458 research outputs found
Pinpointing Gap Minima in Ba(FeCoAs \textit{via} Band Structure Calculations and Electronic Raman Scattering
A detailed knowledge of the gap structure for the Fe-pnictide superconductors
is still rather rudimentary, with several conflicting reports of either nodes,
deep gap minima, or fully isotropic gaps on the Fermi surface sheets, both in
the plane and along the c-axis. In this paper we present
considerations for electronic Raman scattering which can help clarify the gap
structure and topology using different light scattering geometries. Using
density functional calculations for the Raman vertices, it is shown that the
location of the gap minima may occur on loops stretching over a portion of the
c-axis in Ba(FeCoAs.Comment: 4+ pages, three figure
Band and momentum dependent electron dynamics in superconducting as seen via electronic Raman scattering
We present details of carrier properties in high quality single crystals obtained from electronic Raman
scattering. The experiments indicate a strong band and momentum anisotropy of
the electron dynamics above and below the superconducting transition
highlighting the importance of complex band-dependent interactions. The
presence of low energy spectral weight deep in the superconducting state
suggests a gap with accidental nodes which may be lifted by doping and/or
impurity scattering. When combined with other measurements, our observation of
band and momentum dependent carrier dynamics indicate that the iron arsenides
may have several competing superconducting ground states.Comment: 5 pages, 4 figure
A neutron scattering study of the interplay between structure and magnetism in Ba(FeCo)As
Single crystal neutron diffraction is used to investigate the magnetic and
structural phase diagram of the electron doped superconductor
Ba(FeCo)As. Heat capacity and resistivity measurements have
demonstrated that Co doping this system splits the combined antiferromagnetic
and structural transition present in BaFeAs into two distinct
transitions. For =0.025, we find that the upper transition is between the
high-temperature tetragonal and low-temperature orthorhombic structures with
( K) and the antiferromagnetic transition occurs at
K. We find that doping rapidly suppresses the
antiferromagnetism, with antiferromagnetic order disappearing at . However, there is a region of co-existence of antiferromagnetism and
superconductivity. The effect of the antiferromagnetic transition can be seen
in the temperature dependence of the structural Bragg peaks from both neutron
scattering and x-ray diffraction. We infer from this that there is strong
coupling between the antiferromagnetism and the crystal lattice
Quantum oscillations in the parent pnictide BaFeAs : itinerant electrons in the reconstructed state
We report quantum oscillation measurements that enable the direct observation
of the Fermi surface of the low temperature ground state of \ba122. From these
measurements we characterize the low energy excitations, revealing that the
Fermi surface is reconstructed in the antiferromagnetic state, but leaving
itinerant electrons in its wake. The present measurements are consistent with a
conventional band folding picture of the antiferromagnetic ground state,
placing important limits on the topology and size of the Fermi surface.Comment: 5 pages, 3 figure
A polarized neutron diffraction study of the field-induced magnetization in the normal and superconducting states of Ba(Fe1-xCox)2As2 (x=0.65)
We use polarised neutron diffraction to study the induced magnetization
density of near optimally doped Ba(Fe0.935Co0.065)2As2 (T_C=24 K) as a function
of magnetic field (1<H<9 T) and temperature (2<T<300 K). The T-dependence of
the induced moment in the superconducting state is consistent with the Yosida
function, characteristic of spin-singlet pairing. The induced moment is
proportional to applied field for H < 9 T ~ Hc2/6. In addition to the Yosida
spin-susceptibility, our results reveal a large zero-field contribution M
(H=>0,T=>0)/H ~ 2/3 \chi_{normal} which does not scale with the field or number
of vortices and is most likely due to the van Vleck susceptibility. Magnetic
structure factors derived from the polarization dependence of 15 Bragg
reflections were used to make a maximum entropy reconstruction of the induced
magnetization distribution in real space. The magnetization is confined to the
Fe atoms and the measured density distribution is in good agreement with LAPW
band structure calculations which suggest that the relevant bands near the
Fermi energy are of the d_{xz/yz} and d_{xy} type
