7,598 research outputs found
Magnetic structure of Ba(TiO)Cu(PO) probed using spherical neutron polarimetry
The antiferromagnetic compound Ba(TiO)Cu(PO) contains square
cupola of corner-sharing CuO plaquettes, which were proposed to form
effective quadrupolar order. To identify the magnetic structure, we have
performed spherical neutron polarimetry measurements. Based on symmetry
analysis and careful measurements we conclude that the orientation of the
Cu spins form a non-collinear in-out structure with spins approximately
perpendicular to the CuO motif. Strong Dzyaloshinskii-Moriya interaction
naturally lends itself to explain this phenomenon. The identification of the
ground state magnetic structure should serve well for future theoretical and
experimental studies into this and closely related compounds.Comment: 9 pages, 4 figure
The Problem on the Lattice
If the expression of the topological charge density operator, suggested by
fermions obeying the Ginsparg--Wilson relation, is employed, it is possible to
prove on the lattice the validity of the Witten--Veneziano formula for the
mass. Recent numerical results from simulations with overlap fermions
in 2 (abelian Schwinger model) and 4 (QCD) dimensions give values for the mass
of the lightest pseudo-scalar flavour-singlet state that agree with theoretical
expectations and/or experimental data.Comment: 3 pages, talk presented by G.C. Rossi at Lattice2001(theorydevelop
The extended structure of the dwarf irregular galaxy Sagittarius
We present a detailed study of the stellar and HI structure of the dwarf
irregular galaxy Sagittarius. We use new deep and wide field photometry to
trace the surface brightness profile of the galaxy out to ~5.0' (corresponding
to ~1600 pc) and down to mag/arcsec, thus showing that
the stellar body of the galaxy is much more extended than previously believed,
and it is similarly (or more) extended than the overall HI distribution. The
whole major-axis profile is consistent with a pure exponential, with a scale
radius of pc. The surface density maps reveal that the
distribution of old and intermediate-age stars is smooth and remarkably
flattened out to its edges, while the associated HI has a much rounder shape,
is off-centred and presents multiple density maxima and a significant hole. No
clear sign of systemic rotation is detectable in the complex HI velocity field.
No metallicity gradient is detected in the old and intermediate age population
of the galaxy, and we confirm that this population has a much more extended
distribution than young stars (age Gyr).Comment: 11 pages, 14 figures, accepted for publication on A&A. arXiv admin
note: text overlap with arXiv:1404.169
The near-IR counterpart of IGR J17480-2446 in Terzan 5
Some globular clusters in our Galaxy are noticeably rich in low-mass X-ray
binaries. Terzan 5 has the richest population among globular clusters of X- and
radio-pulsars and low-mass X-ray binaries. The detection and study of
optical/IR counterparts of low-mass X-ray binaries is fundamental to
characterizing both the low-mass donor in the binary system and investigating
the mechanisms of the formation and evolution of this class of objects. We aim
at identifying the near-IR counterpart of the 11 Hz pulsar IGRJ17480-2446
discovered in Terzan 5. Adaptive optics (AO) systems represent the only
possibility for studying the very dense environment of GC cores from the
ground. We carried out observations of the core of Terzan 5 in the near-IR
bands with the ESO-VLT NAOS-CONICA instrument. We present the discovery of the
likely counterpart in the Ks band and discuss its properties both in outburst
and in quiescence. Archival HST observations are used to extend our discussion
to the optical bands. The source is located at the blue edge of the turn-off
area in the color-magnitude diagram of the cluster. Its luminosity increase
from quiescence to outburst, by a factor 2.5, allows us to discuss the nature
of the donor star in the context of the double stellar generation population of
Terzan 5 by using recent stellar evolution models.Comment: 7 pages, 4 figure
The extended structure of the dwarf irregular galaxies Sextans A and Sextans B. Signatures of tidal distortion in the outskirts of the Local Group
We present a detailed study of the stellar and HI structure of the dwarf
irregular galaxies SextansA and SextansB, members of the NGC3109 association.
