1,634 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
Investigation into pathophysiology of naturally occurring palatal instability and intermittent dorsal displacement of the soft palate (DDSP) in racehorses: Thyro-hyoid muscles fatigue during exercise
Exercise induced intermittent dorsal displacement of the soft palate (DDSP) is a common cause of airway obstruction and poor performance in racehorses. The definite etiology is still unclear, but through an experimental model, a role in the development of this condition was identified in the dysfunction of the thyro-hyoid muscles. The present study aimed to elucidate the nature of this dysfunction by investigating the spontaneous response to exercise of the thyro-hyoid muscles in racehorses with naturally occurring DDSP. Intramuscular electrodes were implanted in the thyro-hyoid muscles of nine racehorses, and connected to a telemetric unit for electromyographic monitoring implanted subcutaneously. The horses were recruited based on upper airway function evaluated through wireless endoscopy during exercise. Five horses, with normal function, were used as control; four horses were diagnosed as DDSP-affected horses based on repeated episodes of intermittent dorsal displacement of the soft palate. The electromyographic activity of the thyro-hyoid muscles recorded during incremental exercise tests on a high-speed treadmill was analyzed to measure the mean electrical activity and the median frequency of the power spectrum, thereafter subjected to wavelet decomposition. The affected horses had palatal instability with displacement on repeated exams prior to surgical implantation. Although palatal instability persisted after surgery, only two of these horses displaced the palate after instrumentation. The electromyographic traces from this group of four horses showed, at highest exercise intensity, a decrease in mean electrical activity and median power frequency, with progressive decrease in the contribution of the high frequency wavelets, consistent with development of thyro-hyoid muscle fatigue. The results of this study identified fatigue as the main factor leading to exercise induced palatal instability and DDSP in a group of racehorses. Further studies are required to evaluate the fiber type composition and metabolic characteristics of the thyro-hyoid muscles that could predispose to fatigue
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
Non-perturbative approach for the time-dependent symmetry breaking
We present a variational method which uses a quartic exponential function as
a trial wave-function to describe time-dependent quantum mechanical systems. We
introduce a new physical variable which is appropriate to describe the
shape of wave-packet, and calculate the effective action as a function of both
the dispersion and . The effective potential
successfully describes the transition of the system from the false vacuum to
the true vacuum. The present method well describes the long time evolution of
the wave-function of the system after the symmetry breaking, which is shown in
comparison with the direct numerical computations of wave-function.Comment: 8 pages, 3 figure
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
Exact and Truncated Dynamics in Nonequilibrium Field Theory
Nonperturbative dynamics of quantum fields out of equilibrium is often
described by the time evolution of a hierarchy of correlation functions, using
approximation methods such as Hartree, large N, and nPI-effective action
techniques. These truncation schemes can be implemented equally well in a
classical statistical system, where results can be tested by comparison with
the complete nonlinear evolution obtained by numerical methods. For a 1+1
dimensional scalar field we find that the early-time behaviour is reproduced
qualitatively by the Hartree dynamics. The inclusion of direct scattering
improves this to the quantitative level. We show that the emergence of
nonthermal temperature profiles at intermediate times can be understood in
terms of the fixed points of the evolution equations in the Hartree
approximation. The form of the profile depends explicitly on the initial
ensemble. While the truncated evolution equations do not seem to be able to get
away from the fixed point, the full nonlinear evolution shows thermalization
with a (surprisingly) slow relaxation.Comment: 30 pages with 12 eps figures, minor changes; to appear in Phys.Rev.
Enhanced roughness of lipid membranes caused by external electric fields
The behavior of lipid membranes in the presence of an external electric field
is studied and used to examine the influence of such fields on membrane
parameters such as roughness and show that for a micro sized membrane,
roughness grows as the field increases. The dependence of bending rigidity on
the electric field is also studied and an estimation of thickness of the
accumulated charges around lipid membranes in a free-salt solution is
presented.Comment: 9 pages, 6 figures, to appear in Computational Materials Scienc
Exact and approximate dynamics of the quantum mechanical O(N) model
We study a quantum dynamical system of N, O(N) symmetric, nonlinear
oscillators as a toy model to investigate the systematics of a 1/N expansion.
The closed time path (CTP) formalism melded with an expansion in 1/N is used to
derive time evolution equations valid to order 1/N (next-to-leading order). The
effective potential is also obtained to this order and its properties
areelucidated. In order to compare theoretical predictions against numerical
solutions of the time-dependent Schrodinger equation, we consider two initial
conditions consistent with O(N) symmetry, one of them a quantum roll, the other
a wave packet initially to one side of the potential minimum, whose center has
all coordinates equal. For the case of the quantum roll we map out the domain
of validity of the large-N expansion. We discuss unitarity violation in the 1/N
expansion; a well-known problem faced by moment truncation techniques. The 1/N
results, both static and dynamic, are also compared to those given by the
Hartree variational ansatz at given values of N. We conclude that late-time
behavior, where nonlinear effects are significant, is not well-described by
either approximation.Comment: 16 pages, 12 figrures, revte
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
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