2,367 research outputs found
The development of precipitation-hardened chromium-base alloys Final report
Precipitation with refractory metal carbides for creep resistant chromium-base alloy
Atrial high-rate episodes: prevalence, stroke risk, implications for management, and clinical gaps in evidence
Self-terminating atrial arrhythmias are commonly detected on continuous rhythm monitoring, e.g. by pacemakers or defibrillators. It is unclear whether the presence of these arrhythmias has therapeutic consequences. We sought to summarize evidence on the prevalence of atrial high-rate episodes (AHREs) and their impact on risk of stroke. We performed a comprehensive, tabulated review of published literature on the prevalence of AHRE. In patients with AHRE, but without atrial fibrillation (AF), we reviewed the stroke risk and the potential risk/benefit of oral anticoagulation. Atrial high-rate episodes are found in 10-30% of AF-free patients. Presence of AHRE slightly increases stroke risk (0.8% to 1%/year) compared with patients without AHRE. Atrial high-rate episode of longer duration (e.g. those >24 h) could be associated with a higher stroke risk. Oral anticoagulation has the potential to reduce stroke risk in patients with AHRE but is associated with a rate of major bleeding of 2%/year. Oral anticoagulation is not effective in patients with heart failure or survivors of a stroke without AF. It remains unclear whether anticoagulation is effective and safe in patients with AHRE. Atrial high-rate episodes are common and confer a slight increase in stroke risk. There is true equipoise on the best way to reduce stroke risk in patients with AHRE. Two ongoing trials (NOAH-AFNET 6 and ARTESiA) will provide much-needed information on the effectiveness and safety of oral anticoagulation using non-vitamin K antagonist oral anticoagulants in patients with AHRE.info:eu-repo/semantics/publishedVersio
First-principles calculations of phase transition, low elastic modulus, and superconductivity for zirconium
The elasticity, dynamic properties, and superconductivity of ,
, and Zr are investigated by using first-principles methods.
Our calculated elastic constants, elastic moduli, and Debye temperatures of
and phases are in excellent agreement with experiments.
Electron-phonon coupling constant and electronic density of states at
the Fermi level (\emph{E}) are found to increase with pressure
for these two hexagonal structures. For cubic phase, the critical
pressure for mechanical stability is predicted to be 3.13 GPa and at \emph{P}=4
GPa the low elastic modulus (=31.97 GPa) can be obtained. Besides, the
critical pressure for dynamic stability of phase is achieved by phonon
dispersion calculations to be 26 GPa. Over this pressure,
and (\emph{E}) of phase decrease upon further
compression. Our calculations show that the large value of superconducting
transition temperature \emph{T}_{\rm{c}} at 30 GPa for Zr is mainly
due to the TA1 soft mode. Under further compression, the soft vibrational mode
will gradually fade away.Comment: 15 pages, 5 figure
Simultaneous Embeddability of Two Partitions
We study the simultaneous embeddability of a pair of partitions of the same
underlying set into disjoint blocks. Each element of the set is mapped to a
point in the plane and each block of either of the two partitions is mapped to
a region that contains exactly those points that belong to the elements in the
block and that is bounded by a simple closed curve. We establish three main
classes of simultaneous embeddability (weak, strong, and full embeddability)
that differ by increasingly strict well-formedness conditions on how different
block regions are allowed to intersect. We show that these simultaneous
embeddability classes are closely related to different planarity concepts of
hypergraphs. For each embeddability class we give a full characterization. We
show that (i) every pair of partitions has a weak simultaneous embedding, (ii)
it is NP-complete to decide the existence of a strong simultaneous embedding,
and (iii) the existence of a full simultaneous embedding can be tested in
linear time.Comment: 17 pages, 7 figures, extended version of a paper to appear at GD 201
Current Switch by Coherent Trapping of Electrons in Quantum Dots
We propose a new transport mechanism through tunnel-coupled quantum dots
based on the coherent population trapping effect. Coupling to an excited level
by the coherent radiation of two microwaves can lead to an extremely narrow
