1,847 research outputs found
Tunneling through magnetic molecules with arbitrary angle between easy axis and magnetic field
Inelastic tunneling through magnetically anisotropic molecules is studied
theoretically in the presence of a strong magnetic field. Since the molecular
orientation is not well controlled in tunneling experiments, we consider
arbitrary angles between easy axis and field. This destroys all conservation
laws except that of charge, leading to a rich fine structure in the
differential conductance. Besides single molecules we also study monolayers of
molecules with either aligned or random easy axes. We show that detailed
information on the molecular transitions and orientations can be obtained from
the differential conductance for varying magnetic field. For random easy axes,
averaging over orientations leads to van Hove singularities in the differential
conductance. Rate equations in the sequential-tunneling approximation are
employed. An efficient approximation for their solution for complex molecules
is presented. The results are applied to Mn12-based magnetic molecules.Comment: 10 pages, 10 figures include
Bleeding on oral anticoagulants: overview of reversal strategies.
Oral anticoagulants (antivitamin K, direct oral anticoagulants) are routinely prescribed for the prevention or treatment of thromboembolic events, and many patients are now on long-term anticoagulant therapy. However, this complicates the management of urgent surgical conditions or major bleeding. Various strategies have been developed to reverse the anticoagulant effect and this narrative review provides an overview of the wide range of therapies currently available
Compressed sensing subtracted rotational angiography with multiple sparse penalty
International audienceDigital Subtraction Rotational Angiography (DSRA) is a clinical protocol that allows three-dimensional (3D) visualization of vasculature during minimally invasive procedures. C-arm systems that are used to generate 3D reconstructions in interventional radiology have limited sampling rate and thus, contrast resolution. To address this particular subsampling problem, we propose a novel iterative reconstruction algorithm based on compressed sensing. To this purpose, we exploit both spatial and temporal sparsity of DSRA. For computational efficiency, we use a proximal implementation that accommodates multiple '1-penalties. Experiments on both simulated and clinical data confirm the relevance of our strategy for reducing subsampling streak artifacts
Theory of Non-Reciprocal Optical Effects in Antiferromagnets: The Case Cr_2O_3
A microscopic model of non-reciprocal optical effects in antiferromagnets is
developed by considering the case of Cr_2O_3 where such effects have been
observed. These effects are due to a direct coupling between light and the
antiferromagnetic order parameter. This coupling is mediated by the spin-orbit
interaction and involves an interplay between the breaking of inversion
symmetry due to the antiferromagnetic order parameter and the trigonal field
contribution to the ligand field at the magnetic ion. We evaluate the matrix
elements relevant for the non-reciprocal second harmonic generation and
gyrotropic birefringence.Comment: accepted for publication in Phys. Rev.
Biharmonic pattern selection
A new model to describe fractal growth is discussed which includes effects
due to long-range coupling between displacements . The model is based on the
biharmonic equation in two-dimensional isotropic defect-free
media as follows from the Kuramoto-Sivashinsky equation for pattern formation
-or, alternatively, from the theory of elasticity. As a difference with
Laplacian and Poisson growth models, in the new model the Laplacian of is
neither zero nor proportional to . Its discretization allows to reproduce a
transition from dense to multibranched growth at a point in which the growth
velocity exhibits a minimum similarly to what occurs within Poisson growth in
planar geometry. Furthermore, in circular geometry the transition point is
estimated for the simplest case from the relation
such that the trajectories become stable at the growing surfaces in a
continuous limit. Hence, within the biharmonic growth model, this transition
depends only on the system size and occurs approximately at a distance far from a central seed particle. The influence of biharmonic patterns on
the growth probability for each lattice site is also analysed.Comment: To appear in Phys. Rev. E. Copies upon request to
[email protected]
Valley polarization assisted spin polarization in two dimensions
International audienceValleytronics is rapidly emerging as an exciting area of basic and applied research. In two dimensional systems, valley polarisation can dramatically modify physical properties through electron-electron interactions as demonstrated by such phenomena as the fractional quantum Hall effect and the metal-insulator transition. Here, we address the electrons' spin alignment in a magnetic field in silicon-on-insulator quantum wells under valley polarisation. In stark contrast to expectations from a non-interacting model, we show experimentally that less magnetic field can be required to fully spin polarise a valley-polarised system than a valley-degenerate one. Furthermore, we show that these observations are quantitatively described by parameter free ab initio quantum Monte Carlo simulations. We interpret the results as a manifestation of the greater stability of the spin and valley degenerate system against ferromagnetic instability and Wigner crystalisation which in turn suggests the existence of a new strongly correlated electron liquid at low electron densities
Fermionic response from fractionalization in an insulating two-dimensional magnet
Conventionally ordered magnets possess bosonic elementary excitations, called
magnons. By contrast, no magnetic insulators in more than one dimension are
known whose excitations are not bosons but fermions. Theoretically, some
quantum spin liquids (QSLs) -- new topological phases which can occur when
quantum fluctuations preclude an ordered state -- are known to exhibit Majorana
fermions as quasiparticles arising from fractionalization of spins. Alas,
despite much searching, their experimental observation remains elusive. Here,
we show that fermionic excitations are remarkably directly evident in
experimental Raman scattering data across a broad energy and temperature range
in the two-dimensional material -RuCl. This shows the importance of
magnetic materials as hosts of Majorana fermions. In turn, this first
systematic evaluation of the dynamics of a QSL at finite temperature emphasizes
the role of excited states for detecting such exotic properties associated with
otherwise hard-to-identify topological QSLs.Comment: 5 pages, 3 figure
Etude de l’implication des gènes codant la catalase A1 et la Cu,Zn-superoxyde dismutase de Scedosporium apiospermum dans sa défence contre le stress oxydant
Early stages of ramified growth in quasi-two-dimensional electrochemical deposition
I have measured the early stages of the growth of branched metal aggregates
formed by electrochemical deposition in very thin layers. The growth rate of
spatial Fourier modes is described qualitatively by the results of a linear
stability analysis [D.P. Barkey, R.H. Muller, and C.W. Tobias, J. Electrochem.
Soc. {\bf 136}, 2207 (1989)]. The maximum growth rate is proportional to
where is the current through the electrochemical cell,
the electrolyte concentration, and . Differences
between my results and the theoretical predictions suggest that
electroconvection in the electrolyte has a large influence on the instability
leading to ramified growth.Comment: REVTeX, four ps figure
Middle and low latitude ionosphere response to 2015 St. Patrick's Day geomagnetic storm
International audienceThis paper presents a study of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earth's magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the B z component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earth's magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models
- …