1,167 research outputs found
The Metal-Insulator Transition of NbO2: an Embedded Peierls Instability
Results of first principles augmented spherical wave electronic structure
calculations for niobium dioxide are presented. Both metallic rutile and
insulating low-temperature NbO2, which crystallizes in a distorted rutile
structure, are correctly described within density functional theory and the
local density approximation. Metallic conductivity is carried to equal amounts
by metal t_{2g} orbitals, which fall into the one-dimensional d_parallel band
and the isotropically dispersing e_{g}^{pi} bands. Hybridization of both types
of bands is almost negligible outside narrow rods along the line X--R. In the
low-temperature phase splitting of the d_parallel band due to metal-metal
dimerization as well as upshift of the e_{g}^{pi} bands due to increased p-d
overlap remove the Fermi surface and open an optical band gap of about 0.1 eV.
The metal-insulator transition arises as a Peierls instability of the
d_parallel band in an embedding background of e_{g}^{pi} electrons. This basic
mechanism should also apply to VO2, where, however, electronic correlations are
expected to play a greater role due to stronger localization of the 3d
electrons.Comment: 4 pages, revtex, 6 eps figures, additional material avalable at
http://www.physik.uni-augsburg.de/~eyert
Which electronic health record system should we use? A systematic review
The UK government had intended to introduce a comprehensive EHRs system in England by 2020. These EHRs would run across primary, secondary, and social care linking data in a single digital platform. This systematic review's objectives were to identify studies that compare EHRs in terms of direct comparison between systems and evaluate them using System and Software Quality Requirements and Evaluation (SQuaRE) ISO/IEC 25010. A systematic review was performed by searching EMBASE and Ovid MEDLINE databases between 1974 and April 2021. All original studies that appraised EHR systems and their providers were included. The main outcome measures were EHR system comparison and SQuaRE's eight characteristics: functional suitability, performance efficiency, compatibility, usability, reliability, security, maintainability, and portability. A total of 724 studies were identified using the search criteria. After review of titles and abstracts, this was filtered down to 40 studies as per exclusion and inclusion criteria set out in our study selection. Seven studies compared more than one EHR. The following number of studies looked at the various aspects of the SQuaRE respectively. Nineteen studies addressed functional suitability, n=18 performance efficiency, n=12 compatibility, n=25 usability, n=6 reliability, n=2 security, n=16 maintainability, and n=13 portability. Epic was the most studied EHR system and one of the most implemented vendors in the USA market, and one of the top ten in UK. It is difficult to assess which is the most advantageous EHR system currently available when looking at them in accordance with SQuaRE's eight characteristics for software evaluation
Zero mode in the time-dependent symmetry breaking of theory
We apply the quartic exponential variational approximation to the symmetry
breaking phenomena of scalar field in three and four dimensions. We calculate
effective potential and effective action for the time-dependent system by
separating the zero mode from other non-zero modes of the scalar field and
treating the zero mode quantum mechanically. It is shown that the quantum
mechanical properties of the zero mode play a non-trivial role in the symmetry
breaking of the scalar theory.Comment: 10 pages, 3 figure
Anomalous electric conductions in KSbO3-type metallic rhenium oxides
Single crystals of KSbO3-type rhenium oxides, La4Re6Orho(T)=\rho_{0}+AT^{n}(n \approx 1.6)$ in
a wide temperature range between 5 K and 300 K, which is extraordinary for
three-dimensional metals without strong electron correlations. The resistivity
of Bi3Re3O11 shows an anomaly around at 50 K, where the magnetic susceptibility
also detects a deviation from ordinary Pauli paramagnetism.Comment: 13 pages, 7 figures. J. Phys. Soc. Japan, in pres
Quantum Dynamics of the Slow Rollover Transition in the Linear Delta Expansion
We apply the linear delta expansion to the quantum mechanical version of the
slow rollover transition which is an important feature of inflationary models
of the early universe. The method, which goes beyond the Gaussian
approximation, gives results which stay close to the exact solution for longer
than previous methods. It provides a promising basis for extension to a full
field theoretic treatment.Comment: 12 pages, including 4 figure
Charge Ordering and Phase Competition in the Layered Perovskite Lasr2mn2o7
Charge-lattice fluctuations are observed in the layered perovskite manganite
LaSr2Mn2O7 by Raman spectroscopy as high as 340 K and with decreasing
temperature they become static and form a charge ordered (CO) phase below
TCO=210 K. In the static regime, superlattice reflections are observed through
neutron and x-ray diffraction with a propagation vector (h+1/4,k-1/4,l).
