3,545 research outputs found
Comment on "X-ray resonant scattering studies of orbital and charge ordering in Pr1-xCaxMnO3"
In a recent published paper [Phys. Rev. B 64, 195133 (2001)], Zimmermann et
al. present a systematic x-ray scattering study of charge and orbital ordering
phenomena in the Pr1-xCaxMnO3 series with x= 0.25, 0.4 and 0.5. They propose
that for Ca concentrations x=0.4 and 0.5, the appearance of (0, k+1/2, 0)
reflections are originated by the orbital ordering of the eg electrons in the
a-b plane while the (0, 2k+1, 0) reflections are due to the charge ordering
among the Mn3+ and Mn4+ ions. Moreover, for small Ca concentrations (x<0.3),
the orbital ordering is only considered and it occurs at (0, k, 0) reflections.
A rigorous analysis of all these resonance reflections will show the inadequacy
of the charge-orbital model proposed to explain the experimental results. In
addition, this charge-orbital model is highly inconsistent with the electronic
balance. On the contrary, these reflections can be easily understood as arising
from the anisotropy of charge distribution induced by the presence of local
distortions, i.e. due to a structural phase transition.Comment: 10 pages, 2 figures.To be published Phys. Rev.
Anesthesia for percutaneous radiofrequency tumor ablation (PRFA): A review of current practice and techniques
The Bright Side of Hematopoiesis: Regulatory Roles of ARID3a/Bright in Human and Mouse Hematopoiesis
ARID3a/Bright is a DNA-binding protein that was originally discovered for its ability to increase immunoglobulin transcription in antigen-activated B cells. It interacts with DNA as a dimer through its ARID, or A/T-rich interacting domain. In association with other proteins, ARID3a increased transcription of the immunoglobulin heavy chain and led to improved chromatin accessibility of the heavy chain enhancer. Constitutive expression of ARID3a in B lineage cells resulted in autoantibody production, suggesting its regulation is important. Abnormal ARID3a expression has also been associated with increased proliferative capacity and malignancy. Roles for ARID3a in addition to interactions with the immunoglobulin locus were suggested by transgenic and knockout mouse models. Over-expression of ARID3a resulted in skewing of mature B cell subsets and altered gene expression patterns of follicular B cells, whereas loss of function resulted in loss of B1 lineage B cells and defects in hematopoiesis. More recent studies showed that loss of ARID3a in adult somatic cells promoted developmental plasticity, alterations in gene expression patterns, and lineage fate decisions. Together, these data suggest new regulatory roles for ARID3a. The genes influenced by ARID3a are likely to play pivotal roles in lineage decisions, highlighting the importance of this understudied transcription factor
Monopole operators in three-dimensional N=4 SYM and mirror symmetry
We study non-abelian monopole operators in the infrared limit of
three-dimensional SU(N_c) and N=4 SU(2) gauge theories. Using large N_f
expansion and operator-state isomorphism of the resulting superconformal field
theories, we construct monopole operators which are (anti-)chiral primaries and
compute their charges under the global symmetries. Predictions of
three-dimensional mirror symmetry for the quantum numbers of these monopole
operators are verified.Comment: 23 pages, LaTex; v2: section 3.4 modified, section 3.5 extended,
references adde
Polarization Dependence of Anomalous X-ray Scattering in Orbital Ordered Manganites
In order to determine types of the orbital ordering in manganites, we study
theoretically the polarization dependence of the anomalous X-ray scattering
which is caused by the anisotropy of the scattering factor. The general
formulae of the scattering intensity in the experimental optical system is
derived and the atomic scattering factor is calculated in the microscopic
electronic model. By using the results, the X-ray scattering intensity in
several types of the orbital ordering is numerically calculated as a function
of azimuthal and analyzer angles.Comment: 9 pages, 7 figure
What lies beneath? The role of informal and hidden networks in the management of crises
Crisis management research traditionally focuses on the role of formal communication networks in the escalation and management of organisational crises. Here, we consider instead informal and unobservable networks. The paper explores how hidden informal exchanges can impact upon organisational decision-making and performance, particularly around inter-agency working, as knowledge distributed across organisations and shared between organisations is often shared through informal means and not captured effectively through the formal decision-making processes. Early warnings and weak signals about potential risks and crises are therefore often missed. We consider the implications of these dynamics in terms of crisis avoidance and crisis management
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