Toll-like receptor 2 and 4 have opposing roles in the pathogenesis of cigarette smoke-induced chronic obstructive pulmonary disease
© 2018 American Physiological Society. All rights reserved. Chronic obstructive pulmonary disease (COPD) is the third leading cause of morbidity and death and imposes major socioeconomic burdens globally. It is a progressive and disabling condition that severely impairs breathing and lung function. There is a lack of effective treatments for COPD, which is a direct consequence of the poor understanding of the underlying mechanisms involved in driving the pathogenesis of the disease. Toll-like receptor (TLR)2 and TLR4 are implicated in chronic respiratory diseases, including COPD, asthma and pulmonary fibrosis. However, their roles in the pathogenesis of COPD are controversial and conflicting evidence exists. In the current study, we investigated the role of TLR2 and TLR4 using a model of cigarette smoke (CS)-induced experimental COPD that recapitulates the hallmark features of human disease. TLR2, TLR4, and associated coreceptor mRNA expression was increased in the airways in both experimental and human COPD. Compared with wild-type (WT) mice, CS-induced pulmonary inflammation was unaltered in TLR2-deficient (Tlr2-/-) and TLR4-deficient (Tlr4-/-) mice. CS-induced airway fibrosis, characterized by increased collagen deposition around small airways, was not altered in Tlr2-/- mice but was attenuated in Tlr4-/- mice compared with CS-exposed WT controls. However, Tlr2-/- mice had increased CS-induced emphy-sema-like alveolar enlargement, apoptosis, and impaired lung function, while these features were reduced in Tlr4-/- mice compared with CS-exposed WT controls. Taken together, these data highlight the complex roles of TLRs in the pathogenesis of COPD and suggest that activation of TLR2 and/or inhibition of TLR4 may be novel therapeutic strategies for the treatment of COPD
A microRNA-21-mediated SATB1/S100A9/NF-κB axis promotes chronic obstructive pulmonary disease pathogenesis.
[Figure: see text]
Quantitative imaging of concentrated suspensions under flow
We review recent advances in imaging the flow of concentrated suspensions,
focussing on the use of confocal microscopy to obtain time-resolved information
on the single-particle level in these systems. After motivating the need for
quantitative (confocal) imaging in suspension rheology, we briefly describe the
particles, sample environments, microscopy tools and analysis algorithms needed
to perform this kind of experiments. The second part of the review focusses on
microscopic aspects of the flow of concentrated model hard-sphere-like
suspensions, and the relation to non-linear rheological phenomena such as
yielding, shear localization, wall slip and shear-induced ordering. Both
Brownian and non-Brownian systems will be described. We show how quantitative
imaging can improve our understanding of the connection between microscopic
dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of
methodology. Submitted for special volume 'High Solid Dispersions' ed. M.
Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009);
22 pages, 16 fig
'You were quiet - I did all the marching': Research processes involved in hearing the voices of South Asian girls
This article is available open access through the publisher’s website at the link below. Copyright @ 2011
A B
Academic
Publishers.This article provides insights into the outcomes of reflection following two interview approaches used to explore narratives of the lived, individual experiences of South-Asian girls living in West London. In attempting to illuminate and re-present the cultural experiences as told by these girls, the choice of interview approach became critical in allowing the voices to be effectively heard (Rogers, 2005). This article therefore considers how a semi-structured interview approach offered valuable insights into the girls' experiences but became constraining for both researcher and participant in unveiling the complexity and depth of their lives. These constraints emerged through reflection by both participants and researcher. As a result of reflexivity during the research process, the researcher moved towards the use of research conversations during the second phase of the study. Ultimately the study revealed how the girls felt empowered by the opportunity to narrate their individual experiences and tell of their lives. In narrating their reflections on being part of the research, there was a clear recognition that the process facilitated the articulation of new voices and ‘multi-voicedness’ (Moen, 2006
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