sources (USS) taken from the WISH catalog of De Breuck et al.
(2002). Galaxies in these USS fields were identified in deep observations that
were carried out in the K'-band using the OSIRIS imager at the CTIO 4m
telescope. We find a statistically significant signal of clustering around our
sample of USS. The angular extension of the detected USS-galaxy clustering is
theta_c~20" corresponding to a spatial scale ~120 h^{-1}kpc, assuming the
sources are at z~1 in a Omega_m=0.3, Omega_{\Lambda}=0.7 model universe. These
results are in agreement with those obtained by Best (2000) for radio
galaxy-galaxy correlation, and Best et al. (2003) for radio-loud AGN-galaxy
correlation. We have also analyzed the light distribution of the galaxies by
fitting Sersic's law profiles. Our results show no significant dependence of
the galaxy shape parameters on the projected distance to the USS.Comment: Accepted for its publication in Astronomical Journal, 9 figure
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