We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the
Surface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0
mag/arcsec^2. We find that both galaxies are significantly more extended than
what previously traced with surface photometry, out to ~4 kpc from their
centers along their major axis. Older stars are found to have more extended
distribution with respect to younger populations. We obtain the first estimate
of the mean metallicity for the old stars in SexB, from the color distribution
of the Red Giant Branch, =-1.6. The SB profiles show significant
changes of slope and cannot be fitted with a single Sersic model. Both galaxies
have HI discs as massive as their respective stellar components. In both cases
the HI discs display solid-body rotation with maximum amplitude of ~50 km/s
(albeit with significant uncertainty due to the poorly constrained
inclination), implying a dynamical mass ~10^{9}~M_sun, a mass-to-light ratio
M/L_V~25 and a dark-to-barionic mass ratio of ~10. The distribution of the
stellar components is more extended than the gaseous disc in both galaxies. We
find that the main, approximately round-shaped, stellar body of Sex~A is
surrounded by an elongated low-SB stellar halo that can be interpreted as a
tidal tail, similar to that found in another member of the same association
(Antlia). We discuss these, as well as other evidences of tidal disturbance, in
the framework of a past passage of the NGC3109 association close to the Milky
Way, that has been hypothesized by several authors and is also supported by the
recently discovered filamentary configuration of the association itself.Comment: Accepted for publication by A&A. PdfLateX, 16 pages, 11 figures, 2
appendice
On the Geometry of Surface Stress
We present a fully general derivation of the Laplace--Young formula and
discuss the interplay between the intrinsic surface geometry and the extrinsic
one ensuing from the immersion of the surface in the ordinary euclidean
three-dimensional space. We prove that the (reversible) work done in a general
surface deformation can be expressed in terms of the surface stress tensor and
the variation of the intrinsic surface metric
The innovation potential of Islamic crowdfunding platforms in contributing to sustainable development
Purpose: This paper aims at explaining variances in the contribution of Islamic crowdfunding platforms (ICFPs) to sustainable development (SD), by adopting an institutional logic perspective (ILP). ICFPs represent a dual institutional overlap between two logics (the Western-mainstream and the Islamic logic) which have an impact on corporate social responsibility (CSR) interpretations, practices, and decisions and whose conflicts are mitigated by choosing different resolution strategies. The authors aim at showing that this choice affects SD differently. Design/methodology/approach: The authors develop a conceptual typology through the following steps: (1) choice of variables and identification of corresponding variable domains, through literature review. Variables chosen are the elemental CSR dimensions related to various social and environmental corporate responsibilities to whom diverse meaning and emphasis are given under the Western-mainstream and Islamic logics. (2) Identification of three distinct ideal types of ICFPs, building on different resolution strategies to mitigate conflicts between logics; (3) development, for each ideal type, of a set of implications related to SD; (4) implementation of a first test aiming at assigning real cases to each ideal type. Findings: The authors identify Western-mimicking (platforms adopting as resolution strategy decoupling or compartmentalizing strategies), Islamic-driven (platforms focusing on one prevailing logic) and Syncretism-inspired (platforms adopting hybridizing practices) ideal-types. Originality/value: It is the first paper suggesting ILP to explain variances in crowdfunding platforms' role in addressing SD. It focuses on a specific type of CF platforms till now neglected
Myofascial trigger points alter the modular control during the execution of a reaching task: a pilot study
Myofascial trigger points (TP) constitute a conundrum in research and clinical practice as their etiopathogenesis is debated. Several studies investigating one or few muscles have shown that both active and latent TP causes an increased muscle activity, however the influence of TP on modular motor control during a reaching task is still unclear. Electromyographic signals, recorded from the muscles of the shoulder girdle and upper arm during a reaching task, were decomposed with Non-Negative Matrix Factorization algorithm. The extracted matrices of motor modules and activation signals were used to label the muscles condition as dominant or non-dominant. The presence of latent and active TP was detected in each muscle with manual examination. Despite a similar muscle activity was observed, we found that muscles with active TP had increased weighting coefficients when labeled in the dominant condition. No influences were found when muscles were in the non-dominant condition. These findings suggest that TP altered the motor control without co-contraction patterns. As a preliminary evidence, the present results suggest that the increased weighting coefficients in presence of TPs are associated with an alteration of the modular motor control without affecting the dimensionality of motor modules for each individual and reciprocal inhibition
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