current antiresonance. The effect can be used to determine interdot dephasing
rates and is a mechanism for a very sensitive, optically controlled current
switch.Comment: to appear in Phys. Rev. Let
Kondo-Anderson Transitions
Dilute magnetic impurities in a disordered Fermi liquid are considered close
to the Anderson metal-insulator transition (AMIT). Critical Power law
correlations between electron wave functions at different energies in the
vicinity of the AMIT result in the formation of pseudogaps of the local density
of states. Magnetic impurities can remain unscreened at such sites. We
determine the density of the resulting free magnetic moments in the zero
temperature limit. While it is finite on the insulating side of the AMIT, it
vanishes at the AMIT, and decays with a power law as function of the distance
to the AMIT. Since the fluctuating spins of these free magnetic moments break
the time reversal symmetry of the conduction electrons, we find a shift of the
AMIT, and the appearance of a semimetal phase. The distribution function of the
Kondo temperature is derived at the AMIT, in the metallic phase and in
the insulator phase. This allows us to find the quantum phase diagram in an
external magnetic field and at finite temperature . We calculate the
resulting magnetic susceptibility, the specific heat, and the spin relaxation
rate as function of temperature. We find a phase diagram with finite
temperature transitions between insulator, critical semimetal, and metal
phases. These new types of phase transitions are caused by the interplay
between Kondo screening and Anderson localization, with the latter being
shifted by the appearance of the temperature-dependent spin-flip scattering
rate. Accordingly, we name them Kondo-Anderson transitions (KATs).Comment: 18 pages, 9 figure
Two-eigenfunction correlation in a multifractal metal and insulator
We consider the correlation of two single-particle probability densities
at coinciding points as a function of the
energy separation for disordered tight-binding lattice models
(the Anderson models) and certain random matrix ensembles. We focus on the
models in the parameter range where they are close but not exactly at the
Anderson localization transition. We show that even far away from the critical
point the eigenfunction correlation show the remnant of multifractality which
is characteristic of the critical states. By a combination of the numerical
results on the Anderson model and analytical and numerical results for the
relevant random matrix theories we were able to identify the Gaussian random
matrix ensembles that describe the multifractal features in the metal and
insulator phases. In particular those random matrix ensembles describe new
phenomena of eigenfunction correlation we discovered from simulations on the
Anderson model. These are the eigenfunction mutual avoiding at large energy
separations and the logarithmic enhancement of eigenfunction correlations at
small energy separations in the two-dimensional (2D) and the three-dimensional
(3D) Anderson insulator. For both phenomena a simple and general physical
picture is suggested.Comment: 16 pages, 18 figure
Character of eigenstates of the 3D disordered Anderson Hamiltonian
We study numerically the character of electron eigenstates of the three
dimensional disordered Anderson model. Analysis of the statistics of inverse
participation ratio as well as numerical evaluation of the electron-hole
correlation function confirm that there are no localized states below the
mobility edge, as well as no metallic state in the tail of the conductive band.
We discuss also finite size effects observed in the analysis of all the
discussed quantities.Comment: 7 pages, 9 figures, resubmitted to Physical Review
Current-Induced Entanglement of Nuclear Spins in Quantum Dots
We propose an entanglement mechanism of nuclear spins in quantum dots driven
by the electric current accompanied by the spin flip. This situation is
relevant to a leakage current in spin-blocked regions where electrons cannot be
transported unless their spins are flipped. The current gradually increases the
components of larger total spin of nuclei. This correlation among the nuclear
spins markedly enhances the spin-flip rate of electrons and hence the leakage
current. The enhancement of the current is observable when the residence time
of electrons in the quantum dots is shorter than the dephasing time T*_2 of
nuclear spins.Comment: 4 pages, 4 figure
- …