Crystallographic analysis of the CO state demonstrates that the degree of
charge and orbital ordering in this manganite is weaker than the charge
ordering in three dimensional perovskite manganites. A TN=170K a type-A
antiferromagnetism (AF) develops and competes with the charge ordering, that
eventually melts below T*=100K. High resolution diffraction measurements
suggest that that CO- and AF-states do not coincide within the same region in
the material but rather co-exist as separate phases. The transition to type-A
antiferromagnetism at lower temperatures is characterized by the competition
between these two phases.Comment: 9 pages, 6 figure
Formation of topological defects in gauge field theories
When a symmetry gets spontaneously broken in a phase transition, topological
defects are typically formed. The theoretical picture of how this happens in a
breakdown of a global symmetry, the Kibble-Zurek mechanism, is well established
and has been tested in various condensed matter experiments. However, from the
viewpoint of particle physics and cosmology, gauge field theories are more
relevant than global theories. In recent years, there have been significant
advances in the theory of defect formation in gauge field theories, which make
precise predictions possible, and in experimental techniques that can be used
to test these predictions in superconductor experiments. This opens up the
possibility of carrying out relatively simple and controlled experiments, in
which the non-equilibrium phase transition dynamics of gauge field theories can
be studied. This will have a significant impact on our understanding of phase
transitions in the early universe and in heavy ion collider experiments. In
this paper, I review the current status of the theory and the experiments in
which it can be tested.Comment: Review article, 43 pages, 7 figures. Minor changes, some references
added. Final version to appear in IJMP
AAV-mediated ERdj5 overexpression protects against P23H rhodopsin toxicity
Rhodopsin misfolding caused by the P23H mutation is a major cause of autosomal dominant retinitis pigmentosa (adRP), to date there are no effective treatments for adRP. The BiP co-chaperone and reductase ERdj5 (DNAJC10) is part of the ER quality control machinery and previous studies have shown that overexpression of ERdj5 in vitro enhanced the degradation of P23H rhodopsin; whereas knockdown of ERdj5 increased P23H rhodopsin ER retention and aggregation. Here, we investigated the role of ERdj5 in photoreceptor homeostasis in vivo by using an Erdj5 knock-out mouse crossed with the P23H knock-in mouse, and by adeno associated viral (AAV) vector-mediated gene augmentation of ERdj5 in P23H-3 rats. Electroretinogram (ERG) and optical coherence tomography (OCT) of Erdj5−/− and P23H+/−:Erdj5−/− mice showed no effect of ERdj5 ablation on retinal function or photoreceptor survival. Rhodopsin levels and localisation were similar to those of control animals at a range of time points. By contrast, when AAV2/8-ERdj5-HA was subretinally injected into P23H-3 rats, analysis of the full field ERG suggested that overexpression of ERdj5 reduced visual function loss 10 weeks post-injection. This correlated with a significant preservation of photoreceptor cells at 4 and 10 weeks post-injection. Assessment of the outer nuclear layer (ONL) morphology showed preserved ONL thickness and reduced rhodopsin retention in the ONL in the injected superior retina. Overall, these data suggest that manipulation of the ER quality control and ERAD factors to promote mutant protein degradation could be beneficial for the treatment of adRP caused by mutant rhodopsin
A narrow, edge-on disk resolved around HD 106906 with SPHERE
HD~106906AB is so far the only young binary system around which a planet has
been imaged and a debris disk evidenced thanks to a strong IR excess. As such,
it represents a unique opportunity to study the dynamics of young planetary
systems. We aim at further investigating the close (tens of au scales)
environment of the HD~106906AB system. We used the extreme AO fed, high
contrast imager SPHERE recently installed on the VLT to observe HD~106906. Both
the IRDIS imager and the Integral Field Spectrometer were used. We discovered a
very inclined, ring-like disk at a distance of 65~au from the star. The disk
shows a strong brightness asymmetry with respect to its semi-major axis. It
shows a smooth outer edge, compatible with ejection of small grains by the
stellar radiation pressure. We show furthermore that the planet's projected
position is significantly above the disk's PA. Given the determined disk
inclination, it is not excluded though that the planet could still orbit within
the disk plane if at a large separation (2000--3000 au). We identified several
additional point sources in the SPHERE/IRDIS field-of-view, that appear to be
background objects. We compare this system with other debris disks sharing
similarities, and we briefly discuss the present results in the framework of
dynamical evolution.Comment: 7 pages, 6 figures, accepted by Astronomy & Astrophysic
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